Gary can a .312 bullet be loaded in the 321 GNR?

Gary built with no issues at all. Ditto a custom Encore in .327 Federal that also has a .308 bore. I didn't even notice any pressures rising. I must admit though I do not recall the revolver cylinder throat dimensions that so many folks obsess over. IF the round chambers (tight throats could cause issues - but do not seem to in this case - just seat a bit deeper if you need to) the bullet will be fire-sized to whatever the chamber throats are anyway. IF the bore is a bit tighter still then so be it, another gentile size down as it goes down that long custom throat of the forcing cone Gary uses.

I know folks who measure down to the 1/2 thousandths on cylinder throats. Who am I to stop their fun?! But the main thing is it's best if the throats are the same size or slightly bigger than the bore. Of course bullets of appropriate size are desired too. I personally have gotten into a situation of tighter throats than bore and it caused me issues. An ancient Colt New service in .38 WCF. The .401" lead bullets greasily slid through some 0.399-.400" throats to rattle down the 0.403" bore. Quite the reverse of what we are talking about. It would horrify any reasonable gunsmith what I did, rolled up emery cloth in a tight roll where it would just fit in the end of the cylinder. I then spun it by hand, dry, while I watched TV. I was only about 18 or so and thought I had it pretty well figured out. All I had to measure the throat diameter was a cheap set of dial calipers. NOT what you want for accurate measurement of any sort of round hole. But I was blissfully happy. When I got all my cylinder holes (I took care not to get into the chamber part of the cylinder, just the throat area) to mic at 0.403", as best I could tell, I was happy. The soft lead bullets powered by Bullseye or Unique seemed to bump up to cylinder dimensions and take the bore much better. My groups went from about 12" to around 3" at 15 yds., squinty eye'd off hand. I only had a little LEE loader and tapped rounds out with a plastic hammer, dispensing powder with a little red dipper, few tenths of a grain one way or another, good enough for Govt. work.

After all the obsessing over cylinder throats many Rugers in .44 run 0.430-0.431". This if fine of course and I get great results with 0.430" bullets, just what I have as a sizer. But it may be surprising that the largest pin gauge that will fit down a bore is actually 0.417". The smallest dimension of my .44 bore. Those lands do a lot of cutting and displacing of bullet alloy. It all seems to work though, the bullets completely fill the bore and do not allow any gas to pass the projectile. If the bullets are not too soft NOR too hard I do not have any leading issues. I had a tight spot just behind the "Mag-na-ports" once and boy did it create havoc. I almost have it all honed out and while I was working on it the accuracy came suddenly as if you flipped a switch. There is actually still a faint tight spot as the pin gauge indicates but it no longer affects accuracy so why worry.

Lots of rambling but the moral is if it chambers and shoots to great performance don't fret too much over it.

My mid 1980's SBH that someone had Larry Kelly reblue and port. I installed a BH stainless gripframe and parts to replace the MPA satin chrome pieces that had festooned it previously. I grew weary of my knuckles getting whacked in recoil. Grips by Bear Paw (I think).