I marked my case on the side with a marker where my Lee HP SWC would seat at the top crimp line and then took a pencil and marked the measurement On an unsharpened pencil so after I tricked powder in the case I can insert the pencil til it lines up with the mark and measure the max compressed powder charge. To me this would be crushing it so for a max load I would back it down .2 grains.
I used starline brass sized and trimmed to 1.275" with a primer installed to keep the power inside the case. My max, compressed fill line where the base of the boolit would from press the powder when I seat it to the top crimp line was 6.2 grains. So as far as I'm concerned 6 grains would be a max loading so I don't crush the trail boss powder. The 70% reduction came out to 4.34 so 4.4 grains would be a a starting load.
The reason for my post is I see loads all over the place saying you can load up to 7.5 grains or more with a 240 grain SWC? This would be crushing the powder without a doubt. So I am confused by th load data I've seen listed using this powder. This probably explains why I've read that some shooters have had less than spectacular results with fliers. It also makes perfect sense when I tried this powder the summer before last with my devastators. I just went off book and did loads from 6 grains to I think all the way to 8 or 8.5. Don't remember. But I had some 400 fps variances with the sane loads across my chrony. Now I know why, the powder was compressed. Guess when you use this powder I would suggest not to go by what ever load data you see listed in the books and do yourself a favor and measure like I did and and then do the math and start with 70% percent less and work up. I know this common knowledge with trail boss powder but I didn't realize there was no where near the case capacity for the powder loads I've seen listed in a lot of load data I've seen.
I also did the same measurement for some FREE 180 grain hornady xtp's I received from hornady when I bought a die set...or I would have never bought them. The trail boss compression load line was at 9.2 grains. So to me 9 grains max and a start of 6.5 grains since 70% came out to 6.44 grains.
Should be fun. Going to load some up to plink in my wrist braking S&W 329 nite guard. Glad I checked my case capacity this time around. I just loaded some 45 colt with the boolits seated pretty far out and went with a 5.2 grain load with a 255 grain boolit. I'm going to have to find a case or pull one to make sure I have at least 70% powder in them.