Help: Rust/Damage on exterior of AR Barrel?

[greentips]

You should call LMT and send them pictures, and see what they say. You may run into issue when the weapon becomes very hot or when you are shooting at low temp. Metal expands and contracts, using carbon and dirt as a sealant is not a good solution. Loctite and rocksett are not sealants either.

That brown stuff is probably not rust, most likely dried out preservative oil mixed up with carbon & dirt.

 

[Ar180shooter]

I can guarantee you if it has a perfect seal it "May not" -will not impact functionality. Case in point is far too many builders worry about a gas tube restriction before they even consider the seal or even the alignment between the gas port to gas block. The gas block to barrel is the primary source of pressure to the BCG GK that needs to be taken seriously.

The amount of gas lost from a loose fit as pictured is negligible. If it becomes an issue, you replace the gas block. If you are not having issues with function, then leave it alone.

 

[Sqr]

You should call LMT and send them pictures, and see what they say. You may run into issue when the weapon becomes very hot or when you are shooting at low temp. Metal expands and contracts, using carbon and dirt as a sealant is not a good solution. Loctite and rocksett are not sealants either.
That brown stuff is probably not rust, most likely dried out preservative oil mixed up with carbon & dirt.

Here is an excerpt from the PDFs file for a JP gas block.

"Once secured, coat the barrel with Loctite 609 (green) and install all the set screws using Loctite 271 (red). Securing the gas block with the dog point set screw will ensure that it will not move even when subject to temperatures hot enough to soften the Loctite."

As mentioned it's a normal practice.

 

[John Deer]

Here is an excerpt from the PDFs file for a JP gas block.

"Once secured, coat the barrel with Loctite 609 (green) and install all the set screws using Loctite 271 (red). Securing the gas block with the dog point set screw will ensure that it will not move even when subject to temperatures hot enough to soften the Loctite."

As mentioned it's a normal practice.

X 2 on this. If you can use locktite on a diesel engine I don't see why it wouldn't work for this

 

[Ar180shooter]

Here is an excerpt from the PDFs file for a JP gas block.

"Once secured, coat the barrel with Loctite 609 (green) and install all the set screws using Loctite 271 (red). Securing the gas block with the dog point set screw will ensure that it will not move even when subject to temperatures hot enough to soften the Loctite."

As mentioned it's a normal practice.

That's for an entirely different type of gas block. The one pictured by the OP and used on LMT barrels uses a taper pin.

The loctite use on the type of gas block you describe is so that it does not drift... Gas blocks attached using a taper pin cannot drift as the taper pin is driven through a cutout on the barrel. You seriously need to inform yourself on AR construction.

 

[Sqr]

I repaired my leaking by custom barrelled AR. I guess I will not convince anybody that it's important to ensure there is very minimal to zero leak by to optimize gas performance as it's the single most crucial system on any direct impingement rifle. IMHO I feel it's vital and operate my rifles accordingly.

 

[Ar180shooter]

I repaired my leaking by custom barrelled AR. I guess I will not convince anybody that it's important to ensure there is very minimal to zero leak by to optimize gas performance as it's the single most crucial system on any direct impingement rifle. IMHO I feel it's vital and operate my rifles accordingly.

Were you having reliability issues before the swap?

 

[RobertMcC]

I repaired my leaking by custom barrelled AR. I guess I will not convince anybody that it's important to ensure there is very minimal to zero leak by to optimize gas performance as it's the single most crucial system on any direct impingement rifle. IMHO I feel it's vital and operate my rifles accordingly.

Thanks for joining. For most of us, this ain't our first time at the rodeo. You repaired a problem due to aftermarket parts where there was different measurements and a person that fitted it good enough. I built an AR it took 4 gas blocks to find one that worked. JOYS of aftermarkets. Just because you used thread locker doesn't mean its right.

 

[Suputin]

I repaired my leaking by custom barrelled AR. I guess I will not convince anybody that it's important to ensure there is very minimal to zero leak by to optimize gas performance as it's the single most crucial system on any direct impingement rifle. IMHO I feel it's vital and operate my rifles accordingly.

