Quirky ARs

[RBHarter]

I'm not new to reloading or even the mountains of cast that I shoot so this makes my question maybe more perplexing.

I usually load autos from a start load (experience says 10-20% of the load window above start) an work up on paper for function then smallest group which is usually not very far above correct function. The AR however has done a strange thing . I have 15 pieces of brass from 1 lot of 1 gr over/under matched brass to work up 3 shot sets . I usually shoot over a Chrony if for no other reason to save components if I NEED a particular velocity for a particular bullet .

In this work up 18.5-22.0 RL 10X with a 140 gr cast bullet , Federal srp brass, CCI 41. What is odd and sent me back the boards was that the lightest loads of course failed to function , #3 of 8 functions ok and just made the hold open . # 4 however only hooked the follower for hold open . The velocity increase was typical with some steps gaining 15 fps and some gaining 25 fps .

My theory is that the #3 load was the fastest of the string and generated just enough to catch and stay on the hold open (tolerance stacking ,mag springs etc) while the # 4 load was slightly more but didn't hit the catch (writing is good for me, different mag ,different springs , just a touch slower and maybe the cause of the aboration.

Quirk of the platform but not exclusive to it I bet ........

Call this an observation as having considered it as I wrote it down it becomes clear that mag variations are the most likely cause .

[Ranch Dog]

I would think that you figured it out!

[RBHarter]

It just seems a waste to write it all down without posting it.


Actually this has been good because I'm learning a lot about the platform.
It was also pointed out that I could be at a flat in the powder curve or at that perfect point where the bolt is unlocking before before the case releases . Suggested by a guy that is affiliated as I understand with R&D at ARP.

[Ranch Dog]

It just seems a waste to write it all down without posting it.

Nothing wrong with the way it took place. I done this myself. Start to describe a problem and end up writing through to the solution. The information is still valuable and worth recording!