AR15 not cycling - Smith and Wessons M&P Sport II

[Boris]

Locks back manually just fine. Gas block is aligned correctly. What can I check on the gas tube? There is air flow through the tube on its own. I'll try and take pictures this weekend and post them. Sometimes the bolt gets stuck with the second round. I then have to manually pull charging handle back to get it out, the casing is then dented under the neck where the final width of the casing starts if you get what I'm saying. The entire round is bent then when it comes out.

[Boris]

Locks back manually just fine. Ill try to take some photos

[Glockster]

I would also check the gas port on the barrel. Some holes are not drilled to the correct size and it differs between manufacturers. It might well be that it needs to be opened a tad to allow more gas into the system.

[Pirate]

I'm still confused about what the actual nature of your failure is:
1. Failure to cycle, i.e. bolt not moving back far enough and not picking up a newvround from the mag.
2. Failure to feed, i.e it cycles, picks up a round but does not properly feed it into the chamber, ready to fire
3. Does all the above, but does not lock open on empty mag

[Gleock]

Locks back manually just fine. Gas block is aligned correctly. What can I check on the gas tube? There is air flow through the tube on its own. I'll try and take pictures this weekend and post them. Sometimes the bolt gets stuck with the second round. I then have to manually pull charging handle back to get it out, the casing is then dented under the neck where the final width of the casing starts if you get what I'm saying. The entire round is bent then when it comes out.

Bud, people need to know what is happening with the spent case or loaded round.
Is it ejecting and closing on an empty chamber, is it like one of the below failures, etc.

There are lots of possibilities, gun, ammo, improperly shouldering the gun.


bolt-override-jam.jpg
stovepipe-jam.jpg
pressure1.jpg

[FNBROWNING]

Locks back manually just fine. Gas block is aligned correctly. What can I check on the gas tube? There is air flow through the tube on its own. I'll try and take pictures this weekend and post them. Sometimes the bolt gets stuck with the second round. I then have to manually pull charging handle back to get it out, the casing is then dented under the neck where the final width of the casing starts if you get what I'm saying. The entire round is bent then when it comes out.

Is the buffer whacking the back of the buffer tube or is it a very mild recoil. The fact that it sometimes catches the next round half way forward could be a bolt cycling too fast or not going far enough back.Is there any indication of gas leakage from the gas key?. Have you tried hot milspec ammo.Does the magazine follower have good engagement with the bolt release?

[shooty]

In which direction is your cases ejecting that gets ejected. Remember on an AR this direction is clear indication on over or under gassed system. Check Youtube for Over and under gassed direction of ejecting cases of AR's

Check your gas system. Front to back. Make sure Gas block is on tight and alignment correct. If not the gas port hole in barrel is not over the opening to gas block and restricting gas. Also that no debris stuck in your barrel gas hole. Blocking gas flow.

Then check gas tube is clear of debris. Blow some air through it.

Make sure gas key is tight and engages gas tube correctly.

If this does not solve the issue. Then.

Check size of gas hole in barrel. Measure it. You want this to be the same size as gas tube inner DIA. Should any case not be under 2.5mm

When we converted Diamondback 300BLK to go Subsonic and cycle reliably we need to open this little gas hole to 3.25mm but 3mm is good place to start. This is easy to do as the hole is already there so a NEW drill bit will follow the hole through. Just put dowel in barrel or cleaning rod so you can feel once through barrel side as you dont want to push drill bit against opposite side rifling.

Other easy options also which we also did was

Reduce buffer tube weights. Lighter cycles easier.
Buffer spring might be little stiff still from factory. Get lighter one. Dont cut your new one.
But rather remove some of the buffer weights. If he once left rattles to much to your liking just put light spacer in even cotton wool or something else.


NB: Adding a Gas adjustment Block system will not help. As this reduces gas pressure only and can never increase it above normal. This is only handy when your AR is over gassed or your using a Silencer with AR pushing more gas backwards. Then they help.

Also you can check where your cases eject. Which direction this will tell you if over or under gassed. Check youtube alot of vids on this.

[-=zv=-]

Thinking..... When was the last time you stripped down and cleaned the gun (incl. Breakdown of the BCG) lubed it well?
I had a cycling issue with my AR, it was due to the gun being very dirty (running it suppressed) and not being lubed correctly..

[Stevin]

Some okay, and some not so okay information in this thread.


Firstly did the rifle function before you did any modifications to it?
If it did it points directly to the gas block installation.


If it didn't function, then it could be a number of things but I would start with checking gas port location and diameter. My M&P Sport 1 with Carbine Gas had a port diameter of 0.070" (or 1.8mm) anything in the range of 0.0625" to 0.075" is considered a normal range for a 16" Carbine Gas port diameter. I have measured gas ports up to 0.080" too.


Gas Port should 7.5" from the muzzle iirc , and gas tube length is 9.75" long for a carbine system, however I'm fairly confident gas port location should be correct.


If yit has always done this even standard. I would start with the following and work my way down.


1. Bore Scope to confirm gas block to gas port alignment
2. Bore Scope to confirm gas block port to gas tube port aligntment
3. Gas Tube alignment with carrier key, and if it enters carrier key without any binding
4. Carrier Key Tightness.


It must also be noted that excessive bolt speed can also cause similar mafunctions to undergassing, most common being bolt hold open over ride.


Don't change the recoil system, don't remove weights or change springs. The assumption is you are still using the standard Carbine Recoil Spring and CAR buffer that come with these rifles. They are already considered on the weak side for carbine gas systems and designed to work with weakest factory ammo (in a correctly gassed system).

[Glockster]

Some okay, and some not so okay information in this thread.


Firstly did the rifle function before you did any modifications to it?
If it did it points directly to the gas block installation.


If it didn't function, then it could be a number of things but I would start with checking gas port location and diameter. My M&P Sport 1 with Carbine Gas had a port diameter of 0.070" (or 1.8mm) anything in the range of 0.0625" to 0.075" is considered a normal range for a 16" Carbine Gas port diameter. I have measured gas ports up to 0.080" too.


Gas Port should 7.5" from the muzzle iirc , and gas tube length is 9.75" long for a carbine system, however I'm fairly confident gas port location should be correct.


If yit has always done this even standard. I would start with the following and work my way down.


1. Bore Scope to confirm gas block to gas port alignment
2. Bore Scope to confirm gas block port to gas tube port aligntment
3. Gas Tube alignment with carrier key, and if it enters carrier key without any binding
4. Carrier Key Tightness.


It must also be noted that excessive bolt speed can also cause similar mafunctions to undergassing, most common being bolt hold open over ride.


Don't change the recoil system, don't remove weights or change springs. The assumption is you are still using the standard Carbine Recoil Spring and CAR buffer that come with these rifles. They are already considered on the weak side for carbine gas systems and designed to work with weakest factory ammo (in a correctly gassed system).

Thanks Stevin, pretty much what I was thinking and experienced.