Re: Looking to break with the 6.5 creedmoor norm
Reloading for the AR platform in 6.5 Creedmoor:
Rifle is a custom build (JD machine Tech receiver, JP low mass enhanced bolt set Fulton Armory's 6.5 Creedmoor 24 inch NM barrel, Geiselle SSA-E 2 stage trigger, Magpul PRS stock and plastic mags, Apex Machine Gator Grip Hand guard....)
Creedmoor is a great round but the loading from Hornady is a slower burning powder and not the best choice for an AR based rifle.
With a 8 inch twist rate I really wanted to go with the heavier 6.5 mm rounds with high BCs for this rifle... and from initial looking over the selection the Lapua 144 grain FMJ Boat Tail with a quoted ballistic coefficient of 0.636 looks like a great bullet to work with. It is shorter than the HP varieties from Berger (VLD and Hybrid) which end up being too long for AR magazine feed when seated 15 to 30 thousands off the lands. Sierra 142 Match Kings would work as well as the Lapuas 139grain Scenars and 144gr FMJ-BTs selected here.
From a former 3 gun champion I was advised that IMR 4064 would be a very good choice for the AR format. I could not find any information on loads for this exact bullet and powder combination with this case so after a bit of cross referencing of various similar rounds I settled on starting out with 32.0 grains of powder and working up in 0.5 grain increments to 35.5 grains.
The adjustable gas port was opened an additional full two turns. I first shot some of 140gr Hornady A-Max rounds to confirm my scope setting and rifle operation... after three weeks of not shooting and being rushed and antsy, my first grouping of 5 shots was abysmal at almost 2 MOA... the second grouping of 5 of the same was a bit better at about 1.2, all about the center (at 100 yards). Typically I do better than 1 MOA in the groups and the rifle is more capable than that as I have had some 0.5 MOA groups. (Only started shooting again a month ago after a 37 year break from the time I left militia in Canada)
The 32.0 through 33.5 had issues cycling the action and also the shots were from about 1.5 to 1 inch average below center. The scatter was also bad, worst for the 32.0 grain.
At 34.0 grains I hit a sweet spot for grouping the shots at about 0.5 MOA for 5 shots, and the gun cycled fine but the shots were about 0.6 inches below the center.
At 34.5 things got worse again... wider and lower and for some reason the gun didn't cycle for 2 rounds. (Yes I am sure I did not mix up the rounds in the loading order, they were all labelled individually as I loaded them and seated the bullets one at a time).
35.0 and 35.5 grains cycled fine and I pulled a shot or two in each group otherwise 3 in each group of 5 were right on top of each other, and the shots were about back to center too (~0.2 inches low.... within experimental error I think). While not rigorous, I take this as a sign I am at approximately the same velocity as the Hornady A-Max 140 grain.
For all loadings there were no signs of pressure on the case (flattened primers, brass flow at the ejector etc.) I take it I still have some head room but I am satisfied with the 35.5 grain powder charge for this bullet. The primer is CCI BR2 large primer. These being my first ever reloads on spent brass I have to say I am very pleased with this Hornady brass.
Using reloaded ammunition for ARs is a dangerous game if you do not know what you are doing! Shoulder bumping (for head spacing) full length brass sizing, neck sizing/trimming bullet seating depth and seating primers flush or below are all critical to not having an out of chamber mishap. I measure and measure and measure. The bullets were seated about 15 thousandths off of the lands (used a Stony Point (Hornady) guage to determine the seating depth for each type of bullet).
Next months goal: to get a Chrony so I can do better at load development work.
