New 308 build with apparent short stroking. Seek input & comments

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[ARCHIVED THREAD] - New 308 build with apparent short stroking. Seek input & comments (Page 1 of 2)

Posted: 3/26/2017 6:02:10 PM EDT

Hello all,

Just finished building a LR308 using components listed below. What appears to be short stroking with milspec DPMS buffer tube, DPMS 308 buffer and 16" Criterion barrel with rifle length gas system. Issues regardless of mag or ammo brand and yes, I can lock the bolt all the way back manually.

Here is the pattern. Buffer is at all times stock DPMS:

1) Stock Aero carbine spring: Decent ejection, never locks back on last round.

2) Stronger Orange "Sprinco" extra power spring: Fails to feed next round in chamber- jams it at an angle.

3) Weaker Red Sprinco extra power AR15 (not 308) spring: Will eject and chamber next round and usually lock back , but ejection pattern
is quite erratic, even with the same ammo. Sometimes to 2 o'clock, sometimes to 4 and at other times just dribbles out.

In short, it works best (but not 100%) with a LOWER power AR15 spring. The stronger the spring, the worse it gets.

Sounds like a gas issue to me, but I am not sure. Tested various mags and ammo brands. No substantial difference.

Does the group have any collective wisdom to share? Wondering if an adjustable gas block may be needed.

Much appreciated.

Build:

Aero receivers & handguard
Milspec buffer tube and DPMS buffer
Criterion 16" 308 barrel (rifle length gas)
Lantac 308 bolt carrier
BCM standard low profile .750 block installed on existing barrel dimple (double lining up is an issue)
Rifle gas tube- that was quite tough to get it to fit.

Posted: 3/26/2017 6:09:44 PM EDT

[#1]

Running it sloppy wet?

Posted: 3/26/2017 6:53:40 PM EDT

[#2]

An adjustable gas block can't give you more gas, only less. It is used mainly for rifles which are overgassed, or will be when they are suppressed.

Have you checked the alignment of the gas block?

Posted: 3/26/2017 7:45:50 PM EDT

[#3]

Quote History

Quoted:
An adjustable gas block can't give you more gas, only less. It is used mainly for rifles which are overgassed, or will be when they are suppressed.

Have you checked the alignment of the gas block?

View Quote

I will have to re-check, but recall my measurements were good and it is dead center. I've done them on standard ARs before with a jig, every time without incident. AND---this barrel came pre dimpled, so I wonder bad I'd have to screw up to mis-align!

Is there a way to check without heating the loctite and removing the side pin.

Learned one lesson- do NOT side pin until 100% satisfied it works. Idiot......

Posted: 3/26/2017 7:46:20 PM EDT

[#4]

Quote History

Quoted:
Running it sloppy wet?

View Quote

No more/less so than a standard AR.

Posted: 3/26/2017 9:20:50 PM EDT

[#5]

I don't remember if the Criterion barrels take the standard AR-15 rifle length gas tubes or the longer ArmaLite AR-10 gas tubes. Check and make sure the gas tube is extending far enough into the upper receiver.

If the gas tube is the correct one, then inspect the gas tube, gas block and the gas port to make sure there aren't any obstructions.

Posted: 3/26/2017 9:28:54 PM EDT

[#6]

Quote History

Quoted:
I don't remember if the Criterion barrels take the standard AR-15 rifle length gas tubes or the longer ArmaLite AR-10 gas tubes. Check and make sure the gas tube is extending far enough into the upper receiver.

If the gas tube is the correct one, then inspect the gas tube, gas block and the gas port to make sure there aren't any obstructions.

View Quote

Thanks. I removed the hand guard and see nothing amiss. Gas tube length seems to hit the upper receiver about where every AR I have does. I'll likely remove the tube to make sure. For one odd reason it went in VERY hard. Needed to tap with a plastic mallet. Unlike a traditional AR, this barrel nut has no need to align one of the teeth for tube install.

Posted: 3/26/2017 9:43:27 PM EDT

[#7]

I'm sure you already checked, but is it the correct 308 buffer and not an ar15 buffer?

Posted: 3/26/2017 9:50:10 PM EDT

[#8]

Quote History

Quoted:
I'm sure you already checked, but is it the correct 308 buffer and not an ar15 buffer?

