HEADSPACE HOW TO GET IT RIGHT
This Page Can Save You Thousands of Dollars!
Correct headspace is essential to accuracy, reliable functioning, and good case life. Here is how you measure it, make corrections, and also measure throat length.
The first thing you must do is understand that headspace is not a length, which flies in the face of the industry concepts geared to gauging chamber depth. The term has been badly adulterated in common usage to the extent the term is not something the average guy can relate to. But thinking of the term headspace for what it REALLY means, it becomes a very simple concept that is both easy to understand and easy to measure, especially in any break open gun like the TC Encore or Contender/G2. I'll show you how.
Understanding headspace can literally save you hundreds of dollars, thousands of dollars if you are one who does a lot of barrel swapping in your quest for accuracy and the performance dreams, are made of.
This is what it ideally should be, .001" "SPACE" BETWEEN THE CASE "HEAD" AND THE BREECHFACE, "head" "space". .001" to .003" is a good range to work in since it is often difficult to keep ammo consistent to within .001".
But the more space there is, the greater will be the problems associated with it. Conversely, if there is NO space between the case head and the breech face, meaning the case sticks out of the chamber too far, this is also a major problem related to accuracy and even preventing the barrel from closing all the way. If the barrel is not closed all the way, you cannot cock the hammer on the Encore or G2, nor will the Contender hammer block safety be released so the gun can fire.
Here is just one example:
Drawing courtesy of Alan Thompson. Thanks, Alan.
Note that the case shoulder is in contact with the chamber shoulder while there is space between the case rim and the bottom of the rim counterbore, indicating the case is "headspaced" or its forward movement stopped by the shoulder, not the rim, and that the actual protrusion of the case head is .001" less than whatever the barrel-to-frame gap actually measures.
Here is the short course: In the example above you would
1) measure the barrel-to-frame gap with a common feeler gauge set (IF the barrel is not actually hitting on the firing pin bushing,
2) measure where the case head is in comparison to the end of the barrel, (ie. dead flush with the end of the barrel, however many thousandths below the end of the barrel, or in the example above how many thousandths it sticks out of the barrel), then
3) do the simple arithmetic. Let's put some hypothetical numbers to the diagram above.
Let's say the gap is .005." To arrive at the optimum .001" space between the case head and firing pin bushing, the case would have to stick out of the barrel .004". In summary: Gap minus protrusion equals.001".
IF the case were, let's say, .004" BELOW the end of the barrel, the "space" between the case "head" and firing pin bushing it would go like this: Gap, .005", PLUS .004" equals a total of .009". This is WAY too much of course, so you make corrections detailed below. Our simple system of taking measurements lets you track and work out what works best for you, to include controlling the amount of interference on the case head to compensate for a less than tight barrel lockup if necessary, but you monitor and regulate it based on measurements for consistent results, not "guess and by golly." Note in the example above that headspace is regulated by size die adjustment so there is both contact on the case shoulder and .001" clearance behind the case head.... ie, "head" "space."
Another approach is to bump the case shoulder back so it does not touch the chamber shoulder, and the case rim does bottom out in the rim counterbore in the end of the barrel. In this situation, you would shim the firing pin bushing forward as necessary and remove material from the end of the barrel as needed to make that possible. Whichever forward stopping point you choose to use, chamber shoulder or rim counterbore, you take measurements so you know what the resulting headspace is that your method is producing.
You cannot count on magazines, reloading manuals, the TC factory, the local "authority" who has "reloaded for 40 years," or even most of the dealers and TC aftermarket custom shops.
Diagrams in loading manuals don't seem to really help get the concept across. Most gun writers themselves don't seem to comprehend it. If the factory understands anything other than SAAMI steel headspace gauges, it does not show, nor are they helping you understand and work with it. The "local authority" who has double slammed the barrel shut for nearly 40 years certainly is no help, nor is the guy who has worked mostly with fixed barrel bolt actions going to be any help. And some of the worst offenders putting out erroneous information are some of the custom barrel makers. These are usually the ones leaning on headspace gauges for everything.
