The official Mike Bellm's

Bellm TCs


TC Contender, G2, Encore/ProHunter Performance Center

 






Two trends in making both factory and custom barrels have been
1) to lean toward a loose lockup so every barrel will hopefully fire on every frame, and
2) to avoid daylight between the end of the barrel and the frame.

Both conditions can be problematic, but a loose lockup is the worst about scattering shots like a blown shotgun pattern.

Avoid frustration, time, and money spent on barrels that no "working up a load" pouring hundreds of dollars' worth of powder & bullets down the tube or trying a dozen different factory loads can fix when the problem may simply be lockup.

No ammo combination is going to fix a loose lockup!

In reverse order, let's take up daylight at the end of the barrel first, though it is less of an issue generally.

On the Headspace, How To Get It Right page and on You Tube, I make the point about daylight between the end of the barrel and the breech face not being "headspace", yet even many "in the trade" still refer to it as headspace, which it is NOT!

There is no "headspace" with an empty barrel since there is no cartridge case "head" in the barrel, so the barrel alone cannot have headspace.

And for years I saw shooters on forums yelling headspace because they could see some daylight..... which is pure ignorance.

The problem is two fold:

1) The biggest and most common problem is IF the barrel is hitting hard on the breech face, technically the firing pin bushing, it is not able to make full rotation down to make solid contact in the radiused seat in the frame. If it is not seated all the way, the maker can not do a proper job of fitting locking bolts for correct engagement in the frame. If it is not seated in the frame, it is not being held rigidly in the frame and tends to scatter shots.

2) I have seen barrels shooting 3-4 inch groups with factory ammo settle in to 1 inch groups JUST by removing material from the end of the barrel to give it some clearance.

..... and a third point not specifically related to lock up:
If there is no space between the end of the barrel and the firing pin bushing, you cannot shim the firing pin bushing forward to correct excess headspace.

To make this more clear, let's say the barrel is hitting on the firing pin bushing, which is a definite if there is a half moon arc in the barrel finish above the chamber where the firing pin bushing is hitting the end of the barrel. Or, if it is a used barrel you acquired, ink the end of the barrel, open and close the barrel briskly a few times, and see if the firing pin bushing is making a mark in the ink.

In the real world, the barrel maker or custom guy like me has to cut the chamber for the longest bodied ammo and take into account that frame hinge pin hole locations vary by several thousandths also. Then the ammo maker has to make ammo that fits into the most shallow chamber according to industry standards.

If you end up with a somewhat deep chamber and somewhat short ammo, you can have a fist full of headspace, then wonder why you get misfires and/or cases that separate after just a few reloadings.

To correct this you shim the firing pin bushing forward, but must have space for the bushing to be moved forward.

Thus some barrel-to-frame gap or daylight must be present, or, you have to face off the end of the barrel to make space.


See Headspace, How To Get It Right. Click Here.

But there is a problem with facing off the end of the barrel if the locking bolts were fitted to a barrel not making full rotation into the seat!

Once the barrel is faced off, and the barrel can then make full rotation down into the seat, there is a strong chance the locking bolts end up too low in relationship to the frame.

The result is a loose lockup and some real difficulties lie ahead getting taller locking bolts.

So, before you face off the end of the barrel, check to see if it is seating in the frame:

If the barrel is seating in the frame, there will be wear marks on the bottom sides of the barrel, just above the lug.

On Encore and G2 frames, the contact point is back behind the two cut outs in the sides of the frame.... back toward the very rear of the barrel.

On Contender frames, the contact point is just in FRONT of the two cut outs.

Why the difference?
First off, why is the contact not all along the seat in the frame?

The reason is due to tolerances in manufacturing possibly not letting the barrel swing over the radius without binding toward the front end of the seat.... thus not closing all the way.

To compensate for this, the hinge pin hole in the barrel lug is drilled LOW in the LUG, making the barrel HIGHER in the frame and thus clearing the length of the radius.

A simple redesign of frames shortening the length of the seat would seem logical, but in spite of all the good engineering done designing frames, this is one point that has continued to defy all logic. The long seat is like a vestigial organ on an animal that serves no purpose. Or, in plain language, like mammary glands on a boar pig.

Thus, the barrels only make contact toward the rear end of the seat, and in Contenders, there is no seat behind the cut outs in the sides of the frames. The contact point in Contender frames is IN FRONT OF the cut outs.


Check also for high spots in the weld making contact with the seat at any point.

It is quite common for a high spot in the weld to hit in the seat, preventing the barrel from closing all the way and making contact at the rear where it is supposed to.

Grinding or filing down a high spot, like facing off the end of the barrel, can result in the locking bolts being too low in the frame and resulting in a loose lockup.

Soooo, before you face off a barrel, ink the bottom sides, open and close the barrel a few times, briskly, and be certain there are marks in the ink indicating contact in the seat!
On Contender frames, the contact points on the barrel will be in the area corresponding to in front of the cut outs in the sides of the frame.

On G2 and Encore frames, the contact points on the barrel are in the area corresponding to behind the cut outs in the sides of the frame, i.e., the small area of the seat just in front of the breech.



IMPORTANT NOTE ABOUT BARRELS THAT WILL NOT UNLOCK FROM EARLY VINTAGE CONTENDER FRAMES:

The most apparent characteristic of the "early" frames is the trigger guard pivoting at the front of the frame, just below the hinge pin.

Early vintage Contender frames do not have clearance for the later/current style barrel lugs with the step on the bottom of the barrel lug and will not accept the stepped lug barrels.

The early Contender barrels up until about the 1980's were flat bottomed. The next vintage Contender barrel lugs from the early 1980's to date have about a .050" thick step under the locking bolt slot in the lug to reduce the tendency for the lower lip of the barrel lug to bend downward, creating a loose lock up. The step gives the lug more strength for the higher intensity cartridges.

