Diagnosing a bullet strike

[pdentrem]

Place between centers? You can then check the shoulder with indicator.

 

[Dabbler]

cdhknives, the only way we ream chambers and crown muzzles and thread barrels is using a steady rest... My toolmaker friend and I tried a bunch of other approaches, but this way we can achieve tenths concentricity and perfect alignment to the bore - both of which prevent problems such as you are facing. Because we are so careful we install all muzzle breaks and suppressors for out city's tac team - they just don't trust anyone else.

BTW you don't need contact to flip your bullet... we tried a few off centre muzzle breaks with .020 clearance to the bullet... With .005 out of concentricity the bullet yaws considerably at 100m. I presume it is the differential gas pressure/gas velocity that does it.

 

[cdhknives]

Interesting. The little bit of instruction I got was to use a heavy copper wire around the barrel in the 4 jaw and a spider at the left end of the spindle. Not an option here. I have done exactly 2 re crown jobs on my rifles so I am totally green at this but I have cut some tight threads. If I can dial in the bore I am confident I can rethread this. I assume you are chucking the left end in the 4 jaw to handle thrust, as using a driving plate and dog would not hold it securely I think.

I ran the barrel between centers, just turning by hand. The face was dead on but the relief groove shows 2-3 thousandths float on the dial. I do not have a piloted reamer to insure the crown is square/true though, so if the crown job is bad it would not necessary ride on the live center true...???

 

[Dabbler]

The most accurate way to centre the bore we have found is to make a close fitting pilot (we use hard bronze) that fits the barrel perfectly - barrels can vary +/- .0015 from the published spec - we've seen a few +.001. So we always make a tight slide fit pilot and indicate on that. That makes our threading concentric to the bore +/- about .0002 or .0003. Most of the barrels we do (these are very expensive brand new target barrels, mind) are between .004 and .008 out of concentricity (that's how we discovered the bullets 'kicking' sideways in live fire tests). We discovered these concentricity problems over 30 years ago, and some of the manufactures have tightened up their specs, but now the new carbon barrels are worse. The best we've measured has been .008 off concentricity.

 

[wrmiller]

I have threaded a few 1911 barrels for compensators, and I always make a pilot that just barely fits in the barrel and indicate on that to get barrel bore concentric to spindle bore. I then touch up the barrel crown to get it accurate as well, as I use my best live center when cutting the threads. I typically make the bore of the compensator about 10 thou larger than that of barrel.

No issues to date.

 

[cdhknives]

In looking at YHM's threading spec I had a thought. Ref: https://yhm.net/media/pdf/762_PHANTOM_BRAKE_625-24.pdf

There is a 0.060" unthreaded shank behind the threads up to the shoulder. On my barrel this is a relief groove. There is nothing but threads and the back face to align the brake. Is there any chance I can turn that shoulder back about that 0.060" but at the proper diameter to support and align the base of the muzzle brake? Would this take the sloppy threads out of play? There is plenty of unthreaded bore in the brake to match up to this face.

 

[wrmiller]

I don't know. In order to take the loose threads out of the equation, you need sufficient shoulder to align both axially and radially. Sixty thou doesn't sound like enough to me, but I could be wrong.

 

[Silverbullet]

Place between centers? You can then check the shoulder with indicator.

Only problem there is if the tailstock out of alignment . It'll show up.

 

[Silverbullet]

I don't know. In order to take the loose threads out of the equation, you need sufficient shoulder to align both axially and radially. Sixty thou doesn't sound like enough to me, but I could be wrong.

By the way metal is if you scrap the high spot alone it will work. Maybe the brake has been dropped or bent on the barrel . Those breachers do on gun barrels.

 

[pdentrem]

Only problem there is if the tailstock out of alignment . It'll show up.

No it will not. The center alignment has no bearing on the indicator reading.