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January 15, 2016

Comments

Ol' Frat

Forty years ago I went down the same rabbit hole - I was trying to get a 357 Mag rifle load that would have 1000 ft-pounds at 100 yards (if memory serves) - which was the legal minimum to hunt deer.

I couldn't do it. I was messing around with a Powley reloading computer, which was a set of slide rules that considered case capacity, barrel length, Bullet weight, and so forth, to come up with powder recommendations and predict velocities. I think you could find a digital version of it if you looked around.

Turns out that you just can't fit enough powder in the 357 case to get there, and one type of powder has about the same amount of energy as another, given a similar weight and/or volume. The burn rate doesn't impact the velocity as much as you might think, especially out of a long barrel, since pretty much all the powder burns in the first few inches of the barrel. Trading a fast burning powder for a slow one trades initial velocity for a push further down the barrel, and it just doesn't pay off enough to pass the minimum power that I was needing. At one point I had lots of grains of H110 behind a heavy bullet, and those were very uncomfortable to shoot out of a handgun - I had to try it out. It was in the book, so it was safe, but ...

I suppose you could try to find a load for the powder with the greatest density, which you can figure out easily by looking at the Lee powder measure slide rule.
More powder weight will yield more energy. Also, double base powders tend to have slightly more energy than the same weight of single base.

Last suggestion: the Speer book used to have 357 Rifle loading data, and studying that might give you some insight as to what powders to try.

Good luck, and be careful. Sometimes the answer is that you can't do it safely, and you shouldn't try.

Merle

I have never loaded for a carbine, but I did for a TC Contender pistol. I started off with blue dot, then migrated to AA #9. I used load data for a 38 super, since I could seat the bullets very shallow - no feeding issues in a single shot.

Hope this gives you somewhere to start.

Will

I have a vague recollection that the barrel rifling style and twist rate can be a factor at the high, and low, velocity end of loading data. Something you could think about is firelapping, which I suspect has more effect on the breach end of the bore, which might be useful in your search for safer speeds.

Can you mount a pressure transducer near the breach? I'm thinking there are some new types that don't require modifying the barrel. It would be nice to work with actual data, instead of inferring from secondary conditions.

EDITOR'S NOTE: I found a real 9mm Major site where the preferred solution is to ream the chamber just a skosh, maybe five or six thousanths. Assuming the magazines permit it, increasing case capacity a tiny bit by loading long (from 1.144 to 1.150 makes all the difference needed, and can drop pressure by one "+" from +P+ to +P while still maintaining velocity required to make Major Power (and giving me my preferred 1750 fps at the muzzle). If the mags are a skosh tight, changing to a slightly steeper follower and reducing capacity would do the trick, assuming the bolt will still reliably pick up the cartridge as it sits in the modified magazine. This reaming also changes headspace, so has to be done very slowly, say .0005" at a time, checking headspace all the way. All in all, very delicate machining work, could get expensive...but it would keep SAAMI safety closer to hand. I have two of these rifles, and the other one is in 40S&W, loading by Glock magazines. I could rebarrel that one to .357 Sig, normal pressure, and achieve the same results...

Peter Grant

I respectfully suggest that you be extremely careful with the selection of the carbine. Some manufacturers (e.g. Keltec) emphatically state that +P or +P+ ammo must not be used in their firearms, probably for the same reasons that destroyed some carbines with early "hot" ammo. The pressure curve for 9mm. is so volatile that it can "peak" very rapidly, and if the metal can't contain it until the bullet is further down the barrel, giving room for the gas to expand, it can blow the breech open. If that's next to your face at the time . . . not good.

EDITOR'S NOTE: Thanks, Peter, but I am a long-time Kel-Tec customer and am fully aware of their legal position. They are a small manufacturer, and have maintained this position forever, as one moderate lawsuit judgment would put them out of business. The rifle itself is very strong. I am also aware of the physics behind SAAMI standards, and know that those standards are determined by momentary pressure spikes. The careful reloader considers the burn rate of powders, the ignition characteristics of primers used, and bullet seating to a thousanth of an inch. I researched active and frequent competitors in USPSA on their fora to find the information, ALL of which pertains to pistols, not rifles, which have a much stronger construction overall. These guys and gals have thousands of dollars in their pistols, and the barrels especially, and they are NOT going to use data which threatens those expensive guns. I am conservative and use the "work up" principle for all my handloading. I've had this S2000 for ten years, and probably fired 300+ rounds of NATO through it. Actually, with the 16.25" barrel, it should NEVER fire a weak load, because it could be a squib with that long barrel. I am going to start with 6.6gr of HS6 behind the 124CPRN. That load is 12% UNDER what these boys are using in their STI and Czechmark race guns. It might not even be +P, but it certainly isn't +P+. I am aiming for a certain velocity at the muzzle. I do find conflicting info, some of which says use a fast powder and the bullet will "coast" out of the barrel, but my experience loading the 357 MAG hot for carbine tells me to use a slower powder which will energize all the way down the barrel. Due to the short case, there are limits on that, but I will start with 2400 and see what gives. Thanks again.

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