7.62x39 in a 8mm bore question

[nekshot]

I never did this (use reamer in larger bore than reamer) so I assume I will need to make a bushing to fit over reamer for proper bore diameter? Any advise appreciated including "don't do it", just tell me why and I will listen!

[lefty o]

other than the obvious .312" bullet in a .323" bore.

[richhodg66]

Is this to make a 8mm x39 wildcat? Sounds interesting. I like the little 7.62x39 and wonder why more modifications necking up and down hasn't been done with it.

[nekshot]

I never thought of it but yes i guess it will be a 8mmx39. I got the idea from buckshots 95 rebarreled and he said he only shoots reloads because factory pressure levels exceed 95 mauser specs and that got to thinking of a couple 98 mausers I have that I use for any wild hair I get, hence I got the barrel why not!

[seaboltm]

Is this to make a 8mm x39 wildcat? Sounds interesting. I like the little 7.62x39 and wonder why more modifications necking up and down hasn't been done with it.

It has been necked to 22 (22PPC), 22 (5.45x39mm) 6mm (6mm PPC), 6.5mm (6.5 Grendel) and 9mm. Those are just the obvious ones. I bet there have been more. Notice most people go smaller, generally in order to gain velocity, which the 7.62x39 lacks. The necking up to 9mm was to create a subsonic round for suppressed rounds, similar idea to the 300 Blackout. Given the limited number o 8mm bullets and the low velocity that would be expected, doesn't make sense to me.

[SOFMatchstaff]

I load for the 8mmx33, its about what you would end up with by doing what you suggest. It is not up to the 7.62x39 in velocity with the 125gr bullets because of the smaller case, but its close enough to make a decent comparison. As mentioned , the bullet selection is really poor, Hornady makes a run of 125's about once a year and I have to be alert and stock up when I can. You may get more power from a bolt gun compared to the short tube on the STg44, but its still a waste of assets to get all the tooling to make it and then load for it. I'd do the 9x39 if I thought it would do something that the 762 or Blackout wouldnt do.

[Harter66]

I had a 7.62x39 that was actually much closer to 8x39 being 305x316 . I pushed a 200 gr boolit to almost 1800 fps and over 1600 when fitted back to the magazine. That seems like a lot of thump in a little case.

I think the neck and throating will be the real bugs . I had a7x6.8 done a couple of years ago. We intended to use a 7-30 waters to cut the neck and throat but it turns out that the 6.8 SPC II has a larger neck OD than the 7-30.
Check your numbers you may only need the 7.62 reamer and an 8mm throater.
The 8mm bore may be close to the same as the 7.62 if you get a 312 solid reamer, if you have a 308 reamer with a floating pilot you may be able to use an 8mm pilot on the reamer. I can't think of a combination that will allow an 8mm short chamber then finish with the 7.62 to get the body and shoulder . Maybe jus use a x39 head space gauge and an 8x57 reamer . 57-39 =18 so measure an 8x57 OD about .685 up from the head and see if it is close to the rim dia of the x39. You will have a slightly "improved" case but who cares in a Mauser wild cat. You will have to get a blank extractor and fill the bolt face or mill a new bolt as the x39 has about a .411 head while the Mauser is probably. 472-474 .

[cowboybart]

You could look at an 8mm IMHSA. I put one of these on a SR Mauser, but haven't fitted wood to it yet. It is a 300 Savage case with a 38* shoulder. I also have the reamer with a live pilot, so it can be bushed to match your needs.