No its not. As I posted previously the gas system takes in way more gas than it needs and then it shuts off when the carrier moves. Then excess gas is vented out the side of the carrier. A small gas leak at the port or gas block will be insignificant to the overall functioning of the system. I did some experiments with an adjustable gas block and discovered it is possible to greatly alter the gas intake system without compromising the functioning of the rifle. The direct impingement system is quite tolerant of gas volume within some basic parameters.

Clearly the OP's upper functions because it has the carbon buildup to show it has been functioning. Thus the gas leak is relatively minor and should be left alone.

 

[Sqr]

Were you having reliability issues before the swap?

i had an occasional last round failing to lock the bolt back, however this is a delicate wildcat cartridge to hand load and I was eliminating all possible trouble areas. The usual carbine gas system will have enough gas compared to this mid length barrel that is optimized for 1680 powder which I can not get.

 

[RobertMcC]

i had an occasional last round failing to lock the bolt back, however this is a delicate wildcat cartridge to hand load and I was eliminating all possible trouble areas. The usual carbine gas system will have enough gas compared to this mid length barrel that is optimized for 1680 powder which I can not get.

Sounds like a mag issue and not a gas issue.

 

[Sqr]

Thanks for joining. For most of us, this ain't our first time at the rodeo. You repaired a problem due to aftermarket parts where there was different measurements and a person that fitted it good enough. I built an AR it took 4 gas blocks to find one that worked. JOYS of aftermarkets. Just because you used thread locker doesn't mean its right.

I build all of my rifles and painstakingly ensure the fit is bang on, however this high quality ARP .750 barrel and a questionable DPMS block started to leak after only a 1000 rounds.

 

[Sqr]

From one of the best builders in North America at AR Performance.com describing the importance of the gas system.

"................First things first- THE BUILD.
When building seal the gas tube into the gas block(permatex gasket sealer or blue loctite will work). Make sure the gas tube is right side up and pinned properly. Remove the rear set screw of the gas block. Look down through the hole and make sure the gas tube is not obstructing the port in the top of the gas block. If it is drill it out, most will allow a 9/64" bit without damaging the threads at the set screw. When installing the gas block on the barrel use the same sealer to cut down on gas leaks. Place the rear set screw hole over the dimple in the barrel. Tighten the front then install the rear set screw and tighten it. Careful with the loctite the screws are very small and allen wrenches strip easily.
Barrel nut torque 38lbs minimum and 80 max. Be very careful at 80lbs, it could bend the receiver. The receiver vice and receiver will handle 38lbs so it will handle the 15-20ft lbs for the muzzle device. Use YHM or a soft crush washer behind the muzzle device, 15-20lbs max. If the crush washer does not crush before you hit 20lbs throw it away and buy one that will crush as designed. DPMS and Armalite crush washers are usually too hard.

Continue the build. When finished from the rear run a patch with solvent on it through the bore to remove excess oil and any dirt or grit that may have accumulated in the bore during transit and building. Run a dry patch through to remove any excess solvent or oil. Next clean the chamber AFTER cleaning the bore to remove any junk that was splattered into it when cleaning the bore. A 28ga bore mop spun by a drill works well. You can use JB or Iosso bore paste but make sure to clean all of the grit out or the cases may stick.
ETA- The Melonite treated chamber may get sticky when heated up the first time. You can clean the chamber with a good solvent or polish lightly but do not try to remove the black surface or refinish the chamber.

Oil the bolt tail and rings, drop of oil in the hole on the side of the bolt oils the ejector pin. Install in the carrier with the extractor on the right side looking from the rear. Work it back and forth in the carrier a few times. Oil the rails on the carrier.

With a mag in the rifle and no ammo in the mag, pull the charge handle to the rear. Does it lock back by hand?
If not check the follower in the mag to see if it will push the bolt catch up. There have been problems with the "BAD" ambi levers. If the bolt and carrier do not travel rearward enough the buffer or spring could be too long or the screw in the stock could be preventing the buffer from traveling back far enough. Is anything binding when you pull the carrier back and forth by hand? I found a carrier key installed with one side up on the rail of the carrier from the factory.

