We’ve seen how the 6 different .223 Remington and 5.56mm loads have fared in the Big Freakin’ Cartridge Test, but we still have more to talk about. Specifically, we need to discuss what I did wrong (or what I am not satisfied with), and what I plan to do next. This post will concern the former, and a second installment will cover the latter.
First I should say, the BFCT was never intended to start off perfectly – and this means test procedure will improve (that is, change) as time goes on. I always intended the BFCT to be a “crawl, walk, run” operation, and that means it will be (and has been) a learning experience for me, as well as for our readers.
The first change I made to the test procedure actually occurred midway through: I reduced the cooldown time for the chronographing portion of the test from 30 seconds to 10 seconds. The reason for this was simply that 30 seconds wasted far too much time to be worth it. 10 seconds with an immediate firing does not result in an appreciable increase the temperature of the propellant, and any more than that is just a waste of time. Moving forward, cooldown time between chronographed shots will be 10 seconds.
For some reason I’ve quite forgotten now, I decided to conduct the BFCT testing from the bench, rather than from the prone position (which I am very confident with). I don’t have any reason to believe my bench shooting introduced substantial error in the results, but then I don’t know it didn’t, either. A suggestion from the comments was using a fixed mount – which is an obvious solution to the problem, as well. In the future, I intend to conduct accuracy testing using the bench, prone, and a Caldwell Lead Sled Solo to determine which platform or position reduces human error the most.
One thing that stood out from the results of the BFCT was the uniformly higher extreme spreads and standard deviations for ammunition shot out of the 14.5″ barrel. One mistake I made that possibly contributed to this was using a Magnetospeed chronograph alone, and mounting it to the barrel on the 16.1″ and 20″ upper receivers, but on the rail on the 14.5″ upper. Oops. There will be a future test comparing the rail-mounted and barrel-mounted Magnetospeed on the 14.5″ upper receiver, which will use an Oehler 35P chronograph to verify the results (the Oehler was originally going to be used to establish 100 meter ballistic coefficients for all projectiles, but that did not work out for, uh, technical reasons).
Several of my commenters raised the objection that I never fired a known baseline to establish the accuracy of the upper receiver. In effect, that is true, and that is a correction I will make in Batch 2 of the BFCT. I had intended the IMI 77gr RazorCore ammunition to provide this baseline – after all, it is a clone of Black Hills’ Mk. 262 load which is a known quantity with the Criterion barrel. This, however, was a mistake. We don’t know whether the RazorCore ammunition failed to live up to expectations, whether the Magnetospeed wasn’t properly mounted, or whether my bench shooting wasn’t as good as I thought it was. There is too much noise in the data to tell. I intend to establish and use a baseline round for all future BFCT batches. This will be a factory load (ideally from a single lot, although I am not sure I can always guarantee that), not a handload.
Having said all that, I do think the Batch 1 results of the BFCT are still valid – at least until I prove they aren’t. It’s possible that all my 14.5″ data and accuracy testing is corrupt due to one or more of the above mentioned reasons, but we won’t know that until we do.