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

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

Post by smustian »

You have to check what type of gas block that you have. With the prevalence of free float handguards, I would guess they are about 50/50 on having to be offset or not. If not stated in the installation instructions, I would check with the manufacturer or use the methods I described above.
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GSO
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Re: just built an AR 300blk with a 9inch barrel need help

Post by GSO »

I would definitely let it break in for a few hundred rounds before thinking about opening up the gas port and run it really wet (synthetic motor oil usually works well) while breaking it in.

And I second the suggestions to double check the gas block alignment, particularly fore and aft. As stated, some are made to account for the thickness of the front handguard cap and others are not. And I've seen some that have an oblong opening (Geissele if I remember) that will work for either without having to use a shim during install.
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dellet
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Re: just built an AR 300blk with a 9inch barrel need help

Post by dellet »

Easiest way to check port alignment on a set screw type, block is to slide it on upside (down tube removed). The rear set screw hole is drilled the same time as the port. This wil give the exact distance off the shoulder needed, if the barrel even has a shoulder. Mark the position.

The port size MAY, be small. According to the spec on the build kit provided, they use a 3oz carbine buffer which is also out of spec(too light). So it just may work if everything else is correct. A call to the people who put the kit together would answer this.

I am not a fan of drilling ports without knowing that is the actual problem, or having a specific reason in mind. I generally order my barrels with a port of .080" so I control sizing.

I would also check for leaks in the gas system, that will take a fair amount of shooting with supers to show. Suppressed subs it shows up in only a few rounds.
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GSO
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Re: just built an AR 300blk with a 9inch barrel need help

Post by GSO »

dellet wrote:Easiest way to check port alignment on a set screw type, block is to slide it on upside (down tube removed). The rear set screw hole is drilled the same time as the port. This wil give the exact distance off the shoulder needed, if the barrel even has a shoulder. Mark the position.

The port size MAY, be small. According to the spec on the build kit provided, they use a 3oz carbine buffer which is also out of spec(too light). So it just may work if everything else is correct. A call to the people who put the kit together would answer this.

I am not a fan of drilling ports without knowing that is the actual problem, or having a specific reason in mind. I generally order my barrels with a port of .080" so I control sizing.

I would also check for leaks in the gas system, that will take a fair amount of shooting with supers to show. Suppressed subs it shows up in only a few rounds.
This! The website does state that their gun techs can talk you trough troubleshooting many problems over the phone.
I don't collect firearms; they just accumulate...

"Be Prepared" - My motto from an early age.

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austinar15
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Re: just built an AR 300blk with a 9inch barrel need help

Post by austinar15 »

I ordered the Gas block alignment plastic guide tool from HB industries for $6.99 last night. I am going use the alignment tool and make sure it properly aligned but before realigning the gas block I'm am going to mark the position of the gas as it sits now. This was I can see if it was properly aligned as it sits now. If the alignment doesn't work ill call the manufacture and inquire about port size and buffer weight/spring weight.
Also, the kit came with a low profile gas block and the barrel has a shoulder behind the block, along with a free float hand guard. when I take the gas block off ill take picture of the setup and ports on both the barrel and the block.
there was no index or set screw marking one the barrel for the gas block. If there was I wouldn't be concerned about a possible alignment issue.
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Re: just built an AR 300blk with a 9inch barrel need help

Post by Boolit_Head »

if it is a set screw type remove the rear set screw and flip it over. Line it up with the gas hole and then measure off the shoulder. The rear set screw is usually directly under the gas hole. That would giv eyou the distance to set the block off the shoulder. Then your challenge is to center it side to side.
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dellet
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Re: just built an AR 300blk with a 9inch barrel need help

Post by dellet »

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If you do pull your gas block, it should look like the one above with a carbon ring around the port. The port should be very close to centered.
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Re: just built an AR 300blk with a 9inch barrel need help

Post by golfindia »

Boolit_Head wrote:The rear set screw is usually directly under the gas hole. That would giv eyou the distance to set the block off the shoulder.
Unless some magical milling/drilling machine has been invented, the rear set screw will ALWAYS be directly opposite the gas hole in the gas block.
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Re: just built an AR 300blk with a 9inch barrel need help

Post by austinar15 »

I finally had time to finish up centering the GB and put her back together. I used the JB industry plastic dowel thing to get it centered. When I took of the handguard one of the allenscrews was loose and when I took the gas block of I saw the carbon mark on the barrel from the gas block and it wasn't centered right. I would post pictures if I knew how (id appreciate some instruction on posting pics). Ill definitely post again when I get a chance to put some supers and subs through. I got my fingers crossed that the was the whole issue.
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smustian
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Re: just built an AR 300blk with a 9inch barrel need help

Post by smustian »

austinar15 wrote:I finally had time to finish up centering the GB and put her back together. I used the JB industry plastic dowel thing to get it centered. When I took of the handguard one of the allenscrews was loose and when I took the gas block of I saw the carbon mark on the barrel from the gas block and it wasn't centered right. I would post pictures if I knew how (id appreciate some instruction on posting pics). Ill definitely post again when I get a chance to put some supers and subs through. I got my fingers crossed that the was the whole issue.
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