Compession dies

[Major Tom]

What is the purpose of these dies? I assumed seating the bullet compresses the powder.

[Mark Daiute]

In a 45/70 if you manage to compress the 70 grains of powder, with the bullet, to seating depth, you will deform the bullet.

[Sunray]

"...you will deform the bullet..." No you won't. Cast .45-70 bullets aren't hollow based. Not all .45-70 ammo used 70 grains of BP either. Trapdoor carbines, for example, used 55 grains. Shooting a Trapdoor carbine with 70 grains of BP hurts. Had one before there was an Internet. Traded it off in a pre-mature senior's moment.
Compression dies give uniform compaction of the powder and let you finger seat the bullet. At least that's what it says on Cabela's page for Montana Precision Swagging's die.

[13Echo]

Compression dies are for compressing black powder to get a full charge in the case.
To get 70grs of FFg into a 45-70 case and still fully seat the 1881 500gr bullet to match the arsenal load requires compressing the charge into an almost solid mass. If you try to compress the powder by seating the bullet you will deform the bullet. Lesser charges, such as the 55grs of powder used for the 405gr hollow base bullet carbine load generally don't require compression before seating the bullet. Compression of a black powder charge with a compression die is a common procedure in loading for a black powder cartridge rifle whether you are seating the bullet by hand in a fireformed case or using a seating die in a fully sized case.

Jerry Liles
1868 Springfield 50-70, 1884 Springfield .45-70, 1874 Sharps 45-2.4", Rolling block 38-50 Hepburn.

[jmoore]

So, does the compression die effectively replace the drop tube method of improving BP loads?

[13Echo]

The drop tube and compression plug are complementary. With a drop tube you can get more powder in a case than by just pouring it in and it can then be further compressed. Thats how I get 70 grs FFg behind a 500gr 1881 bullet for my Trapdoor.

Jerry Liles

[jmoore]

Thanks! It appears I'm a few years out of the loop, here.
Makes sense, though, considering that just before the smokeless powder "fad" struck, several nations had adopted solid "pellet" loads for their smaller bore loads. 303 British comes to mind immediately.