just built an AR 300blk with a 9inch barrel need help

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themonk
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Re: just built an AR 300blk with a 9inch barrel need help

Post by themonk » Mon Mar 13, 2017 7:54 pm

I agree with smustian that you should do some thorough breakin before going to the gas port work. But GSO is correct that 0.076 is a bit small for subs. My 9" AAC that runs all 4 ways is at .100. I think if you want it to run all 4 ways you are going to need to open up the gas port.

I would be willing to bet that it would run fine with a suppressor but there are others here that know far more about the ideal gas port size for a given use case.

Do you plan to run it with a supressor?

I would add that I personally would run an H2 buffer in that setup vs the carbine that came with the kit but I dont think that has anything to do with your current issue.

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Re: just built an AR 300blk with a 9inch barrel need help

Post by austinar15 » Wed Mar 15, 2017 12:14 pm

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Boolit_Head
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Re: just built an AR 300blk with a 9inch barrel need help

Post by Boolit_Head » Wed Mar 15, 2017 2:16 pm

That gas port did not look lined up. You can see the mark was not centered on the port.

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Re: just built an AR 300blk with a 9inch barrel need help

Post by austinar15 » Wed Mar 15, 2017 6:25 pm

Boolit_Head wrote:That gas port did not look lined up. You can see the mark was not centered on the port.
Yeah I was kinda relieved when I saw that it I didn't look lined up because its gunna be easy fix to get it cycling right if that's the only issue. I used a JB plastic jig thing to center the gas block with the port when I put it back together.
I was also looking at suggested buffer weights for a 9 inch barrel the buffer that cam with kit is so3oz which is on the light side according to what my research suggested but the port on the barrel is on the smaller side. But I don't think I'm gunna worry about that until after I shoot the gun again after I just realigned the port and gas block

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Re: just built an AR 300blk with a 9inch barrel need help

Post by Boolit_Head » Wed Mar 15, 2017 6:50 pm

I'm running a 7.5 inch barrel with a 0.109 gas hole on a carbine buffer and it has plenty of gas. It's cycled perfectly.

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Re: just built an AR 300blk with a 9inch barrel need help

Post by austinar15 » Mon Apr 10, 2017 11:16 am

I finally got some time to go back to the range after centering the gas block with the HB industries plastic jig. The gun cycled supers with no problem but still felts a little rough. Then I tried sub sonics and it picked up the 2 round but failed on the 3rd 3 times in a row. After this is swapped the carbine buffer for the H3 I bought
I then tried supersonics and the cycling was flawless and and felt extremely smooth. However, it still wouldn't cycle subs. I believe that the gas port on the barrel is just to small for to reliably cycle subs without a suppressor to increase gas pressure. I will eventually get a suppressor but I will be a while before I can afford one. So I plan to just shoot supers for now until I can invest in a suppressor bc I think subs are pointless without a can anyways. Also, I got a suggestion to get an adjustable gas block to solve the sub issue but would an adjustable GB make a difference if the gas port on the barrel remains the same?
P.S. now that the gun is actually cycling supers I actually got to use it and wow are 300blk AR pistols fun to shoot it might be my new favorite toy. In the mean time I'm looking forward to developing loads to push the distance and accuracy of this gun

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John A.
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Re: just built an AR 300blk with a 9inch barrel need help

Post by John A. » Mon Apr 10, 2017 11:26 am

An adjustable isn't going to help you shoot subs. It needs more gas than it's getting already, and blocking air flow is going to compound the problem. Whoever gave you that advice probably meant well, but they don't know what they're talking about.

The reason most people use adjustable gas blocks is so when they are running subs (which yours isn't doing), when they want to run supers, they can turn the gas flow down just a little to make it a little softer shooting with the full powered rounds, which isn't bad to begin with.

To me, while having a gas system tuned is one thing and fine, it just an answer to a problem that most people don't have to worry about in the first place.
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Re: just built an AR 300blk with a 9inch barrel need help

Post by austinar15 » Mon Apr 10, 2017 1:22 pm

John A. wrote:An adjustable isn't going to help you shoot subs. It needs more gas than it's getting already, and blocking air flow is going to compound the problem. Whoever gave you that advice probably meant well, but they don't know what they're talking about.

The reason most people use adjustable gas blocks is so when they are running subs (which yours isn't doing), when they want to run supers, they can turn the gas flow down just a little to make it a little softer shooting with the full powered rounds, which isn't bad to begin with.

To me, while having a gas system tuned is one thing and fine, it just an answer to a problem that most people don't have to worry about in the first place.
Thanks for the Advice. You pretty much just sum'd up what I thought that the gas port diameter limits the maximum amount of gas and an adjustable GB can only reduce. I just wasn't sure if there where adjustable GBs that could allow more gas through the tube to the bolt.
I'm just gunna set aside subs until a get a suppressor and then if the suppressor doesn't cycle subs I'll worry about drilling the port and getting an adjustable gas block.

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