Precision Re-Crowning Barrels
Much of the time factory and even a lot of "custom" crowns are cut off-center and/or out of square with the bore. There are other ways to go about it, but this is the best I have come up within the last 34 years.
All too frequently, bores are not centered at the muzzle.
Factory and much "custom work" produces a surface at the end of the bore that is out of square to the bore. With the barrel turning between centers, the end of the barrel wobbles like a bent car rim.
This means that one point of that surface is farther ahead than the other. Gas then escapes behind the bullet from the side that is shorter, kicking the bullet into an exaggerated yaw that results in erratic impact points on the target, ie, poor accuracy.
The bullet needs a uniform push from all around its base at once to get a straight departure from the muzzle.
Just simply holding a barrel by its exterior and making a cut does not give a cut square to the bore IF the bore is not perfectly centered with the outside of the barrel. This is ESPECIALLY true when a barrel is shortened
No bore is perfectly straight, and when you get back away from the end of the barrel, the bore can be very radically off-center.... ie, not in the middle of the barrel. There has to be a correction made for this condition in order to get a square, centered cut, regardless of what shape of crown one uses.
Some like radiused crowns like found on a lot of factory rifles, particularly of older vintage. Some like perfectly flat crowns while some like a more angled crown, and the benchrest crowd theorized the escaping gases leave at an 11-degree angle, no matter what, so 11 degree has become vogue as the precision "benchrest crown".
No matter how it is shaped, it must be centered and square to the bore itself.
Piloted tools in general..... piloted crowning tools specifically: No matter how you slice it, no matter how warm and fuzzy a pilot may make you feel, the fact is that a pilot simply CANNOT, in reality, keep things precisely lined up. There are situations where a piloted crowning tool has some merit, but no matter how you go about it, it is not perfect. It will always have the potential to allow misalignment to varying degrees.
A crown cut with a piloted tool, done right, is better than the proverbial "jab in the eye with a sharp stick," but still not as good as a crown can and should be done.
My method references off the bore itself, dialed in to within .0005" of true center of bore.
Barrels shorter than 20" are done with the Bondo and pipe sleeve method shown below. No matter how far off-center the bore is, the crown is cut centered with the bore to within .0005" and square to the bore. Plus, it protects the barrel's finish.
Yes, there are other ways to go about this, and on 20" and longer barrels I do have a smaller lathe where I can put the barrel through the spindle, then dial in the bore.
One could turn a true section on the end of the barrel and run it in a steady rest. Not pretty.
With a short enough spindle, large enough spindle bore in the lathe, and a long enough barrel, yes, one can certainly put the muzzle in a 4-jaw chuck and dial it in. However, this will usually produce some rather ugly marring of the finish
Too much work!
That is what some folks doing barrel work seem to think about my method. And,
it is a significant amount of work, yes.
Mmmmmm..... which is to say they don't think about you are worth it.
My thought is if it isn't worth doing right, it isn't worth doing, and
you deserve better!
Here's the process I use when recrowning all barrels under 20" and when doing the internal work in my muzzle brakes on all lengths of barrels, starting with a good dose of release agent on the barrel.
Nothing too sophisticated. Most of the time I use some old lithium cup grease. Lately I have been first slathering on some good old fashioned Turtle Wax car wax, letting it dry well, then apply a thin film of grease.
Swiss cheesed piece of pvc pipe slipped on
Flutes in the barrel or ports in the barrel for my muzzle brake provide a "Key" to keep the sleeve from rotating on the barrel.
Plain old Bondo auto body filler is then goobered well into the holes in the pipe filling the voids inside. Before the Bondo "kicks", the previously inserted cleaning rod and patch that kept the Bondo out of the good part of the bore pushes the Bondo and patch out the muzzle.
Use the cheap stuff. "Premium" fillers can adhere too well and are harder than necessary for the job, plus can be more difficult to remove as a result of both.
3/4 in. pvc pipe fits most barrels up through .810" diameter Contender and heavy production TC factory Encore barrels, including the "Pro Hunter" rifle barrels.
