firing oversize (for the bore) bullets

Does any one know of any test/experiment that have been done to see what the increase in pressure is,, with each increment of increase in the neck and bullet diameter with everything else staying the same, especially bore dia.???? Speer, Sierra, or one of the other bullet makers??

Why I ask is the memories of following endeavor.

Many years ago I ended up with a 7.62x54R chamber reamer and a trash can (30-40 gal) full of 7.62x54R ammo. This ammo was a mix-master of all types and conditions. I had plenty of 30 cal barrels and an Enfield #4 action that wasn’t doing anything. So I used a tool post grinder and turned the reamer’s pilot to 0.298” and chambered a Sedgley M1903 barrel to the 7.62x54R and fitted it to the #4. After some magazine work the rifle would feed OK. And after assembling a few spare parts,, I had a No4 in 7.62x54R. With the typical sporterized forearm, looked kinda like a ’T’ with a short barrel, no scope.

Using factory Norma Ammunition. I test fired the rifle in a tire with a long string, after about 20 rounds I could not see any over pressure problems, (web expansion, appearance of primer and bolt lift). I then reloaded those empty Norma cases with American components, 0.311 bullets, and tried again. Results same as before. Then I grabbed a handful (no separation as to diff. kinds) of 7.62x54R from the trash can and tried those. Once more no indications of excessive pressure. But surly there was some, I would just like to know how much.

I fired all the useable rounds out of that trash can and then some more 7.62x54R ammo that I obtained later. I checked the headspace periodically until the ammo from the trash can was gone and found almost no increase (may be 0.001“). I made my own gages of the “washer or coin type” in 0.001” steps. In time the throat grew in length and so did the groups. And I finally ran out of 7.62x54R so change the barrel to something else, a .35 Krag,, I think.


45B20

Don't tell the British NRA, you'll give them a headache!

Nothing comes to mind immediately as to hard data, but several factors could come into play w/ O/S bullets- bearing length, jacket type, jacket thickness, throat geometry, possibly core construction. If only a thousandth or two over, I'm thinking the throat configuration could play a most important part.

If an Arisaka can push a 0.308" projectile out of a 6.5mm bore w/o letting go...

jmoore

I figure there must have been some type of study,, given the warnings people are always writing about firing oversize bullets.

I had read Ackley’s books before I did that little project. Lucky that I did not run across one of those ShKAS rounds. But I had all this ammo and nothing to fire it thru, couldn’t let that continue. 7.62x54R was not that easy to come by at that time. Wish I could remember were I acquired that reamer and what were its’ markings. For some reason I keep thinking military???

Was a real hodgepodge of ammo, some projectiles and cases attracted a magnet, some did not, some trace, some that gave a flash on impacting something hard. I do not remember many misfires, but all gone. I realize all these different types of projectiles would affect pressures, but I was hoping a controlled test would at least give me an idea.


45B20

The Ruger 7.62X39 rifles have .308 groove diameters if that info is of any value.
So do some of the Finn conversions of the MoNag and they ARE 7.62X54R.
I can't remember which version or which barrel but some were .308.
You might check on one of the Rooskie boards.

ireload
Thanks I will try that.

I had one of those 7.62x39" Rugers, as far as I know, I never fired 0.308" dia bullets thru it.

45B20