Problem with JP CTR-02 Low Mass Upper

[The Legion]

I am a novice when it comes to AR-15 and would like to get some feedback on a problem I am having with a new upper I purchased. I purchased a JP CTR-02 Low Mass Upper this week and have had nothing but problems with the upper. I placed the upper on a S&W M&P Lower. I took it to the range yesterday and was only able to shoot one or two rounds out of the rifle before it would either jam or not chamber a rounds at all. The rifle will also not lock back on the last round shot. I am using Magpul 20 round magazines and was shooting Remington UMC 55 gr .223. I did find out that the low mass upper does require a low mass buffer, which I have on order. I am not sure if this will correct the problems. This morning I put the M&P bolt into the JP upper and was still having the same issue. If anyone has any idea's what may be causing the problem it would be helpful. I have sent an email to JP and will try to connect them on Monday. Thank you

Edited June 29, 2013 by washabra

[Troutburger]

Buffer is most likely the issue.

[RichardR]

Sounds undergassed, the low mass buffer might be light enough to clear that up, but I'd also double check the gas port/block alignment to make sure it's not off-set a little just in case.

[The Legion]

I was just doing some research and I was looking at the problem of the rifle being undergassed.  The Low Mass Buffer will help, but I believe you are correct on the gas issue.  I will go to the range later today and see if that is the problem.  The rifle was having the same problem with the M&P Full Mass bolt in it.  The gas issue may be it.  Thanks will update.

[RWF]

if it is a compete upper from JP it has a adjustable gas block, just open up the set screw and check to make sure the set screw is there and not missing

[The Legion]

Hello RWF

 

You are correct it was the gas block.  I just got back from the range and made adjustments to the gas block until the bolt locked back.  After that the gun functioned perfectly. Thanks for all your help folks.  Have a great weekend.

[RWF]

fyi, if you are happy where its set at, put a little blue locklite on it. the set screw has been known to turn up missing. you do not need much, just to keep it from moving till u get some carbon built up in the threads.

[The Legion]

RWF  Thank you I will do that.