View Quote

Yes, thanks. I ordered a 308 stock, buffer, spring and gas tube from Aero when I ordered the "builder's set".

The odd thing is it short strokes (fails to lock on empty chamber) with the stock spring an buffer.

All my tests to date involved changing magazines, ammo and springs. Ammo and mags made no difference.

The only thing which DID make a difference where the springs.

Now that you mention, it, the OEM Aero buffer and tube were very rough. Felt "gritty" and with resistance. I replaced the buffer tube with a Milspec 7" buffer from Rock River, I think, I had laying around. Eliminated the roughness, but I wonder about the buffer. At about 2.5" it is definitely a 308. Not ever having had a 308 AR I a not sure how much resistance when cycling the action is normal. Is it obviously much stiffer than an AR15.

Posted: 3/26/2017 10:26:20 PM EDT

[#9]

BASED ON THESE PICS-- I wonder if it a gas tube/alignment issue...... Look at the filth and where it is after only perhaps 80 rounds. The bolt is "sticky" and rotates with resistance.

Attached File

Posted: 3/26/2017 10:46:55 PM EDT

[#10]

Looks like you're gas tube is too short. It's giving some gas to the key but most is hissing the bolt.

Posted: 3/26/2017 10:56:17 PM EDT

[#11]

Quote History

Quoted:
Looks like you're gas tube is too short. It's giving some gas to the key but most is hissing the bolt.

View Quote

My suspicion as well--and get this--the tube makes contact with the "receiving" end of the bolt carrier where it goes into.

I'll be calling Aero tomorrow and see what they can do, as it is their tube. There is way, way too much carbon and crap in and around the bolt for 80 rounds.

Posted: 3/26/2017 11:17:01 PM EDT

[#12]

You need A LOT more oil on there.

Posted: 3/26/2017 11:25:37 PM EDT

[#13]

Quote History

Quoted:
You need A LOT more oil on there.

View Quote

I normally don't run an AR sopping wet and did wipe some off for clarity. Never had an issue. I typically lube the bolt, carrier riding surfaces and cam, etc.

What troubles me here is the astounding about of crap on the bolt and carrier after only 80 rounds and modest, but discernible impact when the bolt carrier taps the gas tube. The tube does NOT just slide in, so alignment is likely an issue. It's an Aero tube with Aero receivers and Lantac BCG.

That's what's so great about these boards, people helping other enthusiasts!

Posted: 3/26/2017 11:43:09 PM EDT

[#14]

KAK BCG, spring and buffer.

Posted: 3/27/2017 12:17:05 AM EDT

[#15]

I just went through the same thing with a recent build. Mine was a 20" Criterion barrel with rifle length gas system.

I have another gun I built with an 18" rifle length no name barrel I got on a Black Friday sale. This gun runs perfect. So I swapped the lower assembly and BCG and still had short stroking. I knew it was my barrel.

Gas tube was checked. Gas block checked. I even swapped gas block and tube from my good gun to rule it out.

I ended up drilling the gas port. Originally the Criterion gas port was .095"(between a 41 and 42 drill). I opened it up one drill size at a time until it worked. Today I was able to get it to work flawlessly. The final size was a drill bit #38, .1015".

I drilled this on my mill. You could do this with a hand drill. Since you are enlarging the hole the bit will follow the old hole. Use a stop so you don't go and drill the other side. Do one drill bit at a time until it locks the bolt back. Then run a full magazine. If you get some failures you may need to go up one more size.

I like to run M80 ammo and want my guns to run well on that stuff.

Posted: 3/27/2017 12:26:03 AM EDT

[#16]

Quote History

Quoted:
I just went through the same thing with a recent build. Mine was a 20" Criterion barrel with rifle length gas system.

I have another gun I built with an 18" rifle length no name barrel I got on a Black Friday sale. This gun runs perfect. So I swapped the lower assembly and BCG and still had short stroking. I knew it was my barrel.

Gas tube was checked. Gas block checked. I even swapped gas block and tube from my good gun to rule it out.

I ended up drilling the gas port. Originally the Criterion gas port was .095"(between a 41 and 42 drill). I opened it up one drill size at a time until it worked. Today I was able to get it to work flawlessly. The final size was a drill bit #38, .1015".

