I started using 300MP for a 315 gr bullet a few years ago, and would like to switch to a 300 gr bullet, but I cannot find any published load data or the data I used originally, so other than backing off a little on my current charge of 16.7 gr (with 315 gr bullet) , I am not sure how low I should start or how high I can go. Has any data been published for this powder in 38-55?
Thanks!
Joe S

I have been using the same charge, so I am not worried about that, my object is to find out what the recommended minimum and maximum charges are so I know what range I can safely work with.
Joe

frnkeore,

I do not think you will find the data you are interested in.   You are in the same position I have found myself in many times.

For help identifying when you need to start smaller charge increase increments,  try using large pistol primers.  They show signs of excessive pressures much sooner than LR primers.  Also, never use LR Mag primer rs when working up loads.  They will not show signs of excessive pressure in straight tapered cartridges until it is too late.

Flat and/or initial signs of cratering around the firing pin strike is a good sign you have a safe load for the case and a modern material rifle.   
 
I have used 300MP successfully in 285 gr 45 LC rifle loads to 1,550 before showing initial signs of pressure.   

Thanks, I may try some loads of 300MP in my 38-55 with GC design bullets.    Unique and 4198 have become my go to powders for PBBullets.