7383 in the 375H&H...

[Idaho Sharpshooter]

Field test this date of IMR-7383 in my CZ 375 H&H with cast. 26-degrees, and a little wind. I have been told by the guys at T-bird, and a ballistics lab that this powder was created for the 50 BMG Spotter round. I bought mine for $24 per 7lb caddy from Pat's.

OAL: 3.6615"

Suggested starting data:
1. take a fired, fl sized, primed case, and pour it overflowing full of 7383. Level it and weigh it. Ten times, and average the weight. Take 85% of that for J-word bullets, and 75% for cast boolets.

2. My WW-Super 375H&H cases were used. Average capacity was 78.8 grains.
75% of that is 59 grains. Loaded that amount behind my NEI 310gr GC boolets
with Lars45 Carnauba Red Wax and Hornady gas checks. Chrony 12 feet in front
of muzzle. Low recoil, and the five test rounds chronographed as follows:
1. 1675fps
2. 1689fps
3. 1683fps
4. 1740fps (?) turned .8" group into 1.55" group
5. 1678fps

Target at 25yds. Group was 1.55" and vertical mostly about twice as high as wide. 3" above aim point, but iron sights. I am going to stick my 36X B&L scope on it and accuracy test as I creep up in 2gr increments, as this powder is noted to be a bit peaky at about 95% capacity charges.

First three patches came out pretty sooty, and a few granules of unburned powder fell out of each case. No signs of fouling, I like the Lars45 Lube here. I have shot in in my 416 Rigby over 2450fps with out leading.

Five rounds is no real test, but it was a safe start. I intend to test it thoroughly in 9,3x62, 375 H&H, 416 Rigby, and my 505 Gibbs to see if I need to buy a hundred pounds before it, too, is gone.

The Goal: 310gr boolets at 2200fps with out leading, and sub-2moa groups at 100/200yds scoped.

Rich

[PatMarlin]

Sounds like a plan. Keep us posted..

[Jim]

Idaho,
The unburned granules are a result of the pressure not being high enough to burn all the powder. I've been using this stuff for years and the window of usefulness is very small. Below the window, it burns, but not completely. Above the window, the pressure can spike to chamber rupturing levels in a New York second.
Start with 90 to 95% case density volume and work up REAL slow, like a grain at a time. Watch EVERY shot for pressure signs and stop when your primers start to flatten.
This powder is very economical, but it's quirky as all get out.

[James C. Snodgrass]

I shot some last week and it was quite cool also I'm curios as to whether any one has paid any attention to it's temp sensitivity ? I have used it in my Lott with a heavily compressed 500 gr gc boolit and only managed 1850 fps , I get about the same speed withe WC 860. I also found it to leave unburned kernels but to be fairly consistent out of my Whelan and Lott . Good luck and good shootin'

[Ricochet]

I've read about, but haven't noticed, temperature sensitivity with 7383. I'm not loading anything to really high pressures, either. I'll add to the above that it's a bad idea to compress this powder much. I think the grains are fracturing, causing it to burn faster, rather unpredictably.

The only load it was ever put in by design was the .50 Spotter cartridge, which has a specified operating pressure of 38,000 PSI. When you get much above that, you're exploring uncharted territory. I think the powder's optimized to burn at lower pressures by having carbon black dispersed in the nitrocellulose matrix to absorb radiant heat. The grains are black all the way through, unlike most IMR powders.

[Idaho Sharpshooter]

I think I'll just stick with starting at 75% and work up in 2gr increments 'til 90% and then go 1gr at a time. I just retired, and I am in no hurry.

Rich

[Jim]

Idaho,
you can start at 90% case density and work up slow from there. At 75%, all you're gonna accomplish is wasting powder and time. 7383 likes a bit of pressure to burn. Not much, mind you, but just a bit. Two signs to watch for: check your primers after every shot and watch the barrel for unburned powder. When your primers start to flatten and/or you see no powder left in the barrel, you're there. Oh, on the subject of primers, you might wanna use a soft brand like Federal of Winchester to start with. You'll get the flattening signs early and that's a good thing!

[Idaho Sharpshooter]

Jim,

appreciate the advice, but I am approaching this from the standpoint of trying to establish some fps per grain. I'd like to see how much is how much. I am using Winchester primers. 7383 is the last of the cheap surplus powder out there, and I would love to see how it works with all of the big bore rifles I own with cast. There are CZs in 416 Rigby and 505 Gibbs here to test, and my wildcat 550 and 577 Gibbs. I hope to get good practice loads for all of them.

thanks again,

Rich

[Idaho Sharpshooter]

Not much to add today, it never got past 12-degrees, but it was +12-degrees. The nephew bought a new house so we put in some time getting a washer and dryer bought, and took home, and setting them up. Man, I could settle for being 21 again...I think!

61gr went 1773, 1759, and 1775 fps. The outside temp gauge on the Dodge said 8-degrees and we decided discretion was the better part of valor. Next month maybe. No signs of leading and a group that measured about .970" at 50 yards.

Rich