I recently purchased a used .223 Remington built on a custom action. The action came with two barrels, one 18” and one 24”. Both barrels are 1:7 twist. Round count on both barrels was stated to be between 400-500 rounds and after bore scoping the barrels, I believe it. The amount of fire checking is minimal and the bores look good.
I started load development with the shorter barrel. Lake city brass, Fed 205m primers, IMR 8208 and 77gr matchkings. Right off I realized the throat was short and the reamer used must have been for 50-55gr type bullets.
My hope was to run bullets in the 75gr weight range (A-max, ELDM, matchkings, etc.). Using a Hornady modified case I tried all three “long” bullets and the bullet will have to be seated well into the case/neck. Jumping the bullets as little as .005-.010 results in the bullet boat tail/shank junction being well below the neck/shoulder junction of the case and with 23.6-24.0 grains of powder, there’s a bit of powder compression starting with 23.8grs of powder.
I ran some loads through a Magneto speed and the best SD’s we’re about 18fps with ES’s in the 40-60fps range. At 500 yards, vertical dispersion of the groups were bad (10-15inches).
I’ve tried a few component combinations now and results are not getting any better. Headspace seems great, brass only stretches .0015 to .002 and I bump that back when sizing. Using once and twice fired brass I have tried combinations of IMR 8208 with the 77gr tipped matchking and Hornady 75gr ELDM. I have also used the aforementioned with Fed 205M, CCI450, Fed 205AR match and CCI BR4 primers. When none of those combinations showed promise I did the same with Varget. The best SDs I’ve seen were 16fps with ES’s in the 30-40 FPS range. Many of the loads have SD’s in the 30fps range and ES spread as bad as 80-90fps. From low to high book charge weights, bullets are leaving the muzzle around 2700 to 2800fps which is about what I’d expect.
Considering what I’ve tried, I’m wondering if the bullet being seated so deep into the case/neck, is where I’m having the issues with velocity spread?
I’m considering running a throating reamer to extend the throat so I can seat bullets with less shank into the case. Magazine length won’t be an issue, there’s plenty of room in the mags.
Anyone ever run into something like this? Puzzles me why a fast twist barrel designed for heavy bullets would have been throated so short? I can’t seem to tighten up the SD’s/ES’s and any accuracy is just not happening.
