Gas tube rattle

[Sgt5811]

Alright fellas, I'd like to hear it from the proverbial M4Carbine collective horses' mouths;

I recently built a 20" Hbar rifle profiled 6.8 Spc DMR and for some damned reason the gas tube is rattling around in the upper receiver that I had laying around. I think the port in the receiver is slightly oversized. Is there a commercially available grommet or bushing that could aleviate the rattle or do I need to get a new receiver?
Before anyone asks, the barrel torque and indexing specs are spot on. Checked and double, triple checked.

[Iraqgunz]

Unless it is interfering with the operation of the weapon (carrier key is striking it wrong) then don't worry about it. Sometimes it happens.


Alright fellas, I'd like to hear it from the proverbial M4Carbine collective horses' mouths;

I recently built a 20" Hbar rifle profiled 6.8 Spc DMR and for some damned reason the gas tube is rattling around in the upper receiver that I had laying around. I think the port in the receiver is slightly oversized. Is there a commercially available grommet or bushing that could aleviate the rattle or do I need to get a new receiver?
Before anyone asks, the barrel torque and indexing specs are spot on. Checked and double, triple checked.

[motorwerks]

maybe bend it just a hair to put a little tension it against the receiver?

[BufordTJustice]

maybe bend it just a hair to put a little tension it against the receiver?

Do NOT do this. This would mis-align the gas tube with the BCG's Gas Key.

As IG said, if the alignment of the gas tube to the gas key is proper, leave it alone and don't worry about it.

If the rattle bothers you, maybe install another gas tube.

[motorwerks]

Do NOT do this. This would mis-align the gas tube with the BCG's Gas Key.

As IG said, if the alignment of the gas tube to the gas key is proper, leave it alone and don't worry about it.

If the rattle bothers you, maybe install another gas tube.

I didn't mean like a 45* angle. I meant like a smudge. It would be fine. Besides the upper should still keep it with in spec.

[Sgt5811]

It bugs the shit out of me. Other than that, no known issues at this point. It has 6 rounds down the barrel for cylic testing. Chambers and extracts just fine. I just hate that sound though. I wonder if I put some felt or something soft around it and stuffed it in the space between the tube and the receiver...?

[mkmckinley]

I didn't mean like a 45* angle. I meant like a smudge. It would be fine. Besides the upper should still keep it with in spec.

What vast well of experience are you using to come up with this advice?

[JR TACTICAL]

I again agreee with gunz on this matter but if it really bothers you, adams arms sells a bushing that goes with their piston system and is required for use with the piston. I dont know the dementions of the bushing and it may not work with a standard gas tube so you might want to call them and get the inner demention and then take a set of callipers and measure it out

Just a suggestion

[Robb Jensen]

I'd pull the gas tube and try another one. Sometimes the rifle length gas tubes are slightly bent. You can gently bend them back as long as you're keeping the proper carrier key/gas tube alignment good and you don't kink the gas tube.

[Quib]

Before anyone asks, the barrel torque and indexing specs are spot on. Checked and double, triple checked.

And that is why the gas tube rattles.....because the alignment of the barrel nut with the upper receiver is perfect and there is nothing to bind against or pin the gas tube to either side of the upper receiver.

The hole in the upper receiver for the gas tube to pass through is a clover leaf design just for that reason. The points of the clover leaf pattern act as fingers or guides, which hold the gas tube in a relative position to the carrier key, but at the same time, allows the gas tube to free float slightly during cycling, which helps with gas tube to carrier key alignment.

[Neo Mara]

I again agreee with gunz on this matter but if it really bothers you, adams arms sells a bushing that goes with their piston system and is required for use with the piston. I dont know the dementions of the bushing and it may not work with a standard gas tube so you might want to call them and get the inner demention and then take a set of callipers and measure it out

Just a suggestion

I was going to sugest this. I put an AA system on a gun and converted it back to DI. You can't get the bushing back out but the old gas tube goes in just fine.

