Cartridge overall length (COAL) is something that I admittedly have not experimented with. Every rifle cartridge that I load for is set for magazine length. There are some exceptions. For the shorter bullets I will still seat the base of the bullet to the bottom of the neck for adequate tension. The reason that I post this thread is based on recent internet searches that describe COAL for 6.5 creedmoor far shorter than my loadings. I have been shooting 123 sst bullets seated out to magazine length (2.8ish"). This seemed to provide a decent compromise between magazine length and neck tension. The caveat is that I really have no idea how much bullet jump was occurring.
Yesterday I was looking at some other shooter’s recipes with the same bullet and found a post experimenting with seating depth. 2.720 inches was the magic number. Group size shrank at this number. Dramatically.
My question for you all. When have you deviated from magazines length and found a much shorter COAL to be the ticket?
Bullet seating depth is my LEAST favorite variable to mess with. I avoid it at all costs, and we don’t shoot secant ogive/VLDs for that reason. I only tried shorter OAL one time with 6.5 grab ass, and it didn’t make a difference. This was with 140 gr Horn ELD match whatever bullets.
My 6.5 ammo is also just loaded to mag length and a bit longer than some factory stuff I looked at. So my example of one didn’t show any significant difference.
With the K&M arbor press, an L.E. Wilson seating die, and some flash hider shims, you could do experimenting live at the range and see if anything magic happens.
My primary hunting rifle is a .300 Win Mag that I built with a custom chamber longer than SAAMI spec. Typically I shoot bullets seated very close to the lands which is also very close to magazine length. Due to the lack of my preferred components, I’m shooting the Berger 210 gr. VLD. By far the best accuracy I’ve found with this bullet is seated 0.040" off the lands. This is not uncommon with VLD-type projectiles.
My 6.5 Creedmoor ammo is loaded at 2.800" with standard tangent-ogive bullets.
NB: That was the magic number for that guy’s rifle… YMMV.
Given that you’re not actually pressing the bullet into the rifling when chambering, my sense is that longer is better, so loading to mag length (as you’ve been doing) is best.
The most accurate factory 140g ammunition I have fired through my RPR chambered in 6.5 Creedmoor has a C.O.L of 2.812" and a bullet jump of 0.081". The factory Hornady load is 0.028" shorter than magazine length. Any 140g loads I developed with longer C.O.L. were not as accurate and the sweet spot for my RPR is with 0.080" bullet jump with a 140g bullet.
The most accurate factory 120g ammunition fired through my RPR is Hornady 120g A-Max, it has a C.O.L of 2.696" - 2.701" and a bullet jump of 0.108". The barrel had under 300 rounds fired through it when I took the measurements. I don’t have much experience reloading with lighter bullets yet, but I could not believe how much bullet jump there is with a cartridge that is so accurate.
The long bullet jump is contrary to my experience with factory match .308 Winchester and 30-06 cartridges and my best reloads. I had to change my way of thinking when I started reloading 6.5 Creedmoor.
The shorter COAL of the 6.5 creedmoor is a variable that I need to explore. This has been a finicky cartridge for me. Maybe there is something with a shorter COAL that is modifying the internal ballistics enough to negate a presumably detrimental large bullet jump?
Glad I’m not the only one. One week it’s unstoppable, the next is mediocrity time. I’m finally starting to see some sort of consistency out of this ball busting round.
My 30 caliber match reloads have a 0.010" - 0.030" bullet jump and shoot sub MOA. What I had difficulty understanding was factory 6.5 Creedmoor ammunition that had a bullet jump of over 0.100" and shooting sub 1/3 MOA groups at 300 yards.