I drilled this on my mill. You could do this with a hand drill. Since you are enlarging the hole the bit will follow the old hole. Use a stop so you don't go and drill the other side. Do one drill bit at a time until it locks the bolt back. Then run a full magazine. If you get some failures you may need to go up one more size.

I like to run M80 ammo and want my guns to run well on that stuff.

View Quote

Curious-Did you contact Criterion? I wonder if there was an issue. Mine is the 16" "Hybrid" nitrided barrel (Link below).

You may well be right. I'll try fixing what looks like a piss poor gas tube alignment issue- It required a rubber mallet to tap it into the receiver and the BCG strikes it when moving forward! If a new tube does not work then I may have to go there or see what Criterion will do. I checked the gas port alignment, albeit w/o removing it, and it is dead centered and back that tiny amount from the shoulder. Seeing as how the barrel came with a dimple it would have been tough to misalign it!

Barrel: https://msrarms.com/collections/m-o-t-m/products/criterion-barrels-nitride-finish-stainless-steel-hybrid-contour-barrel-308-ar?variant=28384322049

Posted: 3/27/2017 7:39:50 PM EDT

[#17]

Aero is sending a new buffer assembly and gas tubes (standard and melonite). Took one look at the pics and said the gas system is wrong.

Will post after the parts are here and tested. Fingers crossed and thanks to all!

Posted: 3/27/2017 7:44:02 PM EDT

[#18]

Adjustable gas block is what you seek.

Posted: 3/27/2017 7:56:43 PM EDT

[#19]

Quote History

Quoted:
Adjustable gas block is what you seek.

View Quote

I may go there, but wanted to try the easy stuff first. With an obvious defective tube/alignment issue and rubbing buffer I figure I'll fix them first. Figure it can't hurt to try those first before removing my dimpled and pinned BCM gas block.

Per Aero, the recommended gas port size for a 16" barrel is something like .073. Seems small to me, but that's what the rep told me. Criterion tells me their port is .095.

If this does not work then perhaps this adjustable gas block from JP Rifles is in order: http://jprifles.com/buy.php?item=JPGS-5B

Posted: 3/27/2017 8:27:02 PM EDT

[#20]

Quote History

Quoted:

I may go there, but wanted to try the easy stuff first. With an obvious defective tube/alignment issue and rubbing buffer I figure I'll fix them first. Figure it can't hurt to try those first before removing my dimpled and pinned BCM gas block.

Per Aero, the recommended gas port size for a 16" barrel is something like .073. Seems small to me, but that's what the rep told me. Criterion tells me their port is .095.

If this does not work then perhaps this adjustable gas block from JP Rifles is in order: http://jprifles.com/buy.php?item=JPGS-5B

View Quote

Just make sure that will actually fit under your rail and not rub. the JP I have is slightly taller than some other brands I have... that's just from eyeballing it, I havent actually measured. I think the ergo I have is the lower.

Posted: 3/27/2017 10:03:56 PM EDT

[#21]

I did not contact Criterion. I did a lot of reading and found the gas port sizes are all over the place for 308 ARs. So after making sure everything was in order and ruling out all components I then decided to open the gas port up one step at a time.

Until you get your gun to run don't waster time installing an adjustable gas block. Adjustable gas blocks only throttle down the amount of gas directed into the action. It can't add gas. So if it won't run with a standard gas block it certainly will not run with an adjustable.

This is a rule I learn as a young pup. It has serve me well in my 35 years of building and tinkering with machines, anything from lawn mowers to race cars to guns, only change one thing at a time. So get your gun to run reliably first. Then change the gas block to an adjustable if you need it.

When opening up the gas port go one step at a time. A little make a big difference here.

Posted: 3/27/2017 10:28:24 PM EDT

[#22]

Quote History

Quoted:
I did not contact Criterion. I did a lot of reading and found the gas port sizes are all over the place for 308 ARs. So after making sure everything was in order and ruling out all components I then decided to open the gas port up one step at a time.

Until you get your gun to run don't waster time installing an adjustable gas block. Adjustable gas blocks only throttle down the amount of gas directed into the action. It can't add gas. So if it won't run with a standard gas block it certainly will not run with an adjustable.

This is a rule I learn as a young pup. It has serve me well in my 35 years of building and tinkering with machines, anything from lawn mowers to race cars to guns, only change one thing at a time. So get your gun to run reliably first. Then change the gas block to an adjustable if you need it.

