Yesterday I was trying out some new loads for my 375 and 470. I noticed several things that were a bit surprising.
First of all, when shooting soft and solids in both calibers using identical cartridges and powder loads respectively, I found it odd that I consistently got higher velocities with the solids. With both calibers, the solids were about 25-30 fps quicker. Have any idea why?
I also found it interesting how much more accurate the softs were in my double rifle than the solids. Using 500 grain Woodleighs, the softs would almost drive nails while the solids consistently shot about an inch and a half to right with greater variation up and down. I suppose the soft bullet’s taper helped here.
On another matter, I was working up a load for my 375 using 300 grain TBBC's and Woodleigh solids. I found that with 70 grains of RL-15, the solids fired at about 2560-70 fps and the softs at around 2535-40. The accuracy was excellent with both. I then pulled out some factory-made Remington Safari Grade 375's loaded with 300 grain Swift A-Frames. These consistently fired at around 2600-2610 with excellent accuracy. They did shoot about 1 inch higher than my hand loads with the 70 grains, which I attributed to the higher speed. Trying to match the performance of the factory loads, I loaded some with 70.5 and 70.7 grains of RL-15. I then saw why the books list 70 grains as the max for this powder as the bullet would not seat anywhere near the cannelure. The case was too full of powder. I did go ahead and shoot them at that heavy load and got 2600-2624 fps shots, but have no plans to use that load again. My question is (and I know 50 fps isn't a big deal in hunting situations), is there a 375 load that will shoot with the speed and accuracy I consistently found with the Remington factory-loaded bullets? They obviously aren't using RL-15 in there, though I have no complaints with that powder.
Every time I experiment and reload, I see new things, and in the learning process, I frequently find new questions. Do any of you have the answers from those generated yesterday?

Well, what do I know, but you asked for ideas, so here's mine:
The solids are harder into the lands, and so stall and build up pressure, thus the higher speeds. What that means (if true) is that you need to load them down to the speed of the softs if you want the pressure you get with the softs.
As for faster bullets, try a slower powder. For the 300g I might go 4831 or RL 17. Somewhere around 82-3g of powder you might see that velocity. And don't be afraid of a little compressed powder with these slower numbers.
[...] an old Honrady manual lists 84.5 or so of the 4831 for 2600-ish. Start with 78 and see where it leads you. COL around 3.55" right?

RL-15 is THE powder for the .375 Ouch & Ouch!

Try using a long (at least 6 inches) drop tube and you may find that powder compression is much less.

And, as has been pointed out, don't be afraid of powder compression with non-ball powders (ball powders can fuse together with heavy compression). An advantage is that the powder will prevent the bullets being driven into the case by recoil.

cheers,

jpb

As the owner of a double, you are undoubtedly aware that loads can be somewhat critical since they have to account for the "regulation" that makes both barrels shoot to the same point of aim.

the solids are longer with a longer bearing surface.

this nets in a higher velocity as the solids are having a "tougher" time sliding down the bore and there's MORE of it sliding (close enough)

back them off two grains and see


jeffe

Jeffe,
That's an interesting explanation for the additional speed of the solids. Those bullets are definitly longer than my softs (particularly in 375).
As for the issue of "powder compression", Bwana-be, are you basically saying to go ahead and press the bullet further into what appears to be a case overly full of powder?