In fact, when it comes to the TC and NEF Handi-Rifle type break open guns, the best thing to do with steel headspace gauges is toss 'em in the trash.
They are meaningless, and misleading at best. A "gauge" means nothing to you at all when you can take the measurements yourself and KNOW exactly what the headspace is
WITH THE ACTUAL AMMUNITION IN THE CHAMBER.
It is the space between the actual cartridge case head and the breechface you are concerned about, not a steel gauge that may be substantially different from the actual ammo you are shooting. So don't go waste money on steel gauges. You don't need them, and you don't want them. After you have worked with our Headspace Indicator you will understand why.
Whether you shoot factory ammo or reload makes no difference. You still must KNOW what the headspace is in any given barrel and frame combination
You will be able to identify excess headspace with either factory ammo or your reloads. If the headspace is excess with factory ammo, anything over .006," you have grounds to exact a remedy from the manufacturer of the barrel or the ammo manufacturer or both.
Excess headspace is the cause of many misfire situations and eratic ignition which produces poor accuracy. No headspace, meaning the case head is hitting on the breechface when you close the barrel, can cause the barrel to not close all the way. This has been a major cause of misfires with Contenders since the first day they were produced. Or, with Encores and G2s, it prevents the hammer from cocking when the barrel is not closed all the way.
The issue of headspace is simply about making sure ammo fits the gun. This should not be a strange concept. However, believe it or not, ammo that fits right is more likely to work right. Imagine that.
What IS headspace? It is "space" between the cartridge case "head" and the breechface, ie., "head" "space."
The term is tossed around loosely all the time and presumed to be something you have to use a "headspace GAUGE" to measure, which is not only far from the situation, but also grossly misleading. Here is a video about Headspace & Barrel to Frame Gap.
Repeating, "HEAD," as in cartridge case HEAD, "SPACE," as in the space behind the head,or the distance from the case head to the breechface.
Repeating, "HEAD," as in cartridge case HEAD, "SPACE," as in the space behind the head,or the distance from the case head to the breechface.
In the TC guns, it is the distance from the case head to the firing pin bushing in the breechface which actually protrudes out from the frame a few thousandths. This is what headspace is, and it is very easily observed and very easily measured.
Headspace is NOT a length, either!
You read it all the time, everywhere, such as ".... the headspace of the .300 Win. Mag. is .220". Talk about screwed up bs! That .220" figure is the LENGTH of the cartridge from the case head to the top of the cartridge belt dimension. It is used to gauge the depth of the chamber. BUT .220" is NOT the "space" between the cartridge case "head" and the breech face....ie, NOT "head" "space." OR, take the .30/06. The steel gauge used to gauge the depth of the chamber is 1.940" from the head of the case to the midpoint on the shoulder. Everywhere you go, you read or hear, "The headspace of the .30/06 is 1.940". NO.... THE 1.940" DEPTH OF THE CHAMBER IS NOT HEADSPACE.
IT IS THE STANDARD MINIMUM DEPTH OF THE CHAMBER. PERIOD! Those depths of chambers tell YOU nothing at all about where the case head is in relationship to the breech face in YOUR given barrel, ammo, and frame combination. Are we clear on this matter?
Do you get the point? HEADSPACE IS NOT A LENGTH INTO THE CHAMBER!
