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1/16/2020 9:48:49 PM
Posted: 6/27/2008 7:20:21 PM EST
ok guys, I am looking to the masses for help here. I have a 7.5in SBR that FTE and is very ammo sensitive. The gu FTE to extract with almost every brand of ammo I have put through it. I have read everything I can fing here on the subject and keep coming up with the conclusion that it is overgassed. Here is what I am running:

Spikes Tactical lower with RRA parts and 2-stage trigger, Magpul CTR, DPMS Heavy buffer, Wolff extra power recoil spring.

Upper is RRA A3 with a Rainier Arms (WOA?) barrel, Noveske KX3, Vltor gas block, Les Baer Chrome plated SS National Match carrier, LWRC Chrome bolt with dual spring lobster tail extractor. (added extra spring to increase tension)

I have run Remington, Federal, Seller & Belloit, Winchester, Hornady TAP, and some foreign brand. All FTE. I have run XM193 through it with about 80% reliability.

I am at a complete loss. Any suggestions as to what I can do to get this thing to run a wider variety of ammo? I have tried a standard bolt with a D-ring, and still have the same issues. When the gun runs, its a blast to shoot. It fails more often that it runs to the point I am ready to give up on it. The KX3 made a big difference, but not enough to increase the reliabilty. Any suggestions would be appreciated!

Link Posted: 6/27/2008 11:28:32 PM EST
Ever tried one of those Pig tail Gas tubes?, might help.
Link Posted: 6/28/2008 1:46:27 AM EST
Link Posted: 6/28/2008 5:16:45 AM EST
The barrel is from Rainier Arms. I think its made by WOA. It is chambered .223 Wylde and has M4 feed ramps. I don't know if its over gassed. The face that it is leaving the case in the chamber makes me think it is. Thats why I am at a loss. Adding the KX3 actually improved the function of the weapon.
Link Posted: 6/28/2008 7:07:19 AM EST
[Last Edit: 6/28/2008 7:07:59 AM EST by Dano523]
Link Posted: 6/28/2008 7:25:23 PM EST
yes, exactly. I have tried a different bolt with a d-ring and extra power extractor spring, but it still happens. That was leading me to believe that the case was being pulled while it was still expanded against the chamber wall.
Link Posted: 6/28/2008 7:43:03 PM EST
7.5? What a waste. Why not a sub gun? Perhaps a piston is in order.
Link Posted: 6/29/2008 3:09:55 AM EST
Link Posted: 6/29/2008 4:35:00 AM EST
Extractor is good. Like I said, I even tried a different bolt. Guess I will try the chamber next and see what happens.
Thanks for the useful info!
Link Posted: 6/30/2008 11:16:08 AM EST
[Last Edit: 6/30/2008 11:16:59 AM EST by FIGJAM]
I have a 7.5" pistol with a WOA Wylde chambered barrel and a WOA bolt. I'm running a KX3, 7.5" gas tube, H3 (5.4 oz) buffer and a Tubb spring with the D-fender d-ring. Runs 55gr to 75gr flawlessly, NATO and 223. The Tubb spring is full length but because it's flat wire it can be used in the CAR tube. I believe with that and the 5.4 ounce buffer, it increases lock time enough for the case to contract a bit before it's yanked out. Piles the brass at 4 o'clock no more than 4 feet away.
Link Posted: 6/30/2008 6:54:21 PM EST
shoot some rnds then try to stick the empty cases back into the chamber. Will they fit or not?
Link Posted: 7/1/2008 1:21:56 AM EST
Link Posted: 7/1/2008 4:16:05 AM EST
The first barrel in my pistol had the gas port too large and it was definitely over gassed. It would cycle, tear the rim off the case, and then try to chamber another round behind the one stuck in there.
The company who made my upper worked with me for several days trying different things and when no solutions were obtained, I returned the upper. They replaced the barrel with a properly drilled port and no more trouble.
The solution could have also been done by drilling a hole through the side of the gas block and installing a set screw, but since the company was so willing to fix it why dicker with the gas block.
Anyway, I digress. Does yours pull through the rim of the case left in the chamber? If it bends the crap out of the rim or tears it off completely, I'd say you are over gassed too. I would not use a pig-tail tube. They are expensive and there is a cheaper solution.
Most gas blocks are cheap so you might try restricting gas flow with a set screw drilled in the side, between the top of the barrel and the bottom of the gas tube. The VLTOR should be fairly easy to drill or you might want to buy a cheap aluminum DPMS block to experiment on first before drilling the more expensive VLTOR.
Or return the upper if the maker is willing to work with you.

Link Posted: 7/1/2008 4:29:00 AM EST
I had a problem w/ failure to extract/eject when I first built my 7.5. I put an extra power extractor spring & a #60 O-Ring in the extractor & haven't had any problems with it since then.
Link Posted: 7/1/2008 4:55:23 AM EST
It isn't pulling the case rim off, its just slipping off the rim. I am using an LWRC Advance Combat Bolt (ACB). It has the lobster tail extractor with 2 springs. I found a way to add a third spring to beef up the extraction power. It helped some, but still didn't solve the problem. I have been told by several people and discovered from my own experience that the pig-tail gas tubes really don't work. I like the idea of the adjustable gas block. I was just looking at one from PRI and thinking that I could make one rather than spend $70 on one. I have been looking around for the "SBR Chamber reamer" mentioned above, but no luck. My plan is to tear the upper down and polish the chamber real good. Hopefully that helps. Thanks for all the suggestions. I will post results here as this progresses.
Link Posted: 7/19/2008 11:19:56 PM EST
Ok guys, problem solved. I polished the chamber real well and that didn't help much. I kept going back to the bolt for some reason. I was running an LWRC Advance Combat Bolt. I swapped it out for a new CMT standard bolt and the thing runs like its on fire now. Put the LWRC bolt in several other carbines (16 in min barrel) and the bolt worked fine. No idea why it won't run in the shorty.

Thank you all for your help, suggestions, and insight.
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