When opening up the gas port go one step at a time. A little make a big difference here.

View Quote

Extremely well put. I view a larger gas port as an extreme last resort. In fact, I have a call into JP Rifles to see if their device is capable of adding MORE than just a basic gas tube. Seeing as how I have an obvious tube and/or alignment issue as well as a sticky buffer I wish to first address these issues before more drastic action. One variable at a time. First the gas tube, then the buffer and we moe forward from there.

Posted: 3/27/2017 10:29:35 PM EDT

[#23]

I don't think there's anything wrong with your gas tube.

Posted: 3/27/2017 10:35:16 PM EDT

[#24]

Quote History

Quoted:
I don't think there's anything wrong with your gas tube.

View Quote

A brand new Lantac BCG actually strikes it while closing. It may look Ok, but its angle in the receiver appears off. Also, it took far too much effort despite an unobstructed opening to get it into place.

I sent Aero the same pics and they immediately thought the tube is wrong given the great about of crap on the bolt. They think the melanite coating and/or tube itself is out of spec. They are sending me one melanite and one standard to try.

I figure I'll try the new parts before taking more drastic action.

Posted: 3/27/2017 10:44:45 PM EDT

[#25]

Quote History

Quoted:
I did not contact Criterion. I did a lot of reading and found the gas port sizes are all over the place for 308 ARs. So after making sure everything was in order and ruling out all components I then decided to open the gas port up one step at a time.

Until you get your gun to run don't waster time installing an adjustable gas block. Adjustable gas blocks only throttle down the amount of gas directed into the action. It can't add gas. So if it won't run with a standard gas block it certainly will not run with an adjustable.

This is a rule I learn as a young pup. It has serve me well in my 35 years of building and tinkering with machines, anything from lawn mowers to race cars to guns, only change one thing at a time. So get your gun to run reliably first. Then change the gas block to an adjustable if you need it.

When opening up the gas port go one step at a time. A little make a big difference here.

View Quote

What is the internal diameter of a standard gas block?

I had issues with my .308, threw an adjustable on and half turned till it cycled... standard gas block did not work with 87% of the ammo I was shooting.

Posted: 3/27/2017 10:56:21 PM EDT

[#26]

I am going to add something here that is REALLY puzzling me-- and which I will add as a different thread since it may effect others.

Long story short:

I mistakenly ordered two Lantac 308 bolt carriers. Forgot I ordered one in the past and guess what shows up today? These are supposedly top of the line.

When testing both with the Aero Precision upper I find my existing one slides easily in the upper and even has some "slop".

The second? Gotta force it in even before the bolt makes contact with the barrel!

WTF?? Any thoughts?

Link to Lantac: https://www.lantac-usa.com/AR15-M16-M4-Rifle-Accessories/762NIB.html

Posted: 3/27/2017 11:16:54 PM EDT

[#27]

Since it's an applied finish, NiB is inconsistent with regard to thickness.

Unlike Melonite/SBN that adds no dimension due to being a surface conversion process.

Posted: 3/27/2017 11:20:57 PM EDT

[#28]

Quote History

Quoted:
Since it's an applied finish, NiB is inconsistent with regard to thickness.

Unlike Melonite/SBN that adds no dimension due to being a surface conversion process.

View Quote

Makes sense. Now if only I could figure out why two supposedly IDENTICAL Lantac Bolt carriers fit vastly different in the SAME Aero Upper......

I am beginning to think I have much bigger problems than a gas tube.....

Posted: 3/27/2017 11:23:26 PM EDT

[#29]

Quote History

Quoted:
Makes sense. Now if only I could figure out why two supposedly IDENTICAL Lantac Bolt carriers fit vastly different in the SAME Aero Upper......

I am beginning to think I have much bigger problems than a gas tube.....

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:
Since it's an applied finish, NiB is inconsistent with regard to thickness.

Unlike Melonite/SBN that adds no dimension due to being a surface conversion process.

Makes sense. Now if only I could figure out why two supposedly IDENTICAL Lantac Bolt carriers fit vastly different in the SAME Aero Upper......

I am beginning to think I have much bigger problems than a gas tube.....

The big guns aren't at all as easy to build as their little brother.