[Surf]

I didn't mean like a 45* angle. I meant like a smudge. It would be fine. Besides the upper should still keep it with in spec."Fitting" a gas tube is one thing, but bending it to keep it from free movement is not a good idea. As mentioned, it is very common for there to be some movement and that movement generally means a very straight alignment. If you put too much bend to pin it against the side of the gas tube hole in the upper, even a "smudge", this can cause a mis-alignment and the bell end of the gas tube can rub on the gas key. Over time this can wear down the bell end of the gas tube which could create a gas leak which can cause function issues. It is one of the more difficult problems to spot or correctly diagnose for your average rifle owner.

[Sgt5811]

Thanks for the info fellas. I came up with an even better solution. I'm gonna trade it for a bolt gun and build another carbine!

[An Undocumented Worker]

I just recieve a new upper and installed a BattleComp 2.0 on it. I had hone/lap the large shim then tighten/loosen it a few times in order to get it to time correctly and never checked the alignment of the Gas tube prior to doing this.

While checking stuff over I removed the bolt from the carrier, and slid the carrier into the reciever. It slides into place under it's own weight at less than a 45 degree angle, but it does lightly rub the gas tube on one side of the key in the process. I am wondering if a minor amount of contact between the gas tube and gas key is normal on a new upper reciever group.

I slid a BCG from my other rifle in there and there was no noticeable contact between the key and the tube, that BCG has somewhere around 3,000 rounds through it.


The reason I'm paying such retarded attention to this, is I am somewhat concerned I may have torqued the barrel in the reciever in the process of installing the Battle Comp. Though it seems unlikely as the FSB does not appear canted. I don't have enough experience with checking these things in new Uppers to know one way or the other, so any input would be appreciated.

Either way I'm taking it to the range tomorrow to sight it in and check overall function of it.

[Belmont31R]

I just recieve a new upper and installed a BattleComp 2.0 on it. I had hone/lap the large shim then tighten/loosen it a few times in order to get it to time correctly and never checked the alignment of the Gas tube prior to doing this.

While checking stuff over I removed the bolt from the carrier, and slid the carrier into the reciever. It slides into place under it's own weight at less than a 45 degree angle, but it does lightly rub the gas tube on one side of the key in the process. I am wondering if a minor amount of contact between the gas tube and gas key is normal on a new upper reciever group.

I slid a BCG from my other rifle in there and there was no noticeable contact between the key and the tube, that BCG has somewhere around 3,000 rounds through it.


The reason I'm paying such retarded attention to this, is I am somewhat concerned I may have torqued the barrel in the reciever in the process of installing the Battle Comp. Though it seems unlikely as the FSB does not appear canted. I don't have enough experience with checking these things in new Uppers to know one way or the other, so any input would be appreciated.

Either way I'm taking it to the range tomorrow to sight it in and check overall function of it.




Did you shoot the gun?

[An Undocumented Worker]

Not yet, although it was test fired by the manufacturer.

[PatrolRifleGroup]

I attended a carbine course in Iowa recently, and couldn't take my duty rifle because it is an SBR. Consequently, I put together a new rifle for the class. BCM Upper, DD LW Mid-Length 14.5" barrel, pinned BC 1.5, and a 13" Troy Rail.

About 1/2 way through the class, I smacked my rail on a piece of cover, while doing a dry drill with bolt locked open. My gas tube rattled like crazy. I double checked everything that night, nothing had worked loose and all the important stuff was tight.

The gun ran flawlessly for the entire 5 days. I shot 300 rounds of brass on the initial break-in and zeroing, followed by 900 rounds of Wolf. I didn't clean it the entire week, just lubed up each morning with Slip 2000. Zero malfunctions. I plan on doing absolutely nothing to fix the rattle.

[Mr. Goodtimes]

My BCM upper's gas tube rattles around a little. It's nothing to worry about.

[An Undocumented Worker]

I just recieve a new upper and installed a BattleComp 2.0 on it. I had hone/lap the large shim then tighten/loosen it a few times in order to get it to time correctly and never checked the alignment of the Gas tube prior to doing this.

While checking stuff over I removed the bolt from the carrier, and slid the carrier into the reciever. It slides into place under it's own weight at less than a 45 degree angle, but it does lightly rub the gas tube on one side of the key in the process. I am wondering if a minor amount of contact between the gas tube and gas key is normal on a new upper reciever group.

