NEW Build Trobleshooting Help

[The Archangel]

I'm having double feeding issues on my new build. I'm assuming (hoping) that it is a weak extractor spring because it is not pulling the spent casing out before a new round is getting loaded. Also, when it does eject the spent casing, it does not fly out too far from the ejection port. The double feeds happen 2-3 times during each magazine.

Here are the specs of what I'm working with:

Upper
CMMG 16" Mid-Length Upper
LMT F/A BCG (has the Black O-Ring in there already)

Lower Parts
Standard Carbine Buffer / Spring

Ammunition
Prvi Partisan 55gr M193
(This ammo works flawlessly on my FrankenColtish 14.5" & LMT 10.5")

Magazine
Magpul PMAG

Miscelaneous
Generous amount of lubrication
PWS FSC556 (Flash Suppressing Compensator)

I want to start by replacing the extractor spring with a Wolf Heavy Duty spring, but there are too many Wolf springs out there and I don't know which one to get. Can someone provide a link to the specific spring? I found this one http://www.brownells.com/aspx/NS/store/productdetail.aspx?p=16488&st=wolff%20extractor%20spring&s=, but I'm not sure it it's the one I need.

Thanks Gents.

Nick

[GaryXD]

http://www.gunsprings.com/RifleShotgun/1ndex.html

click on AR15

[Dave L.]

I didn't think you needed HD extractor springs on mid-length systems(or the O-ring for that matter).

[tiger seven]

Could it be a tight chamber causing the cases to stick?

Derek

[Dave L.]

Could it be a tight chamber causing the cases to stick?

Derek

That's possible with CMMG's QC track record. Maybe try some other ammo just for trouble shooting purposes.

How is the recoil pulse (normal, soft, hard)?

[MassMark]

I vote: Not a bolt/extractor problem - tight chamber, poorly cut feedramps, (if any) is my guess...

[The Archangel]

That's possible with CMMG's QC track record. Maybe try some other ammo just for trouble shooting purposes.

How is the recoil pulse (normal, soft, hard)? Recoil seemed exactly the same as my 14.5 & 10.5. I don't know what everyone was saying about how mid-length are so much softer recoiling. :confused:

[Failure2Stop]

When it double-feeds, is it one spent and one live?
Are you experiencing in-line double feed/failed extraction (spent round in chamber, live round hitting the base of the spent)?
When the round barely pops out, does it chamber the next round?

If #1 is the predominant issue, I would suspect a weak ejector spring. An o-ring can be over-powering, requiring an increase in ejector pressure. Have you tried firing without the o-ring?

If #2 is happening I would suspect a worn extractor. Even if they are new, I have had some extractors that were not up to snuff. If you don't know how to check an extractor- disassemble the bolt. Drag your finger or thumb over the extractor "inside" (part with the rim relief) to feel the sharpness of the "teeth" It should feel like kitten teeth. (How often do you get firearm diagnostic with the word "kitten" in it?)

If #3 is not reliably happening I would suspect a combination of 1 and 2, and probably some gas issue. What weight buffer are oyu using? I doubt that buffer weight alone is the cause, but it may be a small factor. Have you checked to ensure that the gas tube is correctly pinned and free of obstruction? I assmue that you have already checked the gas-key to make sure it is tight. You might want to check the gas-rings as well.

Oh, and make sure you stagger the gas-rings :rolleyes: . J/K

I also do not find middies to be "softer" than shorties, but "smoother", if that makes any kind of sense.

-F2S

[The Archangel]

When it double-feeds, is it one spent and one live?
YES

Are you experiencing in-line double feed/failed extraction (spent round in chamber, live round hitting the base of the spent)? YES

When the round barely pops out, does it chamber the next round? YES

If #1 is the predominant issue, I would suspect a weak ejector spring. An o-ring can be over-powering, requiring an increase in ejector pressure. Have you tried firing without the o-ring? No I haven't tried firing without the O-Ring. I did order the Wolff heavy duty springs to start off.

