Blow Back Ar-15

clandestine · Jan 7, 2019

Magnumite said:
I thought the longer gas system actually reduced gas problems. I used a rifle length upper with full skirt carrier (M16) on a standard carbine lower and it wouldn't cycle. A short skirt carrier did stop the lack of cycling but it cycled softer.

I guess the midlength is just enough to still cause issues. Learn something new every day.

IMO, an 18" should have a rifle gas system to soften things out. Mid gas on an 18" barrel has a lot of dwell time.

andy41567 · Jan 7, 2019

clandestine said:
Ejection pattern is not a reliable indication of gassing.

Overgassed is a common problem with most AR's.

It may need to be inspected to determine what's going on.

Is the Gas Key impacting the lower receiver? That will cause harsh recoil.

You can adjust at the Gas Block (BRT Gas Block Port Restrictor, BRT Restricted Port Gas Tube, or a SLR adjustable Gas Block), or you can adjust on the back end (Buffer, Buffer Spring).

Adjustable Gas Keys and Bolt Carriers are not worth using.

Just the man I wanted to here from. Not that I did not care about the rest of you. I did take this apart to look it all over based on all ur comments. I just was not able to shoot it to test it any more in the house. Lol. I probably would of had to sleep some where else that had bars on the windows.

Any how... I have a BCM buffer tube on this gun with the stock spring and buffer that comes with it. I did check the BCG per ur video to make sure the gas key was not hitting the tube. I had plenty of clearance. The pic below just shows the gun with the problem on top and gun without on bottom. All I was doing was pulling trigger as fast as I could but I think you can see that shots are spread out a lot more on top (gun with problem). If that even helps or is even a valid test.
Thing is no matter hom much I have changed this gun around it has always felt "over gassed". I have a colt h3 coming which I will try first. And then the adjustable gas block I guess would be the next thing for your recommendation right.

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danb · Jan 7, 2019

Magnumite said:
I thought the longer gas system actually reduced gas problems. I used a rifle length upper with full skirt carrier (M16) on a standard carbine lower and it wouldn't cycle. A short skirt carrier did stop the lack of cycling but it cycled softer.

I guess the midlength is just enough to still cause issues. Learn something new every day.

Well, but you seem to have a carbine buffer in a mid-length gas upper. The recoil spring and buffer provide inertia against the gas pressure. Mid and rifle length gas have lower gas pressure, which usually means less wear and tear and a smoother recoil (trade off is lower cycling rate but you are not running full auto). However, if you have too light a buffer or spring, it can negate all of that because there is not enough force on the bolt.

holesonpaper · Jan 7, 2019

Not to add insult to injury but several years ago in clandestines class, me noted the overgassing being a common theme on DI AR's (some under as well but). Since that time, I've converted all my AR's but if you pay attention to the clicks (closing the gas coming back to the BCG) and inspect the location of the restriction in the block before installing, most reliably cycle with less. When you run suppressors, this becomes more pronounced. To each their own, but for me I tweak my gas block giving it slightly more than I need for my lightest load unsuppressed. I used to get all that block back in my face (again a lefty) and since paying attention in a SOTAR class and playing afterwards, I'm a happy camper. I haven't had this concern in several years...

DaemonAssassin · Jan 7, 2019

clandestine said:
IMO, an 18" should have a rifle gas system to soften things out. Mid gas on an 18" barrel has a lot of dwell time.

I don't mean to side track the class here, but I have a question about that statement. Does the same apply to a 18" 308 barrel?

andy41567 · Jan 7, 2019

OK so if we are thinking that I am over gased and I can not change the barrel because I of course would have to buy a new one with a rifle length port... Can get a longer gas tube... I remember seeing ones that had a Corkscrew in them. But was not sure what they were for. I mean does having a longer tube change anything.

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holesonpaper · Jan 7, 2019

andy41567 said:
OK so if we are thinking that I am over gased and I can not change the barrel because I of course would have to buy a new one with a rifle length port... Can get a longer gas tube... I remember seeing ones that had a Corkscrew in them. But was not sure what they were for. I mean does having a longer tube change anything.

