Opinion needed on 7.62 x 39 conversion

[gerard488]

I had a badly bubbaed Surrey sporter no4 Mk1 that is a candidate for a conversion which I have already started. My next question is, Is the barrel too skinny or tapered too much for the 7.62 x 39 chamber pressures? It is a 5 groove No4 barrel that was already shortened, I just had it cut and rethreaded. Just hoping to get a few opinions.

 

[H Wally]

First off, this' speculation, and free, so take it for what it's worth.

Looks like you've taken a fair bit off around the chamber? Then again, you're also planning to shoot 7.62x39, so providing the chamber hasn't been re-reamed for some reason and moved forwards considerably, the area around the shoulder and throat should be ok. You also don't mention what the barrel diameter at the receiver is, which seems to be the area where the major alteration occurred. I'm guessing it was machined and threaded straight through at shank diameter? The only other thing to mention is that the No5 Mk1's did have considerable lightening cuts made around the chamber while still in 303, so in theory you should be good if you stayed larger in OD than they did at their narrowest. In all events, proof test it if you're at all unsure.

Sorry that it isn't a conclusive yes-no answer to whether it's safe, but it's a start.

 

[slug]

The locking nut will beef up the chamber area, so that will help. Also, the cartridge is one where the pressure impulse is short. The bullet only has to move a short distance in the barrel for the gas volume to be doubled. Compare it to an over bore capacity magnum where the bullet has to travel a long distance for the gas volume to double, and pressure to decrease. The pressure is a short, sharp jab, rather than a full roundhouse punch. Hope this makes sense.
I'm sure you've searched the net to see what others have done. It sounds interesting.

 

[tiriaq]

If it were mine, I wouldn't worry about it.