seating depth along with powder charge

[JAnderson94]

Hi guys,

I'm working on a load for my 20 bull barrel ar15. I started out doing the ladder test with the powder charges. Sweet spot is 25-25.2 grains benchmark with speer varmints 52 grains. Will my powder charge need to be tweaked due to a seating depth change or does that not matter? Gun holds about 3/4in 5 shot groups right now

Thanks,
James

 

[Wachsmann]

So I think once you find a good powder charge then u can start working on the seating depth. But this can be done in reverse as well. I think after that you go back U will need to finally tune the powder charge for best results. I started a ladder test using single charge weight and was working around seating depth. I read on another post that once you find your seating depth then almost any charge (within reason) should shoot well...I'm thinking 1MOA or better. But honestly I would be disappointed with only 1MOA after conducting all the work. So I somewhat have the same question as you do...Once best seating depth is found will powder charge change grouping a whole lot or, are we mainly changing our velocity. Thinking about this my 6.5x284 works best or were I stopped testing at .100 from the lands. I used this same seating depth with 3 different powders at max loads to see what was the best velocity. All 3 powders shot between 3/4 inch group to 1/2 inch group at 100yards. So I think it may be that seating depth plays a greater roll in group size. But it would still be good to hear from other that has done this many time over. For me I still picking up on things that help refine my reloading process to find what is the best load for my rifles. Working with two 300 RUM loads at the current time. Good luck.gun)

 

[JAnderson94]

I agree that at least at short range seating depth plays a factor. I'm just shooting a little .223. But I had loads from 2.260 to 2.215. The 2.215 group 3 at 3/8s with a flyer at 1/2in. The really bad flyer in the group was all my fault. The 2.260 did 5 at 3/4 of an inch or so. But nothing in between was accurate at all. But maybe a different powder charge would help those also

 

[FearNoWind]

I typically start with a seating depth at .020 - .025 off the lands and find a powder charge that is within SAMMI specs. that provides the best groups on target. The "sweet spot" for my load is identified when a range of powder charges within .2 grains of each other (e.g. 24.8, 25.0, 25.2) all print on target with approximately the same grouping, with a SD goal of less than 10. Then I use the middle load (in the example that's 25.0) to work on seating depth. After that I run a final series of samples to validate and, if necessary, fine tune the finished load.
Loading with over-all lengths that place the bullet into the lands is something I avoid. There is no scientific evidence that loading into the lands offers any benefit to accuracy. I have never found loading into the lands to offer any advantage and, often, find it actually produces inferior results.
Just for the record, I get better results with H335 than Benchmark with those types of loads.