Posted: 3/27/2017 11:27:08 PM EDT

[#30]

Quote History

Quoted:
Running it sloppy wet?

View Quote

This is probably the #1 culprit. My 901 will run dry on full power .308 Win all day, but it only makes it a couple hundred rounds before it starts short-stroking on 7.62 NATO. Worse if it's shitty underpowered foreign 7.62. Needs plenty of lube for those.

Posted: 3/27/2017 11:33:30 PM EDT

[#31]

Attached File

Is it possible for your extractor pin to come out when the bolt is fully extended like this?

Posted: 3/27/2017 11:50:54 PM EDT

[#32]

Quote History

Quoted:

Is it possible for your extractor pin to come out when the bolt is fully extended like this?

View Quote

No, it seems quite snug and about the same resistance I'd expect on a "standard" AR extractor pin. What is WEIRD is how a second Lantac I received just today is machined somewhat differently and does not fit the same. It is MUCH snugger and does not slide freely. See pics. The first "used" one hss the smaller extractor lug Look at the extractors, which are different. Some of the machining is not quite the same and hard to get on camera, but my finger shows the general area.

Attached File

Posted: 3/27/2017 11:54:33 PM EDT

[#33]

Quote History

Quoted:
Aero is sending a new buffer assembly and gas tubes (standard and melonite). Took one look at the pics and said the gas system is wrong.

Will post after the parts are here and tested. Fingers crossed and thanks to all!

View Quote

Why Aero will send you the buffer assembly? The buffer seems to be correct size.

I also built M5 308 recently and had short storks issue, and was about to post my problem when I saw your post. Probably will wait to see if I can learn from your thread and solvent my problem.

Have you measured the distance from gas block shoulder to the barrel breach face? I measured mine and it's about 13 7/32 inch, same as my 18" AR15 rilfe. Both are rifle length gas system. I asked this because I saw a comment about the gas tube too short. But it seems fine.

Have you also measured your gas port? But if your port size is 0.096" based on edgephoto's comment it is big enough according to this data. Mine is between 5/64 and 6/64 (I do not have proper gauge to measure more accurately)
308 Gas Port Size

I came across this post with same short stroke issue, and his gunsmith help to open the gas port from 0.081" to 0.091" to make it cycle reliably. This is exactly what edgephoto did but the final gas post is much smaller.
MDShooters

Posted: 3/28/2017 12:02:59 AM EDT

[#34]

Quote History

Quoted:

Why Aero will send you the buffer assembly? The buffer seems to be correct size.

I also built M5 308 recently and had short storks issue, and was about to post my problem when I saw your post. Probably will wait to see if I can learn from your thread and solvent my problem.

Have you measured the distance from gas block shoulder to the barrel breach face? I measured mine and it's about 13 7/32 inch, same as my 18" AR15 rilfe. Both are rifle length gas system. I asked this because I saw a comment about the gas tube too short. But it seems fine.

Have you also measured your gas port? But if your port size is 0.096" based on edgephoto's comment it is big enough according to this data. Mine is between 5/64 and 6/64 (I do not have proper gauge to measure more accurately)
308 Gas Port Size

I came across this post with same short stroke issue, and his gunsmith help to open the gas port from 0.081" to 0.091" to make it cycle reliably. This is exactly what edgephoto did but the final gas post is much smaller.
MDShooters

View Quote

Allow me to address in order:

Why Aero will send you the buffer assembly? The buffer seems to be correct size.

It rubs in their brand tube.

Have you measured the distance from gas block shoulder to the barrel breach face? I measured mine and it's about 13 7/32 inch, same as my 18" AR15 rilfe. Both are rifle length gas system. I asked this because I saw a comment about the gas tube too short. But it seems fine.

Length is OK. How hard it was to insert and angle while in the upper are are different matter.

Have you also measured your gas port? But if your port size is 0.096" based on edgephoto's comment it is big enough according to this data

According to Criterion it is 0.095 (or 96, I forget)

Posted: 3/28/2017 12:54:23 AM EDT

[#35]

Quote History

Quoted:

Allow me to address in order:

Why Aero will send you the buffer assembly? The buffer seems to be correct size.

It rubs in their brand tube.

Have you measured the distance from gas block shoulder to the barrel breach face? I measured mine and it's about 13 7/32 inch, same as my 18" AR15 rilfe. Both are rifle length gas system. I asked this because I saw a comment about the gas tube too short. But it seems fine.

