AR adjustable gas blocks (Read 1044 times)

robtmc

AR adjustable gas blocks
« on: April 13, 2022, 11:12:32 AM »
Anyone else use them?
If so, have you run into ammo that did not want to cycle at your initial setting?

Flapp_Jackson

Re: AR adjustable gas blocks
« Reply #1 on: April 13, 2022, 12:37:32 PM »
Anyone else use them?
If so, have you run into ammo that did not want to cycle at your initial setting?

I've used them on 2 AR15s.  I always use 5.56 ammo.  Cycling hasn't been an issue.  Once I set the adjustment to just above the "doesn't cycle" point, I haven't seen any failures.

Basic adjustment process I used:

1.  Load the ammo with the lowest velocity rating you have/normally buy.
2.  Adjust the gas block to be "totally open".
3.  Fire 10 rounds to make sure everything's working.  This eliminates any other variables that might confuse you when making adjustments.  You're basically starting from a "non-adjustable gas block" setting.
4.  Start making adjustments 5-10 rds at a time.  As you reduce the amount of gas, pay attention to the sound and recoil felt.
5.  Repeat Step 4 until the rifle no longer cycles.
6.  Increase the gas pressure slightly (less than the last adjustment in Step 4).
7.  Keep increasing the gas until every test round cycles.
8.  You now have the least amount of gas needed to cycle the "weakest" ammo being tested.  Make one more small adjustment to increase the gas.  This is a "buffer" in case some of the ammo doesn't produce the exact amount of pressure expected.
9.  Test that setting with the rest of your ammo.  If you started with the lowest pressure rounds, all the rest should cycle.  Had you started with the highest velocity ammo, it's predictable you will have cycling issues with less-pressure-producing ammo.

If the sound or felt recoil seems "off", but ran fine when wide open, check that your bolt is well lubed, the gas tube is perfectly aligned with the BCG's gas key, the gas block is perfectly aligned with the gas port in the barrel, and that you're using a standard weight buffer.  Your gun may already be allowing less gas pressure than it should, and any amount of adjustment may cause it to be under-gassed.

Once you get it balanced just above the point where it ejects the brass and loads the next round properly every single time, you're at the "sweet spot" that hopefully reduces felt recoil and stress (i.e. wear) on the rifle.

If you're using a suppressor and/or subsonic ammo, the same adjustment procedure should work. 

The rifle's gas system length can also affect the results.  The carbine-length gas system produces more pressure in the action than the mid-length gas system, and the mid-length system creates more pressure than the rifle-length system.  Some think the only reason to choose a particular length gas system is for the location of the gas block on the barrel so you can use the particular front sight or handguard style you prefer.

Quote
....
The current consensus is, all else being equal, a longer gas system is better. How much better
and for what, depends on to whom you are talking. I have heard longer gas-system lengths reduce
felt recoil, muzzle climb, heat in the action, fouling, bolt-carrier speeds, DMV wait times, ozone
levels, bad cholesterol and premature hair loss. It may help to understand how varying pressures
affect the DGI system to see the advantages of different gas-tube lengths.
....
Different gas-system lengths come into play as bullets move down their barrels, reducing the pressure
behind them. A longer gas tube corresponds to a gas port placed farther down the barrel (toward the
muzzle), yielding lower port pressures, since there is more room for the expanding gases behind the
bullet as it passes the gas port. Once the bullet leaves the muzzle, pressure drops off. Therefore, a gas
port closer to the muzzle reduces the amount of time that highly pressurized gas has to act on the
operating system after the bullet passes the port, usually referred to as "dwell time." When comparing
two barrels of equal length—but with different gas systems—the longer gas tube will produce a reduced
dwell time. The practical results are usually slower bolt-carrier movement and a slight reduction in felt recoil.
The latter facet is quite apparent to some shooters but can go completely unnoticed by others. I regularly
shoot all three gas-system lengths, and I can feel the difference in otherwise-like barrels.
https://www.shootingillustrated.com/content/ar-gas-system-lengths-explained/

The gas system is just that -- a system.  The barrel length, gas system length, buffer weight and ammunition all play a part in how close to the optimal amount of pressure is created and channeled into the gas key on the BCG.

