New S&W AR 15 Sport Help

gunnut38 · Jul 16, 2018

OK, I have over 45 years of firearm, hobby gunsmithing, reloading and mechanical experience. But I have little to no experience with the AR platform other then shooting someone's over the years. My son bought a brand new S&W M&P 15 Sport 2 in 5.56 on Saturday. When we shot it yesterday we experienced a problem when feeding from the new thirty round magazines. It ran flawlessly with the factory ASC ten round mag and with the brand new Magpul MOE PMAG 30 AR/M4 Gen M2 mags when loaded to ten rounds or less. With more then ten rounds , the first round charged would chamber and fire, but the round feed off the mag would be bent and stuck part way in the chamber. The bullet tip is striking something bending the case neck and bullet down and bulging the case just below the shoulder. The ammo is brand new bulk pak American Eagle "Military Grade" 55 grain fmj 5.56x45. Do the new mags just need to left loaded to relax there springs somewhat? Or does the rifle just need more shooting for break in?

DAPSRT · Jul 16, 2018

So a majority of ar malfunctions are caused by magazine problems. Try another mag would be my first "fix". That being said, thereare a number of things that can cause issues.... i even found an m&p one time that had an ejector that was machined long and caused issues feeding. Make sure at least to start that the bolt carrier is nice and wet with oil and see if that helps some.

If its consistently an issue, consider sending it back to smith but i have found they have been pretty good rifles overall.

gunnut38 · Jul 17, 2018

Thank you for the reply. I was beginning to think I posted in the wrong spot. We had to two brand new Magpuls and both did the same thing. Bolt and carrier were wet with oil. I thought that would be best for break in. it looks pretty good for the price range and shot very well other then the feeding issue.

Stomper · Jul 17, 2018

Get your hands an a USGI magazine and give that a try. That's all I've ever used since '85, never an issue.

Bones2586 · Jul 17, 2018

If the magazine swapping doesn't fix the issue, look at changing out the buffer and spring. If the spring is weak you'll have issues feeding, as it won't strip the next round from the magazine cleanly. I'd swap one component at a time (spring first with original buffer, then original spring with replacement buffer), so you can narrow down the culprit.

If your troubleshooting still doesn't fix it, may be a gas problem. Carbon buggered up the gas hole in the gas block, hole might be too small (open the hole up some, recommend a Gunsmith do this if not familiar with it), run a pipe cleaner through the gas tube with lots of solvent, and see what happens.

All else fails, maybe contact Smith & Wesson and send it back to them to take a look at. If warranty is still good, should be no charge!

Member 34319 · Jul 17, 2018

A couple things to understand about AR15s for first timers.

Mags can affect feeding. If one works but one doesn't. There you go. It's the mag.

Ammo can affect feeding and cycling. It may be a decent load, but it may be to weak to cycle the action fully. So you may get a "short stroke" and have feeding or ejection issues. It may look like the mag or other things, but could just be cheap ammo.

Lubrication plays a factor in ARs. Not lubed well enough when new can cause similar malfunctions to bad ammo, no lube can cause poor feeding and cycling. Just like bad ammo. So they look very similar.

The guns system can cause problems. If you are running a very heavy buffer and you don't need to be, it can cause short stroking and feeding issues.

Likely the MP has a carbine buffer and regular spring.

Likely you guys didn't lube it on your first go?

Did you use good manufactured regular powered ammunition like some M855?

That's all I got.

ARs run great when they run great, but not understanding the factors that can cause them to hiccup can be frustrating.

gunnut38 · Jun 19, 2019

Disassembled, cleaned and lubed everything. Problem was resolved. Leaned a AR lesion.

Boboclown · Jun 20, 2019

Stomper said:
Get your hands an a USGI magazine and give that a try. That's all I've ever used since '85, never an issue.

Its not the 80s anymore. You can use dishwasher safe tupperware now.

308 · Jun 20, 2019

gunnut38 said:
Disassembled, cleaned and lubed everything. Problem was resolved. Leaned a AR lesion.

The ARs like a slightly wet bolt
If you don't have any lube when out shooting, get some off the dipstick of your vehicle, smear it on the bolt carrier and you will be back up and running. After a few hundred rounds the new parts should start playing nice with each other, but until then....