Length is OK. How hard it was to insert and angle while in the upper are are different matter.

Have you also measured your gas port? But if your port size is 0.096" based on edgephoto's comment it is big enough according to this data

According to Criterion it is 0.095 (or 96, I forget)

View Quote

Thanks. I also have M5 set the gas tube went in pretty easily.

Seems there's some friction that BCG has to overcome in you gun. Hopefully you can get it running with new gas tube and buffer without enlarge the gas port.

A side question, do you feel the Sprinco red spring is softer than Aero carbine spring? I am thinking to try red spring on my build, have to buy one though.

Posted: 3/28/2017 1:28:15 AM EDT

[#36]

Quote History

Quoted:

Thanks. I also have M5 set the gas tube went in pretty easily.

Seems there's some friction that BCG has to overcome in you gun. Hopefully you can get it running with new gas tube and buffer without enlarge the gas port.

A side question, do you feel the Sprinco red spring is softer than Aero carbine spring? I am thinking to try red spring on my build, have to buy one though.

View Quote

Yes, most certainly the Sprinco red is softer than the stock Aero. My experience with them is, from strongest to weakest: Sprinco Orange --> Aero "stock" spring --> Sprinco Red. It would seem 308 springs are by nature necessarily stronger than those meant for 556. Swapping among the 3 was part of my testing. I tended to think under gassed based on how performance improved as the buffer spring became weaker. The significant evidence of poor gas flow into the BCG more or less confirmed my suspicions.

Posted: 3/28/2017 9:36:27 AM EDT

[#37]

With regards to gas port size these rifles are a different animal than it's little brother.

7.62x51 is lower pressure than .308. This is the opposite of 5.56x45 and .223.

You may find a .096" gas port makes your gun work reliably with heavy bullet .308 ammo. I want my gun to run on 7.62x51 M80 ammo. I have lots of this stuff in my ammo collection. So depending on what ammo you want to use your gas port size will vary. If you do some Googling, like I did, you will find there is no "standard" gas port size like with an AR15.

I plan to install an adjustable gas block on my gun now that I got it running properly. I will be shooting suppressed and I like to dial the gas down.

If your bolt carrier is binding get a BCG that fits. There is no Mil-spec with these guns so there are more fitment issues than you get with AR15 builds. I have Aero uppers in both my builds and use AIM surplus BCGs. One is Nitride and one is NiB. Both BCGs fit the upper with no binding and headspaced properly with my Criterion and No name barrel.

You can remove the bolt from the carrier and then slide the carrier only into the upper to check for binding and if the gas tube fits without effort. Once this is fixed reinstall the bolt and go try it.

To the OP, fix all your binding parts, verify your gas block is lined up properly with the gas port and then go try it. Put one round in the magazine and shoot it, see if the bolt locks back. Do this 5 times to make sure. Then if this works try to shoot a full magazine.

Lastly if you are trying to shoot handloads, set those aside until things work on commercial ammo. Buy 100 rounds of what you plan to shoot regularly and a box of something in .308 with a heavy bullet. If it fails with your standard ammo try the heavy bullet stuff. If it works with that you then have to decide wether to use that ammo or open open the port.

Posted: 3/28/2017 10:02:55 AM EDT

[#38]

Quote History

Quoted:
With regards to gas port size these rifles are a different animal than it's little brother.

7.62x51 is lower pressure than .308. This is the opposite of 5.56x45 and .223.

You may find a .096" gas port makes your gun work reliably with heavy bullet .308 ammo. I want my gun to run on 7.62x51 M80 ammo. I have lots of this stuff in my ammo collection. So depending on what ammo you want to use your gas port size will vary. If you do some Googling, like I did, you will find there is no "standard" gas port size like with an AR15.

I plan to install an adjustable gas block on my gun now that I got it running properly. I will be shooting suppressed and I like to dial the gas down.

If your bolt carrier is binding get a BCG that fits. There is no Mil-spec with these guns so there are more fitment issues than you get with AR15 builds. I have Aero uppers in both my builds and use AIM surplus BCGs. One is Nitride and one is NiB. Both BCGs fit the upper with no binding and headspaced properly with my Criterion and No name barrel.