Based on the description above, you will likely see more effect when placing an adjustable gas block on a carbine-length AR than you will on a rifle-length AR.  If you already have a mid-length or rifle-length AR, the impact of an adjustable gas block may not be significant enough to notice.

Hope that helps.

p.s. I found a cheap and easy way to perfectly align the gas port in the barrel with the port in the gas block:  toothpicks or spaghetti.   :geekdanc:
Truth, when not sought after, rarely comes to light.  -- Oliver Wendell Holmes, Sr.

I need some new conspiracy theories. All my old ones turned out to be true.

Hamburger Helper only works if the hamburger really wants to be helped.

robtmc

Re: AR adjustable gas blocks
« Reply #2 on: April 13, 2022, 03:40:36 PM »
1.  Load the ammo with the lowest velocity rating you have/normally buy.
Pretty much how I adjust them until now with .308.  Set it for M80 ball, figuring heavier slugs would have more gas pressure.

Have a 5.56mm now and need to set it up. 
How to determine lowest energy ammo is a mystery without a chrono and a variety of ammo.  Is there some reference for commonly available stuff? 

Flapp_Jackson

Re: AR adjustable gas blocks
« Reply #3 on: April 13, 2022, 03:55:24 PM »
Pretty much how I adjust them until now with .308.  Set it for M80 ball, figuring heavier slugs would have more gas pressure.

Have a 5.56mm now and need to set it up. 
How to determine lowest energy ammo is a mystery without a chrono and a variety of ammo.  Is there some reference for commonly available stuff?

The numbers only matter when comparing brands and varieties of ammo.  if you can get the manufacturer's specs, you can sort them by FPS (velocity).  Racking and stacking the ammo is all you're after.  Once you find the least "powerful" brand/type, that part's done.  Everything else creates plenty of pressure to operate the action.

There's enough variance within one brand/type of ammo that you're not going to be able to set the gas block to a "wafer thin" margin between "success" and "failure".  That's why you do a 10 rd test as you adjust, as the pressure will vary to some degree round-to-round.  You're looking for the lowest common denominator -- one setting that's open enough to accommodate the lowest pressure round observed.  In time, you may have to increase pressure if you run across a batch of ammo that isn't cycling.

If you're reloading, I assume you have the means to determine the specs yourself -- and that you have a QA process that maintains production standards within a certain margin of error?   :thumbsup: :D    If you have the means to calibrate the ammo you use, why even bother with an adjustable gas block?   "Adjustable Ammo!"  :geekdanc:
Truth, when not sought after, rarely comes to light.  -- Oliver Wendell Holmes, Sr.

I need some new conspiracy theories. All my old ones turned out to be true.

Hamburger Helper only works if the hamburger really wants to be helped.

Flapp_Jackson

Re: AR adjustable gas blocks
« Reply #4 on: April 13, 2022, 04:10:48 PM »
From further reading, the test setups for determining pressure ranges (high, low and average pressure) of factory ammo are accurate enough, "because pressure barrels used for testing are chambered and rifled to absolute minimum SAAMI dimensions. Manufacturers of mass-produced barrels are allowed to keep them within a minimum/maximum allowable tolerance range, and while factory ammunition fired in the former will produce higher pressure than in the latter, it should still be at a safe level."

Rifling, twist rate, and dimensions of the barrel interior will have an affect on your results, but using the factory-supplied data will be a safe starting point.  Since they all should be using industry standard procedures and equipment based on SAAMI requirements, the test results -- and subsequently the specs listed for each ammo type -- should be at least very close to an apples-to-apples comparison.

Even the amount of oil you have in the barrel can affect velocity and pressure, but as long as the same variables exist in all of your tests, the relative data between batches shouldn't be affected.

https://www.rifleshootermag.com/editorial/critical-factors-affecting-rifle-chamber-pressure/83492
Truth, when not sought after, rarely comes to light.  -- Oliver Wendell Holmes, Sr.