Here is a video about Barrel to Frame Gap. Headspace is NOT the distance from the end of the barrel to the breechface, as is so often said erroneously. The distance from the end of the barrel to the breechface has NO bearing whatsoever on headspace, and this gap, referred to as the barrel-to-frame gap, also has absolutely NO bearing on the quality or function of the barrel. And contrary to statements by at least one purveyor of custom barrels, there is NO optimum gap for accuracy. It can be a little, or it can be a lot, as much as 1/8" and still have absolutely no bearing on accuracy. While to some it may be more esthetically pleasing to not be able to see daylight between the closed barrel and breechface, the amount of the gap has no bearing whatsoever on the quality of the barrel, the function of the barrel, or the headspace. In fact, there SHOULD be some gap between the end of the barrel and the firing pin bushing. If the barrel hits on the firing pin bushing, it can do two things:
1) It can prevent the barrel from dropping into the frame far enough to allow the barrel to close all the way and thus prevent it from firing, and
2) we are finding that if it is not hard contact it can often cause severe vertical stringing of shots that ruins accuracy. In other words the end of the barrel is just bumping randomly on the firing pin bushing during the firing cycle. Both the barrel not closing all the way and vertical stringing related to the barrel hitting on the firing pin bushing should be corrected by facing material off the end of the barrel via filing, lathe turning, or milling.
There should be at least a few thousandths clearance between the end of the barrel and the firing pin bushing.
Do not worry about taking off too much material. The barrel-to-frame gap can be up to 1/8", approximately the depth of the extractor slot. While this is extreme, and it is not necessary to remove this much material, the point is that the amount of gap has no bearing whatever on headspace unless it is a rimmed case, and you take off more than about .050."
A gap of .003 to .005" is ok both esthetically and functionally, but taking off more than this does not hurt anything either. To set up a barrel and frame combination so that there is no gap or minimal gap can be a gross mistake, one discovered when the barrel is later installed on a frame whose hinge pin holes are somewhat closer to the breechface than the frame the barrel was set up on.
HINGE PIN HOLE LOCATIONS DO VARY FROM FRAME TO FRAME. I have only found about a .003" variance from frame to frame while some report as much as .008" variance. But once again, a barrel that hits on the firing pin bushing on one frame may not close on the next frame if the hole in that frame positions the barrel closer to the firing pin bushing..
Background behind the Bellm Headspace Indicator
The Bellm Headspace Indicator was developed as a result of my many years of measuring case head protrusion from the ends of barrels to determine the proper depth to ream chambers and is THE EASY WAY for the average reloader and real pro alike to quickly and accurately determine EXACTLY what the headspace is with his resized cases, rimfire ammo, and with factory ammo as well, of course!
For years I used a depth micrometer in the shop for measuring how far a case or headspace gauge protrudes from the chamber, but after all these years a depth micrometer is still rather touchy to get an accurate measurement with while balancing it over the end of a case head and being very careful to sense when the quill of the micrometer actually contacts the end of the barrel. Getting lazy, or smarter in my old age, I started using a dial indicator set up on the cross feed of the lathe to measure how far the case heads stuck out. But few people have a lathe handy for doing this. For about a year I toyed with the idea of making this task simple and accurate for the amateur and real guru alike. I think I have "bingoed," and once you try it, I think you will wonder how on earth you ever managed with the old ill-infomred methods we all used for years.
Keep this TIP in mind as you read on: You will also find that there is a "sweet spot" where the case head is neither too far from the breech face of the frame or jammed forward by the breech face when the barrel is snapped shut. This "sweet spot" is where mysterious Contender misfires disappear, failure to cock with Encores and G2s disappears, case life improves, and where the gun shoots its best. It will also prevent many extraction problems that result from cases improperly sized being crammed into the chamber and then not readily extract. Understanding what to do and being able to take the measurements tells you exactly what you have so you can get it right.
The Bellm Headspace Indicator lets you take the same measurements I have to take. You expect me and anyone else cutting a chamber to cut it to a certain depth, and for good reason. Things have to fit right to work right. So how much sense does it make for you to either cram a round in that is too long in the body and sticks out of the barrel too far OR falls too far down into the chamber? Either is bad. Both cause problems. I am expected to do my part, now I am enabling you to intelligently do your part. It is very, very simple and easy. And, frankly speaking, if you are not willing to take these measurements and take a few simple corrective measures on your own as the need arises, sooner or later you will be happier dumping the interchangable, break open barrel systems in general and going back to fixed barrel guns such as bolt actions. No gizmos are needed! No comparators, no modifed cases, no Stoney Point type equipment is needed.