If #2 is happening I would suspect a worn extractor. Even if they are new, I have had some extractors that were not up to snuff. If you don't know how to check an extractor- disassemble the bolt. Drag your finger or thumb over the extractor "inside" (part with the rim relief) to feel the sharpness of the "teeth" It should feel like kitten teeth. (How often do you get firearm diagnostic with the word "kitten" in it?). It was a brand new LMT F/A BCG.

I'll try that when I get home, but I have never felt any teeth in the pussies that I've touch. You're a harder man than me for doing sticking my finger, or anything else in a pussy with teeth.

If #3 is not reliably happening I would suspect a combination of 1 and 2, and probably some gas issue. What weight buffer are you using? Standard CAR Buffer & Spring I doubt that buffer weight alone is the cause, but it may be a small factor. Have you checked to ensure that the gas tube is correctly pinned and free of obstruction? I assmue that you have already checked the gas-key to make sure it is tight. You might want to check the gas-rings as well.

Oh, and make sure you stagger the gas-rings :rolleyes: . J/K

I also do not find middies to be "softer" than shorties, but "smoother", if that makes any kind of sense.

-F2S


Thanks for the tips. The PWS FSC reduces recoil so much that all of my rifles feel the same. The ones that are suppressed have even less recoil, but a big part of that is probably due to the big chunk of steel attached to the end of my barrel.

[Failure2Stop]

FWIW- I have a relatively brand-new LMT bolt that does not have predominant "pussy teeth" on the extractor. I haven't had any issues with it, so I tossed it into my tool-box, behind the spare bolts.

It seems to me to be a combination of gas and extractor/ejector issues.

I would swap bolts with a "known performer" carbine (I know you have a few ;) ) to diagnose. Remove the "o-ring" for the trial if it does not work initially. If the problem is still there with no-issue parts, the gas system/barrel/chamber/etc must be at fault, which is above my pay-grade.

Hope you get this beyotch back in-line.

-F2S

[The Archangel]

Weapon in question:

http://www.mustangmods.com/ims/u/128/11621/242919.jpg

The ghetto-surefire is temporary until I can afford something better. It works for now.

[ADC]

If you do trade out known good carrier/bolt and still are having the same problem I would look hard at the chamber, it could have a min. cut (tight) chamber and that could cause just what you are having.
Try shooting just one round at a time with the mag in place, if the case still sticks and the bolt locks to the rear at least you know you have enough gas, on rare cases it could be too much gas, but with a good extractor/spring and o-ring it should pull it out.

[The Archangel]

Drag your finger or thumb over the extractor "inside" (part with the rim relief) to feel the sharpness of the "teeth" It should feel like kitten teeth.

The extractor lip feels sharp to me. There have been less that 400 rounds through this LMT BCG.



If you do trade out known good carrier/bolt and still are having the same problem I would look hard at the chamber, it could have a min. cut (tight) chamber and that could cause just what you are having.
Try shooting just one round at a time with the mag in place, if the case still sticks and the bolt locks to the rear at least you know you have enough gas, on rare cases it could be too much gas, but with a good extractor/spring and o-ring it should pull it out.

Thanks for the tip about shooting one round at a time. The BCG is a LMT so quality should not be the issue. Once the HD Wolff extractor spring comes I'll try that first.

[The Archangel]

Installed the new Heavy Duty Extractor Spring (Green). I have not had a chance to test fire it, but when I do, I will post another update.

http://www.mustangmods.com/ims/u/128/11621/243076.jpg

[T-TAC]

I recently completed a M4 build and had similiar problems. I got the gun home and cleaned it. Then checked things out.
The extractor had a very thick, Heavy spring with a black bumper. I couldn't pull the extractor hook towards me with my finger. I replaced the Extractor and put in the standard lighter spring with a blue bumper.
The gas rings wouldn't hold the carrier when stood on the Bolt face, so I replaced them with a McFarland. and I polished the feed ramps with a cratex bit.
This new heavier Extractor spring and black bumper that everybody says the M4 needs, I don't really see a need for. The Ar platform has been fine with the standard spring for a long time.