AR556 MPR will not cycle

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happyC@mper

Bearcat
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Mar 20, 2018
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I bought a brand new ar556 MPR last week. I took it out on Saturday and shot 20 rounds, only 3 of them cycled. The rest of the shots either failed to grab the next round or stove-piped. In all cases, the included pmag had 3 rounds to start with.

I took the gun home and disassembled it. I cleaned and generously lubricated the BCG. Today I took the gun out again and had the same result. 16 rounds fired, each time with 1 round in the magazine. The bolt locked back only 2 times.

Today I also tried some other things.

BCG - I borrowed the BCG from my friends Ruger AR556 and tried in my gun - same failure to lock back the bolt. I tried my BCG in his rifle - cycled and locked back as it should. Summary: my BCG is not the problem.

Magazines - I have the 30 rnd pmag that came with the rifle and also 2 brand new 30 round pmags. I tried each - same failure to lock back the bolt. Summary: magazines are not the problem.

Ammo - I tried several different kinds of ammo. SSA (Nosler) 556 55gr BT, TulAmmo 223 55gr HP, 223 55gr handloads. All ammo behaved the same - same failure to lock back the bolt. Summary: ammo is not the problem.

I don't feel any burs in the chamber or barrel. I have cleaned / lubricated it. It appears to be shiny and smooth to my eye.

I think my problem is either the gas block or the buffer / spring. I have not yet removed the hand guard because I thought the gas block was pinned. Does anyone know if that is true? What would I look as far as issues with the buffer / spring?

It is discouraging to get a brand new gun and have issues like this. Anyone have any suggestions?

Thank you.
 
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Explain in detail why you think it is the gas block or buffer spring. Who told you that?
What locks the bolt back when the gun is empty on a AR or just about every semi auto with a detach mag.?
 

happyC@mper

Bearcat
Joined
Mar 20, 2018
Messages
6
I don't have any other brand of magazine. The gun came with a pmag, it should work with a pmag.
 

happyC@mper

Bearcat
Joined
Mar 20, 2018
Messages
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I have sent the description to Ruger. They are closed till Monday. I am trying to be proactive and learn. Sending the rifle back takes time and money.
 
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They pay the shipping, it took them 2 weeks to replace a cracked factory brand new stock my a rifle last year.. That will get the problem fixed. Read the instructions in the booket.
Do each and every one of these steps.
Make sure the bolt will lock open without a mag it it. You should know how to do it. If it will not lock open you have a rifle problem, send it back. Next place empty mag in it, make sure it is seated ALL the way tap the thing. Try and pull the mag out without pressing the release. If it comes out, it was not seated. Pull bolt back see if it locks back. Place the mag in the gun with the bolt closed, pull back and try it with a open bolt. Do that with different mags. Go buy a different brand made of aluminum. See if that works. You need more mags anyway.
#1 problem people do not seat a mag all the way, highly likely.
#2 problem not common, mag release/catch on rifle not working right.
If you want tear the rifle apart go ahead, not recommended.
Answer my first questions.
 

happyC@mper

Bearcat
Joined
Mar 20, 2018
Messages
6
Without a mag, the bolt does lock open if I hold the bottom of the catch while pulling back the charging hammer.

If an empty mag is inserted when the charging hammer is pulled back then the bolt does lock open.

However, the bolt does not lock open when I try the 1-round shot test. The brass is extracted but the bolt does not lock open.

I have the pmag that came with the rifle as well as 2 other brand new pmags. The problem happens on all 3 magazines.
 
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If you want further help from me. Answer my questions in my first post and do EACH STEP I listed in my second post. No reason to waste my time.
No need to repeat your stuff from your 1st post.
 
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This is another one of those posts. Guy has a new gun and has problems asks for help.
Claims he knows it is not caused by this or that, replaces parts or tears into the gun.
He really does not know what he does not know and when asked will not have a dialogue. We can all guess but, until common easy to check drills or tests are not done who knows. I caulk it up to operator error.
 

happyC@mper

Bearcat
Joined
Mar 20, 2018
Messages
6
I called Ruger and described what I have done to diagnose the issue. They summarized that it looks like an issue with the gas block. They are sending an RMA.
 
Joined
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Cool, hope that is the fix. Pmags are good mags. but they will not seat 100% of time and you may not know unless you check them. Best to have another mag of the GI type made of aluminum. Until you have both you will never see/feel the difference.
 
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