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Adjustable gas block... Clandestine usually recommends the SLR and that's worked fine for lots of us.. There's other ways but most are gimmicks.

clandestine · Jan 7, 2019

andy41567 said:
Just the man I wanted to here from. Not that I did not care about the rest of you. I did take this apart to look it all over based on all ur comments. I just was not able to shoot it to test it any more in the house. Lol. I probably would of had to sleep some where else that had bars on the windows.

Any how... I have a BCM buffer tube on this gun with the stock spring and buffer that comes with it. I did check the BCG per ur video to make sure the gas key was not hitting the tube. I had plenty of clearance. The pic below just shows the gun with the problem on top and gun without on bottom. All I was doing was pulling trigger as fast as I could but I think you can see that shots are spread out a lot more on top (gun with problem). If that even helps or is even a valid test.
Thing is no matter hom much I have changed this gun around it has always felt "over gassed". I have a colt h3 coming which I will try first. And then the adjustable gas block I guess would be the next thing for your recommendation right.

Sent from my SM-G965U using Tapatalk

Based on an internet diagnosis (not accurate), I think it is likely overgassed. A new barrel is the only option if you don't want adjustable gas or a restricted gas block/gas tube.

The problem with a restricted gas block/tube is there is no one port size that can run everything on the civilian market. An adjustable gas block will give you great adjustment range BUT it adds another failure point. You have to maintain the gas block (add oil after shooting and cycle the adjuster).

If you are shooting military spec ammo a smaller port or gas tube will work great but it won't cycle weaker port pressure ammo like the steel cased stuff.

An adjustable gas block will allow almost any ammo to cycle if you have a large enough port in the barrel and spend time learning what ammo has what adjustment.

As far as the groups go, if you are shooting fast, an overgassed gun will sometimes print larger groups due to the barrel heating up, or the overgassed causing more barrel whip.

It's also possible the barrel is not a thermal fit/bedded in the upper which can allow it to shift when it heats up.

I also noticed you have kns pins in that gun. It can cause inconsistent groups depending on the lock time which can cause larger groups.

holesonpaper said:
Not to add insult to injury but several years ago in clandestines class, me noted the overgassing being a common theme on DI AR's (some under as well but). Since that time, I've converted all my AR's but if you pay attention to the clicks (closing the gas coming back to the BCG) and inspect the location of the restriction in the block before installing, most reliably cycle with less. When you run suppressors, this becomes more pronounced. To each their own, but for me I tweak my gas block giving it slightly more than I need for my lightest load unsuppressed. I used to get all that block back in my face (again a lefty) and since paying attention in a SOTAR class and playing afterwards, I'm a happy camper. I haven't had this concern in several years...

Thanks for the kind words.

DaemonAssassin said:
I don't mean to side track the class here, but I have a question about that statement. Does the same apply to a 18" 308 barrel?

Indeed.

andy41567 said:
OK so if we are thinking that I am over gased and I can not change the barrel because I of course would have to buy a new one with a rifle length port... Can get a longer gas tube... I remember seeing ones that had a Corkscrew in them. But was not sure what they were for. I mean does having a longer tube change anything.

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holesonpaper said:
Adjustable gas block... Clandestine usually recommends the SLR and that's worked fine for lots of us.. There's other ways but most are gimmicks.

Holesonpaper is correct. SLR is the best adjustable if you go that route.

The pigtail gas tube is not a great option. The do delay unlocking more but don't reduce the gas flow. They can also go offtrack as they heat up causing gas tube alignment issues.

holesonpaper · Jan 7, 2019

Just playing devils advocate for a second. If I'm a barrel manufacturer and I want to deliver a barrel to the masses that doesn't need to be modified - you really want something slightly over gassed. What that slightly is - more gas than necessary to properly cycle your BCG. But if wide open and your gun doesn't cycle (under normal loads - say 55-62 grain 5.56), then ultimately folks will complain and you'll receive poor reviews (the way the world works). Certain manufacturers might tailor the gas system for a specific setup but when you don't have all the factors and you want reliability (or the notion of), more is better than less. Then throw a suppressor on the host, jump to a low mass carrier, or a heavier buffer and the amount of gas necessary changes.

