Advise for BP Sub (777) Volume Measure

Barnacle Brad · March 12, 2009, 01:45 PM

Springfield 45-70 Trapdoor Cartridge.

I am new at reloading BP Subs and did a test to find how full a case is when using a drop tube versus straight from the powder measure (RCBS). The result is that the case containing the charge from the drop tube is maybe .25 lower in the case than the other (to be expected).

My question is about compression. For the 60gr charge specified in the Hodgdon manual a compression of .100 is noted. So when does powder compression begin for unsettled powder thrown from a powder measure? Is it when the bullet/wad touches the powder, or when it reaches the level of the settled powder as from the drop tube?

On another note, what is the best primer to use for the triple seven/45-70 trapdoor?

So many questions - so little time...

darkgael · March 12, 2009, 02:36 PM

Hodgdon tells us that 777 should not be compressed to the same extent as either BP or Pyrodex. Because compression, in any case, is so small, comparatively, when I used 777 I did not bother with compression.
You may get other answers about compressing BP and Pyrodex but here's mine: I use a drop tube to load the case and then, when seating the bullet add an additional bit - just a crunch.
I use your basic Win or CCI LR primer but a magnum primer might work better with 777.
Pete

Barnacle Brad · March 12, 2009, 02:48 PM

I am concerned about increasing the chamber pressure, by getting too much compression. I can calculate how much compression I get if I know how full the case is. Trouble is, measuring the distance from the powder to the top of the case is difficult. And this goes back to my original question - the settling issue.

I guess I just shouldn't be overly concerned, but it is hard not to be!

Thanks for your help!

Barnacle Brad · March 13, 2009, 05:25 PM

One final word on the subject. I re-read the 777 information on the Hodgdon website and they say that minimal compression is recommended up to .100. So going forward, my technique will be to use a bullet with a dia smaller than the case so that I can get a better idea where the bullet will seat and adjust the volume of powder accordingly.

As long as I don't exceed the 60gr charge, it should be a winner...

March 12, 2009, 01:45 PM	#1
Barnacle Brad Senior Member Join Date: March 12, 2009 Location: Greybull, Wyoming Posts: 416	Advise for BP Sub (777) Volume Measure Springfield 45-70 Trapdoor Cartridge. I am new at reloading BP Subs and did a test to find how full a case is when using a drop tube versus straight from the powder measure (RCBS). The result is that the case containing the charge from the drop tube is maybe .25 lower in the case than the other (to be expected). My question is about compression. For the 60gr charge specified in the Hodgdon manual a compression of .100 is noted. So when does powder compression begin for unsettled powder thrown from a powder measure? Is it when the bullet/wad touches the powder, or when it reaches the level of the settled powder as from the drop tube? On another note, what is the best primer to use for the triple seven/45-70 trapdoor? So many questions - so little time... __________________ Brad

March 12, 2009, 02:36 PM	#2
darkgael Senior Member Join Date: February 9, 2006 Location: Homes in Brooklyn, NY and in Pennsylvania. Posts: 5,473	BP/compression/777 Hodgdon tells us that 777 should not be compressed to the same extent as either BP or Pyrodex. Because compression, in any case, is so small, comparatively, when I used 777 I did not bother with compression. You may get other answers about compressing BP and Pyrodex but here's mine: I use a drop tube to load the case and then, when seating the bullet add an additional bit - just a crunch. I use your basic Win or CCI LR primer but a magnum primer might work better with 777. Pete __________________ “Auto racing, bull fighting, and mountain climbing are the only real sports ... all others are games.” Ernest Hemingway ... NRA Life Member

March 12, 2009, 02:48 PM	#3
Barnacle Brad Senior Member Join Date: March 12, 2009 Location: Greybull, Wyoming Posts: 416	BP/compression/777 I am concerned about increasing the chamber pressure, by getting too much compression. I can calculate how much compression I get if I know how full the case is. Trouble is, measuring the distance from the powder to the top of the case is difficult. And this goes back to my original question - the settling issue. I guess I just shouldn't be overly concerned, but it is hard not to be! Thanks for your help! __________________ Brad

March 13, 2009, 05:25 PM	#4
Barnacle Brad Senior Member Join Date: March 12, 2009 Location: Greybull, Wyoming Posts: 416	One final word on the subject. I re-read the 777 information on the Hodgdon website and they say that minimal compression is recommended up to .100. So going forward, my technique will be to use a bullet with a dia smaller than the case so that I can get a better idea where the bullet will seat and adjust the volume of powder accordingly. As long as I don't exceed the 60gr charge, it should be a winner... __________________ Brad

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