I found no difference between 4350 and 7383 with respect to bore fouling. Incidentally, the .243 will be out of service for awhile because I fired 15 rounds of what turned out to be rather old Rem. 100gr. PSP factory loads in it the other day. One primer blew completely, the other leaked badly: gas vented throughout the action. Even the bottom of the scope had powder residue on it. Both pitted the breech face enough to make me send the entire rifle back to Ruger. When I pulled the remaining 5 rounds, I found caked powder and bullets essentially oxidized onto the case necks. Bummer!

Thanks for the info, Maven!

Sure looks to me like 7383 is pretty much a 4350 clone within the range of loads that'll fit in these "standard" cases, which is considerably less than the maximum for 4350. I haven't tried it with magnum cases where a maximum load of 4350 leaves a good bit of air space and as much 7383 would likely fit. Differences might show up there. I do like the stuff, don't care about black soot in the bore (which doesn't affect the shooting, if anything it keeps copper away), and don't mind shooting at less than maximum velocities. Bet my .22-250 barrel outlasts most, since I'm really shooting it like a hot .223.

Haven't posted it yet, but just for the heck of it I tried CCI 250 magnum primers instead of the 200s in .22-250 with 36 grains of 7383 and a 55 gr. FMJ. Average muzzle velocity dropped 40 FPS with the magnum primers, and accuracy declined.

I think the reason for this sort of result is that the magnum primers cause a higher initial pressure spike when they fire and start the bullet moving before the powder has time to ignite. A good crimp can sometimes hold the bullet in the case when a primer fires, and I think that's happening in my case with the standard primers. The powder has to burn and build up some more pressure before it can pop the crimp and start moving. That gives the hot gas time to spread through the whole charge and get every grain lighting off before it moves. Or perhaps a slower ignition basically accomplishes the same thing whether the bullet's free to move or not.

Bartsche, Ricochet, et al, While reviewing my notes for IMR 4350 and the OAL of the Sierra 85gr. SP, I found that at 2.71" OAL (in a Ruger #1) 42gr. IMR 4350 -> 3,066 fps with a standard deviation of 32 fps. By comparison 42gr. IMR 7383 with the same bullet, primer (Win. LR), OAL and ambient temp. (85 deg. F) -> 3,066 fps plus or minus 26 fps. Are the two powders "clones" of each other? Not really since 4350 occupies less space in the case. Moreover, it is possible to use 45gr. 4350 as a max. charge with 85gr. to 90gr. bullets according to Lyman's "Reloading Handbook, 48th Ed.." but I wouldn't dare try or recommend using more than 42.5gr of milsurp 7383. (It's a non-canister, meaning non-standard propellant. The "speed" of different lots can vary significantly.) ...Maven

Maven, I've used up to 41gr. of 7383 with a number of 80gr. pills and they all looked like light loads. But when I cleaned the rifle the black whatever took forever to remove. DIRTY!!!!!!!! Did you find this to be true. roger

Thanks Maven. good info. roger