My point is - just in principal alone, reasonable over gassing is fairly common for a reason. Many/most don't realize or care. The ones of us who are lefties that enjoy the crap in our faces, care a bit more. This over gassing is why there's tons of solutions in the market.

Ok.. now back to work..... Just follow Clandestine's direction and you'll be good...

andy41567 · Jan 7, 2019

clandestine said:
Based on an internet diagnosis (not accurate), I think it is likely overgassed. A new barrel is the only option if you don't want adjustable gas or a restricted gas block/gas tube.

The problem with a restricted gas block/tube is there is no one port size that can run everything on the civilian market. An adjustable gas block will give you great adjustment range BUT it adds another failure point. You have to maintain the gas block (add oil after shooting and cycle the adjuster).

If you are shooting military spec ammo a smaller port or gas tube will work great but it won't cycle weaker port pressure ammo like the steel cased stuff.

An adjustable gas block will allow almost any ammo to cycle if you have a large enough port in the barrel and spend time learning what ammo has what adjustment.

As far as the groups go, if you are shooting fast, an overgassed gun will sometimes print larger groups due to the barrel heating up, or the overgassed causing more barrel whip.

It's also possible the barrel is not a thermal fit/bedded in the upper which can allow it to shift when it heats up.

I also noticed you have kns pins in that gun. It can cause inconsistent groups depending on the lock time which can cause larger groups.

Thanks for the kind words.

Indeed.

Holesonpaper is correct. SLR is the best adjustable if you go that route.

The pigtail gas tube is not a great option. The do delay unlocking more but don't reduce the gas flow. They can also go offtrack as they heat up causing gas tube alignment issues.

OK perfect. I think i know what to do now. I will try the H3 buffer first and see what that does.

Yes that was the first time shooting that gun with that new barrel. Again I am assuming the gunsmith did the head spacing check but I am unsure. He did on my last gun. I have a message out to him but did not hear back yet. I did oder my own go no go gauges to check it myself. Just cause that could still be a problem to right.

I did put about 200 rounds through the gun before that target. Yet that still might not have been enough to heat everything up to seat everything.

If H3 doesn't help then I guess I will go to the rifle length gas system with another new barrel!

As for the KNS pins... I have the rise box trigger in that gun. When I got the new GS2... I put that in my kick ass gun and put the rise in this gun instead of throwing it away cause this gun was going to be mostly a paper puncher and or a longer distance gun based on my skill and ability. So I would not depend on this gun for my life. So I switched the KNS pins over to this gun. And put all the good stuff to the G2S in the other gun.

So am I on the right track. I am not to interested in the gas block and trying to figure out what ammunition uses what pressure and so on. I just want to pop ammo in and shoot.

But since I have noticed this problem from day one... When it was a carbine setup and making the changes I did... I basically did not really change anything... When I went from a 16" barrel with carbine gas setup to 18" barrel mid-length gas system... I did not make the problem better... I just now had a longer barrel with loner gas system... Some same problem on a bigger scale. Right

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clandestine · Jan 7, 2019

andy41567 said:
OK perfect. I think i know what to do now. I will try the H3 buffer first and see what that does.

Yes that was the first time shooting that gun with that new barrel. Again I am assuming the gunsmith did the head spacing check but I am unsure. He did on my last gun. I have a message out to him but did not hear back yet. I did oder my own go no go gauges to check it myself. Just cause that could still be a problem to right.

I did put about 200 rounds through the gun before that target. Yet that still might not have been enough to heat everything up to seat everything.

If H3 doesn't help then I guess I will go to the rifle length gas system with another new barrel!

As for the KNS pins... I have the rise box trigger in that gun. When I got the new GS2... I put that in my kick ass gun and put the rise in this gun instead of throwing it away cause this gun was going to be mostly a paper puncher and or a longer distance gun based on my skill and ability. So I would not depend on this gun for my life. So I switched the KNS pins over to this gun. And put all the good stuff to the G2S in the other gun.

So am I on the right track. I am not to interested in the gas block and trying to figure out what ammunition uses what pressure and so on. I just want to pop ammo in and shoot.

