Adventures with with breeching washers

[boatbod]

I had the day off today and wanted to occupy myself with something other than a honey-do chore. Luckily I was the only one home, so I was able to spend the day in my shop fiddling with machine tools and guns.

Anyone who has followed my other thread and the saga of the sticky chamber will know that despite my best efforts, I have decided to replace the barrel on my .308 M1. Aside from these extraction/short stroking issues, one of the other significant problems is that the barrel is barely hand tight when correctly indexed in the receiver. At the time, I proposed to fix this by making a breeching washer and cutting back the shoulder. With nothing to loose except time, I figured I'd give it a go.

First I turned a piece of steel down to 1.10" dia to match the barrel's OD, then I bored it to 0.970" to be a nice snug fit over the threads and tenon. After that, I parted it off with a nice sharp tool to leave a finished thickness of 0.090", and smoothed away the burrs on a diamond stone.

Next I chucked the stripped barrel in the 4-jaw and cut the shoulder back by about 0.085" as a starting point. Although I've only got a smallish (10" swing) lathe, I was able to screw the receiver onto the barrel with it still in the chuck so I could take a succession of light cuts and test fits to get the receiver + washer to come up hand tight around 4:30.

The barrel and breech washer were then cleaned and blued before final assembly using the ubiquitous barrel vise and receiver wrench.

Headspace tested out just fine - the bolt still doesn't fully close on a .308 NOGO gauge, and although the right hand locking lug is a touch further rotated than before, there is about a 3/16" gap between it and the receiver rail. A FIELD gauge obviously comes nowhere close to closing.

If I were to go through this again, I'd target the 5:00 position for hand tight. It was a real effort getting the last few degrees rotation using a 12" receiver wrench handle, and I thought I was going to need to find a breaker bar to help things along.
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[muffett.2008]

Did you take the opertunity to check that chamber again with the barrel out?

[boatbod]

Did you take the opertunity to check that chamber again with the barrel out?

I looked at it with a loupe and flashlight, but to be honest it's hard to see anything specific because that only focuses at a fairly shallow depth. Where the barrel was originally short chambered it was apparently done very coarsely. If I ever see one like that again, I'd use a full finish reamer to smooth it up before setting headspace with the pull-through (which only cuts at the shoulder).

[arado]

Been there, done that for my FAL projects. Made possible by my Harbor Freight $350 lathe. Avoided buying a bunch of factory washers. made the washer to precise specification. better than issue. Timing perfect. Torque by feel. gary

[boatbod]

Gary, what sequence of operations did you use when making your washers?

Like I mentioned above, I turned the OD, bored the ID and then parted off at the desired thickness. Never would have thought about another method were it not for a youtube video showing someone turning, grooving and then boring. I can see how that way might give you a more controllable thickness, but at the expense of less accurate ID if the part separates before you're ready.

[arado]

As you. turned OD, bored ID. I had access to a surface grinder to reach the needed thickness for each build. That access is gone. Now it is a file. gary

[boatbod]

As you. turned OD, bored ID. I had access to a surface grinder to reach the needed thickness for each build. That access is gone. Now it is a file. gary

How do you fixture something as thin as a washer so you can surface grind it?

[arado]

How do you fixture something as thin as a washer so you can surface grind it?

I used a rare earth magnet and my hand. It was not a production run.Grind and measure.

[boatbod]

I used a rare earth magnet and my hand. It was not a production run.Grind and measure.

Interesting, thanks. I've yet to have the pleasure of playing with a surface grinder, although I can certainly see how useful it would be.