For starters, put them away if you have them, and if you don't have them, save your money, along with a lot of frustration, until you understand headspace and what goes on in a chamber. With the Bellm Headspace Indicator you also measure the distance from the ends of the rifling to the breechface, the firing pin bushing, once again eliminating the need for other measuring devices to determine rifling-to-breechface length, ie, overall cartridge length based on bullet contact at the riflings. Using the barrel itself as the only TRUE gauge for the ammo and frame you are working with, you use the Bellm Headspace Indicator to also measure bullet seating depth. Starting with a bullet seated out a bit far, you measure how far the loaded round sticks out of the chamber, then seat the bullet deeper until the loaded round's case head-to-end-of-barrel reading is the same as with an empty case with its known headspace produced. The barrel IS your gauge. You do not need any other gauging device or gimick to do this. Nor do you have to buy anything else to go from one chamber to the next. You don't even need a caliper or micrometer, and there is no error to be made transferring information from one tool to another. You simply and accurately measure what occurs in YOUR chamber.
No gadget that measures a length on a case, case body, rim, or belt measures headspace. It can measure only ONE parameter, a length (or a thickness) but this is NOT headspace. You must know where the breech face (firing pin bushing) is in comparison to that length. I will make an exception to the above, and that is to verify the consistency of the headspace from round to round using a comparator or a measuring device like the one sold by Innovative Technologies to save time reloading.
(See also their belted mag size die that corrects the bulge just above the case belt not sized completely by some size dies. This bulge can cause problems preventing the case belt from making contact in the chamber like it is designed to do).
redding and others make measuring devices for use in reloading presses, but the Innovative Technologies gauge stand offers a wider range of uses with nothing more to buy and is preferred.
Without taking the barrel off the frame and checking every round, you can use this indicator stand to identify those cases that have the shoulder pulled forward excessively by the size die expander ball. When resizing cases you note that some cases come out of the size die harder than others. Well, guess what.
That strain on the neck going over the expander ball also pulls the shoulder forward. If you doubt this effect simply remove the decap stem and measure the headspace created by a case sized without the decap stem/expander ball installed and compare its body length to cases sized with the decap stem/expander ball installed. I suggest using this type of indicator & stand but with body length verified by cross checking the actual headspace of a round in the chamber. It also serves as a short cut setting up size dies once the headspace produced by a given round is clearly established from the barrel and frame combination measurements, but should be verified from time to time and as loads/pressures change.
Changes in the amount of frame flexing due to changes in pressures result in changes in actual body length the size die produces. Also, case shoulders of all rimless bottleneck cases with long sloping shoulders collapse to some degree under the impact of the firing pin. The result is a case body .003" or more shorter than before firing if the pressure is not high enough to stretch it. Decreasing the headspace produced by shorter cases will result in less stretching when fired again at higher pressures that will stretch it.
Due to: 1) case shoulder collapse from the firing pin impact and
2) stretching of the case along with frame flexing under high pressure,
3) cases fired in the break open guns do NOT represent the actual shoulder to breech face dimension of the barrel and frame combination, and
4) therefore, cannot be used with this measuring device to establish a headspace baseline case body length in the break open guns, nor
5) do moderate loads fired in rigid fixed barrel guns create a true representation when the case shoulder collapses under the firing pin impact and pressure is not sufficient to stretch the case all the way back to the breechface. Take your measurements from the barrel, frame, and ammo combination FIRST, then use the indicator stand to monitor your work reloading.
CRITICAL INFORMATION! PAY ATTENTION!
