M&P15 Sport Malfunctions

[mstewart440]

I received a brand new M&P 15 Sport for Christmas this week.

So far I have not been able to fire two consecutive rounds from it. Each round, after it is fired, fails to eject. Manually ejecting the round by pulling the charging handle is very difficult. I have tried .223 and 5.56 rounds with same effect. The ejected casings have several scratch marks longitudinally from the shoulder to within 4-5mm of the rim. Additionally, fired casings seem to be slightly ballooned.

We cleaned and oiled it twice with no change in performance.

Any suggestions?

 

[MichiganScott]

Sounds like crud in the chamber or barrel lugs. You need a chamber brush or a bore swab to assure it's clean.

Most AR's, and particularly new ones, like to be run wet. Stay away from grease and use any good quality gun oil or CLP.

 

[JaPes]

*Factory ammo cases look "balooned"
*Scratches on cases
*Extraction issues.

Call S&W. Maybe an out of spec chamber? Make use of the best feature of the 15-Sport, the lifetime service policy.

If you have pictures, that may help.

Do you see any unusual witness marks in the upper or the BCG?

 

[mstewart440]

Crud or a burr in the chamber was my first thought so I ran a brush and swab through it with no effect. I kept 6 cases with the marks on them. I'll post some pics tonight. They are not deep scratches, but enough to catch my eye.

The balooning is what has me concerned the most though. I've never looked at spent cases close enough to know if that's normal or not. My less-than-scientific method was to lay an unspent cartridge on a straight edge and then compare a spent cartridge. It is very slight, less than a millimeter, but they are definitely swelled. I can manually cycle new rounds through it with no problem, but a fired round is very stubborn to get out.

And S&W is closed until after the first of the year. <sigh>

 

[HotRoderX]

I would try a different brand of ammo before anything else. Most the time when I go to shoot a brand new gun I bring along two different ammo brands.

I have found some guns just don't like certain manufactures for what ever reason. I have a 1911 that chokes on Aguila ammo but runs fine on everything else.

 

[Stebo]

"Fails to eject" means the bolt stays locked?

Just something to try - Break down the bolt carrier group, clean and generously lube. Insure gas rings are not aligned. Reassemble and make sure bolt moves cleanly with a little initial resistance. Extend bolt and stand on end, BCG should not collapse on the bolt.

 

[mstewart440]

I mean the round is stuck in the chamber...most stubbornly stuck. <thats fun to say fast three times>

 

[Stebo]

The scratches are a bit confusing. A reloader can comment on the "swollen" cases, but there has to be swelling for the case to seal. The rifle shoots OK, right? And you've shot it several rounds if I understand you.

You are able to manually cycle rounds in and out with no issue, the rounds load and eject. I still suggest looking at the BCG. Also, what brand, weight, bullet are you shooting?

 

[BlueOvalBandit]

A headspace issue would lead to case stretching, which can also lead to stuck cases.

 

[oneyeopn]

Before you took it out to shoot did you disassemble it and clean it and lube it very well? The cases will balloon slightly that is why before we can reload the cases we have to full length resize them. What kind of ammo are you shooting if I may ask? Also when rounds are stripped from the magazine and pushed into the chamber it is very common to get scratches from the feed lips. I would take some kind of rifle bore brush and really clean the chamber out and please post some pics of the cases, if you can side by side a couple with unfired rounds that will help.
Improper headspace can lead to these problems but with a 5.56 nato chamber your not going to get that much stretch because the leade is that much longer. I almost want to believe it is packing/shipping grease hardened and stuck to the chamber walls.

 

[mstewart440]

Yeah, it will go bang...once. But then it takes a significant amount of force to pull the charging handle back and eject the spent cartridge. The next round will chamber fine. I can manually eject it easily too, but if I pull the trigger, we're stuck again.

Ammo...brass 5.56 (didn't notice the brand) and steel Wolf.

