321 GNR
Good morning Gary,
Ive been mulling over what you said about the 30 carbine blackhawk rechamber and have looked at the 321 quite a bit. My only major aversion to it is that its 312 and not 308, Im not at all worried about 312 cast bullets in a 308 barrel but I would feel a bit differently about jacketed. What I would really like is to use this plethora of 357 brass I have and a speer 110 grain hollow point 308 jacketed bullet. I ran a few pieces of 357 through a 300 blackout die just to get an idea of what the 321 would look like and the resulting case is pretty well exactly what I would want save the slight case taper which Im afraid would cause setback issues.
I even looked at the 300 GNR as Im not afraid of case forming (I make all my 17 fireball from 5.56 lake city brass) but the Herret load data I found looks a little anemic compared to standard 300 blackout data (using cfe black for lower pressure). I wish you had a 308 cartridge based on the 357 because that would make this an easy decision.
I know you're not in the business of providing free advice and I can't tell you how much I appreciate what you've provided so far, but do you think the taper on a 300 blk is enough to bind a cylinder if pushed into the 36k pressure range? Ive seen you write before that if 1 person asks for it there are usually 15-20 more that would buy it and I can tell you that having a convertible cylinder "3057 GNR" is something that at least this 1 person would start scraping money together for, just for the availability of 30 carbine and 30 Mauser bullets.
Josh, somewhere along the line somebody gave you
some wrong info. The 321 which is a 357 mag case using 311 or 312 bullets but has a 308 bore. That is normal and the main benefit is extreme accuracy. There is no problem with pressure with jacketed bullets.
Next the 300 Whisper, which some assholes stole from J.D. Jones and started calling it the 300 Blackout, will not beat the 30 Herrett or the 300 GNR when shot in equal length barrels. The Whisper is intended for suppressor use and is normally a sub sonic round.
Also extra cylinders are no problem either, although I don't really know what the 3057 GNR caliber you mentioned is.
Yeah TC, Dan Wesson,Marlin,Gary, and lots more
all use .308" bores for the old traditional .311-.312" caliber cartridges like the .32 H&R, .32-20 etc. It makes things lots easier and when you fire the round it becomes .308" for sure. Works perfectly. I load .309" cast bullets in all my calibers like that including .327 Federal.
The .300 GNR is very close to a .41 Magnum necked to .308" If you really wanted to get technical it is exactly in spec with a .401 Herters necked so! Not that anyone ever thought of that I accidentally found that from forming Herters from .30-30 cases. And YES I had to try one .41 Magnum FL in a .300 GNR die, it don't work, almost but no.
So Gary actually does make your .308-.357 cartridge, he just named it the .321 GNR. The Europeans measure groove to groove and would call that the .320! Gary once re-bored a .30 Carbine cylinder for me to .300 GNR it worked fine.
Only one rare tid-bit; the Ruger .30 Carbine has a strange rate of twist, 1:16.5" I think. It is fine for bullets up to 115 gr. but not beyond. Gary's re-barreled package guns have rifle rates of twist and can handle 60-170 gr. at least. That's what I've shot in .300 GNR. I have one of his .327 Federal barrels in an Encore Pirate. I also have some 230 gr. cast rifle bullets slated to try sub-sonic. We'll see if they hit point on!
This is an actual .401 Herters and a .300 GNR case with custom shorter neck (same case OAL as .30 Carbine). I bet Gary never even realized that. Even the .30 Herrett (1972? Much longer case too) on the .30-30 came after the Herters died.
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