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Posted: 8/4/2006 12:53:20 PM EDT
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I have a 6.8SPC upper that I built that is short stroking. Here was my original setup : 12.5" SS WOA barrel from GTS (w M4 feedramps) Mega upper (no extended M4 feedramps) LW AIC and ACB low profile gas block from AR15 barrels (had it left over) CMMG SBR lower Enidine buffer with standard buffer spring VLTOR stock and buffer tube At the very beginning I had short stroking problems as well as jamming issues. I replaced the AIC with a RRA carrier and the jamming issues went away and most short stroking. So then I replaced the Enidine with a standard buffer and I thought all the short stroking went away. Well today it cam back with a vengence. The most I could string together was three rounds. I would charge the rifle, pull trigger and it would go boom, then pull trigger again and it would go click. Examining the top of the rounds showed drag marks but not all the way from the rear to the front of the case. Most started about a quarter inch from the rim. Also, on the last round it would not lock back. I experimented with changing the buffer (standard, enidine, and 9mm buffer), changing the carrier (LW AIC, Young chromed carrier, and RRA carrier), changing bolt (matching bolt and LW ACB) and ammo (T's Guns and Ammo and Remington). Everything I did resulted in the same problem. I also checked the gas block and it was nice and tight, however, there was some black fouling on the SS barrel that appears to be coming from underneath the gas block. I have never owned a SS barrel before so I don't know if it is normal for fouling to seap from the gas block. If the fouling is normal, then what size should my gas port be on a 12.5" 6.8SPC barrel? I can't seem to find any info relating to 6.8SPC gas port sizes, only 5.56. Any suggestions? |
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Just talked to Denny on the phone and he said it is NOT normal for any fouling to be coming out from underneath the gas block. I didn't know since I have always had barrels that were black. Anyway, I will be getting a LaRue from Denny when he gets more in next week. I will update the thread when I shoot again with the new gas block. |
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We need more of the cover story, Are you shooting reloads, and if so, are you sure that the cases have been trimmed correctly (read short enough for your chamber)? Chamber conditions, just how long ago have you given the chamber a really good cleaning, including spinning a CLP soaked 30 cal mop in it to get the last of chamber fouling out that the chamber brush sometimes misses. Granted that it could be the gas block letting loose (way too much blow by), but you will always get a little bleed out from the block if this is a bottom point type screw attachment system. The only type of blocks that will totally seal off around the barrel is the C type blocks that suck up around the barrel as they are being tightened. |
I have the problem using Remington box ammo as well as T's Guns and Ammo new ammo. I have cleaned this upper more thoroughly than I have ever cleaned an upper and I still get what appears to be short stroking. And yes the gas block is the type that has two set screws at the bottom. I really hope it is the gas block as this is very frustrating.
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