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UPDATE - SOLVED!
I had issues with a new Grendel build short cycling. I started with Hornady Black 123 ELD, and then moved on to reloads, hoping things would "loosen up". I tried both AA 17 Round Grendel mags and several USGI mags, tried the upper on 3 different lowers, and had the upper apart twice looking for problems. I was able to get a few rounds of Hornady to randomly cycle at one point, but that was it. After measuring the gas port, I began thinking it might be too small. I didn't want to mess up my new barrel with a handheld drill, particularly since I wasn't totally convinced that was the problem, so I handed the gun off to our club's AR guru (ffl). He looked everything over and also concluded the 0.088" gas port was too small, so he locked the upper in his milling machine and reamed it out first to 0.093". That got everything cycling, but only my factory Hornady Black ELD ammo would lock the bolt open. My softer reloads would not. So he reamed it out to 0.098". I just tried 5 singly loaded reloads, and each locked the bolt back with the cases landing in a nice little pile at 4:00. Problem solved.
The Build
New Grendel build, 18" Wilson Combat RLGS barrel, Wilson Combat gas block, Fail Zero BCG, Magpul UBR 2.0 stock, Strike Industries flat wire buffer spring, standard weight buffer.
Until I could get it to the gunsmith, I did some load development with a chronograph and 5 shot groups at 100 yards. (Manually charging each round.) A combo of CCI 450 primers, 27.5 grns of AR Comp, with 123 SMKs gave the best results.
100 Yd, 0.62" Group
Everything else I tried from 26.3 grns to 28.1 grns still shot well, 0.87" to 1.15", but with bigger velocity spreads. With the gas port now bigger, I may or may not need to refine that load. I'm also hoping it will do even better since I recently bought an actual shooting rest to use instead of rolled up carpet and sandbags.
I had issues with a new Grendel build short cycling. I started with Hornady Black 123 ELD, and then moved on to reloads, hoping things would "loosen up". I tried both AA 17 Round Grendel mags and several USGI mags, tried the upper on 3 different lowers, and had the upper apart twice looking for problems. I was able to get a few rounds of Hornady to randomly cycle at one point, but that was it. After measuring the gas port, I began thinking it might be too small. I didn't want to mess up my new barrel with a handheld drill, particularly since I wasn't totally convinced that was the problem, so I handed the gun off to our club's AR guru (ffl). He looked everything over and also concluded the 0.088" gas port was too small, so he locked the upper in his milling machine and reamed it out first to 0.093". That got everything cycling, but only my factory Hornady Black ELD ammo would lock the bolt open. My softer reloads would not. So he reamed it out to 0.098". I just tried 5 singly loaded reloads, and each locked the bolt back with the cases landing in a nice little pile at 4:00. Problem solved.
The Build
New Grendel build, 18" Wilson Combat RLGS barrel, Wilson Combat gas block, Fail Zero BCG, Magpul UBR 2.0 stock, Strike Industries flat wire buffer spring, standard weight buffer.
Until I could get it to the gunsmith, I did some load development with a chronograph and 5 shot groups at 100 yards. (Manually charging each round.) A combo of CCI 450 primers, 27.5 grns of AR Comp, with 123 SMKs gave the best results.
100 Yd, 0.62" Group
Everything else I tried from 26.3 grns to 28.1 grns still shot well, 0.87" to 1.15", but with bigger velocity spreads. With the gas port now bigger, I may or may not need to refine that load. I'm also hoping it will do even better since I recently bought an actual shooting rest to use instead of rolled up carpet and sandbags.
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