TESTING- place 1 factory round in the mag, chamber and fire it while holding the stock firm to your shoulder. Does the bolt lock back? If not it is short stroking.
When first testing newly built uppers and rifles always use factory ammo, Hornady 110-120gr. We use 120gr Hornady loads to set the gas port sizes with a standard carbine buffer and spring.
If the rifle shorts strokes when shooting factory ammo start checking things on the rifle. If it locks back on factory ammo but does not with the handloads then there is a problem with the handloads.
DO NOT try to get this barrel to cycle with a low pressure book load producing 42,000psi!!

Short stroking
Be sure the rear set screw of the gas block is in the CENTER of the dimple in the barrel, that is why the dimple is there.
Short stroking could be caused by low powered ammo such as Remington when talking about the 6.8, in the 6.8 it is also common to see short stroking with light bullets 80-90 gr and fast powders using light published loads since many in reloading manuals produce 45-50000 psi. With the 6.8 and the fast rifle powders it burns it is best not to use a H2, H3 or hyd. buffer or aftermarket springs. IF you want to use heavy buffers or springs you will need to drill out the port in the barrel to function with the heavier/stronger parts.

Keep everything lubed up well for the first 200 rounds but, DO NOT put a heavy coat of oil in the chamber or barrel, always run a dry patch through to remove excess oil.

Port sizes for 6.8. If you are able remove the gas block and look at the soot ring(soot left on the barrel by the large hole of the gas block)
It should be completely around the gas port in the barrel. if it is not make witness marks with a sharpie to the rear of the port and align the gas block with it. While you have the gas block off check to see if the gas port in the barrel is clear, sometimes when they are drilled a small flap of metal is left hanging and when the first bullet passes it shoves it back into the port. On Mid length 6.8 systems using a car stock and buffer the port should be .076"-.078"(5/64) in diameter, rifle should be .093-.096. You can slide a 5/64" drill bit in a mid length to check and 3/32" in a rifle length to check. If you are building using an A2 rifle stock and buffer you will need to open the port up apx .004". Some new light bullet loads are even slower than before, those and Remington need a larger port to function. You can drill them out .004-.006" larger just be careful not to ding the barrel on the far side of the bore. IMO you should not drill ports or do anything else that is not reversible as a first attempt as finding a cure. If you have an adjustable gas block drilling the port out a little larger isn't a big problem, just adjust it back down to obtain a 3-4 Oclock ejection.


If you are using handloads be sure your size die is squeezing the base down to .417-.420. Most chambers are .422 in dia at the base, some dies size to .422 and a semi-auto needs at least .002 clearance to chamber and needs .004" to be reliable when hot and dirty.

If the rifle in question is older the gas tube could be clogged, remove the gas block and tube assembly from the rifle and try spraying brake cleaner through the tube to remove powder residue. Be sure the gas tube is right side up.

Make sure the gap in the gas rings on the bolt do not line up.
.078=5/64
.082"=#45 wire size bit
.086=#44
.093=3/32
.096=#41

The chamber hardness will prevent anyone from removing any machining marks with a bore paste. Bore paste will remove the black and shine or make the surfaces sllicker but anything short of sandpaper run at 2000rpms for a few minutes will not remove any machining marks or grooves.

To test accuracy- Load 28.5-28.6gr AA2200 behind the Hornady 110gr HPBT to 2.258- 2.26" then see below. The factory Hornady 110gr HPBT load is very accurate in a ARP chamber with a .085 freebore but it may need to be loaded .015-.060 longer to be as accurate in a SPCII chamber.
oooooooooooooooo.................................. ...................

This forum editing software is screwed up and can't count........................

eeeeeeeeeeee lousy forum software.................
............................

 

[-[Crosshair]-]

green loctite

If you want to cement it there forever use the green... For everything firearms related I use blue loctite or at worst the red one so it never comes loose without heating it work a small torch. [/armourer]

 

[RobertMcC]

From one of the best builders in North America describing the importance of the gas system.

