38-55 HiWall -- Heavy bullets -- Black Powder

[mehavey]

For those who think 18:1 is too slow for BP

325gr/Accurate Molds (another one ordered on Saturday/Arrived in Thursday/Cast on Friday/Shot on Saturday)

 

[Unclenick]

Nice group! How long is that bullet?

 

[mehavey]

1.18"


post: I lied.
QL predicted 1,155fps from an earlier/lower trial from which I'd tweaked the Miller K-factor for Swiss 1.5
LABRADAR showed actual to be 1,159fps

 

[Unclenick]

Stability factor of over 1.7. High end of optimal, so stability should be just fine and looks like it is!

 

[the Black Spot]

Nice!

 

[T. O'Heir]

The twist is about the bullet weight. Not the propellant. 1 in 18 is apparently common for the .38-55 though. Who told you it wasn't?
Mind you, the BP cartridge guys argue about twists too.
http://www.bpcr.net/forum/viewtopic.php?t=2369
https://www.assra.com/cgi-bin/yabb/YaBB.pl?num=1202346186

 

[mehavey]

The twist is about the bullet weight. Not the propellant

Bullet Weight --> ~ length
Black Powder --> ~ speed

Miller's is all about length/diameter and speed re twist.

I one looks at "The Internet" one finds all sorts of opinions as to 38-55 heavy weight reqm'ts and performance... ranging from 12:1, 14:1, 18:1 ... and all sorts of "that's too slow a twist" for BP speeds. In fact, straight Greenhill's likes a 14 twist for those lengths/diameters/speeds Still, things are a bit more complex that straight Greenhill.

So like UncleNick, I went to both JBM & Berger w/ real data on real bullet and real lower-bound speeds and plugged it in for an 18 twist:

. . . and it appears that theory and actual shooting data do overlap.


.

 

[Jim Watson]

My .38-55 has a 15 twist by rebore from .32-40.
It does well with the 336 gr Lyman "Mini-Snover."
I load 40.6 gr Swiss 1 1/2 because that gives compression the thickness of the over powder card wad with the top lube groove just covered.

Won't knock down all the 500 metre rams I hit, though.