CASE SHOULDERS COLLAPSE WHEN THE FIRING PIN DRIVES THE CASE FORWARD! With the exception of sharp shouldered cases such as the 40 degree Ackley-type cartridges,
THE IMPACT FROM THE FIRING PIN COLLAPSES CASE SHOULDERS FROM .003" TO .006" TO AS MUCH AS .010" TO .012" ON THE FRAIL SHOULDER OF ROUNDS LIKE .35 REMINGTON! You can very easily demonstrate this for yourself! It should be as obvious as the proverbial train wreck......, however, few shooters are aware of it. Even though evidence of it shows up, it is nearly always ignored. DO THE FOLLOWING:
1) Remove the extractor.
2) Chamber an EMPTY resized and PRIMED RIMLESS bottle neck case.
3) Measure where the case head is relative to the end of the barrel. For example, let's say it sticks out of the barrel .003".
4) Fire the primer.
5) Open the barrel. With no extractor to move the case, you will find the case head is now anywhere from .003" to .006" FORWARD of where it was before you fired the primer. The long sloping shoulders and/or shoulders with a very small shoulder area collapse the most.
Quick examples are: .308 Win., about .003" .35 Whelen, about .006" .35 Remington as noted above, about .010" to .012" .280 Ackley Improved, usually less than .001" Thus if headspace is a bit on the generous side, say more than .003", the instant the firing pin drives the case into the chamber deeper, headspace is increased to or in excess of the .006" that is generally accepted as maximum. You will also find that if you start with published starting loads and work up, shooting without the extractor the cases will stay forward in the chamber and not even move back to fill the barrel-to-frame gap until loads approach maximum.
Tapered cases will move back at lower pressure than will straight walled cases like .308 Win. .308 Win. cases will not move back until nearly published book maximum loads. This is one of the main reasons why you cannot rely on a fired case to determine case body length to establish a baseline for correct headspace. The Bellm Headspace Indicator is made for both Encore and Contender/G2 barrels. The Bellm Headspace Indicator base is made double ended, with one end at .810" for Contenders and the other at 1" for Encores.
To go from Contender to Encore mode, just loosen the set screw in the side of the base and insert the dial indicator's stem from the opposite end. Matching up the diameter of the appropriate end of the indicator base with the breech end of the barrel positions the quill of the indicator over the solid head of a case in the chamber, just outside of a large rifle primer pocket. You hold the indicator base on the end of the barrel with your finger and thumb gripping the base and barrel togehter. This keeps the base centered over the end of the barrel while the offset indicator quill contacts the head of the case, missing both small and large primer pockets. It is set up to work this way with any cartridge from .22 Hornet up through the belted magnums and .404 Jeffery type rounds.
It is also used with rimfire barrels, but the base must be moved over slightly to position the indicator quill over the head of the case. The ends of the base are recessed .1" so that when positioned on the end of the barrel with a case in the chamber, the case can project out of the barrel while the base itself is sitting flat on the end of the barrel.
(Note: Early production bases were recessed only .050," but to make it easier measuring throat length, we went to .1".)
Let's start. First measure the barrel-to-frame gap.
Using a common set of feeler gauges you first determine what the gap is between your barrel and frame's breechface by closing the barrel on successively thicker blades placed in front of the plug in the breechface until you find the blade that is gripped by the closed barrel. The thickness of the thinner blade just below the one that is tight in the gap is the gap's measurement you use. Make note of this amount.
If you use the barrel on more than one frame, you should make a note of the serial number of that frame since the barrel-to-frame gap will vary some from one barrel to the next and from one frame to the next. Due to normal acceptable manufacturing tolerances each barrel and frame combination can be different. I usually scribe or stamp the barrel-to-frame gap on the bottom of the barrel lug for reference later when switching from frame to frame or as a means of monitoring a frame for signs of stretching. An increasing barrel-to-frame gap is an indication metal is moving, meaning the frame is stretching.