"................First things first- THE BUILD.
When building seal the gas tube into the gas block(permatex gasket sealer or blue loctite will work). Make sure the gas tube is right side up and pinned properly. Remove the rear set screw of the gas block. Look down through the hole and make sure the gas tube is not obstructing the port in the top of the gas block. If it is drill it out, most will allow a 9/64" bit without damaging the threads at the set screw. When installing the gas block on the barrel use the same sealer to cut down on gas leaks. Place the rear set screw hole over the dimple in the barrel. Tighten the front then install the rear set screw and tighten it. Careful with the loctite the screws are very small and allen wrenches strip easily.
Barrel nut torque 38lbs minimum and 80 max. Be very careful at 80lbs, it could bend the receiver. The receiver vice and receiver will handle 38lbs so it will handle the 15-20ft lbs for the muzzle device. Use YHM or a soft crush washer behind the muzzle device, 15-20lbs max. If the crush washer does not crush before you hit 20lbs throw it away and buy one that will crush as designed. DPMS and Armalite crush washers are usually too hard.

Continue the build. When finished from the rear run a patch with solvent on it through the bore to remove excess oil and any dirt or grit that may have accumulated in the bore during transit and building. Run a dry patch through to remove any excess solvent or oil. Next clean the chamber AFTER cleaning the bore to remove any junk that was splattered into it when cleaning the bore. A 28ga bore mop spun by a drill works well. You can use JB or Iosso bore paste but make sure to clean all of the grit out or the cases may stick.
ETA- The Melonite treated chamber may get sticky when heated up the first time. You can clean the chamber with a good solvent or polish lightly but do not try to remove the black surface or refinish the chamber.

Oil the bolt tail and rings, drop of oil in the hole on the side of the bolt oils the ejector pin. Install in the carrier with the extractor on the right side looking from the rear. Work it back and forth in the carrier a few times. Oil the rails on the carrier.

With a mag in the rifle and no ammo in the mag, pull the charge handle to the rear. Does it lock back by hand?
If not check the follower in the mag to see if it will push the bolt catch up. There have been problems with the "BAD" ambi levers. If the bolt and carrier do not travel rearward enough the buffer or spring could be too long or the screw in the stock could be preventing the buffer from traveling back far enough. Is anything binding when you pull the carrier back and forth by hand? I found a carrier key installed with one side up on the rail of the carrier from the factory.

TESTING- place 1 factory round in the mag, chamber and fire it while holding the stock firm to your shoulder. Does the bolt lock back? If not it is short stroking.
When first testing newly built uppers and rifles always use factory ammo, Hornady 110-120gr. We use 120gr Hornady loads to set the gas port sizes with a standard carbine buffer and spring.
If the rifle shorts strokes when shooting factory ammo start checking things on the rifle. If it locks back on factory ammo but does not with the handloads then there is a problem with the handloads.
DO NOT try to get this barrel to cycle with a low pressure book load producing 42,000psi!!

Short stroking
Be sure the rear set screw of the gas block is in the CENTER of the dimple in the barrel, that is why the dimple is there.
Short stroking could be caused by low powered ammo such as Remington when talking about the 6.8, in the 6.8 it is also common to see short stroking with light bullets 80-90 gr and fast powders using light published loads since many in reloading manuals produce 45-50000 psi. With the 6.8 and the fast rifle powders it burns it is best not to use a H2, H3 or hyd. buffer or aftermarket springs. IF you want to use heavy buffers or springs you will need to drill out the port in the barrel to function with the heavier/stronger parts.

Keep everything lubed up well for the first 200 rounds but, DO NOT put a heavy coat of oil in the chamber or barrel, always run a dry patch through to remove excess oil.

