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Discussion Starter · #1 ·
Hello, I've got an AR that won't cycle with the Federal Fusion MSR ammo (link here http://www.federalpremium.com/products/details/rifle.aspx?id=1053).

The rifle has a 16" ARP bull barrel, a Daniel Defense bolt carrier, and a DPMS bolt. ARP was back ordered, or I would have bought their bolt. Barrel has mid-length gas system.

Recoil spring is stock, and rifle cycles fine with Hornady, and my own loads.

I thought it could be the bolt being DPMS and not ARP causing it, thoughts?

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That's not uncommon for the 115 fusions to not cycle, H ports the barrels to cycle with Hornady ammo, it's loaded a little hotter.

I've built several 16" scout barrels that will cycle the fusion ammo and I think they are ported .082.

You might ask H @ ARP to see what your barrel is ported at, it might be .078.


Another thing, are you using a carbine 3 oz buffer and spring?




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Discussion Starter · #4 ·
Wassman, no, I'll take a look at that, didn't think about the gas tube alignment. I plan on swapping hand guards on it soon, so that will be the perfect time.

Semi_cop, I don't know the port diameter, might be worth looking into. I didn't see my barrel on their web site anymore.

I'm using the standard carbine recoil spring and buffer in my Tapco commercial 6 position stock.


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Wassman, no, I'll take a look at that, didn't think about the gas tube alignment. I plan on swapping hand guards on it soon, so that will be the perfect time.

Semi_cop, I don't know the port diameter, might be worth looking into. I didn't see my barrel on their web site anymore.

I'm using the standard carbine recoil spring and buffer in my Tapco commercial 6 position stock.

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If the barrel is a few years old it may be ported .082 or .086 if so it should cycle the 115 fusions. You could confirm with Harrison.

As Wassman stated: check your gas block alignment to make sure it's aligned over the barrel port and make sure your gas block and gas tube ports are aligned and clear.

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If it functions correctly with your handloads and with Hornady factory loads, then I doubt seriously that you have a problem with the gas block. It is more likely a port diameter issue as already stated.

Another place to look is the stock and buffer set up. If you have a 16" ARP barrel, then it is most likely a mid gas set up. Using an adjustable stock and carbine buffer set up with a mid gas barrel could be part of the problem. All of my ARs are 16-18" mid gas, in several different calibers. and all have functioned flawlessly from the first round. But, they are all set up with A2 stocks and standard buffers. Ejection is perfect, regardless of bullet used or powder used, at 4 o'clock. Box stock ports, low profile gas blocks. This was a deliberate choice on my part, driven by a reliability/functionality standpoint.

If you want to be able to shoot everything, then open up the port and install an adjustable gas block. You can get to the same place if you handload by tailoring loads with the bullets you want for your current set up. The easiest fix, however, is just stop using the sub standard Federal ammo.
 

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Stating that using an adjustable carbine stock, buffer and spring being a function problem is a complete contradiction from Harrison's FAQ section of his web site. He generally ports the barrels to function with the most common components which is exactly an adjustable stock, standard carbine buffer and spring while shooting Hornady, S&B and Federal XM68GD.

Being that your gun runs with the Hornady ammo it's not uncommon for the gun to not function correctly with federal MSR ammo especially if the gun is not broken in and tight. The MSR ammo either needs to be loaded hotter or have a slightly slower burning powder and loaded hotter to function with the S&B, Hornady and Gold Dots, IMO.


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Discussion Starter · #8 ·
I think you're onto something semi_cop. The upper has less than 200 rounds on it.


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I think you're onto something semi_cop. The upper has less than 200 rounds on it.

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I've built several that function with the 115 fusions and carbine stocks, buffer and spring. A guy I work with built one and it would not function, he copied my gun, ARP barrel, stock and all. I told him to clean the chamber really well and lube the cam pin, bolt body and gas rings as well as the carrier rails. He brought the gun to me and had me look at it. He even e-mailed Harrison asking about the gas port and was going to send it to him to open the barrel port. I told him that wasn't necessary if the port was .082 it would most likely function if not it was easily done himself. After cleaning the chamber, checking the barrel port and lubing the BCG he took it out and tried again and didn't have any feeding or cycling problems. His gun was 100% new and tight, that coupled with the Fusion ammo didn't help. The fusion is pretty accurate for me and by brothers 16" scout builds, I just wish it was a little hotter.

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Discussion Starter · #10 ·
Thanks for the info! I'll be sure to clean and lube it well!

How would I go about checking the gas port alignment? Do I need a tool to do so?


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Thanks for the info! I'll be sure to clean and lube it well!

How would I go about checking the gas port alignment? Do I need a tool to do so?

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If you know about the age of the barrel send constructor a PM or e-mail him at AR15 Performance. Otherwise you could check with a #45 drill bit or a pin gauge.

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+1... needs break-in and a good chamber cleaning

fed 115's never cycle well in my builds till they are well broken-in
 
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