Some Early Trials of Alliant 300-MP Powder in the 450B

[pitted bore]

NOTE: This post and the following one include some data I used in reloading the 450B. The loads I assembed using these data did not cause my rifle to blow up, and did not give the appearance of high pressures. However, if you attempt to duplicate these loads and fire them in your rifle, it may be that parts of your rifle and of your body will become detached and litter the landscape, and all the king's horses and all the king's men may not be able to put either you or your rifle together again.

The first two posts in this thread were written as a response to a question about 300-MP from another thread in the reloading forum. (Link to thread: Alliant 300-MP powder?.)

PART 1 of 2 parts

On this site, Siringo first mentioned this powder in May 2010, before Alliant had released it for retail sale. (Link to thread:Power Pro 300 MP.) Alliant told Siringo that they had no data for reloading the 450B with 300-MP.

In summer 2010 I was working with both the 450B and the 218 Bee cartridges. (There is a remarkable overlap in powder types that are suitable for these two cartridges.) My interest in the 450B was focused then on light weight bullets. I bought 300-MP from Powder Valley, and assembled some loads using 185-grain 0.451 diameter Prvi Partizan jacketed hollow-point bullets. Here's what the bullet and loaded cartridges looked like, with Hornady 250-grain rounds for comparison:
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My first trial with 300-MP used 4X fired Hornady brass and Win WSR primers, with bullets crimped in the case with the modified Lee 45-70 Factory Crimp Die. To get some idea of starting powder weights, I looked at the 460 S&W data using 300-MP on the Alliant on-line Reloader's Guide. The infomation there has expanded since 2010. Then there were a few loads listed, with values of about 26 grains, altho the bullets were pretty heavy in the 460 S&W.

I loaded five cases with powder weights of 26, 27, 28, 29, and 30 grains. C.O.L was 2.005.

My concern with using these loads was that they were substantially less than case-filling. Alliant info on the powder indicates it's a spherical powder and made in the USA. I'm pretty sure this means it's made at the St. Marks FL ball powder plant, run by General Dynamics. Based on this, I assumed that 300-MP probably has the same problems as 296 and similar ball powders with loads that don't fill the case. However, the loads in the Guide for the 460 S&W were less than case filling, so I proceeded cautiously.

On 13 Aug 2010 (a nice 80-degree day & sunny) I fired these from my 1903 bolt gun with the 20-inch barrel. The gun was placed on a range bench and sandbagged in a rest with the barrel pointed across a chronograph at 10 feet from the muzzle. There was no target downrange other than the tall berm at 100-yards. I tucked all my body parts behind a big thick tree to the rear of the range benches and fired the rifle with a 20-foot string on the trigger.

Velocities were: 26 grs=1258 fps, 27 grs=1482 fps, 28 grs=1491 fps, 29 grs=1550 fps, and 30 grs=1602 fps. The cases were all heavily sooted, and there was a lot of unburned powder in the barrel.

I loaded another series of 5 cartridges using 31 - 35 grains of powder. With a set up similar to 13 Aug (sandbags, string, tree) I fired these on 22 Aug 2010 and obtained the following velocities: 31 grs=no reading, 32 grs=1718 fps, 33 grs=1722 fps, 34 grs=1800 fps, 35 grs=1852 fps. Again, the cases were sooted and unburned powder granules remained in the barrel; there was less unburned powder with the 35 grain load.

I assembled yet another similar series, using 36-40 grains of 300-MP. Firing these on 6 Sept 2010 produced mixed results, at best. There were real problems with ignition, including some hangfires (click-Bang). Much unburned powder remained in the barrel, and there was some smoke coming from the action after some shots. The smoke must been a moist acid resulting from incomplete powder combustion, because the surface of the action showed rust within a couple of hours after the tests.

The chronograph showed odd readings, with only one that seemed reasonable: 38 grains = 1968 fps. The other readings were all less than 500 fps. Maybe the low readings were real. Fifteen minutes later, values with 218 Bee loads seemed realistic and about as expected.

None of these results were reported in this forum. I did refer to them in a post on 1 December 2010 (Link to thread: Sub-Sonics):
"I've worked briefly with a new powder, Alliant Power Pro 300-MP, that is described as being a bit faster than Lil'Gun in burn rate. With loads that were less than case filling, there were no ka-boomy pressure problems, but there were some click-pop fizzles with lots of unburned powder. I took those as a sign that I was on the edge of perhaps major difficulties, and quit trying to use that powder for a job it wasn't designed to do."

I'll emphasize here what I reported then: The loads I used may have been on the borderline of danger zones. As wildcatter has stated several times on this forum, really bad events can be caused by too-light loads of ball powders.

[pitted bore]

PART 2 of 2 parts

The 300-MP project went on the back burner for a year. In August 2011, after more experience with light bullets and similar powders, I loaded a series of five cases with a bit more 300-MP powder.

Cases were Hornady fired 9X, primers were CCI #41, bullets were the same 185-grain Prvi Partizan and crimped as above, The powder series was 47.5 to 51.5 grains in 1-grain increments.

These were fired on 16 August 2011 in my Model 70 bolt gun with the 26-inch barrel. Again, I did not use a target. Velocities at nine feet were: 47.5 grs=2265 fps, 48.5 grs=2345 fps, 49.5grs=2440 fps, 50.5 grs=2403 fps, 51.5 grs=2205 fps.

There seemed little unburned powder and little sooting. However, the plateau and then decrease in velocity with increasing charge was characteristic of other powders, indicating that light bullets were moving down the barrel before the charge of powder could be ignited and burn satisfactorily.

At this point I abandoned efforts to use 300-MP powder with lighter bullets in the 450B. The case was about full, and the velocities were rather lower than those produced by other powders.

Shortly after these trials, in a post in September 2011, wildcatter indicated he'd just purchased some 300-MP and was hopeful it would be useful in applications similar to 296 (Link to thread: Duplexing?). In December 2011, he was still working with the powder and had not yet decided on its usefulness (Link to thread: powders for 450).

Alliant likes the powder in the 454 Cassull and the 460 S&W mag with bullets weighing as little as 260 grains. In the 450B, the situation is likely similar. However, based on my experience, it isn't likely to do well with bullets 200 grains and below. If somebody finds otherwise, then their reloading techniques are likely to be especially interesting.

[Stealthshooter]

Your results don't surprise me with the lighter bullets. I'm betting 300-MP is going to be the most useful for the 300+ grain bullets.

[wildcatter]

PB, I read your results and like Hoot, as expected, the burn rate for the MP powder is far too slow in light for caliber bullets and in that respect, there was no surprises. And, I do believe you were the first to use this powder, in our cartridge, which may pan out to be the best, in some respects.

Hoot, prolly, you will find the 250's will function and group well, it's just not the most efficient powder of choice. The 275's will fair much better and you'll prolly like the MP powder well, at that point. As you go up in bullet weights, 300's, you will find even better results. But, the burn rate, for the MP really won't take-off until you hit 325's or better. At that point, we'll make you a born again Heavy-Weight Shooter, as if 200gr isn't a heavy bullet (200gr in a 300 mag is a brute), but when we get you shooting the 275's and better on a regular basis, it might just Rock Your World.

But all my hyperbole on the side, I will wait with baited breath, for your results with those 300's. And can't wait for the results you obtain using the 275 Barnes. To which, you can find better powders for the 275's but as a one stop shopping kind of thing, 300MP will be a Great Trade-Off.. When you get to resized 350's (resized .458's to .452's), you will be astound at the results.

..t