Quote:
Originally Posted by id10t
My AR in 72x39 is more accurate with the cheap Wolf/Tula steel case ammo than my very similar .223 AR build is with PMC ball ammo. My hunting loads in my 762x39 bolt action (Howa mini) run just over 1moa consistently, using a .308 bullet in a .310 bore - I should be able to get a sub-moa load going if I ever spend the extra money on .310 bullets....
Steel cases still have the case mouth expanding while firing, etc. just they spring back closer to original spec than brass does. The biggest issue is increased wear on extractors.
None of the cheap steel case stuff has been made with corrosive powder or primers since the old stashes of Norinco, etc. dried up forever ago.
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Thank you, that is great information. I know nothing about this stuff (and I can prove it). Way, way outside of my areas of interest, so I have just never owned these kinds of rifles. It's nice to hear from someone who really knows what's going on with them.
One thing I had heard was this thing with their .310" groove diameters. What a PIA, really, but I suppose there must have been some reason for it. Maybe no more than Cold War paranoia regarding interchangeability and all of that.
It is surprising to me that a .308" bullet, a jacketed one at that (I assume) could shoot well at all in a .310" groove diameter. What we think we "know" about all of this tells us that a jacketed bullet won't "bump up" to fill the rifling like a soft lead cast bullet can. I have heard, from many people, that this actually does work fairly well.
My experience is with old black powder cartridge arms. Many originals were chambered in such a way that they would only chamber a cartridge loaded with a bore diameter bullet. The modern convention is to use cast bullets about .001" larger than groove diameter, so they swage down going through the throat and the leade. They seal much better that way.
Rounds loaded with these oversize bullets will not, however, chamber in many 19th century black powder cartridge rifles. They were still learning. Muzzle loaders, by design, simply cannot be loaded with oversized projectiles, and they worked o.k., didn't they? They were all loaded with bore diameter or smaller bullets, weren't they? We counted on black powder to "bump up" soft lead bullets, and it does. So that's how cartridge rifles started.
And it works. With dead soft lead bullets wrapped in a paper patch, the precursor to the copper jacket. With dead soft grease groove bullets, yeah, still kinda works, but we get a lot of leading. We want to shoot oversize grease groove bullets to avoid all of that, but we can't. So unless we want to paper patch (a monstrous PIA, by the way), we're kind of stuck.
I have a first year (1885) Winchester Highwall chambered in .40-70 Sharps Straight that was chambered that way. I tried everything, including paper patching, which was the only thing that worked. I got tired of rolling paper onto bullets and finally sent it off to my favorite black powder gunsmith. He opened up the chamber for me so I could load groove diameter + bullets. What a difference - it now shoots extremely well with bullets cast .001" over groove diameter. Here it is, along with a round loaded with a 300 grain bullet from an RCBS mold, next to a .30-'06 round:
But, yeah, back to that 7.62x39 and .310" groove diameters and .308" diameter bullets. That relationship worked with black powder and soft lead bullets. It's not supposed to with jacketed bullets and smokeless powders. But it does. Sometimes everything we think we "know" goes right out the window.