Hey all,
After watching Jim’s reloading videos I switched to mandrels rather than just using the expander ball in the FL sizing die. I am shooting 7 PRC, the mandrel size I bought was .282. Went to the range and now I am getting 80fps slower than I was (2820 now vs 2900) is all. My question is should I increase powder weight or should I try a smaller mandrel? I definitely want more speed than 2820. I’m hesitant to switch powder weight (64.5g H1000) because ES is good and accuracy is great.
I should add that the mandrels did seem to lower ES so I would like to keep using them.
Either way you’re increasing the peak pressure so I think whichever variable seems more easily controlled might be the right answer. May not make a difference either way, so maybe whichever is cheaper is the right answer. I would be curious if you used the smaller mandrel with the same amount of powder, if you’re velocity would increase, but maintain your SD and ES?
Its extremely unlikely that neck tension on its own would account for 80fps.
I can’t imagine that the neck tension change on the mandrel would have any bearing on that velocity swing. I’ve never seen that.
Yeah it was weird.. I ordered some smaller mandrels and will see what happens with the same powder charge. Really appreciate the replies. I’ll report back.
Because of brass springback if you don’t have a set of pin gauges you have no way of knowing if you’re setting the neck tension you want or if its consistent. That being said, for bolt actions, as long as the bullet isn’t moving around, there shouldn’t be a problem.
Yeah it was really odd. This was all averaged over 40-50 rounds each session and I can’t think of anything i did differently other than the Mandrel expanders. I’ve ordered the .2815 and .281 mandrels and will do a little test and report back.
Did you switch powder lots? primer lot? Neck tension alone won’t account for such a large change in Velocity. In the end though, with good ES and over 2800 fps (bullet gr?) this won’t affect your ability to harvest an animal. If I had a recipe that gave great results but was a bit slower I would still use it.
That’s the weird thing, I didn’t change anything other than the mandrels that I can think of. Same powder, same primers. You’re right, I could definitely still harvest an animal but it was super consistent at 2900 prior to this last shooting session so I’m just scratching my head a little bit. I’ll go out again soon and see what happens. I was hoping to get out this weekend but I may not make it. Appreciate the replies - I really didn’t know whether neck tension could have large affects like that or not so I appreciate the input.
Another thought, did you happen to clean the barrel? Typically, a barrel will speed up as it gets ‘dirty’ and then cleaning it will decrease the speed again. Hornady has a podcast addressing this issue in the ‘Should I clean my barrel’ series and how often should I clean.
I did clean the barrel but I tend to clean it every time I shoot it. New mandrels don’t come until Monday. I’ll do a little test when I can get out shooting next. 5 shots at .282, 5 shots at .2815, and 5 shots at .281, and 5 shots with the expander ball in the FL die. Could humidity in the powder make that big of a shift? I do tend to just keep my powder in the trickler hopper. In Phoenix humidity is fairly constant but when it rains you can really feel it.
That’s interesting though, I didn’t know velocity increases with a dirty barrel. That would be an interesting test. Shoot 500 (or however many) rounds and plot velocities in an excel spreadsheet.
I think humidity can play a big role. Jim recommends humidity control bags to use in his powder and not store in hopper. Also, Do you wet clean or tumble dry your brass? Once I had 100 FPS difference in a load and realized my brass probably didn’t get fully dry in the dryer so now I leave them in there overnight.
Honestly.. that could be it. Good thinking. I wet clean my brass and it’s possible I still had some moisture there.