Question for all you AR15 experts

S

schumy

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I replaced the 16" barrel with an 11.5" one and a different gas block. Ever since then, my brass gets flung forward at about 2:00 o'clock. What could cause this and is it detrimental to the operation of the gun? Everything else cycles normally and I didn't get any ftf or failure to lock on last round.

S&J barrel carbine length (unknown gas port size)
H2 buffer (unknown spring strength)
Full auto BCG
A2 birdcage
No changes in ammo or anything else, just barrel, gas block, gas tube.
 
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because of the difference in distance to the barrel gas port, you are getting more energy back at the bolt... You need a heavy buffer, an adjustable gas block, or some other way of mtigating the increased gas pressure and bolt speed...

IMHO anyway... Maybe the gas port on the barrel is too large even... what make is it?

I even rolled the thought through my head of pinching the gas tube in the vice to slow the gas down... but never tried myself. It may work also, but it is theoretical... It may cause issues I hadn't thought of.
 
bobbynewmark said:
because of the difference in distance to the barrel gas port, you are getting more energy back at the bolt... You need a heavy buffer, an adjustable gas block, or some other way of mtigating the increased gas pressure and bolt speed...

IMHO anyway... Maybe the gas port on the barrel is too large even... what make is it?
Click to expand...

It's an S&J barrel. I measured the port, but couldn't get a decent measurement, I got approximately 0.1" but I doubt that's precise.

I'm running an H2 buffer already, not certain of the spring strength.

I'm curious though, wouldn't the pressure be lower since the bullet has less distance before it reaches the muzzle after the gas port? 3.5" on the 11.5" carbine length vs 8.5" on the 16" carbine length.
 
Need more details on what parts are in the rifle,
Semi auto carrier or full auto carrier?
Standard carbine buffer or heavy buffer? I'm guessing it doesn't have a rifle buffer system and has a carbine buffer tube, spring and buffer.
Brand of barrel? Some of the earlier S&J barrels had way to large of a gas port. This ensures cycling even light loads but over gasses the rifle when shooting standard loads.
Do you notice the trigger reset is very harsh and actually mildly hurts your trigger finger?

It doesn't sound like you're very far off so I would start with simply trying a heavier buffer and then if it still isn't cycling how you want it to try a full auto carrier (they're heavier), if that doesn't work and since you can buy adjustable gas blocks for under $100 that would be my next item to try.
Most rifles don't need an adjustable gas block unless the barrel port was drilled way too large or someone has made a drastic change to the barrel length and not changed any other parts. For the most part it's a solution to a problem that never existed in the first place but in some instances it will make your life easier. I feel it would be most useful to a competition shooter who wants to tune his rifle exactly to the load he is using in order to make the rifle as smooth as possible and not for a general tuning tool on a gun that is out of balance because of improper or incomplete parts selection when modifying it.
An AR requires the gas system and the recoil system to be balanced with each other. Making changes to one and not the other usually ends up giving a rifle that still functions but isn't as smooth or reliable as it used to be. Luckily parts are relatively cheap and easy to install so it won't be hard to get it running smooth again, a little experimenting with a couple different parts should get it back shooting the way you remember it.

https://shopquestar.com/shopping65/shopexd.asp?id=2610&bc=no
https://shopquestar.com/shopping65/shopexd.asp?id=1203&bc=no
Either of these should help. There are other places to buy these parts so shop around for the best price and also search the EE for a used one to save some more money

Good luck

Edit since you posted while I was typing.
Are you running a FA or SA carrier?
What muzzle device? Some produce more backpressure than others.
Did you change ammo?
 
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schumy said:
It's an S&J barrel. I measured the port, but couldn't get a decent measurement, I got approximately 0.1" but I doubt that's precise.

I'm running an H2 buffer already, not certain of the spring strength.

I'm curious though, wouldn't the pressure be lower since the bullet has less distance before it reaches the muzzle after the gas port? 3.5" on the 11.5" carbine length vs 8.5" on the 16" carbine length.
Click to expand...

I run the exact same barrel..lol

I also noticed the brisk ejection on mine, but it doesn't bother me. I thought maybe you had a pistol length gas system, but SJ barrel has carbine length.

A new gas tube is $20... If I were going to try anything it would be slightly crushing the tube to retard the flow.. versus $100 adjustable block
 
If the gun was 0ver gased. Then the gun wh0uld we sh00ting the caseings 0ut at 5 O'clock. 0r FTE because the gun is cycling so fast then its jumping the exstract0r.
Run the gun as is untill you run into any problems.
The last 500 bbls we made we ran colt specs 0n the gas p0rt. As per lenght.11.5 14.5. 16.5.
N0 idea 0ff hand what it was.
BBB
 
FTR Simon, my runs flawlessly.. very fond of the little guy :) with a TRS-25 as the cherry on the top it is much fun

Mine is over a year old though, so different production run I am guessing...?
 