But since I have noticed this problem from day one... When it was a carbine setup and making the changes I did... I basically did not really change anything... When I went from a 16" barrel with carbine gas setup to 18" barrel mid-length gas system... I did not make the problem better... I just now had a longer barrel with loner gas system... Some same problem on a bigger scale. Right

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The BRT Tube Gas Tube would be the easiest swap for you. They can likely give you a recommendation on the size to select.

Most Gunsmiths don't have or use the proper gauges on .223/5.56 AR's.

May I ask what gauges you ordered?

Forster/Brownells is the only one who sells the proper ones.

The specs are as follows:

.223 GO 1.4636
5.56 GO 1.4646
.223 and 5.56 can use the same Field Gauge. That's a Colt II in 1.4736

No-Go is not needed.

andy41567 · Jan 7, 2019

Brownells was sold out. So I ordered from Pacific Tool Company I hot both the go and no go for. 223 I did not know if I need the field gauge so I did not order one. Both my barrels are. 223 WYLDEs
But yes the specs are the same as what you listed.

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clandestine · Jan 7, 2019

andy41567 said:
Brownells was sold out. So I ordered from Pacific Tool Company I hot both the go and no go for. 223 I did not know if I need the field gauge so I did not order one. Both my barrels are. 223 WYLDEs
But yes the specs are the same as what you listed.

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For Wylde use the 1.4646 for the GO Headspace check.

andy41567 · Jan 7, 2019

I can't find a 1.4646

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clandestine · Jan 7, 2019

andy41567 said:
I can't find a 1.4646

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I believe only Forester makes it. The funny thing is Forester and most other gauge manufacturers mark the gauges improperly.

The .14636 GO by Forster and other Manufacturers are often labeled 5.56 GO or NATO GO.

The 1.4646 Forster gauge is marked .223 GO.

It's backwards!

The proper 5.56 or Wylde GO Is called the 1.4646 SPECIAL PURPOSE Gauge.

This is it through brownells:
Part # 100-010-713MB
5.56mm Colt Spec Go Gauge

andy41567 · Jan 7, 2019

Yes that is exactly what I was finding. A lot of people were saying that the gauges say the gun is a no go but yet in there other guns they have been firing for ever that are known good would fail as well. So i guess I need to pay close attention to that.

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Magnumite · Jan 7, 2019

danb said:
Well, but you seem to have a carbine buffer in a mid-length gas upper. The recoil spring and buffer provide inertia against the gas pressure. Mid and rifle length gas have lower gas pressure, which usually means less wear and tear and a smoother recoil (trade off is lower cycling rate but you are not running full auto). However, if you have too light a buffer or spring, it can negate all of that because there is not enough force on the bolt.

Thank you for the responses. I understand the quoted points which was why I was surprised about is the middie gas system with the 18" barrel causing what John from MD stated. Clandestine indicated the longer dwell time was the reason. So I am assuming the longer dwell time referred to length of barrel after the port the bullet must pass through. Dwell time before the port is longer than the carbine (2") so it allows more time for the pressure to blow down (unless the load still develops substantial pressures and gas volume at that distance).

I poked around and found this out. I think I may be starting to understand this arm a little more. Or maybe I'm sniffing mustard gas.
-The carbine gas system on a 16" barrel has 9" of barrel after the port.
-The middie gas system on an 18" barrel has 9" of barrel after the port. OP's set up. So the effects using the after port dwell time would seem similar
to or a little less with very similar character to that of the 16" carbine.
-The middie gas system on a 16" barrel has 7" of barrel after the port. I have one of these waiting to be tried...the wait may be over to try it.
-The rifle gas system with a 20" barrel has 8" of barrel after the port but 70% more distance for the gas pressure and volume to blow down.
-The rifle length system with an 18" barrel would have 6" of barrel after the port, a 25% decrease in after port dwell time.

andy41567 · Jan 7, 2019

Yep just as I thought. I just basically recreated the same problem with lo ger parts.

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clandestine · Jan 7, 2019

Mid gas will have a softer impulse than carbine gas unless the mid has is grossly over ported. The pressure is much lower at the mid gas port than carbine gas.

Lots of dwell time just amplifies an overgassed port.

Magnumite · Jan 7, 2019

Ah, I get it just a little more. Thanks.

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