Can carbon sealing gas block leaks make ARs over gassed?

[riffraff]

I put an adjustable gas block on an AR today, kinda a 1st go messing with this stuff.

The rifle had been perfect for 2000 rounds then somewhere later exhibited signs of over gassing causing FTE, completely resolved by heavier buffer and spring. A better fix I think is to address the gassing so going the AGB route...

I thought what probably triggered the onset was erosion of the gas port, an explanation that is common, but unquestionably it looks factory machined perfect. However my gas tube is really well carboned a couple inches up anyway, and hopelessly stuck to the original block and that got me thinking. Is it possible sometimes we start with leaky gas blocks/tubes that later seal off and increase gas flow to the BCG?

[ms6852]

Not trying to be coy or a wiseguy but I would really like to know what the benefit of using an adjustable gas block be over a regular one? It seems that the regular ones work well and are proven and I am just an old dog trying to learn some new stuff. Thank you for your response.

[44 AMP]

The advantages of an adjustable gas block is that #1, it gives people something to play with.
#2) it possibly allows you to tune the rifle to function if you are shooting ammo outside the normal range, or your rifle is outside the standard parameters.

Some weapons have an adjustable gas system to allow for different ammo levels without needing to replace parts. Others have an adjustable system so the amount of gas can be increased to compensate for a highly crudded up system. The intent is not to run the system wide open but to have a little more "push" available if you are in a combat situation and your weapon starts choking from fouling and you can't take the time to clean it.

having no idea what kind of tolerances exist in your gas system, it is quite possible some leakage is intentional.

If your system was running correctly (and leaked a bit, that you didn't notice) and then carbon build up sealed the leaks, and now there's too much gas, why not just CLEAN IT? and see if that returns it to its previous operating condition??

Makes me wonder if you've replaced buffer and spring and now gas block when a good soak and flush might have returned your rifle to running the way it was...

[Mobuck]

However my gas tube is really well carboned a couple inches up anyway, and hopelessly stuck to the original block and that got me thinking.

Obviously some leakage going on. I have carbines that have been used for years w/o showing such carbon fouling. Had you noticed it blowing gas previously? I see this often when the utoobers are doing "destructive testing". The barrel droops and gas starts exiting the handguard.

[ms6852]

@44 AMP, thanks for the response to my inquiry.

[Metal god]

completely resolved by heavier buffer and spring. A better fix I think is to address the gassing so going the AGB route...

I'm with 44 and Mobuck and will add that if you go with an adjustable gas block you should also go back to the original buffer and spring . If you don't then there's no need for the adjustable gas block then is there if the rifle is working fine with the heavier buffer etc .

?

[riffraff]

Thanks for that guys!

As far as MS's question, I dont understand why so many AR10 variants come over gassed out of the box or get that way but but if you go looking around its real common. One result is they fail to eject, things are just moving too fast. Could be the range of ammo out there and the fact that the stuff many of us run the most of is at the top end as far as velocity.

As far as what I did, seemed silly to have all the extra power that requires the heavy spring/buffer to tame when you can just dial back the power in the first place. I did go back to a new stock spring and original buffer in this process.

It worked phenomenally, 10 shots in I had adjusted a real smooth 3 oclock eject. Someone wanted feedback on the AGB I was using, will post more on that later. I was really just wanting feedback on the gas leak thing.

[riffraff]

Originally Posted by Mobuck

However my gas tube is really well carboned a couple inches up anyway, and hopelessly stuck to the original block and that got me thinking.

Obviously some leakage going on. I have carbines that have been used for years w/o showing such carbon fouling. Had you noticed it blowing gas previously? I see this often when the utoobers are doing "destructive testing". The barrel droops and gas starts exiting the handguard.

I never noticed it but based on the amount given my round count it was a small leak. This rifle might have seen 3000 rounds in that configuration.

[Fishbed77]

I dont understand why so many AR10 variants come over gassed out of the box

Because manufacturers want the rifle to cycle with as wide a variety of ammo as possible, and don't want to deal with warranty returns from customers complaining that their rifle won't cycle such-and-such ammo.

[44 AMP]

I dont understand why so many AR10 variants come over gassed out of the box

Could be the range of ammo out there and the fact that the stuff many of us run the most of is at the top end as far as velocity.

Could be that the guns are designed to shoot 7.62x51mm NATO, which is NOT the same loading as .308 Winchester.

GI 7.62NATO was designed to replicate USGI .30-06, a 150gr @ 2750fps +/-

Look at .308 specs and see the difference. Shoot ammo in the 28-2900fps range in a rifle built to run lower ammo and it will seem "over gassed".

You can see the same thing shooting commercial sporting .30-06 ammo in an M1 Garand. The civilian sporting ammo is simply hotter than the rifle was built for.

[Metal god]

Could be that the guns are designed to shoot 7.62x51mm NATO,

No I don't think so . first the 7.62x51 is not as hot as the 308 Winchester . It's been my understanding that it's the opposite of 223 vs 5.56 . You don't want to shoot 308 out of a 7.62x51 stamped barrel .

Yes the "AR-10" may have been originally intended for military use but the commercial variants were/are not . Also the design is well suited to adjusting the gas system in many ways like gas port size , buffer weights , spring tension , dwell time etc etc . where as the M1 garand was not .

[Bartholomew Roberts]

Originally Posted by riffraff

I thought what probably triggered the onset was erosion of the gas port, an explanation that is common, but unquestionably it looks factory machined perfect.

On the barrel exterior or from inside the bore? If you look at an eroded gas port by removing the gas block and looking at the exterior of the port, you won’t notice much. You need a borescope to see gas port erosion from inside the bore.

