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Discussion Starter · #1 ·
Hello I`m new building ar`s and I`m looking for a little bit of help. I have a smith wesson m&p decided to get a 20" fn barrel low profile gas block and a rile length gas tube I went out and shot it yesterday first three shots worked great then it started ejecting the empty case but would not pick up the next round from the mag I tied two different mags same thing i was looking around online and some videos point to the buff system on it I'm wanting to know if I go get I lighter buffer spring or buffer without going to a rifle length buffer tube. Any help would be much appreciated thank you
 

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First, I've never had this problem... But I'm just going to speculate here. I don't think you need a lighter buffer and definitely don't screw around with the spring. It might be cycling too fast. The bolt could be outrunning the magazine feed. With that situation, a heavier buffer would be the solution. I'm betting that you have an H1 standard buffer. I run an H2 in a couple of rifles and pistols for various reasons, depending on the caliber, barrel length, etc...

Help me understand though. Did you go to a longer barrel as well as a new gas block? I think that's what I understand you to say. Is it a non-adjustable gas block? I'm guessing that it is. Did you make sure the gas block has stayed tight? If the first few rounds loaded properly, loosening would be a thing to check on the gas block.

Just rattling off ideas...
 

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I have to agree with ponycar, sounds like you need to look at the gas block and make sure it is centered and tight. If it isn't precisely above that hole in the barrel, you aren't going to get enough gas to push your bolt back far enough to pick up the next round. I have had this same thing happen to me in a few of my builds and that is what remedied the problem.
 

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As mentioned several times already, the gas block may not be centered over gas port. I had it happen on one of my builds. If the problem persists, a shim may be needed between the gas block and barrel shoulder to keep it centered.
 
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Discussion Starter · #10 ·
First, I've never had this problem... But I'm just going to speculate here. I don't think you need a lighter buffer and definitely don't screw around with the spring. It might be cycling too fast. The bolt could be outrunning the magazine feed. With that situation, a heavier buffer would be the solution. I'm betting that you have an H1 standard buffer. I run an H2 in a couple of rifles and pistols for various reasons, depending on the caliber, barrel length, etc...

Help me understand though. Did you go to a longer barrel as well as a new gas block? I think that's what I understand you to say. Is it a non-adjustable gas block? I'm guessing that it is. Did you make sure the gas block has stayed tight? If the first few rounds loaded properly, loosening would be a thing to check on the gas block.

Just rattling off ideas...
I tore it back apart last night and checked everything made sure the gas block was properly aligned and made sure it was tight I just took it out and dumped two mags without a problem
 

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I tore it back apart last night and checked everything made sure the gas block was properly aligned and made sure it was tight I just took it out and dumped two mags without a problem
I was just brainstorming right along with you, but I'm glad you got it working! I hate it when you know something isn't quite right, but you don't know what it is. I just tore a Ruger SR9 I was working on back down and chased a bur on the trigger connector down to get the striker to drop. I gave up troubleshooting after the install last night and had to wait all day to troubleshoot it today. Things like that'll drive ya' crazy! :)
 
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