The barrel-to-frame gap measurement must be taken at a point directly above the chamber, between the firing pin bushing and the end of the barrel. Because the firing pin bushing sticks out of the frame a few thousandths, you cannot slide the blade in. You must close the barrel on the blade.
The thinnest blade in most feeler guage sets is .0015," while some go to .001." If the barrel closes on the thinnest blade, call the gap Zero.
To use the Bellm Headspace Indicator itself,
first loosen the knurled knob at either 10 o'clock or 2 o'clock. This knob locks the dial face in position.
Next, place the base on a flat surface such as a smooth table top. With the indicator quill contacting the surface the base is sitting on, turn the dial face so the hand lines up with "0." Lightly tighten the dial face lock so the face will stay where you set it.
The pointed tabs over the dial face are for setting upper and lower limits of measurements. Normally, for what we use these indicators for, we do not use them, but you may. Remove the barrel from the frame, and if the extractor sticks out of the barrel too far, you may have to remove it also by driving out the roll pin that holds it in.
With the indicator zeroed and then placed on the end of the barrel with a sized case in the chamber, it will then show exactly whether the case head is below the end of the barrel, flush with the end of the barrel, or by how much the case head sticks out of the barrel. Just be sure to always watch what direction the indicator needle is moving, up or down, in relationship to your "zero," ie, the end of the indicator base/end of the barrel.
Note that the case head should ideally never sit below the end of the barrel,
even if the barrel is tight on a .001" or .0015" feeler guage blade, which is usually the thinnest blade in a set. With a really close barrel-to-frame gap, the case head should be flush with the end of the barrel and never more than about .002" below the end of the barrel. This would result in an actual headspace of about .003".
If it is more than .002" below the end of the barrel, you will need to shim the firing pin bushing forward, BUT since there is no room to move the bushing forward, you will have to face off the end of the barrel to make room for the bushing.
Nor should the case head stick out more that what the gap actually measures. The ideal is to have the case head stick out about .001" LESS than what the gap measures.
I.E., if the gap is .003," then have the heads of sized cases stick out .002." This gives a heaspace of .001." Many folks don't understand what headspace is. Here you see it. It is the actual distance, space, between the case head and the breech face. If the case head sticks out MORE than what the barrel to frame gap is, this is referred to as "negative headspace." Having case heads stick out more than what the gap measures causes all sorts of problems, and getting cases sized right cures the vast number of problems that plague shooters of break open guns.
Summary of Headspace Conditions:
If the case head is perfectly flush with the end of the barrel, the headspace will be what the barrel-to-frame gap measures.
If the case head sticks out of the barrel any at all, the headspace will be the barrel-to-frame gap MINUS how much the case sticks out of the barrel.
If the case head falls below the end of the barrel, add the distance from the end of the barrel down to the case head to the barrel-to-frame gap measurement. This total is the actual headspace.
If the headspace is more than .006" it exceeds SAAMI industry standards, and the condition should be fixed.
Headspace as it relates to misfires:
The greater the headspace, the more distance the firing pin has to drive the case forward in the chamber until it comes to a dead stop and the firing pin can expend its energy denting and firing the primer. If too much energy is lost moving the case forward, there may not be enough energy remaining to fire the primer even though the primer may appear well dented. Thus, minimal headspace is mandatory not only for best accuracy, but even useable accuracy and reliable functioning of the gun.
If the case head sticks out of the barrel more than the barrel-to-frame gap measures, it prevents the barrel from closing all the way and the locking bolts from traveling far enough under the frame's "locking table" for an adequate lockup.
In Contenders, the result is that the hammer block is not fully released so it can freely drop fast enough to clear the hammer. The hammer knicks the top of the hammer block and even though it may still dent the primer, too much energy may be lost hitting the hammer block to still fire the primer. THIS IS ONE OF THE MAIN CAUSES OF CONTENDER MISFIRES!
In G2s and Encores, incomplete lockup due to the case sticking out too far prevents cocking the hammer
Until now, there has been no convenient way for the average person to accurately measure the distance the case head sticks out the barrel.