I need some new conspiracy theories. All my old ones turned out to be true.

Hamburger Helper only works if the hamburger really wants to be helped.

drck1000

Re: AR adjustable gas blocks
« Reply #5 on: April 13, 2022, 04:11:25 PM »
Anyone else use them?
If so, have you run into ammo that did not want to cycle at your initial setting?
I don't, but I have seen folks that use them on piston driven guns.  However, those were full auto and suppressed guns, which we can't own in HI.

Are you having cycling with a specific gun?
Pretty much how I adjust them until now with .308.  Set it for M80 ball, figuring heavier slugs would have more gas pressure.

Have a 5.56mm now and need to set it up. 
How to determine lowest energy ammo is a mystery without a chrono and a variety of ammo.  Is there some reference for commonly available stuff? 
I have somewhat of a log of underpowered ammo from use.  Stuff like Remington UMC and PMC Bronze.  Where some of my mid-length guns worked very well with say M193, but crappy on the underpowered stuff. 

Many folks do tuning for ammo power with springs and buffer weights.  I used to play/test with that before, but not anymore.

Flapp_Jackson

Re: AR adjustable gas blocks
« Reply #6 on: April 13, 2022, 04:22:05 PM »
I don't, but I have seen folks that use them on piston driven guns.  However, those were full auto and suppressed guns, which we can't own in HI.

Are you having cycling with a specific gun?I have somewhat of a log of underpowered ammo from use.  Stuff like Remington UMC and PMC Bronze.  Where some of my mid-length guns worked very well with say M193, but crappy on the underpowered stuff. 

Many folks do tuning for ammo power with springs and buffer weights.  I used to play/test with that before, but not anymore.

I ordered 2 heavier buffers from PSA.  A rep called me the next day to ask why I was ordering them.  I told her for my own education.  I wanted to see what the heavier weights do to my rifle.  I was curious what slowing down the action might do -- less felt recoil or whatever.

She said she just wanted to check that I wasn't trying to "fix" something that the standard weight buffer isn't causing.  I guess they get a lot of returns from people "trying different things" to fix cycling issues.  I appreciated the personal attention to make sure I wasn't wasting time and money from not knowing what I was doing.

IIRC, the weights I ordered were H2 and H3.  I could tell they made a difference, but no benefit since there was no problem with the standard (H1?) buffer.
Truth, when not sought after, rarely comes to light.  -- Oliver Wendell Holmes, Sr.

I need some new conspiracy theories. All my old ones turned out to be true.

Hamburger Helper only works if the hamburger really wants to be helped.

drck1000

Re: AR adjustable gas blocks
« Reply #7 on: April 13, 2022, 05:19:59 PM »
I ordered 2 heavier buffers from PSA.  A rep called me the next day to ask why I was ordering them.  I told her for my own education.  I wanted to see what the heavier weights do to my rifle.  I was curious what slowing down the action might do -- less felt recoil or whatever.

She said she just wanted to check that I wasn't trying to "fix" something that the standard weight buffer isn't causing.  I guess they get a lot of returns from people "trying different things" to fix cycling issues.  I appreciated the personal attention to make sure I wasn't wasting time and money from not knowing what I was doing.

IIRC, the weights I ordered were H2 and H3.  I could tell they made a difference, but no benefit since there was no problem with the standard (H1?) buffer.
While I did testing with different weights at one time in my "AR education journey", I have stopped a while ago.  At one point I did test with the weights and buffer springs to "tune" the ejection pattern.  Wasn't trying to fix anything needed other than testing, as well as to a certain extent listening to what other AR users had stated.  The consistent ejection to 4-5 o'clock, or it if flies forward, it's overgassed, etc.

