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Ejector, haven't messed with the extractor spring at all yet
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Example of what has been caused by failure to eject...
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I have experienced your exact same issue.
When I first got into short barrels. I started with an 11.5" Centurion barrel. To my surprise, it would not cycle anything reliably. 5.56 would often cycle, but frequently experienced live-round-on-unextracted-case-double-feeds. Stout .223 would not reset the trigger. Weak .223 (Tula) would not even make an attempt to extract the old case. This was true even with a carbine buffer. I contacted Monty, who told me that he was not sure without being there.
I measured the gas port to be around .0625, and after doing some research decided that the port was probably too small and started to open it up gradually and monitor the results. At .0628 I still experienced frequent failures with stout .223, and had to open up to .071 before it functioned reliably. I suspect that your gas port has been opened up some, but perhaps not enough for what you are shooting.
If operational envelope is your concern, I would recommend going up to 12.5". With the even-more-increased dwell time, a CA 12.5" barrel with a .0625 gas port and a NIB BCG cycles anything thrown at it 100% and locks back 100% with anything but Tula unsuppressed. At the same time, it seems a lot quieter and the recoil impulse is less sharp than the shorter barrels with larger gas ports (my use of adjustable gas ports has taught me that gas port size and not just barrel length makes a substantial difference in perceived noise and blast). The smaller gas port also leads to less gas blow back if you are shooting suppressed.
Between the smaller gas port and added length, a 12.5" gun with a flash hider is the shortest length that I personally do not find obnoxious to shoot unsuppressed. Frankly, I do not notice the difference between it and my 14.5" uppers. It is also easier on the suppressor than the shorter barrels if you are not going to use a brake, which for me makes unsuppressed use impractical.
I have a 10.5" SBR too, and for me they are best for dedicated suppressed use. An adjustable gas port and A5 buffer help a lot with the recoil and I have found mine to be very reliable when tuned appropriately although the operational envelope will be a bit tighter. (In other words, it will be a little harder to balance weak rounds cycling and hot rounds not creating excess pressure with a single gas port size.) Regardless, you are still going to have a really short barrel with a larger gas port (the only way to make up for lost dwell time) when optimally tuned and the noise and blast are still going to be obnoxious even with a flash hider. A lot more annoying than an extra 2 inches. A 10.5" with a flash hider will eat the blast baffle on your suppressor a lot faster than a 12.5" too, and I would never want to regularly shoot any SBR with a brake unsuppressed.
If you want to stick with the 10.5", I suspect that it will work when you get the gas port right. An easy fix would be to open up to .076-.078, get a Syrac gas block, and adjust down on the gas until you find the optimal setting.
Last edited by calvin118; 09-13-13 at 23:47.
They opened it up once, and looked at the whole upper/bcg after the first time. I don't feel I should keep having to send it back to get the dang thing to run right, I'm prob gonna go at least an 11.5 or 12.5 as much as I like the length shorter, if it won't run I don't want it, as the original plan was to replace my carbine with this sbr for work....
Not with the issues I'm having, I'm hoping centurion will get back to me and work things out, but I haven't heard anything since thursday. I've seen some 10.5s run well, but I'm lacking confidence as finicky as mine is.
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No need to apologize, justy trying to help you understand the language so you can trouble shoot your carbine. If my post sounded curt, it's because I was typing minutes before heading out to test a new lower and had to keep it brief.
Let's fix one thing at a time. As the cases are extracting but not ejecting, focus on the ejector first. If you have some dummy rounds, load them into a mag and cycle them through the action and see if they extract and eject. If they don't eject, you'll know to take a close look at the ejector.
Note: Don't try cycling fired empties as they sometimes will get stuck in the chamber.
Caution: Don't try cycling live rounds because if you do something stupid, you have a negligent discharge which could result in injury or death.
Another thing you can try is remove the BCG from the rifle and place an empty into the bolt face. Slide the case rim under the extactor and push with a finger so it presses the ejector plunger. Quickly release the case and see if it flips out vigorously. If not, you have a weak spring, a sticking ejector or both.
While the BCG is out and you're attempting to hit the girlfriend's cat by flicking empty cases at it with the bolt, check to see if the extractor is worn, bent or chipped. If the extractor cannot hold the case against the bolt face and properly press the ejector, ejection will be erratic
In any case, don't worry about any other problem (if any) until the ejection issue is solved. If you try to fix two things at once, it will be difficult to determine what fixed what or if it fixed anything at all.
Don't worry about extractor springs or o-rings right now. You're problem is ejection, not extraction. Don't worry about opening up the port size any further. Porting a rifle to run on ammo generating low pressure means it will run too hard on normal ammo. Here's a thread on an SBR Grant set up to run reliably suppressed and unsupressed
https://www.m4carbine.net/showthread.php?t=33743
Last edited by MistWolf; 09-07-13 at 23:40.
INSIDE PLAN OF BOX
- ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
- MATCH SCRATCHES ON MATCH-BOX
- MATCH LIGHTS FUSE TO TNT
- BOOM!
- HA-HA!!
-WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"
I am American
Well I tinkered with three BCGs (Brand New LMT M16, Proven Armalite Semi with 1000-2000 rounds, and the Centurion C4 M16), and the ejector compared between the three all seems to be about the same, and was smooth. However, the extractor on the Centurion does not seem to grab quite as well (as the Armalite and LMT) and had a small brass build up under the rim. Its possible I misread the malfuntion in the gun, and it was indeed a failure to extract instead of a double feed (this would make sense)? I ran some dummies through the gun, and was able to replicate a failure to extract once by hand with the C4 BCG, but not with the LMT.... The LMT extractor seems stiffer as well, as I was replicating by hand with a case. Am I onto something, or could this be normal with running the gun by hand (no riding the handle!)?
I may take the new LMT M16 and run it in it, and see if that eliminates any issue. I have a hard time believing a brand new BCG (Centurion) is the culprit.... Any ideas? I apologize for not being the most proficient with terms, and I am fairly new to the AR side of the gun world.
You're on the right track. The extractor could be gripping the rim well enough to remove the case from the chamber but not well enough to hold it in place against the ejector. There's a good chance you've found your problem
INSIDE PLAN OF BOX
- ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
- MATCH SCRATCHES ON MATCH-BOX
- MATCH LIGHTS FUSE TO TNT
- BOOM!
- HA-HA!!
-WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"
I am American
I won't get to the range until mid week, I'll keep you posted...I ordered a BCM comp for my 16 inch gun last night, and threw a BCM extractor kit in the cart as well. I have the new LMT BCG, and the Centurion BCG to tinker with, and I am thinking it is extractor related at this point.
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Last edited by bigredneck61088; 09-08-13 at 12:44.
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