54R Breech Block modification questions

[Vincent]

I am modifying another breech block for 7.62x54R. The one I had been using is missing. So I have a couple of questions.



I modified the internal radius of the extractor or whatever you call the part where the rim fits in the extractor.



The extractor in the 54R bolt is sticking up in the picture. ( The DP .303 bolt is for comparison. ) Does it matter that the extractor is like that?

Also, when I am done modifying the breech block will I still be able to shoot .303 with it?

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Peter Laidler]

I think that the raised part of the modified extractor (left end picture) WILL foul on the extractor way of the piston extension. You MIGHT get away with the slightly higher raised ramp of the extractor stay. Just my opinion based on the tight tolerances of the .303 and 7.62mm guns.

How did you set about machining the bolt face for the larger dia 7.62x54 cartridge?

[Joe H]

Vincent,

When i modified my bolt I did nothing to the extractor. I opened up the bolt for the larger 54 R rim diameter. Set the bolt with a shim in a 4 jaw and bored out the hole to the larger dia. I'm pretty sure I used a carbide bit. You still will be able to shoot .303 without any modification.

You also can use the modified 54R bolt for 8x56R if you have a ZB39 barrel & mag.

Joe

[Peter Laidler]

I stand corrected regarding the slightly raised extractor.

[Vincent]

How did you set about machining the bolt face for the larger dia 7.62x54 cartridge?

I did it the same way Joe H did his, with a 4-jaw chuck, shims and a carbide cutter.

The interesting part was getting it indexed (centered) in the lathe. I thought I could turn a rod into a very long firing pin tip. The long tip would stick out through the center and I could index from it. You’re probably already thinking this is a bad idea.



I made the rod and it was looking good up to this point.



Then I learned something. The bolt channel is at an angle. So the long tip of the rod I made is also at an angle and couldn’t be used to center the breech block in the chuck.



My next idea was to turn a plug and press it into the bolt face. Then I found some new sockets I had to make into screwdrivers for the Bren and one was a perfect fit!

I held the bolt in the chuck with shims on the two flat sides, paralleled the face to the chuck and used a shim on the bottom side to move bolt while centering it. Basically, the bolt was just held by two jaws on the flat sides.

Vincent,
When i modified my bolt I did nothing to the extractor. I opened up the bolt for the larger 54 R rim diameter. Set the bolt with a shim in a 4 jaw and bored out the hole to the larger dia. I'm pretty sure I used a carbide bit. You still will be able to shoot .303 without any modification.
You also can use the modified 54R bolt for 8x56R if you have a ZB39 barrel & mag. Joe

Thanks, Joe. That’s good information. I have a ZB39 barrel and mags.

[Joe H]

Vincent,

I just used a test indicator held in a chuck in the tail-stock and centered the bolt to the rim of the existing .303 recess.

Joe

[Vincent]

Vincent,

I just used a test indicator held in a chuck in the tail-stock and centered the bolt to the rim of the existing .303 recess.

Joe

I had to use a dial indicator. My test indicator was stolen along with a lot of other tools. I guess I need to buy a new one.

[TactAdv]

( The DP .303 bolt is for comparison. )

.....Okay, I guess not enough coffee this morning yet......I'm reading, and looking at the pictures......thinking "DP bolt".....'Degtyarev'......What????

-TomH

[Vincent]

.....Okay, I guess not enough coffee this morning yet......I'm reading, and looking at the pictures......thinking "DP bolt".....'Degtyarev'......What????

-TomH

DP = “Drill Purpose” only. Not to be used in an active weapon. They painted them with that copper colored paint.

I didn’t want anyone to get excited by mistakenly thinking I was going to use it in a real gun.

The nice folks who sold it to me left out the little detail that it’s a DP.

Oh well, it could have been worse. Like the Vickers breech block I paid $300 for, only to find out it is DP when it arrived.

[Peter Laidler]

There's certainly a lot of ingenuity amongst you US Bren fixers............... I'd been wracking my brain about it. Left and right side OK.......... but centreing top to bottom AND doing it square to the breech face had defeated me - up until now!

The 7.62 x 51 barrels are moving forwards by the way..........