The early frames do not have clearance in the trigger housing for this step.

The result is a stepped lug barrel installed on an early frame does not allow enough upward travel for the cams in the trigger housing to retract the locking bolts and allow the barrel to unlock from the frame.

Unfortunately, I do not have the frame serial number range to tell you what frames are lacking this clearance.


I don't know of any firearm that has undergone as many internal changes as the Contender. There are no doubt records of the changes, but I do not have them to offer.

Don't ask me why the lack of clearance escaped me for years. For years I told folks to dress down the top of the locking bolts until the barrel opened ok..... and I apologize for the erroneous information I put out.

It appears these early trigger housings can be milled out to give clearance for the stepped lug barrels, but at this writing I need to look at this more closely to verify it can be done ok, and if so I may offer this service.

On these early frames, occasionally I have seen barrels that unlock from the breech ok, but won't open all the way......
Usually this is due to the bottom, front corner of the barrel lug being a bit too thick and binding on the trigger guard housing.

It can be seen as a marred spot on either the bottom front of the lug or inside the frame, just behind where the trigger guard housing pivots. Once again, inking with a felt tip pen will indicate where the two parts are binding.

The best solution is to grind away some clearance on the trigger guard housing.... as opposed to leaving bare metal showing on the barrel lug.

On Encores, once in awhile I see barrels that will unlock, but not open all the way. This is most often due to the front tip of the extractor binding between the barrel and frame and not being cammed back by the front wall of the frame.
The fix is to grind back the angle on the bottom/front end of the extractor.
Generally it is better to simply move that angled surface back, i.e., shorten it, as opposed to changing the angle.

At this writing, I don't recall this happening on G2 frames, but have seen it many times with Encore barrels.



Now, down to the issue of lockup.


OK, the barrel has to be able to rotate all the way down in the frame's radiused seat solidly with the locking bolts wedging it tightly in place.

In the 3 examples below we'll look at the relationship between the locking bolts and the frame's "locking table," the surface just below the breechface that the locking bolts slide under to wedge the barrel down tightly in its seat in the frame.


1) Minimum lockup example:

Minimum lockup is enough to push the interlock back in the frame to permit the sear to rotate and allow cocking the hammer.

If you cannot cock the hammer, the interlock is simply doing its job when the locking bolts are not engaged far enough in the frame to safely fire a round.

The top surface has been blackened with a felt tip pen, then the barrel opened and closed a few times. The shiny surface toward the bottom edge is where the locking table in the frame has marred the ink to show how far the locking bolts are going into the frame, under the bottom edge of the breech face.

2) Correct lockup example:

Below is an optimum engagement of the locking bolts, roughly 1/2 way up the slope of the engagement surface.

With the engagement at the midpoint on the engagement surface, there is still at least a couple thousandths of an inch of tightening potential before the locking bolts are extended as far as they can go.

At the same time, the locking bolts are low enough to allow cocking the hammer on frames that are on the tighter end of manufacturing tolerances.

3) Loose Lockup due to locking bolts being too low and in this example, also too soft:

Note that the ink has been marred almost to the very top of the slope, indicating the locking bolts have been extended as far as they will go.

If the locking bolts cannot wedge the barrel down tightly into the frame, the loose lockup will tend to fling shot up and down as well as scattering shots side to side.

The barrel must be wedged down tightly into its seat in the frame making the barrel and frame a more rigid, solid unit for best accuracy.

Pic rotated to better show where the engagement slope ends and how far up the slope the ink has been marred.

I have also enlarged it to show the left locking bolt has deformed and rolled a ridge of steel up at the top of where the bare steel is exposed. This rolled up ridge prevents the locking bolts from engaging further into the frame.

So, the problem is two fold.
1) The soft metal has been deformed, and
2) once deformed, too low, and now the ridge prevents the locking bolts from traveling farther into the frame to tighten lockup.

The obvious solution to this condition is properly sized locking bolts correctly hardened.

Locking bolt hardness.
Early TC factory locking bolts were quite hard and apparently made of investment cast case hardened 8620 nickel steel, which was an excellent choice in that the hard surface at about Rockwell C scale hardness 60 resisted wear and deformation while the core of the steel only hardened to about Rc 40 was ductile, meaning it would be more likely to bend than to just snap off.

8620 nickel steel is often used for parts to be case hardened because of its low carbon content, the 2 in its analysis, which will only harden to about Rc 40, still in the ductile/bendable hardness range.
Chemical analysis of the locking bolts I had tested came out to 8640, the 4 being the points of carbon in the steel. The higher carbon content likely from the carbon added to the surface during case hardening. Thus the assumption they were made from 8620 steel.

Later locking bolts appear to be a higher carbon content steel heat treated all the way through at about Rc 40 which has proven to wear well and not be prone to breaking.

Locking bolts made by the custom barrel makers who make their own are similar to current TC locking bolts in hardness, which should be in the range of about Rc 38 to 42 ideally, though some may test slightly harder.

Locking bolts softer than about Rc 35 tend to deform/wear readily with loose lockup being the result.

Bergara's locking bolts are made by the powdered metal process, called MIM for Metal Injection Moulding, and test out around Rc40.

Whether MIM-ed, investment cast, or machined, locking bolts in the Rc40 range hold up well normally with little sign of deformation or wear. Whether deformation occurs or not depends on how much force a cartridge puts on the locking bolts under pressure, meaning for example that softer locking bolts may not be deformed by a .30/30 Win. barrel, but would be deformed by a .300 Win. Mag. barrel.

More to come...... so check back in a few days.


 

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