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Posted: 3/17/2020 5:40:05 PM EDT
| Got the stamp today, picked up the upper, mated same to my ADM lower and went to the range. I have a 16" CMMG upper so no concern about cycling, but the balance on the SBR is so much better. Ran fine with factory ammo and with some various softer loads. The very softest load wouldn't consistently cycle the bolt to pick up the next round; with that I have a starting point for competition. Weight with a Holosun 510C and riser is 5 lbs./15 oz. Recoil with factory ammo is mild and with the softer loads it's near 22lr, all with standard carbine buffer setup. Going to be lots of fun and good practice for whatever short barrel caliber I elect for home defense. |
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Quoted:
Radial Delayed Blowback? Do you plan on running it suppressed? I did a Form 1 for mine and it is awesome. It's almost like shooting a 10/22 with 147 grain Gold Dot. I'm really looking forward to comparing muzzle velocity of the 8" and 16" barrels, but of course there's plenty of data out there |
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Word of caution, the RDB ejector spring is a known issue where for many folks myself included can't get to approx 1k of trouble free use. Mine actually started to hiccup around the 500 round mark. Some have had no trouble at all and have gone well beyond the 1k mark so it really is hit and miss it seems.
Dig around this sub forum especially from posts from @Amphibian. He's documented this symptom pretty extensively. If your planning on using this for competitions the worst way to find out your ejector spring is going tits up is right in the middle of a match. I bought mainly as a toy and knowing there might some tweaking involved. I plan to put a can on mine later this year. When it works compared to a typical 9mm blowback setup it's great. Fortunately with all the information posted out there at least I'm not stabbing completely in the dark to try and trouble shoot it. YMMV |
| Noted. My 16" upper has seen certainly more than 1000 rounds without issue. I'll keep an eye on things and get the necessary spare parts. I'm official and old fart and not traveling for big matches to a gun failure is no big deal, but I do enjoying shooting the PCC as a change of pace. |
| rdtompki... a favor, when you pull your 16" down, would you check the condition of the polymer insert in the extractor spring... mine had hardened at the 1000-1200 mark and caused problems for me... would like to see if the hardening problem is across the board, or just with mine... replacing my extractor not ejector spring has apparently cured my problems... thank you... Les L747 |
| I've found the new bolt (that came with the 8" upper) won't cycle anything below factory load level with FTE's frequent. Even the 147gr SD stuff sees FTE with the new bolt. I'm currently running the upper with the older bolt. The extractor spring on the new bolt is definitely stouter, but I don't know this has anything to do with the issue. CMMG (Brian) has been helpful and I have a kit with replacement springs and a new extractor on the way. |
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Quoted: I've found the new bolt (that came with the 8" upper) won't cycle anything below factory load level with FTE's frequent. Even the 147gr SD stuff sees FTE with the new bolt... Not cycling on a pistol with light loads calls for a lighter recoil spring. How about using a lighter buffer spring? Also, are you using the 3 oz. buffer or a heavier one? Taking out some mass or using a lighter buffer spring may solve your problem. I see not cycling and FTE's as different problems. |
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I should have been more precise. With the "good" bolt and a standard carbine buffer setup (haven't weighed the buffer) both barrels cycle soft loads although I need a bit more powder with the short barrel , otherwise the bolt won't retract enough to pick up the next round although the spent case is still ejected; this is sort of business as usual. The FTE issue really isn't load related since while the stock 8" upper appears to work with the 124gr Blazer brass it won't even eject the first case out of a 147gr magazine. There are essentially no FTE with the bolt that came with the original 16" Guard upper. I've also order some BCM extractor springs, but I'm skeptical that a heavier spring is the solution since it's the softer spring in the old bolt that appears to work. Update: tried the new extractor spring, but not change. While the new bolt will cycle 124gr Blazer it won't cycle 124gr Freedom Munitions (which is softer than the Blazer) and won't cycle the Win 124gr PDX. CMMG is sending me a new bolt. In the meantime CMMG did send a new extractor assembly and I'll install that and see what happens; this will eliminate the extractor, itself, as the culprit. The bar bolt will be the only component now swapped out. |
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