IMR 7383 (Surplus) Powder in 7.7mm

[Safeshot]

Yesterday I loaded some 7.7mm Japanese rifle ammo with IMR 7383 (Surplus) Powder, 185 grain cast bullets with gas checks, and CCI (not magnum) primers. Everything seems good with this load: no (measurable) case head expansion, primers look normal, no loose primer pockets, easy bolt lift and extraction, fired cases resize easily, and had no indication of "click bang" or "hangfires" that some have reported with this powder. I will try to shoot a few groups at 100 yards and post results when I can. Has anyone had experience loading 7.7 Japanese, .308 Win or 7.62 NATO, 8 x 57mm, or 30/06 with this powder?

[GonHuntin]

Safeshot

Where does 7383 fall in burn rate? I'm assuming it is a very slow powder?

[1st cav sgt ret]

Ive heard of 7828 but not this one,where did you find it,if its the same as 7828 (maybe mismarked?)then its slower than H4831

[Safeshot]

I do not know much about IMR 7383 (Surplus) Powder . I got the powder from "Hi Tech Ammunition". It came with very limited loading data. It was not defined as to burning rate. Various individuals have indicated that it is similar to a number of different powders. I am not comfortable with comparing it to any known powder. I was told that it is the powder (possibly downloaded) that was used in the .50 cal. Ammunition for the .50 Cal Spotting Rifle used with the 106mm Recoiless Rifle. (This is NOT the same ammunition as the .50 M2 Machine Gun Ammunition.) The only thing really good about the powder is that it was CHEAP (less than $4/lb). Some of the individuals using this powder have reported good results with some calibers with jacketed bullets on other forums. I am interested in the results of anyone else that has used this powder, especially with cast, gas checked bullets.

[Bobcat]

Hey Y'all,

I just talked with the tech at IMR. He said the ONLY thing this powder was ever designed or used for was the .50 call spotter round as stated above. It was never intended to be used in any commercial cartridges and it will never be made again. They do not recommend using it for rifle hand loading. Take this as you will. Just a heads up.

Bob

[GonHuntin]

If that is what it was made for, then it will probably be too slow to develop decent velocities in the cartridges you mentioned. I have used some of the slower surplus powder (5010) in my 416 Rigby with cast bullets......it does alright for plinking, but it's not the best choice.

[Ricochet]

The .50 cal M48A2 Tracer/Incendiary round that this powder was designed for is NOT the .50 BMG. It's got about half the body length of the BMG round, looking much like a 7.62x39 vs. a .30-06. This cartridge was fired in the spotter rifle mounted on the tube of the 106mm recoilless rifle, and the cartridge was designed to duplicate the 106's trajectory. When a target was spotted, the gunner would aim through the telescopic sight and fire a .50. When he saw it hit (with a bright flash and puff of smoke), he'd fire the big shell immediately. It saved ammo for the big gun, and firing the .50 spotter made a lot less attention-drawing commotion than firing the big reckless rifle.

This powder is comparable to IMR 4350. It replaced the M48A1 round, which was loaded with 120 grains of IMR 4831, and according to Army specs it launched the same bullet weight at a 75 FPS lower velocity with 38000 PSI vs. 35000 for the older load, using 110 grains of 7383 vs. 120 of the 4831. You can see from that it's a little faster than 4831. I've been shooting it in .22-250 and .30-06, and the velocities I've been getting for charge weight match just about exactly with 4350 at the charges I can get in the case, which are at starting load levels for 4350 with the bullet weights I've been using. The powder is bulkier than most IMR powders (that's why Hi-Tech sells it in 7 pound jugs that normally hold 8 pounds.) In .30-06 I can vibrate a fired, neck-sized Federal case full to the mouth and get 56 grains in, which with a 150 grain bullet gets me right to 2700 FPS. I can't use the full-to-the mouth load with my boattail 165 and 168 grain bullets, so I fill them to the bottom of the neck. That's 53.5 grains in Federal cases, 52 in Remington. I get about 2525 FPS with those loads. In the .22-250 a shaken-down caseful to the mouth is just about 37 grains. I get 3415 FPS with 55 gr. bullets, 3255 with 60 grainers. Check the loading manuals for 4350 and you'll see a close match for all these numbers. That might not hold in the larger magnums, and I can tell you that this stuff doesn't burn well at very low pressures, like in .45-70 with a 340 grain cast bullet. Shot about 1300 FPS with 50 grains, all that would fit. It was consistent enough, but every powder grain was about half burned and it was just too messy.

This powder has two compositional differences I've noted from other IMR powders:

It's very smoky and the gas blown out the muzzle smells strongly of ammonia. These are signs of nitroguanidine in a powder. That's usually used in artillery powders to reduce flash and bore erosion, and isn't usually found in small arms powders. I haven't been able to find an expert who can confirm this, but Stan Watson ( "OKShooter" ) told me that he'd heard the military had experimented with small arms powders from DuPont containing nitroguanidine at about the right time period for the M48A2 cartridge's adoption. He thought the advantage was supposed to be improved temperature stability, but wasn't certain. I think it's in a coating on the powder grains, as I smell the ammonia in the muzzle cloud but not in smoke coming from the breech or the cases. It's all in the first-formed gas that gets blown out first.

The other difference is that those half-burned grains spewed from and left in my .45-70 were jet black, unlike the usual honey color of partially burned IMR powders. This stuff has carbon black mixed in it to regulate combustion. (It helps the powder burn more evenly and efficiently at lower pressures, by absorbing radiant energy from the incandescent gases on the surface of the powder grains, heating the surface layer. Remember the 38000 PSI max average pressure of the M48A2 round?) This stuff shoots very well, but leaves the inside of the bore BLACK!

I've got a good supply of this stuff and plan to be using it for a long time. But I think its best application is for mild jacketed loads in cartridges of the .30-06 class, and also for hot, heavy cast bullet loads in those cartridges. Pretty much where you'd use 4350. I haven't experimented with it in magnum loadings. Full load pressures in those cartridges are well over the working pressure of the cartridge this powder was specifically designed for, and the burning rate might change at high pressures, so work up any loads in those carefully. Hi-Tech says it's comparable to 4064 or 4320 as far as loading data goes. That's clearly a very conservative recommendation. In my opinion, starting with beginning loads for those powders is a good point, but I think that one could slowly and carefully work up with the maximum loads of 4350 as a potential goal, as long as no pressure signs showed up earlier. But you're strictly on your own if you do so; I haven't tried it. Be careful and sensible. I think you'll have a hard time overloading it in the 7.7mm Japanese, though. I'd worry about potential for hangfires and maybe SEE with less than full capacity loads.

Hey Bob, if you've got a line to the IMR tech guy, ask him about the nitroguanidine! I've been just dying to find someone with the original DuPont specs for this stuff!
;D

[Safeshot]

Ricochet, thanks for the info on the IMR 7383 powder. I am loading a slightly compressed load in the 7.7 Japanese cartridge. I will try to get to the range and check accuracy as soon as the weather clears. I will post accuracy results when available. Safeshot

[Ricochet]

I'll bet it works great. Won't give top velocity, but I'll be surprised if it's not pretty accurate.