Tapered barrels require some tape wrapped around the barrel or toothpick size wood shims, etc. to shim the pipe kinda centered with the barrel
Barrels require drilling and tapping for a sight screw to anchor the pipe sleeve when recrowning.
Barrels ported for my muzzle brake use the ports to anchor the Bondo and sleeve.
That's a screw with Bondo goobered to it sticking up at the rear of the pipe.
When the Bondo is well hardened, the barrel is then run between centers turning the pipe sleeve and body filler down to the inside diameter of the bearing that will be put snugly on it.
984 in. is perfect for the 25mm bearing I use for most jobs.
Heavier barrels require a larger bearing. For the larger diameter barrels I use a bearing with a 1.180" inside diameter.
The bearing is then put on, hopefully with a little effort, but not enough to break the Bondo loose.
Shop rag across the ways helps keep the mess under control. Any type will do. It does not have to be a floral pattern like this one :-).
A little lightweight oil does wonders, and if the bearing goes on a bit too easily, grease snugs things ever so slightly while giving the sleeve a little bit of "float" that tool pressure tends to equalize.
Note that "live centers" have a certain amount of runout in them, so I use nothing but a carbide "dead center" in the tailstock, except for the largest bore sizes, .45 and over, for which I do not have a carbide center large enough
The steady rest is then installed, and a dial test indicator is used to make sure the steady rest posts are adjusted to true center of the bore.
As the steady rest posts are brought into contact, the outer bearing race is pushed back toward the headstock, firmly holding the chamber end against the center in the chuck.
From the side it looks like this.
For inquiring minds, the lathe is a 1980 South Bend 14x40 I bought new and have worked on exclusively these last approx. 30 years.
Note that I do not use a dead center in the spindle.... for a couple reasons.
1) I use an adjustable back chuck that is very closely dialed in, and I do not want to disturb it, even though, yes, I can dial it in again..... but why?
2) I lathe turn a bar of steel in the chuck so that the center is then as precise as the bearings in the headstock. I do this every time I install a center to turn something between centers.
It is a choice of the lesser of the evils. This is the evil I like best.
Note the fancy brazing job on the bolt extending the lathe dog to reach the chuck jaws. Why so long? Works best for Contenders, which is what it was originally made for over 20 years ago. Not the prettiest, but an old friend.
With compound set for 11 degrees off of square, cut is made such that as much tool pressure as possible is directed outward, away from the bore, to minimize tool pressure inward that tends to roll a burr to the inside.
I use mostly tool steel with some rake, lots of clearance, very sharp, and dress it with a Diamond EZE Lap before each final cut.
Those who are familiar with machine work understand the terms. For the Laymen, get some books on machining
Note that if the original crown or a saw cut is not perfectly square to the bore, the cone shaped center cannot "see" the true center of the bore. Most barrels require squaring the original crown or saw cut first, then turning the sleeve a second time, farther back to get the sleeve's surface concentric with the bore.
And, by the way, a big percentage of barrels leave here shorter than they were when they arrived. This is another example of "Have it YOUR way"!
An accumulation of end cuts at the saw. Note most of the shorter pieces are buried under the longer pieces tossed in on top
Much of the break open single shots' handling qualities are lost to overly long barrels on one hand, and on another, there are many, many applications where a shorter barrel simply makes more sense for use in close cover or where compactness is really needed on an atv or as a quick handling "truck gun".
Then of course there is the option to cut down a rifle barrel to get the weight and length you want in a handgun barrel. I also drill and tap rifle barrels for the handgun forend screw hole spacing.
Quite a few muzzle loader barrels also get abbreviated, both with plain, beveled crowns for easier bullet seating or with the "QLA" or "Bore Guide Muzzle" precision cut.
Any indication of runout in the bore is a result of either the center not "seeing" true center of a badly out of square end of the barrel or the steady rest pushed the bore off center.
You can see runout pretty easily, especially with the tool next to the spinning edge of the bore. Or, use a dial indicator or coaxial indicator to measure your runout.