Port sizes for 6.8. If you are able remove the gas block and look at the soot ring(soot left on the barrel by the large hole of the gas block)
It should be completely around the gas port in the barrel. if it is not make witness marks with a sharpie to the rear of the port and align the gas block with it. While you have the gas block off check to see if the gas port in the barrel is clear, sometimes when they are drilled a small flap of metal is left hanging and when the first bullet passes it shoves it back into the port. On Mid length 6.8 systems using a car stock and buffer the port should be .076"-.078"(5/64) in diameter, rifle should be .093-.096. You can slide a 5/64" drill bit in a mid length to check and 3/32" in a rifle length to check. If you are building using an A2 rifle stock and buffer you will need to open the port up apx .004". Some new light bullet loads are even slower than before, those and Remington need a larger port to function. You can drill them out .004-.006" larger just be careful not to ding the barrel on the far side of the bore. IMO you should not drill ports or do anything else that is not reversible as a first attempt as finding a cure. If you have an adjustable gas block drilling the port out a little larger isn't a big problem, just adjust it back down to obtain a 3-4 Oclock ejection.


If you are using handloads be sure your size die is squeezing the base down to .417-.420. Most chambers are .422 in dia at the base, some dies size to .422 and a semi-auto needs at least .002 clearance to chamber and needs .004" to be reliable when hot and dirty.

If the rifle in question is older the gas tube could be clogged, remove the gas block and tube assembly from the rifle and try spraying brake cleaner through the tube to remove powder residue. Be sure the gas tube is right side up.

Make sure the gap in the gas rings on the bolt do not line up.
.078=5/64
.082"=#45 wire size bit
.086=#44
.093=3/32
.096=#41

The chamber hardness will prevent anyone from removing any machining marks with a bore paste. Bore paste will remove the black and shine or make the surfaces sllicker but anything short of sandpaper run at 2000rpms for a few minutes will not remove any machining marks or grooves.

To test accuracy- Load 28.5-28.6gr AA2200 behind the Hornady 110gr HPBT to 2.258- 2.26" then see below. The factory Hornady 110gr HPBT load is very accurate in a ARP chamber with a .085 freebore but it may need to be loaded .015-.060 longer to be as accurate in a SPCII chamber.
oooooooooooooooo.................................. ...................

This forum editing software is screwed up and can't count........................

eeeeeeeeeeee lousy forum software.................
............................

Come back when you built more then 1 AR. You goop up a gas system to fix something that shouldn't be needed. Your the only one that pushing to use green loctite. And your the only one that said to use it. Nobody agreed with you yet ( use of the sealant and the importance of the gas system )

Many of us here built over a dozen ARs and shot 100000s of rounds thru them. You can post articles, doesn't make one an expert.

 

[Trinimon]

I was recommending Rocksett as a thread locker not as a sealant. I wouldn't want to use a sealant to stop a leaky gas block. To me, that's like using duct tape to patch a leaky water hose. I'd just buy a different gas block that can mechanically seal the gas than rely on a sealant.

 

[Sqr]

Come back when you built more then 1 AR. You goop up a gas system to fix something that shouldn't be needed. Your the only one that pushing to use green loctite. And your the only one that said to use it. Nobody agreed with you yet ( use of the sealant and the importance of the gas system )

Many of us here built over a dozen ARs and shot 100000s of rounds thru them. You can post articles, doesn't make one an expert.

I guess your manhood is also bigger.

 

[Sinasta]

I was recommending Rocksett as a thread locker not as a sealant. I wouldn't want to use a sealant to stop a leaky gas block. To me, that's like using duct tape to patch a leaky water hose. I'd just buy a different gas block that can mechanically seal the gas than rely on a sealant.

Doesnt KAC use rocksett for their gasblocks?

 

[RobertMcC]

Doesnt KAC use rocksett for their gasblocks?

They don't want it to come off. Apparently they put that #### on every wheres ( even barrel nut ) and their gas blocks are hydraulic press fit on. So being needing a press. There's a tight fit to begin with.

 

[mikethebike]

They don't want it to come off. Apparently they put that #### on every wheres ( even barrel nut ) and their gas blocks are hydraulic press fit on. So being needing a press. There's a tight fit to begin with.

Aside from this post, ive never ever seen a gas block come off on its own through normal wear and tear. But I dont jump from helicopters and run around in the sand, so...

Do they really come off on their own?
If so isnt that a major design flaw?
Must be a reason why KAC puts that shiat in it!