Gunsmithing Barrel crowning question

[Stringer]

So my friend was complaining about his beat up old Argentine 1911 shooting a foot high and left at 25 yds, something that started when he inherited an old junky barrel from another shooter. When he showed me the pistol, I noticed a fair amount of damage around the crown, and presumed this was the problem. He wanted a new barrel anyways, so he gave me the damaged barrel. Since I work in a machine shop part-time, and have full-time access, he asked if I could recrown it.

OK, so the extent of my "gunsmithing experience" has been making/modifying small parts for my rimfire. I have done no barrel work, but I'd love to learn to recrown a barrel, especially since I'd like to cut and recrown one of my rimfire rifle barrels eventually.

Our best non-CNC lathes are two Hardinge HLV's each with 5Cs and a 6-jaw and a 4-jaw.

How would I go about taking off a couple thousanths? I was thinking a boring bar might be the best tool for this. Another problem is that while my rifle barrel can fit a collet, I think I'll need the 4-jaw for the 1911. I'm not so sure I can pull that off without making some other tooling.

Suggestions? Precautions? Warnings? Should I leave this to the experts?

 

[chpprguy]

Re: Barrel crowning question

Can you use a collet system to clamp close to the muzzle end and then verify that the id is true to the od?

Then a light diagonal or perpendicular cut with a boring bar should be good.

I have also seen (in a book

)
A brass ball turned in the end of the muzzle with lapping compound to smooth out nicks/dings,
but I have never tried it myself,
Andy

 

[neutronics]

Re: Barrel crowning question

Is the gun a Sistema? Just curious.

Center the barrel by the bore. Turn down a piece of .50" brass rod until it fits snugly in the bore. Ideally it should fit the entire length of the bore plus stick out of the muzzle 4-6 inches. Put two dial indicators on the rod and get them both as close to zero runout as you can.

Alternatively you could put one dial indicator on the rod... not as precise as using two but probably adequate for a clapped-out handgun.

The barrel probably tapers from the muzzle toward the locking lugs so bear that in mind when clamping the barrel into your chuck.

While you're turning your brass rod down, take another small piece and leave it full OD. Then use a file (or whatever's handy) to shape one face to a round. After you cut the crown, dip the brass round into non-embedding polishing compound and use it to burnish your new crown while the barrel is still in the lathe chuck.

 

[Stringer]

Re: Barrel crowning question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: chpprguy</div><div class="ubbcode-body">Can you use a collet system to clamp close to the muzzle end and then verify that the id is true to the od?</div></div>
I'm not quite sure what you mean by this. There are two OD's: appox. 0.5" of the muzzle is flared about .020-.030 relative to the rest of the barrel. I could clamp the muzzle end in a collet, but what would I measure then? By "ID true to the OD," do you mean concentricity?

Thank you chpprguy and neutronics for your excellent suggestions. The brass rod sounds like a great way to indicate it, and the brass ball sounds like a simple-to-do finishing method.

neutronics--I'm not sure what make the pistol is, but I do know it was an Argentinian-issued military pistol. I think it's not technically called a 1911; I think it's called a 1928. Sorry, I know only two things about pistols (and Jack just left town.)

I think I may want to refer to a gunsmithing book with a nice section on crowning. Any reading suggestions?

 

[chpprguy]

Re: Barrel crowning question


I was assuming the muzzle end of the barrel was straight,
sorry.

Try Steve Ackers "the gunsmith machinist"

http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=213961

jerry kuhnhausen also has alot of books,

like.... http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=199119

hope this helps,
Andy

 

[beanland]

Re: Barrel crowning question

You can put a flat crown on it and even recess it if you like without dialing it in. Epoxy a ball bearing into the end of a fired case. Use lapping compound on the ball bearing with light pressure to finish the crown. No need to dial in if you are cutting a flat crown.

 

[BLAWTON]

Re: Barrel crowning question

Bean with damage already on the crown what you suggest will not work. A small boring bar on a high angle turning tool pointed left about 45 degrees or so will work just fine as long as nothing is going to touch but the tip. Center this in a four jaw chuck and set your crose feed at 11 deg. Then cut till you have clean the whole surface up. the i put a 60 deg champher just inside the crown and make a very small 90 deg cut on the very outside of the barrel just to make it look better.

 

[beanland]

Re: Barrel crowning question

Didn't realize he was working on a pistol. Thought he was working on a rifle, just saw that he tried to put a rifle barrel in the lathe. You can fixed damaged rifle barrels the way i described.

 

[BLAWTON]

Re: Barrel crowning question

They can be a pain to work on.

 

[Stringer]

Re: Barrel crowning question

Thanks so much for these great responses! My big plan is forming in my little mind.

beanland: I will try ball bearing lapping on my 10/22 barrel. It sounds easy!

NotAGuru: I really like the idea of using the 4-jaw for this project, and your instructions make lots of sense. From your post, it's clear that the 90 degree cut is cosmetic, but is the 60 degree chamfer also cosmetic? I'd imagine the angle and size of the chamfer could affect the POI. It's gotta be a tiny cut, right?

Thanks in advance! This is AWESOME info.

 

[beanland]

Re: Barrel crowning question

When i crown my rifle barrels after chambering. I cut to length with band saw. I then put back in the lathe in my 6 jaw. I use a flat 90 degree step crown. I do not dial in if i am using a flat crown. I then have a piloted 60 degree chamfer that i use by hand. I just put the tool in the muzzle with a pilot that fits snug but not too snug and turn the lathe by hand while holding the cutter in the other hand. I run in just enough to chamfer the edge a little. Maybe a .010 to .020 flat. I have not been able to tell any difference from the 11 degree crowns that i use to do dialing in on the bore. They both shoot good. You can use the ball bearing with compound in place of the 60 degree chamfer, but of course you must have the lathe running instead of turning by hand.

 

[BLAWTON]

Re: Barrel crowning question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Stringer</div><div class="ubbcode-body">Thanks so much for these great responses! My big plan is forming in my little mind.

beanland: I will try ball bearing lapping on my 10/22 barrel. It sounds easy!

NotAGuru: I really like the idea of using the 4-jaw for this project, and your instructions make lots of sense. From your post, it's clear that the 90 degree cut is cosmetic, but is the 60 degree chamfer also cosmetic? I'd imagine the angle and size of the chamfer could affect the POI. It's gotta be a tiny cut, right?

Thanks in advance! This is AWESOME info. </div></div>


No its there to protect your rifling at the crown intersect.