In any event, runout means you start all over, turning another section of the pipe with the barrel between centers to get the bore running true, on center in the bearing.
Checking runout with a dial test indicator
As noted above, an out of square muzzle or the steady rest posts pushing the bore off axis results in a crown that is less than concentric with the bore.
The dial test indicator lets you tweak the steady rest posts to get the bore on axis. If it cannot be brought back on axis, then the muzzle end is squared, and the process repeated.
I shoot for a .001" or less T.I.R., that's "total indicator reading" to the layman, meaning the bore is on axis to within 1/2 thousandth, .0005" on axis in any direction.
For barrels over 19", I can also do crowns dialed in as above but with the longer barrels stuffed through the headstock on a smaller lathe.
This requires a bushing/sleeve over the barrel closer to the chamber end to center it in the spindle of the lathe and protection of the barrel's finish at the muzzle end. Stainless steel shims are used to get the bore adjusted so it is running true with the same minimum runout as described using the Bondo-ed pvc pipe sleeve above
This is what the end product should look like, no pun intended. You can see the outline of each land and groove.... NO BURRS smudged over.
Note I break the outside corner of the barrel instead of leaving a sharp corner like factory barrels that tend to put excessive wear at the muzzle end of gun cases.
There are mixed feelings about the extreme edge of the bore and ends of rifling. Some like to give this area a light polish with fine emery paper, though I prefer a clean enough cut that no polishing is necessary.
However, I have been known to do both and feel there is nothing compromised by breaking the sharp edge with emery paper pressed against the end of the bore while the barrel is turning. It could also be argued that a uniform and slightly radiused edge is better and less susceptible to damage as from cleaning rods, jags, etc.
As a final test, I like to drag the shank of a cotton swab over the edge of the cut. If it feels sharp and drags on the shank, I polish a little until the shank of the cotton swab glides smoothly across the edge.
This is the same setup I use for lathe boring the expansion chambers inside my muzzle brakes, as well as doing the crown inside at the ends of the rifling.
The difference is I am using indexable carbide boring bars to do the internal work
It is messy work, somewhat tedious work, but the only practical way I know to get the job done accurately while protecting any finish.
All the epoxy dust and crud gets into everything and requires some health, thorough "sanitizing" afterward. That is the reason I batch the work rather than going through the whole process turning the dead center in the chuck, setting up the compound for the cut, and doing all the extensive cleanup for just a job or two
Why do it? You deserve it done as right as I can do it.
Is it mandatory for every barrel? No. Interestingly, some pretty crappy factory crowns still shoot well, so if this applies, it ain't broke, so don't fix it.
I also have a method to clean up light burrs on crowns without all the above work and do it no charge. However, the touch up can only do that, touch up. It cannot correct for lack of symmetry and squareness that can only be done between centers, referenced directly off the bore and with no runout.
If the crown looks reasonably good, shoot it first and see what it does, but some are so pitifully, sloppily done there simply is no choice but to redo them.
Why make this information available?
It underscores the difference between what you get in most crowns and what a crown should be. If a crown is not perfectly symmetrical about the bore, and you cannot see the outline of the riflings..... well, something is just not right.
If it doesn't look right, it probably isn't. And if it does look right, there is a much higher probability that it IS at least reasonably right. However, I have been surprised a number of times when a crown looks pretty darned good, but when put between centers the crown cut wobbled all over the place, totally out of square to the bore it is supposed to be referenced off of.
I've spent 30 years scrutinizing every vintage of TC crown, bitterly disappointed day in and day out. Were it not so, I would not have gone to the extent I have to correct them.
I also firmly believe we need more high quality local support for all shooters, particualarly fellow TC shooters. I certainly cannot do it all, and in these somewhat tough times and times ahead, it will likely become more and more important to have local access to guys with a lathe that give a damn about you, their fellow shooter.
And..... I'm no longer 32 years old and feel it's time to pass more along to others.
The Bottom Line:
If you are going to do it, do it right.
While piloted crowning tools are better than nothing, there is no way they can keep the crown cut truly square to the bore like you can when the bore is dialed in.
All the best,