Worse yet, the vast majority of Contender and Encore shooters don't have the foggiest notion about how to adjust the size die to get the correct headspace. And the travesty is that those who do often attempt to use SAAMI gauges, which in the real world is no where nearly correct when hinge pin holes in barrels and frames vary as much as they do.
You HAVE to first know what the gap is then MEASURE where the case head is situated relative to the end of the barrel. This set up lets you do it accurately and easily, just like I have to do when cutting the chamber and throat length to the correct depth.
You expect the chamber to be cut to the right depth, but unless you can take the necessary measurements, you will never consistently make the cases or loaded ammo the right length. The fact is that with handloaded ammo the depth of the chamber is not important IF you make the ammo fit the chamber. Precise measurements let you do this. And if you shoot factory ammo, you still need to measure the actual headspace since it is very common to see a "stacking of tolerances" that create really excessive headspace resulting in misfires and poor accuracy due to eratic ignition.
A combination of a chamber on the deep end of the .006" tolerance limit, factory ammo on the short side of the .006" tolerance limit, and a frame hinge pin hole on the forward side of tolerances can result in headspace well over .010." And with belt height variations on belted magnum ammo, headspace can be well over .016."
What happens when a round is fired?
The firing pin has to drive the case forward in the chamber until it comes to a solid stopping point. This can be the case shoulder, the case rim, or the belt on a belted magnum round.
It takes energy to move the round forward. The farther it has to be moved by the firing pin, the less energy is left to fire the primer. If the distance is too great, the primer recieves a softened blow instead of a brisk strike..... like getting pushed with a pillow versus a quick jab with a stick.
If the strike from the firing pin is too soft, primer ignition may be eratic or it may not ignite at all even if it is dented pretty well. While a stronger hammer spring will ususally stop misfires due to excess headspace, the stretching of the cases that occurs can cause them to fail quickly if they are reloaded.
when a round is fired, the break open actions flex from the force coming out the chamber end of the barrel. How much the frame flexes depends on how much thrust there is from the case head pushing on the breech face. High pressure, large diameter rounds like 7mm Rem. Mag. and .300 Win. Mag. exert the most force on the frame, and the smaller diameter and/or lower pressure rounds like .22 Hornet exert the least. Of course the rimfires exert the least of all, but are not what we are concerned about here.
There is a certain amount of "play" in the locking bolts, the hinge pin, and the general fit of the barrel in the frame. Plus, the long, thin slab sides of the TC frames are somewhat springy compared to a bolt action rifle where the locking lugs on the bolt are close to the end of the barrel.
Thus, when these break open guns are fired and the barrel and frame flex, the cartridge case moves and/or stretches back. While the frame returns to its normal "at rest" dimensions, it does not force the case back to its original dimensions and leaves it too long to go back in the gun without some force on the case head.
This extra length must be removed or the breech will be cramming the case in and up in the chamber the next time it is reloaded and fired. Size dies must be adjusted to push case shoulders back the correct amount to produce a protrusion of the case head that is not greater than the barrel-to-frame gap measures, and preferrably just protruding .001" LESS than the barrel-to-frame gap measures.
Resizing to bring a case back to the correct protrusion from the end of the barrel can ONLY be accomplished by full length resizing. If the full length size die will not push case shoulders back far enough when the shell holder is run all the way to the bottom of the die, then the die must be shortened from the bottom end until it will move the case shoulder back where it needs to be.
While neck resizing may work at lower pressures and for just a resizing or two, sooner or later cases will become too long and have to be full length resized. Any attempt to push case shoulders back with a neck sizing die can result in the cases bulging outward below the shoulder and sticking in the chamber.
Correctly adjusted full length resize dies are the only way to go for reliable functioning.
Here you have a round sticking out of the barrel less than .004", correct for a .004" barrel-to-frame gap
Note there is no extractor in the barrel so that when it is fired the case head will be in the same place it was after firing.
