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          Am working on Hornady 125 gr XTPs  in different powders to see the difference in accuracy, if any or much. Once fired Starline brass (soft original load) and the load data I find asks for a COL of 1.455". That seems to have the crimp hit just a scad short of the cannelure on the projectile. (the bullet seems to wants to be set deeper into the case to have the crimp centered in the cannelure) Suggestions, comments?

          And a general question,  I was taught to use as little crimp as possible on 38 special cases. Some reloaders don't crimp them at all if they are soft loads. How drastically does a heavy crimp effect the pressure of the discharged round? I would imagine a heavier crimp would tend to retain the projectile more and cause a higher pressure inside the case? Is that significant?

 

 

Hornady 9th is showing 1.450” COL for the 125 XTP.  0.005” difference from your load data, which I would think is no big deal.  Also showing 1.145” and 1.155” for trim and max case lengths, respectively. What are your sized case lengths?

On the crimp issue - Heavier crimp usually goes along with higher initial pressure to get the bullet moving, but I haven’t seen anything that suggests the difference would be drastic.  If you’re looking for slight differences in accuracy due to changing powders, then you need to keep all other variables constant - like primer, case volume, crimp, case length, and seating depth.  Use enough crimp to keep the seating depth fixed if you’re loading and firing multiple rounds or go with no crimp and load/fire one round at a time to make sure recoil isn’t corrupting the seated depth on rounds 2, 3, 4….  The amount of crimp will change with variations in case length also. So, make sure all cases are the same length before crimping.

I only crimp my .38's enough to remove the case flair, but I shoot them in a S&W 686, which is a heavy gun and being a 357 mag has some room in the cylinder if a bullet tended to walk out a little.

While I go nuts with case prep, measurement, powder, distance to lands, etc. for my rifle loads.  I tend to pick a near bottom load with whatever powder I have and stick with it for my target/plinking loads for my pistols.