I went round and round on cartridge for a long time and finally decided to do what might be considered the Sane thing - I settled on 6.5 PRC (after .280 AI, 7mm Sherman Short, 6.5-284, and a few others) I may still revisit the Shermans once I get this and the 6 Dasher sorted. But it’ll probably be a long action build - so Sherman Max or Mega
So - things that I find interesting but not overly concerning.
- Clickers caused by expansion at the .200 line (just above the web) - This seems to be endemic to the entire family of short-fat cartridges (all the PRC’s, the SAUM and all of it’s variants, and several others) - Solutions: 1. Maybe a sizer die that sizes low enough (which means a die that does set the shoulder bump by raising or lowering the die in the lockring. (SAC, Cortina - probably a couple others - not sure this is an actual solution, but I’m going to try) 2. The AW2 .535 reamer - bumps out the base by about .02 giving the expansion space (seems to work - not a solution I’m fond of). 3. Roll sizing (works great, not cheap). 4. Retire the brass when it starts being a problem.
What I learned about Jump and the SAAMI chamber spec
Max magazine length for a short action, and high-BC bullets (Burger 156) pose an interesting problem: You really can’t adjust jump by changing the seating depth - you’re already about as deep as you want to be (shank is partially below the junction, and you’re eating into case volume) and deeper will almost surely run into powder compression. The Max COAL is 2.955 for metal AICS mags with no binder - that leaves (usually about .005 clearance, which is next to nothing). So you can’t seat out to reduce jump.
At that COAL, the jump for a SAAMI chamber is between .100 and .115 (yeah, that’s a long jump), and as the barrel erodes, it doesn’t get shorter. To my knowledge (still quite limited) - the JGS AW2 reamer has the SAAMI throat (.188) and the .535 base - and BPM can supply a SAAMI base, with the shorter .130 throat.
Why a shorter throat than SAAMI? to get the jump into the range Burger recommends - they would like you to start at .015 and increment in steps of .015 - and hopefully land somewhere around .030 and .060 - which isn’t possible with the 156EOL while still having the shank in the neck (more or less) - If you load to 2.955 COAL you’re jump is about .107 (average)
There is a note on the BMP reamer: handloads only, which seems to be based on the factory COAL, not the best seating depth for the lighter bullets. (calculated jump table based on chamber and bullet specs) Since and ELD-X seated to 2.955 puts the ogive very close to the lands (different shape than the Burger hybrids)
I had Grok run this up based on the two “standard” reamers I could find and the SAAMI specs and the published specs of the bullets. This is a small .xls spreadsheet with calculated jumps based on specs for the two reamers.
So - it’s clear that there is no way to seat the bullet out on any bullet where the junction is already longer than the Magazine COAL. And if you’re getting a 0.107 jump on the 156, you have no way to make that shorter (without hand feeding - and I haven’t looked at any of those numbers). If you want less jump, you cut a shorter-than-SAAMI throat.
Why does that matter? - It may not; the hybrid bullets are very jump-insensitive the Factory Burger 156 load works fine in the SAAMI chamber with that .107 jump, and yet Burger recommends starting jump at .015 and incrementing by .015 - ideally hitting somewhere between .030 and .060. (WAY beyond the actual starting point - and that’s before barrel erosion - from which I conclude that messing with seating depth to improve accuracy is way down the list of changes that will matter.
As to Barrel life - my solution is to use a .6mm Dasher for my fun time/practice (shooting a 400-yard KYL plate rack - 12" 10" 8" 6" 4" 2" - 12 rounds 2 minutes, move on after hit; stick to the 2" if you get that far and have rounds left). Use the 6.5 “for hunting and long range (1000 yards)”. I’m also going to start without the time limit 