After firing and with no extractor to move the case you can measure how much more the case head sticks out of the barrel than the gap measures.
Here you can plainly see it is sticking out .006" as indicated on the dial, .002" MORE THAN THE GAP MEASURES.
With no extractor in the barrel, the case head remains wherever it was after the shot. Removing the barrel from the frame and measuring the protrusion of the case head, you can see that with a .004" barrel-to-frame gap, this mild .30/06 load leaves the case head sticking out of the barrel .006", which is .002" more than the gap.
This means that if you do not bump the shoulder back at least .003" in this particular situation, the frame will be jamming the case into the chamber when fired the next time.
****You not only need to remove this excess BODY length (not to be confused with overall/trim length) by running the case farther into the size die, but you need to know HOW MUCH change you make. This means you must take measurements of how far the case sticks out of the chamber. It must not be more than the gap measures and ideally should be .001-.003" LESS than the gap measures, but it should NOT fall below the end of the barrel.
As stated above, you can NOT determine headspace by measuring the length of a fired case!
Period. Amen. End of Conversation. It cannot be done with any accuracy at all.
There is a school of thought carried over from the bolt action arena where size die adjustments are based on duplicating fired case body length..... which is totally bogus with the break open guns!
Due to variances that occur in THIS mechanism it can NOT be done. To think otherwise is simply missing some important facts Please excuse me if this comes across as a tirade, but I am tired of trying to correct all the misinformation put out by a number of "experts" including much of the firearms industry as a whole.
Facts are facts, whether you personally have paid enough attention to the right things to see it yourself or not.
ou can easily see it IF you will just look. If any of this offends you,
it is better you take offense now and get rid of the system if you won't accept and deal with the facts,
OR, lay your problems and arguements at someone else's feet. I am developing zero tolerance for stodgy, bone-headed stupidity.
I'm here to fix the lack of knowledge and don't keep a baseball bat handy to fix stupid.
Here are the FACTS! All you experts out there pandering erroneous ideas.... open your eyes! Pressure level, case shape, and brass thickness control how much the case moves back in this springy mechanism.
- With a full normal max load in most rounds as clearly shown above, the frame flexes, and play at the locking bolts and hinge pin allow the case to move back or stretch back MORE than the barrel-to-frame gap measures AT REST.
- Loads light enough to NOT move the case back will leave the fired case FORWARD in the chamber, giving a false indication that the distance from the shoulder to the firing pin bushing is shorter than it really is. All you have to do is remove the extractor and start measuring and shooting. With no extractor to move the case, you can see and measure exactly where the case head is both before firing and after.
- You will find for example that straight wall cases like .308 Win. are driven forward by the firing pin at least several thousandths, and it is not until nearly full maximum loads that the case even comes back even with the end of the barrel or touches the firing pin bushing.
- On the other hand, more tapered cases like .30/06 & .270 Win. especially will move back and protrude MORE than the at rest barrel-to-frame gap measures.
- The bottom line is the case head can end up anywhere after the firing cycle has completed.
- It can end up WELL below the end of the barrel, FAR away from the firing pin bushing.
It can end up sticking out substantially MORE than the barrel-to-frame gap.
- by coincidence only, it can end up ON the firing pin bushing without enough force to flex the mechanism and thereby accidentally giving a true reflection of the actual distance from the shoulder to the firing pin bushing.
These comments are geared to bottleneck cases primarily because this is the realm where most errors occur.
- When you measure a fired case from shoulder to headstamp, the fact is the case may be much shorter than actual dimensions in the gun itself, or it may be substantially longer.
- It is not only a waste of time and money to attempt to measure headspace based on a fired case, it is simply gross ignorance of the gun and what actually happens when the gun is fired. To cling to that mindset is gross stupidity that is greeted rather brusquely when you lay your problems related to it at my feet.