Alliant 300-MP Powder - my observations

After seeing the somewhat dazzling velocity performance listed by Alliant and even Hornady load data for this powder, I decided I had to try it out.

The Hornady data listed a max of 17.0gn for a 158gn bullet, while Alliant listed a max of 18.6. So, I worked my initial loads up in 0.3gn increments with a max of 17.0gn. I shot them from my Ruger 357mag GP100, 5" barrel, Hornady 158 XTP bullets.

I was somewhat puzzled by the results. The velocity peaked at about 1200fps with a charge of only 16.1gn. Going from 16.1 to 17.0 saw NO velocity increase at all, but I saw absolutely no pressure signs. I can get that velocity with several other powders, so I was surprised to see my data differ so much from the published data. I stuck the bottle of 300-MP on the back shelf and forgot about it for a while.

My thoughts went back to the 300-MP when I started playing with loads for my 16" Rossi M92 357mag carbine. I went back and looked at the load data again, and it finally hit me that the barrel length of the Hornady data (max charge of 17.0gn) was from a 8" barrel, and the Alliant data (max 18.6gn) was from a 10" barrel. Could they have stopped going up in charge simply because the velocity stopped increasing? Could it be that the longer barrel worked better with the higher charge? (This is one reason why they should post pressure readings, IMHO).

So, I started where I left off, working up from 16.0 to 17.0gn, but shot them from my 16" Rossi. This time, I saw a linear progression in velocity with the increasing charge. Again, no pressure signs, so I worked up another set of loads, this time from 17.3 to 18.5gn. I once again saw a linear progression in velocity all the way up to 18.5, with no primer pressure signs at all, but did start seeing some case head expansion (nothing to worry about, though) at 18.5gn. At 18.2gn, I was getting exactly 1800fps. I also had the best group size yet from that gun, 5 shot groups about 1.5" @ 50 using a rear peep sight, but the other charges grouped well also. For the carbine, I was using the Hornady 158 FP/XTP bullets.

I know that slow burning powders won't burn completely in short barrels, but I still expected to see a velocity increase with increasing charge even from a short barrel. This does not appear to be the case with 300-MP, though.

Does anyone else have an experience with 300-MP they would like to share?

 

What length barrels?

One good thing about the last "big event", it forced a lot of people to try new powders they probably would not have tried otherwise.

 

I don't understand the "moon and stars" statement. From everything I am reading here, the barrel length is the real variable regarding the performance of this powder. I was getting decent standard deviations, and good accuracy, even in my 5" revolver. In the short barrel I just wasn't seeing any benefit over other powders, but it really shines in my 16" carbine. The other comments here seem to back that up.

What do you mean by "erratic"?

 

At a recent gun show, I picked up a 44mag 20" Rossi. I could hardly wait to work up some 300-MP loads for it. I took them out today to shoot them, and I was very happy with the results. I was using Zero 240 JSP bullets, and Win large pistol primers.

I worked up from 22.5 to 24.5gn in 0.5gn increments. The best standard deviation was with the max load of 24.5gn, 1726fps, 8.6sd (5 shots). With just the stock rear buckhorn sight, the max load resulted in 1.6" group at 50 yards. I was very happy with that. The load data that I have shows a max charge of a full grain more, and I saw no pressure signs, so I may test a few more loads from 24.5 to 25.5.

It will be interesting to try these loads in my 10" revolver.

As a side note, I also had some test loads for my 20" Winchester 94 30-30, and I was getting almost the same muzzle energy with my 44 (1600 ft/lbs). After 70 rounds total, my shoulder was starting to complain.

 

What gun were you using?

 

Toprudder, that's interesting.

I worked some loads using 300MP with Hornady's 140 gr. XTP. Only because at the time, 2400 wasn't available. Shot them out of a 2 1/4" and 4" barrel. Pretty stout loads. Didn't chrony them.

I'm waiting for word back from the LGS about a Ruger 77/357. If all works out, I would try the 300MP in the 18.5" barrel.

Toprudder, thanks for posting your results.

 

Well, actually I did recognize it. When the primers are very round, and case head expansion is low, the pressure reached was never near max SAAMI pressure. Technically you are correct that I did see pressure signs, but they were for low pressure, not high pressure. I will try to be more clear next time.