I understand that the short barrel does not match up with much existing load data and this is going to make you question what powders are best if you are trying to push velocities.
The following Quickload info is not load data, but it might help you deal with the short barrel concerns.
I have seen lots of posts with folks running Unique and have seen 10.4 gr listed as max with a 250. Quickload goes a little further, but I would not exceed published data with Unique. It is too easy to just use a different powder if you want to go faster.
The 5744 seems to get some use in the 38-55 and the info below says it will get you close to top velocity with a lot less powder used.
RL 7 is worth trying if you want just a little more than 5744 will do.
If you are really trying for maximum speed, 3031 seems to be your best pick.
Code:
Cartridge : .38-55 Win.
Bullet : .379, 250, LEE C379-250-1R
Cartridge O.A.L. L6: 2.510 inch = 63.75 mm
Barrel Length : 16.0 inch = 406.4 mm
C A U T I O N : any load listed can result in a powder charge that falls below minimum suggested
loads or exceeds maximum suggested loads as presented in current handloading manuals. Understand
that all of the listed powders can be unsuitable for the given combination of cartridge, bullet
and gun. Actual load order can vary, depending upon lot-to-lot powder and component variations.
USE ONLY FOR COMPARISON !
Powder type Filling/Loading Ratio Charge Charge Vel. Prop.Burnt P max P muzz B_Time
% Grains Gramm fps % psi psi ms
--------------------------------- -----------------------------------------------------------------
IMR 3031 108.2 35.7 2.31 1790 87.0 30458 6053 1.185 ! Near Maximum !
Hodgdon H4895 103.1 36.4 2.36 1757 79.4 30458 5692 1.196 ! Near Maximum !
Alliant Reloder-7 88.1 30.1 1.95 1739 93.2 30458 5236 1.216 ! Near Maximum !
IMR 4064 108.7 36.3 2.35 1710 76.8 30458 5253 1.205 ! Near Maximum !
Accurate 5744 72.3 24.4 1.58 1690 93.4 30458 4815 1.212 ! Near Maximum !
Alliant UNIQUE 53.4 12.1 0.79 1381 100.0 30458 2307 1.323 ! Near Maximum !
Alliant UNIQUE 45.6 10.4 0.67 1265 100.0 23300 2007 1.486