6.5 Creedmoor build not running until I cut buffer spring?

giannid

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Mar 20, 2017
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So I recently just finished up a 6.5 creedmoor build using all aero components except a 16 inch faxon barrel and superlative adjustable gas block. When I put the aero enhanced 308 carbine buffer tube kit, I noticed the spring was very tight. I dimpled the barrel with a jig to make sure I had proper alignment of the gas block.

Today I went out and shot some test rounds to check function of the rifle prior to load development. With the gas block wide open, the gun would barely eject a round and would not load a second round or stovepipe one in the chamber. Shot a few rounds with a can and it ran fine. After checking and double checking everything, I figured I'd try cutting the spring to see if I could get it to run. Started cutting one coil at a time until I got it to function without the can and end up taking 4 turns out of the spring to get it to run dependable.

Not a big fan of having a cut spring in the gun. I did get it to run reliably but I'm wondering if I should be looking at something else. I haven't built many AR10's and most of my experience building is with the standard AR15's. Comparing the ar10 spring to an ar15 spring, I notice they are very different. I installed a regular ar15 spring in the gun and it seems to close up the bolt fine but I did not try running rounds through it.

Where should I go with this? I'm wondering if I should buy one of the fancy spring kits or just run the cut spring, or something else. One though I had was the gas port isn't big enough but rather not mess with opening it up. This is going to be primarily a thermal hunting rig and I want this gun to run like a sewing machine.
 

KimberGuy

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Nov 2, 2007
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Get an A5 tube, regular H2 or H3 buffer, and then choose the appropriate recoil spring. I like the Tubbs flatwire spring or SR25 carbine spring.

I am not a fan of standard carbine tubes and short buffers.
 
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giannid

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Mar 20, 2017
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Why a carbine length tube and spring on a large frame gasser?

This is the kit I purchased for this gun. Figured I'd use it as it's all aero components and figured it would work well with it.

You guys think this could be causing my problem? I figured it was the way to go as I wanted an adjustable stock.
 

Jigstick

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  • Jul 21, 2017
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    Could be a multitude of things. You running handloads or factory ammo? Is the ammo underpowered? Sounds like you got enough gas with your can on. It can be a bitch to tune the large frame guns. Ammo, gas port placement and size, BCG weight, buffer length and strength all have to work together.
     

    hlee

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  • Jul 14, 2012
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    All of the above, and gas guns sometimes just need to wear in for a bit, before you really get a good running gun.
     

    giannid

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    Mar 20, 2017
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    I'm running hand loads which are 42 grains of H4350 under a 120 grain sierra bullet. This is a moderate load and on the higher end of the reloading data.

    I haven't played around with the large frames AR's before, but both my prior builds ran fine which were 6mm creedmoor builds. Both those used a rifle buffer tube. I'm relatively certain the gun will run as it's running suppressed and with the spring cut. Didn't want to cut the spring but figured it was a cheap fix to see if I could get it to run. I'm just not a fan of modifying stuff and rather it run right without a cut spring.
     

    hlee

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  • Jul 14, 2012
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    Maynr the gun just needs to wear in all of the mating surfaces.

    Maybe the gas port is small.

    Maybe it is partially obstructed. Do you have a bore scope? The best use for one that I have found is checking the alignment of a gas block.

    If it is running and not damaging anything- like the receiver extension tower, run it for a while. See how it goes.
     

    richiecotite

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    Oct 13, 2018
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    a5/armalite buffer tube or a rifle length buffer would likely help. Dont like the idea of cutting coils on the standard buffer spring, but if it works it works.