 

[oneyeopn]

Please post the pics when you can. If you can pull the charging handle back that is a plus, I have had one or two stick where you couldnt pull the charging handle back....I am starting to wonder if the gas system is working, has it ever shot more than one shot? The best way to test the gas system is to separate the upper and lower, pull the bolt carrier and charging handle out. if you hold it with the barrel down in the top of the upper receiver you will see the gas tube. I dont know what you would have thats handy that is an aerosol with the little red spray tube, like WD-40 or something but you need to spray it down the gas tube and make sure it drips out of the inside of the barrel not the outside of the barrel. that would show your gas system to be clean and clear, while you have it like this take a flashlight and look down into the chamber and see if you see anything. If your gas system is plugged up the rifle will also act just like you are saying.
Grover

 

[rojodiablo]

Tear down the rifle. Get a small, good light. Look into the chamber as best you can from every possible angle. Look for anything that would seen suspicious.
While torn down; use Brake cleaner spray and shoot it liberally down the gas tube. If there is any grease or oil in there, you will need a substance like this to break it down. If you shoot a 3 second blast and do not see any fluid coming down out the barrel, the gas block may be misaligned.
If you have compressed air, try to blow air down the gas tube. 5psi is plenty for this.
After all this, if you have venting going on thru the gas block, it's time to look at the buffer and make sure it moves freely. All you need to do is push it back an inch with a finger. If it moves, you are good for the most part.
Bolt; Brake cleaner everything, and then use a light gun oil on all parts. As had been mentioned, check locking lugs, check for extractor issues. Reassemble BCG after oiling.
If you can manual rack ammo 5 times in a row without firing, then you are generally assured it's not magazine related.
98% certain this is gas system issue, or something very screwed up in the chamber.

 

[BillyMagg]

Sounds like your chamber is out of speck, while any of these issues by itself would lead to questions, all them together say send it back to S&W, sounds like the chamber may be out of round? The scratches would have to be upon extraction if the unfired rounds chamber normally? The difficulty with extraction would confirm that. A friend had an older AR, a nice one go off before it was fully into battery, not fun, blew the mag out the bottom of the gun, case welded into the chamber, maker replaced the entire top end. Billy

It was not S&W, but another well respected brand.

 

[Stebo]

Stewart,

When you get this resolved, would you post the fix? I'm thinking Grover and Rojo have this right but would like to know for certain for future reference. Thanks.

 

[mstewart440]

I'll take the rifle down again tonight and check the chamber again as well as check the gas system. I'm leaning towards something being out of spec with the chamber though. A gas system problem or lubrication problem might prevent it from reloading automatically, but I can't see how any of that would make it nearly impossible to manually pull the bolt back and extract the round. The fired rounds are usually stuck so hard it takes both hands to do it, while unfired rounds are easy.

On a positive note, the thing is freaky accurate, even with my aging eyes and iron sights. I shouldn't be surprised I guess...my old 4506 was the same way right out of the box. Still is 24 years later.

 

[oneyeopn]

Mr Stewart; When you fire the bullet it expands into the chamber which does make it harder to come out than to go in, if you can use the charging handle, albeit difficult. to remove the brass or steel case it is not stuck that hard. I have seen cases get stuck so hard that you have to use tools to remove the case. If the case was sticking and the gas system functioning I have seen the extractor pull off of the case head or pull a bit of the case head rim off. You are getting none of these symptoms which keeps leading me back to an issue with the gas system. It is possible that the gas tube was installed upside down which wouldnt let the gas system work but when the gas system works properly it jerks the spent case out pretty forcefully. I am under the assumption that you havent installed a heavier buffer or spring so your rifle should have the full force on the BCG to extract a shell. Just how I am looking at it.

 

[Stebo]

Stewart,

Another positive note - you could sell it today, as is, and still make money.

I think Grover described the most likely cause, given the symptoms, and it's a blocked or nearly blocked gas system. Whatever the cause, hopefully it's an easy fix for you.

 

[mstewart440]

I hope you guys are right! Although I've read about them for years, this is the first AR type rifle I've owned so I defer to those with more knowledge. I'll keep you posted.

And thanks!

 

[oneyeopn]

When I was first messing around with my sport, I one time didnt get my gas block lined up correctly and turned my rifle into a single shot. I couldnt pull the charging handle back with both hands, but once I got the bullet out it would chamber another and unless I fired it I could eject them very easily. It took me a little bit (about 4 minutes) to realize that I had something not together right so I came home and realigned my gas block and then stepped out back and racked of 10 shots without a problem. But I shot 4 shots where it took all I could to get the bullet out, which included a small prybar and the bottom of the BCG. I didnt scratch anything and have shot thousands of rounds through her since but I learned that lesson fast.