You can remove the bolt from the carrier and then slide the carrier only into the upper to check for binding and if the gas tube fits without effort. Once this is fixed reinstall the bolt and go try it.

To the OP, fix all your binding parts, verify your gas block is lined up properly with the gas port and then go try it. Put one round in the magazine and shoot it, see if the bolt locks back. Do this 5 times to make sure. Then if this works try to shoot a full magazine.

Lastly if you are trying to shoot handloads, set those aside until things work on commercial ammo. Buy 100 rounds of what you plan to shoot regularly and a box of something in .308 with a heavy bullet. If it fails with your standard ammo try the heavy bullet stuff. If it works with that you then have to decide wether to use that ammo or open open the port.

View Quote

edgephoto, you explained very clearly. Did you get a chance to shoot more powerful .308 before you opened up your port to see how the gun run?

My new 308 build is also having short stroke issue, but I did not test with 308 ammo yet.

Posted: 3/28/2017 11:07:04 PM EDT

[#39]

Quote History

Quoted:

edgephoto, you explained very clearly. Did you get a chance to shoot more powerful .308 before you opened up your port to see how the gun run?

My new 308 build is also having short stroke issue, but I did not test with 308 ammo yet.

View Quote

I did try to shoot .308 with a 147gr bullet. It had the same short stroke issue.

After I opened up the gas port it ran good on .308. I only had one box of 20 left. Then I switched to 7.62x51 and it ran on that too.

Ultimately there will be an adjustable gas block on this gun because it will host a suppressor at times. I have an SLR adjustable to install but am thinking about maybe going with the Govna because that is more of a switch. You have a regular and a suppressed port.

Posted: 3/28/2017 11:08:02 PM EDT

[#40]

dupe

Posted: 3/28/2017 11:21:15 PM EDT

[#41]

Quote History

Quoted:

I did try to shoot .308 with a 147gr bullet. It had the same short stroke issue.

After I opened up the gas port it ran good on .308. I only had one box of 20 left. Then I switched to 7.62x51 and it ran on that too.

Ultimately there will be an adjustable gas block on this gun because it will host a suppressor at times. I have an SLR adjustable to install but am thinking about maybe going with the Govna because that is more of a switch. You have a regular and a suppressed port.

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Question: Many seem to suggest an adjustable gas block. What is not clear to me is if one can INCREASE the amount of gas over and above a plain gas tube. Is this possible, or does it merely allow for decreases in gas?

Posted: 3/28/2017 11:24:06 PM EDT

[#42]

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Quoted:
Looks like you're gas tube is too short. It's giving some gas to the key but most is hissing the bolt.

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I don't know... looks correct to me. The gas tube (as in an AR15) should end mid point in the cam pin cutout (which is how it appears in the photo).

Posted: 3/29/2017 12:05:28 AM EDT

[#43]

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Quoted:

I did try to shoot .308 with a 147gr bullet. It had the same short stroke issue.

After I opened up the gas port it ran good on .308. I only had one box of 20 left. Then I switched to 7.62x51 and it ran on that too.

Ultimately there will be an adjustable gas block on this gun because it will host a suppressor at times. I have an SLR adjustable to install but am thinking about maybe going with the Govna because that is more of a switch. You have a regular and a suppressed port.

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Thanks. But it seems strange that you need to open the gas port to above 0.1". You barrel is from quality manufacture and original 0.096" gas port is already not small. Do you notice any abnormal friction inside between BCG and receive and inside the buffer tube? You have A2 stock and did you actually check the spring and buffer weight?

Posted: 3/29/2017 11:18:29 AM EDT

[#44]

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Quoted:

Thanks. But it seems strange that you need to open the gas port to above 0.1". You barrel is from quality manufacture and original 0.096" gas port is already not small. Do you notice any abnormal friction inside between BCG and receive and inside the buffer tube? You have A2 stock and did you actually check the spring and buffer weight?

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No abnormal friction. I removed the bolt and check the carrier for smooth operation and it was. The gas tube alignment was spot on as it fit the key very nice. I checked head space too on this barrel and bolt.

I have another gun that I assembled with a barrel I bought from the EE here as new. No sure of the brand but it does have a Spike's logo on it but I am not sure if that means anything. This gun works like a champ. I put my upper on that lower and the short stroke still happened. I tried the BCG too and same issue. I even used the gas block and tube from the good gun.