A couple of things:

1) Adjustable gas blocks are worse than useless

2) Pinching the gas tube will become a disaster quite quickly - you now have a constriction, which is fine, if gas was the only thing travelling down your gas tube. A pinched gas tube will clog with carbon, and when (not if) it does, you won't be able to clean it. Additionally, pinching a tube shaped object weakens it, could be quite nasty in combination with the aforementioned carbon build up.
 
badboybeeson said:
If the gun was 0ver gased. Then the gun wh0uld we sh00ting the caseings 0ut at 5 O'clock. 0r FTE because the gun is cycling so fast then its jumping the exstract0r.
Run the gun as is untill you run into any problems.
The last 500 bbls we made we ran colt specs 0n the gas p0rt. As per lenght.11.5 14.5. 16.5.
N0 idea 0ff hand what it was.
BBB
Click to expand...

By the way, I will mention that even with my crappy shooting, this 11.5" is as accurate as my old 16". S&J did a great job.
 
bobbynewmark said:
because of the difference in distance to the barrel gas port, you are getting more energy back at the bolt... You need a heavy buffer, an adjustable gas block, or some other way of mtigating the increased gas pressure and bolt speed...

IMHO anyway... Maybe the gas port on the barrel is too large even... what make is it?

I even rolled the thought through my head of pinching the gas tube in the vice to slow the gas down... but never tried myself. It may work also, but it is theoretical... It may cause issues I hadn't thought of.
Click to expand...

11.5 would still use a carbine length gas system as a 16.

The port on the 11.5" barrel must be enlarged slightly more. So only thing you can do is change the gas block to a adjustable. Since you got a F/A BCG, and Heavy Buffer.
 
enefgee said:
A couple of things:

1) Adjustable gas blocks are worse than useless

2) Pinching the gas tube will become a disaster quite quickly - you now have a constriction, which is fine, if gas was the only thing travelling down your gas tube. A pinched gas tube will clog with carbon, and when (not if) it does, you won't be able to clean it. Additionally, pinching a tube shaped object weakens it, could be quite nasty in combination with the aforementioned carbon build up.
Click to expand...

you're offering a lot of criticism, but ZERO actual help...

A gas tube is $20, and considering he already has a heavy buffer what is the alternative - seeing as how you state an adjustable gas block is worthless (with NO explanation??)

Offer up your wisdom for a solution... do tell

If it were me... I would weld up the hole in the gas block, then re-drill it to a smaller size,... but the gas tube pinch was the easiest way barring the use of more complicated tools... Plus who cares if you have to clean out the gas tube with some brake cleaner once in a while..I didn't say pinch it closed ffs

If it makes you feel better I will suggest a swage at the tip as it goes into the bolt carrier.. like the choke on a shotgun
 
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enefgee said:
A couple of things:

1) Adjustable gas blocks are worse than useless

2) Pinching the gas tube will become a disaster quite quickly - you now have a constriction, which is fine, if gas was the only thing travelling down your gas tube. A pinched gas tube will clog with carbon, and when (not if) it does, you won't be able to clean it. Additionally, pinching a tube shaped object weakens it, could be quite nasty in combination with the aforementioned carbon build up.
Click to expand...

I would tend to agree with most of this. If everything is running fine, who cares where the brass lands? If you really feel that you want to play with it I would start with a heavier buffer, heavier bolt carrier, a heavier spring or a combination of these. I would go to the adjustable gas block as a last resort. Under no circumstances would I pinch the gas tube.
 
8 ball said:
I would tend to agree with most of this. If everything is running fine, who cares where the brass lands? If you really feel that you want to play with it I would start with a heavier buffer, heavier bolt carrier, a heavier spring or a combination of these. I would go to the adjustable gas block as a last resort. Under no circumstances would I pinch the gas tube.
Click to expand...

This is true of course.. but the OP implied it was a situation that was less than acceptable... and was looking for solutions.

Personally, unless the gun malfunctions I would leave it alone. I have the same barrel and even though the bolt slams back harder and the brass flies farther I just left it as is. When you shoot for accuracy however, the jolt can be disconcerting and I can understand why someone may want to tweak it and smooth it out.

To each their own

you state "under no circumstances would I pinch the gas tube.." but offer no reason as to why. I don't see how making a rounded depression gently in the tube will do anything.. It is STEEL for goodness sake... I think you guys may be thinking on the more extreme side of the word 'pinch' than I was...
 
I tend to agree with you guys on the "if it ain't broke, don't fix it" mantra. However, it seems that the brass beig flung forward is a symptom of an underlying issue that if left uncorrected can lead to premature wear or failure. At the least, I can eliminate some of the kick that the overgassing is causing.
 
Pinching the gas tube is like leaving the choke half on to make your lawnmower run. It would indicate that there is a deeper problem that would be better solved directly.
If you were in a desperate situation and pinching your gas tube would make it run for a time, go for it. But then repair both issues as soon as you are able.
 
bobbynewmark said:
I run the exact same barrel..lol

I also noticed the brisk ejection on mine, but it doesn't bother me. I thought maybe you had a pistol length gas system, but SJ barrel has carbine length.

A new gas tube is $20... If I were going to try anything it would be slightly crushing the tube to retard the flow.. versus $100 adjustable block
Click to expand...

Crushing the gas tube slightly is a viable option if the gun is over gassed. That being said My 11.5 S&J barrel works very well and is not over gassed IMO
 
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