I slid a BCG from my other rifle in there and there was no noticeable contact between the key and the tube, that BCG has somewhere around 3,000 rounds through it.





The reason I'm paying such retarded attention to this, is I am somewhat concerned I may have torqued the barrel in the reciever in the process of installing the Battle Comp. Though it seems unlikely as the FSB does not appear canted. I don't have enough experience with checking these things in new Uppers to know one way or the other, so any input would be appreciated.

Either way I'm taking it to the range tomorrow to sight it in and check overall function of it.

Well I took it to the range today and everything functioned perfectly fine. The only failure was a bolt override due to inserting a 20rnd Pmag on a closed bolt. No extraction issues and no signs of the brass being overpressurized, or being extracted while under pressure. Bolt locked back everytime on an empty mag using Federal 55grn .223 walmart valuepack.

The upper is a custom DD 18" midlength S2W barrel with a F marked FSB, DD 12" FSP middy Lite Rail and DD upper & BCG, assembled by DD, and DD a1.5 rear buis.
The lower has a Vltor A5 reciever extension/buffer/spring and Emod stock and a generic RR lower parts kit. (all I could find when I was building the lower last year)
I guess you could say this is my version of an A5 rifle.


Though I still would like to know how normal it is for the carrier key to brush one side of the gas tube (on a new gun) when going into battery, and yes it slides home under it's own weight (excluding the resistance of the gas rings).



Oh and BTW I'm pretty sure I didn't torqued the barrel in the reciever when installing the battle comp because the rear sight only needed 2 clicks to the left off of centerline to zero at 25yrds.

[az doug]

Did it rattle with the bolt closed? Just curious.

[An Undocumented Worker]

Negative, mine doesn't rattle with the bolt open or closed. This thread seemed the most relevant to the questions I have.

[Doc Safari]

And that is why the gas tube rattles.....because the alignment of the barrel nut with the upper receiver is perfect and there is nothing to bind against or pin the gas tube to either side of the upper receiver.

The hole in the upper receiver for the gas tube to pass through is a clover leaf design just for that reason. The points of the clover leaf pattern act as fingers or guides, which hold the gas tube in a relative position to the carrier key, but at the same time, allows the gas tube to free float slightly during cycling, which helps with gas tube to carrier key alignment.

This is exactly what I have come to believe. Sticking only to top-tier quality weapons, my Colts and BCM's all have some play in the gas tube at the receiver--some rifles more than others. I am NOT talking about a gas tube that rattles just from jiggling the whole weapon a little, but if you hold the gas tube between two fingers you can definitely wiggle it at the upper receiver. Here's another thing: Unless I'm horribly mistaken everybody discovers the play in the gas tube with the handguards removed and the handguard spring untensioned. It's my belief that with the handguards in place and the delta ring spring under tension that most of the play in the gas tube goes away.

[MistWolf]

The gas tube is supposed to free float where it goes through the upper receiver. It's supposed to rattle

[Doc Safari]

The gas tube is supposed to free float where it goes through the upper receiver. It's supposed to rattle

Amen. People get all hung up on everything being nice and tight, neglecting to understand that looseness of some components is necessary for them to function properly.

[Iraqgunz]

Was there a particular reason for the resurrection?


This is exactly what I have come to believe. Sticking only to top-tier quality weapons, my Colts and BCM's all have some play in the gas tube at the receiver--some rifles more than others. I am NOT talking about a gas tube that rattles just from jiggling the whole weapon a little, but if you hold the gas tube between two fingers you can definitely wiggle it at the upper receiver. Here's another thing: Unless I'm horribly mistaken everybody discovers the play in the gas tube with the handguards removed and the handguard spring untensioned. It's my belief that with the handguards in place and the delta ring spring under tension that most of the play in the gas tube goes away.

[Doc Safari]

Was there a particular reason for the resurrection?

Just going back and doing some reading on old threads on AR maintenance and whatnot. I've also been watching a lot of Youtube AR videos. I was reading a thread on another forum where a lot of the posts were of the opinion that there was something definitely wrong with the gun if the gas tube wiggles. Then I came here and found this thread. I was really impressed with a couple of the responses. I guess I was just giving a "high five" to them.

Sorry if I shouldn't have done that.