So I then opened up the port one step at a time until I got it functioning. The gas port on the 18" rifle length barrel is also .101" and that was factory drilled to that size. Before you say anything about the 18" vs. 20" needing different sized ports take a look at the port dimensions for AR15 barrels with rifle length gas. Both 18" and 20" have the same size. So I am comfortable with the fact my 308 AR barrels are the same size.

My gun works and works well now so it is fixed.

Posted: 3/29/2017 1:03:12 PM EDT

[#45]

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Running it sloppy wet?

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This advice cured my newly built, short stroking Xanthos 6.5 CM.
Thanks man!!

Posted: 3/29/2017 1:50:16 PM EDT

[#46]

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Quoted:

No abnormal friction. I removed the bolt and check the carrier for smooth operation and it was. The gas tube alignment was spot on as it fit the key very nice. I checked head space too on this barrel and bolt.

I have another gun that I assembled with a barrel I bought from the EE here as new. No sure of the brand but it does have a Spike's logo on it but I am not sure if that means anything. This gun works like a champ. I put my upper on that lower and the short stroke still happened. I tried the BCG too and same issue. I even used the gas block and tube from the good gun.

So I then opened up the port one step at a time until I got it functioning. The gas port on the 18" rifle length barrel is also .101" and that was factory drilled to that size. Before you say anything about the 18" vs. 20" needing different sized ports take a look at the port dimensions for AR15 barrels with rifle length gas. Both 18" and 20" have the same size. So I am comfortable with the fact my 308 AR barrels are the same size.

My gun works and works well now so it is fixed.

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Thanks for the details, very clear. My barrel is 18" rifle length barrel Andro brand, made by Basaltic Advantage, the gas port size is between 0.08" to 0.09". I got short stroke (with 147gr 7.62 rounds) but extracting and feeding are fine. I am running on A5 buffer tube with Armalite 1095 buffer spring and AR15 buffer. I will do a few more tests this week to see if I can get it to work with more powerful 308 rounds and weaker spring. If still not working, probably will contact the manufacture (do not think I am able to open up the port by myself).

Posted: 3/29/2017 6:47:41 PM EDT

[#47]

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Quoted:

Question: Many seem to suggest an adjustable gas block. What is not clear to me is if one can INCREASE the amount of gas over and above a plain gas tube. Is this possible, or does it merely allow for decreases in gas?

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Not possible. An adjustable gas block can't MAKE more pressure, only REDUCE what is already there.Only ways to increase pressure are 1) drill gas port hole bigger or 2) use hotter ammo.

Posted: 3/29/2017 7:24:08 PM EDT

[#48]

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Quoted:
Not possible. An adjustable gas block can't MAKE more pressure, only REDUCE what is already there.Only ways to increase pressure are 1) drill gas port hole bigger or 2) use hotter ammo.

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Quoted:

Quoted:

Question: Many seem to suggest an adjustable gas block. What is not clear to me is if one can INCREASE the amount of gas over and above a plain gas tube. Is this possible, or does it merely allow for decreases in gas?

Not possible. An adjustable gas block can't MAKE more pressure, only REDUCE what is already there.Only ways to increase pressure are 1) drill gas port hole bigger or 2) use hotter ammo.

Installing a suppressor will also spike pressure.

Posted: 3/29/2017 8:48:30 PM EDT

[#49]

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Quoted:

Thanks for the details, very clear. My barrel is 18" rifle length barrel Andro brand, made by Basaltic Advantage, the gas port size is between 0.08" to 0.09". I got short stroke (with 147gr 7.62 rounds) but extracting and feeding are fine. I am running on A5 buffer tube with Armalite 1095 buffer spring and AR15 buffer. I will do a few more tests this week to see if I can get it to work with more powerful 308 rounds and weaker spring. If still not working, probably will contact the manufacture (do not think I am able to open up the port by myself).

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Was out shooting with a friend last week. He was shooting a new, factory assembled Aero with a 20" barrel.
He shot it about twenty rounds and started to have this issue as well. We swapped in the buffer and spring from my LMT and it didn't do a lot of good.
Mag change didn't either, however, passing him some of my m118lr did help.

*** forgot to mention, he was using some junk 168gr Americans Eagle that was marked "for m1A use"