Nothing beats 300-MP, so far anyway

[Stonechucker]

So I am a huge fan of large revolver cartridges in carbine length rifles. These straight walled moderate capacity cartridges are extremely efficient, and will perform way above what most people think they should, especially in stronger action single shots like the TC Encore. Over the past year or so I have completed a moderate amount of testing with three different powders, w296/H110, AA 1680, and 300-MP. By far the best performing powder in the two cartridges I shoot, the 357 Maximum and the 445 supermag is 300-MP. This has been somewhat of a surprise to me as you just don't here a lot about this powder, heck the only reason I knew anything about it was that I couldn't get other powders at the time. My first experience with it was in my 20 inch 357 Maximum Encore barrel using 158 grain Fury short spitzer bullets. A friend had given me some W296 and I was getting around 2450fps with 28.7 grains. Above 28.7 I started to see slight cratering on the primers so I backed back down to the 28.7. I thought this was awesome performance with this little cartridge and it was, but then I tried 300-MP. I worked up to 28.7 grains with no pressure signs, then 29 grains no pressure signs. I finally leveled off at 30 grains and really could not fit any more powder in the case and still seat the bullet, again no pressure signs. Final velocity was 2560fps with good accuracy. With the 140 grain Hammer, Shock Hammer bullet I was able achieve 2,657fps, again the brass and primers looked good and with good accuracy. As always please work loads up carefully yourself each gun is different. I started with about 25 grains for both w296 and 300-MP and worked up slowly from there. With the 445 Supermag the difference was even more dramatic. I bought some AA 1680 at a good price, and had heard how good it was in the 445. So I gave it a try, well in a 20 inch Encore barrel anyway I was not very impressed, slower than expected velocity, and fairly dirty. I think I wasn't getting complete powder burn. Now bring in 300-MP. Working my loads up slowly I landed on 40 grains of 300-MP under a 250g Fury pointed soft point bullet, brass and primers looked great and the brass pulled out easily. This particular load achieved 2,413fps! That is absolutely amazing and calculates out to over 3200 ftlbs of energy! The thing I have noticed is that 300-MP likes full house loads, and works best even a little compressed, ,again please do not start at this load. So 300-MP give it a try and see if it works as good for you as it has for me.

 

[Stonechucker]

The loads mentioned above are heavy loads and there is no load data for 357 maximum or 445 supermag with 300-MP powder. Please realize you need to start much lower and work your way up. Load at your own risk.

 

[kcofohio]

I'm still trying to get 300-MP loads worked up in a 77/357. I don't see much data out there for 357, and what I have read, I expected much higher velocities than I got.

But the powder shoots well with 300 BLK subs. So it won't be a total waste if I don't get it figured out in 357.

 

[WrongHanded]

I'm still trying to get 300-MP loads worked up in a 77/357. I don't see much data out there for 357, and what I have read, I expected much higher velocities than I got.

But the powder shoots well with 300 BLK subs. So it won't be a total waste if I don't get it figured out in 357.

What bullet are you working with for your 77/357?

 

[Stonechucker]

Well what I have noticed is it does much better with close to max or max loads, much lower and I found it to he a little dirty, and velocity not overwhelming, but load it up and the exact opposite seems to be true in my case any way.. Alliant powder does have some load data on their site for 300-MP in the 357 magnum btw, there is just no 357 Maximum data.

 

[kcofohio]

What bullet are you working with for you 77/357?

Hornady's 158 gr. XTP-FP and 180 gr. XTP.
With the 158 gr. I went up to 18.5 gr. And with the 180 gr. I went up to 17.0 gr.

 

[kcofohio]

Well what I have noticed is it does much better with close to max or max loads, much lower and I found it to he a little dirty, and velocity not overwhelming, but load it up and the exact opposite seems to be true in my case any way.. Alliant powder does have some load data on their site for 300-MP in the 357 magnum btw, there is just no 357 Maximum data.

I used new Starline brass. And there is very little soot in the fired cases.

 

[WrongHanded]

Hornady's 158 gr. XTP-FP and 180 gr. XTP.
With the 158 gr. I went up to 18.5 gr. And with the 180 gr. I went up to 17.0 gr.

I've run 18.6gr with a 158gr Speer Gold Dot. It's max according to alliant. I don't feel like it quite enough to hit the sweet spot. But it was going at least mid 1800s from a 20" barrel. I'd have to check for exact number. Honestly I think more than 18" of barrel is probably too long.

 

[WrongHanded]

@kcofohio you said a 158gr XTP-FP. Is that a shorter bullet than the XTP hollow point? If so, you might be able to up the charge a little to compensate.

What's your barrel length, and what velocities were you getting?

 

[kcofohio]

@kcofohio you said a 158gr XTP-FP. Is that a shorter bullet than the XTP hollow point? If so, you might be able to up the charge a little to compensate.

What's your barrel length, and what velocities were you getting?

I was getting in the low 1400s with both max. I'm sure the flat point is shorter.
18 1/2" barrel.

With your post of velocities. It leaves me to believe my Chrony is not getting good readings. I shot it some time ago, missed the electronics, but busted the sensor windows badly. I replaced the windows and housing. I need to take a known good load, before the lead poisoning, and verify whether good or bad. If bad, I'll need to see about sending it in. It's a Prochrono.