How critical is the muzzle crown on a barrel used exclusively to fire saboted bullets?

[Bruce in WV]

I’m getting down to the end on my project rebuilding a badly abused American Knight 50 cal. Lapping the barrel got it to shoot OK, so I’m just fine-tuning whatever variables are left. I’m considering doing a clean-up on the muzzle crown using a brass muzzle crowning lap and 600 grit to recut the crown just enough to get back to a clean exit hole.
The muzzle is worn and the rifling and lands are not perfectly aligned at the end of the barrel.
It may be unnecessary: I don’t know if a saboted bullet needs a perfect crown. I’d appreciate input from the experts here.

 

[az jerry]

Had the same problem with my tc scout. we just ground the taper a little deeper. now all of the rifleing meets at the end. the man that did it had a tapered stone. worked just fine.

 

[Bruce in WV]

Had the same problem with my tc scout. we just ground the taper a little deeper. now all of the rifleing meets at the end. the man that did it had a tapered stone. worked just fine.

Did it improve the accuracy of the barrel?

 

[snapbang]

Its got to help Bruce. That was one of the lessons I learned from Mcphersons book on accurizing a rifle. Think of the tremendous pressure pushing on the base of the bullet/sabot as it exits the barrel. All is well until for one part of an instant the pressure drops on a partial of the edge. Thats got to handicap the accuracy.

 

[az jerry]

Did it improve the accuracy of the barrel?

100 %

 

[az jerry]

We only had to grind the taper A little bit deeper, not very much. Now the round ball sets in there very nicely. And conicles don't deviate in all different directions.

 

[az jerry]

Just make sure it's set up perfectly so that you grind evenly all the way around, perfectly straight. I finished the end off with a little steel wool and touched it up with some Blueing. You can't even tell any work was done.

 

[Squint]

Did it improve the accuracy of the barrel?

I purchased 45 caliber Lyman a couple of years ago that had been kind of abused and was missing the rifling on one side at the end of the barrel probably for an inch and a half. The first shot out of a clean Barrel would shoot six inches to one side and then move over as the barrel got dirty to a different spot. After visiting with some people, I took a round file and took the same amount of rifling off the opposite side and don't you know but the gun shoots pretty much the first shot the same as the second third and fourth. It was one of those deals if it didn't work I was just going to shorten the barrel about two inches and that would have done the same thing but I was curious about this rifling deal.
Squint

 

[snapbang]

I used a ball bearing and grit paste to do my crowns.

 

[az jerry]

I used a ball bearing and grit paste to do my crowns.

That's a great idea

 

[Bruce in WV]

"I used a ball bearing and grit paste to do my crowns."

I have to admit my ignorance: I have no idea how to use a ball bearing and grit paste to do the crown. Please explain

 

[snapbang]

Apply grit to the crown. Set the appropriate size ball bearing on top. Work the bearing in circles, twist, turn, spin.

 

[Ga.Smokey]

After shooting a cvs scout that shaved plastic. I found the crown as important in loading as in the bullet leaving.
After recuting the crown face to 11 degrees I used a 45 degree cutter to put a heavy start bevel on the crown .ID polished up slick.
No more shaving plastic.
Gun now has a much better seal and shoots much better.

 

[anonymouscowherd]

After shooting a cvs scout that shaved plastic. I found the crown as important in loading as in the bullet leaving.
After recuting the crown face to 11 degrees I used a 90 degree cutter to put a heavy start bevel on the crown .ID polished up slick.
No more shaving plastic.
Gun now has a much better seal and shoots much better.View attachment 41892

Darn near from the book on accurizibg rimfires too

Have you shot it enough to see if it leaves a nice even snowflake like pattern on the muzzle?

 

[Ga.Smokey]

Darn near from the book on accurizibg rimfires too

Have you shot it enough to see if it leaves a nice even snowflake like pattern on the muzzle?

The spray pattern is very even. I call it a star burst. Lol
I been around the rimfire block a couple times.
Really any rifle can benefit from a 3 angle crown job.
The physics are the same.
Neutral to 11 to 45 I had to go a little more than I wanted on the 45 to clean out the factory recess without setting up in the lathe and whiping the face clean.
I will admit the lathe is the preferred method with a single point tool working from inside out..
That being said a crowning face cutter does a near equal job with some patience.
I make a pilot after pin gauging the barrel.
In this case I knew from sizing what diameter to cut the pilot. .4505
I think that adds to the results.
John

 

[Ga.Smokey]

Darn near from the book on accurizibg rimfires too

Have you shot it enough to see if it leaves a nice even snowflake like pattern on the muzzle?

There is a new post detailing the whole process from start to finish in the smokeless area

 

[Confederate rifleman]

A lesson from the dreaded T/C QLA.
An off center QLA is death to conicals. Put a wad or a sub base under it and accuracy often dramatically improves. Sabot loads will shoot just fine however. My own experience bears this out.
This is because the bullet has already exited the muzzle by the time the wad/ sabot does. The gasses escaping off square to the base don't have a chance to tip the bullet.
Barrels with run out have the same issue as an off center QLA. With patched ball it's a non issue. All a ball can do is drift, so a simple sight adjustment does the trick. Sabots too only need a sight adjustment. Conicals are another, sad, story. But a wad or sub base will generally put them right.

 

[Ga.Smokey]

A lesson from the dreaded T/C QLA.
An off center QLA is death to conicals. Put a wad or a sub base under it and accuracy often dramatically improves. Sabot loads will shoot just fine however. My own experience bears this out.
This is because the bullet has already exited the muzzle by the time the wad/ sabot does. The gasses escaping off square to the base don't have a chance to tip the bullet.
Barrels with run out have the same issue as an off center QLA. With patched ball it's a non issue. All a ball can do is drift, so a simple sight adjustment does the trick. Sabots too only need a sight adjustment. Conicals are another, sad, story. But a wad or sub base will generally put them right.

Yes I have one of those dreaded crooked QLA barrels shoots pretty good with sabot loads.
However that is not what I've done.
I have corrected a problem that is glaring to me. Now on 2 separate rifles.
The test will come when I go back to sized bullets.
Quite possibly it won't shoot with sized bullets.i will report back

 

[bronko220002]

I cut the barrel down on an Encore to make it a muzzleloading pistol and I went to the hardware store and bought an appropriate size cap nut and bolt., cut the head off the bolt and put in in my drill. Installed the capnut on the other end and applied some 320 grit lapping compound and placed the cap nut on the muzzle and spun it until I got the crown I wanted. It didn't take long at all and it was symetrical and smooth.