Gassing and Function Sept 10, 2015 13:20:59 GMT -8
Post by mosigdude on Sept 10, 2015 13:20:59 GMT -8
I'm a few hundred rounds into load development with my 18" AR-Platform AM30 now and finding a scattering of potential loads for hunting use. I have played with several diffferent bullets in the 125gr range and 7 different powders with varying degrees of success. The common issue I'm having is this rifle simply does not like to run with RL7 powder, which is unfortunate since I'm having some decent luck with that powder in terms of accuracy. The action cycles enough to eject but not quite enough to pick up the next round in the magazine. I have turned the gas all the way off and slowly worked my way up so I am very certain that I am not overgassed. The rifle has functioned/cycled flawlessly with other powders including CFE223, Ramshot X-Terminator, IMR4198, H4895, H322 and H335 (for the record, I am not saying these are all good powders for this caliber, some are, some aren't, these are just the ones I experimented with - I'll post a thread with these experiments a little later), some of these powder charges were at or near max and some only pushed the 125gr pill around 2000 fps and were clearly well below max but still cycled flawlessly. So I'm looking for a few answers from experience to maybe optimize this rifle for the RL7 loads...
So here is my set-up for reference: 18", mid-length, 1/11 twist, fluted semi-bull. M-16 bolt carrier, Standard 6.8SPC bolt, extractor and ejector polished, standard carbine buffer/spring, I am running a BTE adjustable gas block (wide-open right now). I used some wire-sized drill bits as a gauge when I first got the barrel and my gas port is at, or near .083".
When I first assembled this rifle, my break-in loads were copied from someone else on here (I forget who, exaclty) and were mid-upper-end loads with RL7. Then, like now, they did not function/cycle fully. At the time, I did not have the BTE gas block so when it arrived I placed a new gas tube in that block and replaced the original, still the same symptoms. I gave the carrier and bolt a once-over and, after not seeing anything obviously out of the ordinary (gas key is tight and staked, gast key ID and Gas Tube OD are in spec, gas rings in good condition), I replaced the carrier and bolt with another known-good set from another rifle and still the same result. I also measured the location of the gas port on the barrel and the gas port in the gas block and they seem aligned perfectly. Considering this rifle runs flawless with anything except RL7 powder, I'm guessing with my combination of components in the build, including the slightly heaiver M16 carrier, I just need slightly more gas for this specific powder. How large can I safely ream the gas port? Anything else in here that might be obvious to someone else that I'm missing?