[riffraff]

Originally Posted by Metal god

No I don't think so . first the 7.62x51 is not as hot as the 308 Winchester . It's been my understanding that it's the opposite of 223 vs 5.56 . You don't want to shoot 308 out of a 7.62x51 stamped barrel .

Yes the "AR-10" may have been originally intended for military use but the commercial variants were/are not . Also the design is well suited to adjusting the gas system in many ways like gas port size , buffer weights , spring tension , dwell time etc etc . where as the M1 garand was not .

Well Id actually say his logic is correct - design it for 7.62 nato then run .308 and my understanding is you are increasing the gas - correct?

As far as "military" versus "commercial" - I sorta agree as far as if you got a model designed to run in full auto mode that the military actually buys you really ought to be tuning in the formula better during rigorous quality control. But then it begs the question what really makes the difference in design, as even AR10 variants are basically all nearly the same - doesn't mean its a pattern where you can swap parts all willy nilly just saying nothing ground breaking is going on with this half century old design that the commercial market shouldn't have picked up..

Could it just be ammo? Military standardizes it while civilians run everything under the sun so its impossible to really sell a model tuned right for everyone?

[riffraff]

Originally Posted by Bartholomew Roberts

On the barrel exterior or from inside the bore? If you look at an eroded gas port by removing the gas block and looking at the exterior of the port, you won’t notice much. You need a borescope to see gas port erosion from inside the bore.

Yes exterior, but I guess if its a straight hole and the diameter at the exterior stays the same, I dont see how a bevel from erosion inside plays a role? As in a bottle neck at stock diameter still exists.

[Bartholomew Roberts]

This thread describes the physics of it (read the posts by lysander), as well as why an adjustable gas port can increase port erosion. It also has some nice pics (both from exterior and interior views). https://www.ar15.com/forums/AR-15/-A...687750/?page=1

The short version is a straight hole lets less gas through due to turbulence. Erosion makes it more like a jet nozzle.

[Ricklin]

I've done a lot of pneumatic engineering, I can assure that the shape of the port will change the flow characteristics. I'l be the first to admit my experience @ around 100 PSI may not be directly applicable, it does make a difference.

[riffraff]

Cool, thanks for that guys. So maybe I have errosion in there that did speed things up.

[44 AMP]

Also the design is well suited to adjusting the gas system in many ways like gas port size , buffer weights , spring tension , dwell time etc etc . where as the M1 garand was not .

Being the nitpiker I am, I disagree with the use of the word "adjustment" in this case. Replacing original parts with new parts with slightly different specs is NOT adjustment, it is modification.

Once you have modified the gun with adjustable parts, changing settings on those parts is an adjustment, but installing them is a modification.

The standard gas system of an AR is not adjustable. If you put an adjustable gas block on it, you have modified it, not adjusted it. If you replace buffers or springs with heavier weights its a modification, not an adjustment.

you are doing it in order to adjust the performance of the system to the desired result, but you are modifying the gun to do so.

[Metal god]

Being the nitpiker I am, I disagree with the use of the word "adjustment" in this case. Replacing original parts with new parts with slightly different specs is NOT adjustment, it is modification.

No it's not when you are not firing the same cartridge ( 7.62 vs 308 ) It's not any different then an AR pistol , or 300blk or 458 socom etc etc etc etc etc etc . All of those need different dwell times , powders , BCG , buffer weights , gas port sizes , ejection port sizes in any number of combinations or configurations . If the manufacture is going to make the chamber and stamp the barrel to a specific spec . Then they should spec the rest of the rifle correctly as well and not just spec it to some 70 year old original design that's irrelevant to the new cartridge and it's needs . I mean it's pretty hard to put a rifle length gas system like the one on a M-16 on a 10.5" AR pistol . Modifying that firearm to operate correctly seems pretty reasonable to me . I have to assume what you are saying is all modern m4's are just modified m-16's ? Ok sure lets say that's true , so ?? They are still spec'ed correctly for there "new" configurations .

I stand by my original point .

Last I checked just about every good firearm has mods as it relates to there original design . Can you say 1911 , AR-15 , Glock 19 I could go on and on with examples . Every time there is a "mod" they are trying to make it better or operate correctly for the new cartridge . Again it's the manufacture's responsibility to spec out the firearm correctly .

EDIT :

I should clarify that when I originally said adjustable gas system I meant by the manufacturer of the firearm and not the end user .

[44 AMP]

we're almost talking past each other. Let me clarify, the way I see it,

IF the manufacturer does it, it's a design change.

It may be a modification of an earlier design, almost all firearms are, but its a design change, because the manufacturer does it.

if the user removes the original factory part and replaces it with another slightly different part (from any maker) it is a modification. Changing an 18lb recoil spring for a 22lb spring is a modification.

if the user does it, changing a setting, by moving a part, turning a screw or nut or a catch, its an adjustment. Moving the rear sight by turning a screw (or with a drift punch) is an adjustment.

Taking off the fixed stock of an AR and replacing it with an adjustable stock is a modification. Changing the length of the adjustable stock is an adjustment.

clear as mud now?

[Mobuck]

"clear as mud now?"

Unfortunately, I think you lost most of those still stuck on the .308 vs 7.62x51 conundrum.

[Metal god]

we're almost talking past each other.

I agree and in large part it's likely my fault . I could/should have used better wording in my original postings when it comes to adjusting the firearm . I meant the designer of the new firearm could easily adjust the old design to work for there new configuration . Yes technically they are redesigning it but in reality they are just adjusting the old design because it still operates pretty much exactly the same with some minor adjustments .

Clearer mud yet ??