I’m using a 16″ AR Performance barrel with a Wylde chamber. A friend and I have done a fair amount of testing with the 69 RMR bullets with TAC and X-terminator. My barrel shoots faster than most. You will likely need more powder than I use to get the same velocity.
My rifle prefers 23.2 grains of TAC, which runs about 2650 FPS depending on conditions. Being a ball powder, velocity varies quite a bit with temperature. I’ve had good groups from this charge weight at temps from mid 60’s through high 90’s (velocity was about 2695 in the heat). I use Wolf Gold brass, CCI 450 primers, and OAL averages about 2.249″ (1.878″ CBTO on my Hornady comparator). For these, I use a Lee full length sizing die with the expander turned down to .2220″. This produces necks that won’t accept a .2210″+ pin gauge but .2205″+ fits all the way through. So, there is a little over .003″ interference fit between bullet and case neck. No crimp.
Often I shoot at 50 yards prone with a backpack for a front rest and a rear squeeze bag, not exactly a precision setup. 1-6X scope. Groups are as much a measure of my shooting ability for a given string as what the load can do. I flub some at times and get some stringing. I’m still working on learning to shoot more consistently with this setup. If everything isn’t just right groups with any ammo open up. I mention this because shooter error can contribute very significantly to group size. Gas guns are particularly sensitive to how they are supported. I’ve recently fired three good 5 shot groups with the 23.2 TAC load during 3 different shooting sessions. Two each measure .33″, and yesterday’s was .36″. All at 50 yards.
22.3 grains of X-terminator produces similar velocity (slightly slower) and also seems to be a good spot for that powder. There is another node up around 22.9 grains of X-terminator, but that runs 2700ish in cooler weather and would be too stout in the heat.
If you haven’t already, test a range of loads in fixed increments. I go with either .2 or .3 grain increments in .223. Test over a decent range of charge weights. You’ll want to repeat this several times to find the trends and help rule out shooter error as you zero in on the nodes. You’ll find the good spots. There can be quite a difference in only a few tenths of powder.
My friend, also using a 16″ ARP barrel, tested seating depth with these bullets, firing 5 shot groups at 50 yards using 24.0 grains of TAC. He used .005″ increments measured to bullet ogive (COAL from approximately 2.260″ to 2.240″). No discernable difference was found. All groups were good, ranging from .40″ to .46″. I experiemented a little with seating depth and didn’t find obvious differences either. YMMV.
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