Trouble shooting help. It pains me...

[Caduceus]

to even ask.

Firearm: S&W M&P 15OR, purchased Oct 2011. Other than replacing grip and forearm, stock.
Round count: Approx 1400, approx 400 either Silver Bear or Wolf
Ammo in question: Federal M855, Federal M193, Ventura Munitions 5.56 reman, Romanian SS109
Mags used: Colt (new, green follower), D&H (Magpul follower), Defense Solutions Group(Magpul Follower), E-lander 20 rd

Problem:
Approx May 2013 had several rounds fail to feed properly; Ventura Munitions at the time and an Elander mag. Rounds would not feed up the ramp and into chamber, consequently pushing the bullet back into the casing. This actually happened initially on a LMT upper and later the S&W. I thought at the time the mag was the problem. It later happened with a DSG magazine (same ammo). I sent the weapon back to the factory, where they replaced the gas key. I included the mag in question and the pushed-back bullet.

Took several classes; same ammo, different mags, same gun. Same problem. Swapped out ammo, worked well rest of first class. Went back to the VM ammo with DSG mags, problems again. Therefore, I assumed the remanufactured ammo was the source of the problem.

Last week, using the Romanian SS109 with D&H mags, had failure to extract, while normally feeding a round from the mag; this resulted in another pushed back bullet, as the incoming round was slamming into the still-chambered round. This happened several times. This ammo worked fine in a different rifle, as did the mags. Therefore, given the same gun with different ammo and mags having same problem, I surmised possibly the extractor. Replaced the spring with a 5-coil from Sprinco, leaving the rubber insert and O-ring. Today, same problem, both with 855 and Romanian SS109, using D&H and new Colt magazines. Replaced the entire bolt with a new bolt from BCM, and had same issue with M193.

In short, I've had probelms with 4 different magazine manufacturers, 4 different ammo types, 2 different bolts, and one return to manufacturer. Problem remains that round fails to fully extract before feeding next round.

Thinking perhaps replacing buffer or buffer spring to slow the BCG return? Issue with the chamber? Any other ideas?

[Col_Crocs]

What buffer weight are you using now?

[Iraqgunz]

I would like to know the buffer/spring combo and any other mods done. I suspect you may have a tight chamber that is preventing the round from extracting. This is obviously internet diagnosis and you should consult a trained professional if your extraction issues last more than 4 hours.

[Caduceus]

Stock spring, stock buffer (no markings, I assume H?). Mods: Magpul stock, foregrip and handgrip. BCM Charging Handle.

As mentioned in OP, the other night I tried a different extractor spring, then today swapped the entire bolt (leaving BCG) assembly. No other mods.

[SeriousStudent]

.............. you should consult a trained professional if your extraction issues last more than 4 hours.

Well played, old boy.

[Col_Crocs]

Clean the chamber and get an H2 buffer (you currently have a CAR). You could check your spring if it still falls within spec but then again, you could just get one while youre at it.

[Iraqgunz]

The last S&W I fired was a midlength (back in May) and it was overgassed enough that the carbine would run with an H3 buffer with 3 different ammo loads. I suspect you have a tight chamber.

Stock spring, stock buffer (no markings, I assume H?). Mods: Magpul stock, foregrip and handgrip. BCM Charging Handle.

As mentioned in OP, the other night I tried a different extractor spring, then today swapped the entire bolt (leaving BCG) assembly. No other mods.

[Caduceus]

Clean the chamber and get an H2 buffer (you currently have a CAR). You could check your spring if it still falls within spec but then again, you could just get one while youre at it.

I could throw in a new Sprinco Blue and suppose I could throw a H2 (I have an H3 lying around) on there too.

IG, would a tight chamber only show up 1400 rounds later? I'm not big on a chamber brush, but I could take it up in there and give it a few whirls. Usually I just bore-snake it.

[Col_Crocs]

If you have an H3 lying around, go ahead and use that for now... From IG's experience with a SW middy and yours being a CAR, it should work.
That might be your answer right there... Give it a good cleaning. It should help solve the issue. I agree with your chamber possibly being on the tight side which is further aggravated by it never having been cleaned.
Bore snakes are ok but they do no more than a chamber mop IMHO.

[Caduceus]

If you have an H3 lying around, go ahead and use that for now... From IG's experience with a SW middy and yours being a CAR, it should work.
That might be your answer right there... Give it a good cleaning. It should help solve the issue. I agree with your chamber possibly being on the tight side which is further aggravated by it never having been cleaned.
Bore snakes are ok but they do no more than a chamber mop IMHO.

I can give it a shot. Unfortunately my nearest range is hit and miss on using an AR (sometimes they OK it, sometimes they don't). The outdoor range is a rare event; this thread may be on "pause" for a while until I can try this combo!