IMR-7383 chronograph data

[singleshotbuff]

Gentlemen,

The mercury finally climbed near 40 degrees here today, so I was able to chronograph some of the IMR-7383 loads I have working on. I thought the data might be of interest to others using this powder. These loads appear safe in MY GUNS, your mileage may vary. In other words, please be careful with surplus powders.

7.62X54R M44 carbine

Primer: WLR
Case: Graf
Bullet: Remington .310" 180gr RN jacketed
Powder: IMR-7383
Charge: 48.0grs
Velocity: 2270 f.p.s.
S.D.: 15.8
E.S.: 57

Powder: IMR-7383
Charge: 49.0grs
Velocity: 2308 f.p.s.
S.D.: 8.6
E.S. 32

7.5X55mm K-31 Swiss

Primer: WLR
Case: NNY (from Prvi Partizan ammo)
Bullet: Military pulldown 150gr FMJ BT
Powder: IMR-7383
Charge: 45.0grs
Velocity: 2475 f.p.s.
S.D.: 22.9
E.S.: 75

Powder: IMR-7383
Charge: 46.0grs
Velocity: 2502 f.p.s.
S.D.: 16.1
E.S.: 41

All figures are an average of 10rds fired. Chronograph was 10ft from the muzzle.

Hope others find this useful/interesting.

Would appreciate comments, particularly on how this compares with your experiences with this powder.

If the weather holds, I may get to chrony some more loads later today, and of course I'll post the numbers.

SSB

[singleshotbuff]

Gentlemen,

I got a chance to chronograph 2 more loads in the 7.5X55mm K-31.

Primer: WLR
Case: NNY (from Prvi Partizan ammo)
Bullet: Military pulldown 150gr FMJ BT
Powder: IMR-7383
Charge: 47.0grs
Velocity: 2583 f.p.s.
E.S.: 44
S.D.: 13.1

Powder: IMR-7383
Charge: 48.0grs
Velocity: 2639 f.p.s.
E.S.: 42
S.D.: 14.9

SSB

[Ricochet]

Yeah, that's comparable with the results I've gotten with similar loads.

[singleshotbuff]

Ricochet,

Is 2700 f.p.s. safely achieavable with a 150gr Jword bullet in 7.5X55mm with 7383? I'm thinking 49grs may be a max load, which should get darn near 2700. I'm just very cautious with my K-31 as I have no idea what pressure signs (IE sticky extraction) would be like in a straight pull rifle.

SSB

[Ricochet]

The maximum rated pressure for these rifles is 45,000 PSI. (Doubtless meaning CUP from the age of the data, but it's not specified.) You'd exceed that before getting signs of case expansion or primer flattening, as that's below the normal working pressure for a .30-06. I did find that 3.7 cc of it under a 200 grain cast boolit gave sticky extraction, and that scared me. Dunno if 2700 FPS with a 150 grainer is safely reachable or not, but it doesn't sound outlandish. With a 168 grain bullet I've loaded 4.0 cc (which crunches a little on seating the bullets) and gotten something like 2435 FPS, I think. I've got the data around here somewhere. That was a safe load with no pressure signs, and the velocity was just a hair under what the GP-11 military and Prvi Partizan factory loads give with a 174 grain bullet. I called it maximum. It was all that'd fit, anyway. I'd be leery of putting that much under a 180 grain bullet, which would also compress it more severely. 7383's pressure seems to climb rapidly when it's crunched hard or when used at high loading densities under heavy-for-bore-diameter bullets.

[singleshotbuff]

Ricochet,

With 48grs under the 150gr bullet, the powder is not compressed at all. However, the primers are just starting to flatten. This could be due to the fact that with this lot of brass, the primer is seated quite a bit below flush (deep primer pocket) and may be getting a "running start" against the bolt face under pressure. I may try 49grs tomorrow, and if I get near 2700 f.p.s., I'll call it good enough. I'm just leary of sticky extraction in a straight pull rifle, since I have no idea what to look for.

SSB

[Ricochet]

My thinking exactly.

[singleshotbuff]

Gentlemen,

Cabin fever finally got the best of me, so I had to try chronographing a few more loads today with IMR-7383 in the 7.5X55mm Swiss.

Using a 150gr FMJ BT (military pulldown),

48.5grs = 2663 f.p.s. ave

49.0grs = 2668 f.p.s. ave

The temp was about 15 degrees, so I think these loads would probably hit 2700 f.p.s. in the spring or summer.

HOWEVER

I did start to get a slight hint of sticky extraction, so I think I'll call 48.0grs max in this rifle at 2639 f.p.s. That's all I need for my intended use with this rifle. I will chronograph 48 again when it's warmer to see how much velocity changes.

SSB

[felix]

SSB, no need to re-shoot in the spring. You have already found the sweet spot with that load because extra powder does not influence the velocity. In fact, drop down to where you see a sharper dropoff, and then come back up a snort, say half grain. Then re-test that load in the spring/summer, and if the accuracy is the same, then you are in good shape with that load all year. ... felix

[singleshotbuff]

Felix,

Thanks for your input. I'll have to wait for warmer weather to do ANY accuracy testing LOL, shooting offhand over a chronograph is one thing, sitting at a bench is another in this weather. Now that I have established a safe maximum, I'll do as you suggest to fine tune the load.

SSB