I wanted to give 300 mp a try but really hate the lack of book data on this powder. Alliant has data for 260 and 300 gr bullets with max load of 31gr (both)... I am going to load the 240gr hornady mag bullet.

Thinking I could go at least a grain higher but more likely to run in 30-31.5gr region.

Any other published data out there? I cant find anything in Hornady 9th or Lyman 50th..

I feel like alliant sometimes doesnt want u using their powders. Like I am just an annoyance for wanting data. Wont be trying anymore of their new powders after this.

Edit: Yes, I already have H110 loads. I want to compare... Got plenty of both powders.

Update: 2/19...

I shot the 300MP and H110 loads yesterday.

The H110 loads were at the upper end 36gr+. Those are some powerful loads. I had worked up the load a month or so ago but wanted to test tighter in that upper range. I was pretty happy right around 36gr but may actually test a little lower for more accuracy. Also, the cases started getting a little harder to extract above the 36 so I may need to back down.

With the 300MP, the loads (especially below 31gr) did not burn right. I am using Remington 7.5's which is commonly used for this caliber. I tested 30-31.5gr. None of the loads had much recoil. I actually checked to make sure I didn't have a squib. All bullets exited the barrel but with not much bang.

The lower charges were dirty as hell. In fact, after 5 lower charges rounds, the gun was caked on with residue - almost as if I was shooting black powder. It looked like residue, not unburnt powder.

Made it difficult to chamber more rounds (as well as remove the rounds in there). I should have brought a cleaning rod.

I am guessing I was having poor burn of the powder. Above 31 gr, it was a little better but not much.

I would like to test higher loads but without published loads, I am reluctant. Maybe I will ask Alliant first.

Thoughts?

Once I have something working, I may chrono... right now, it's not worth it.

With 296/H110 and AA #9 why bother with anything else?

I actually seem to get better accuracy results from my S&W 686 357 with 300mp than H110. I kept H110 around for my 45LC loads. I started using it in 454 but accuracy results are mixed (but need more trigger time with gun). I want to do a head to head comparison this weekend with 300MP and H110 in 454...

I like 300 MP for 300 Blackout and 357 Mag and am trying it in 458 Socom.

I loaded some 44 mag with 300 MP for my brother and he complained about a huge amount of flash.  I think he's wanting to go back to H110.

Made some 300MP rounds tonight. I stayed in the 30-31.5 range. Will test them head to head with some H110 loads on Saturday.

Thanks for the replies. Will post my results.

Update in OP...

I sent them a note with questions. I also asked about 460S&W data as I was hoping to load that next with same powder and bullets. I noticed their data for that cartridge is more confusing in that they have 10gr difference for same bullet weight...  Cant figure out why those two bullets would require such a difference in charge.

In normal Alliant fashion... Here is their reply:
If you are using the data from Alliant, that is not the correct data. The Alliant data is for Speer bullets, not your Hornady bullets. Load data is developed for and specific to the bullet, not the propellant alone. Looking to the newly published #10 Hornady Reloading Manual, they do not list the Alliant Power Pro 300-MP as an option for either of these cartridges.
I will submit your request to the engineering lab for possible future development. But, there is no timetable as to when this may be looked at for development.

Basically useless.... same type of response when I sent them a message a couple years ago.

I asked about both casull and 460 with basically no help at all.

This will be the last time I buy anything "new" from Alliant.

Alliant says 31 grains is a compressed load with the gold dot bullet. Maybe try increasing your neck tension and or more crimp.