Since then, as long as the gun functions, that's the main thing.  That said, since then I did have guns that even with the "standard" H1 buffer, I would get a bunch of malfunctions with crappy under-powered ammo.  I did get the guns to function fine with the C buffer.  But now I just shoot the crappy ammo with my carbine length guns and they all run fine.  That said, knowing that, I do know that my carbine gassed guns eat pretty much all crappy, steel cased, etc ammo that I've tried. 

robtmc

Re: AR adjustable gas blocks
« Reply #8 on: April 13, 2022, 07:54:57 PM »
I first started fiddling with adj gas on my first build, a carbine length .308.  Was a very harsh shooter.   By the time i had the JP gs block dialed in, it was a soft dream to shoot.
The relative lack og grunge from reduced gas was a benefit.

AR.308 system does not had the plethora of buffer weights and springs as .223.  The the gas adjust was it.   Now i stick with mid length thank you very little.   Adjusting the gas is straightforward and intuitive.   Springs and buffers, not so much.

So much .223/5.56 ammo out there, was worried i might run into some ammo on the low side of pressure from what i tune for.Think I will keep the two Allen wrench sizes I need for adjust in the Bravo Co hand grip, just in case.  Two, as I added in an adjustment lock screw.

mill8316

Re: AR adjustable gas blocks
« Reply #9 on: April 13, 2022, 07:58:00 PM »
PMC bronze .223 is well known as being one of the lighter pressure/recoil loads. So that is what I tune all my 5.56 gas systems to function fully with that ammo. And then I mostly shoot XM193 and M193

robtmc

Re: AR adjustable gas blocks
« Reply #10 on: April 13, 2022, 08:09:50 PM »
PMC bronze .223 is well known as being one of the lighter pressure/recoil loads. So that is what I tune all my 5.56 gas systems to function fully with that ammo. And then I mostly shoot XM193 and M193
Good info thanks.    Think I have mostly IMI and some real heavy bullets on hand, will look for PMC at the wretched local shop.

New to the mouse cartridge after 50 years.

changemyoil66

Re: AR adjustable gas blocks
« Reply #11 on: April 13, 2022, 10:59:58 PM »
Sorry to highjack, why would u want to adjust it when not using a supressor? 1 or 2 points. Anything more and its above my grade.

My AR shoots any range ammo.

Sent from my SM-G991U using Tapatalk

Flapp_Jackson

Re: AR adjustable gas blocks
« Reply #12 on: April 13, 2022, 11:11:03 PM »
Sorry to highjack, why would u want to adjust it when not using a supressor? 1 or 2 points. Anything more and its above my grade.

My AR shoots any range ammo.


I listed a bunch of variables that can affect the amount of pressure directed into the BCG gas key:

barrel length
twist ratio
gas system length (carbine, mid-length and rifle-length)
alignment of ports between the barrel and gas block
amount of oil in the barrel
weight of the buffer
amount of lube on the BCG
and, of course, the ammo used.

If the combination of these factors isn't giving you the smooth-running rifle you always dreamed of, it might be a simple problem of the operating system being over-gassed. 

If it's under-gassed, an adjustable block isn't the solution -- unless swapping the blocks fixes a misalignment, which was a build problem, not a part problem.

The rifle might be working now, but that doesn't mean it can't work better.
Truth, when not sought after, rarely comes to light.  -- Oliver Wendell Holmes, Sr.

I need some new conspiracy theories. All my old ones turned out to be true.

Hamburger Helper only works if the hamburger really wants to be helped.

changemyoil66

Re: AR adjustable gas blocks
« Reply #13 on: April 13, 2022, 11:19:44 PM »
So building ur own one and an unforseen problem of it cycling. Next step to get an adjustible gas block and adjust as needed.

Right?

Sent from my SM-G991U using Tapatalk

Flapp_Jackson

Re: AR adjustable gas blocks
« Reply #14 on: April 13, 2022, 11:22:40 PM »
So building ur own one and an unforseen problem of it cycling. Next step to get an adjustible gas block and adjust as needed.

Right?

I never said that.

"The rifle might be working now, but that doesn't mean it can't work better."
Truth, when not sought after, rarely comes to light.  -- Oliver Wendell Holmes, Sr.

I need some new conspiracy theories. All my old ones turned out to be true.

Hamburger Helper only works if the hamburger really wants to be helped.

drck1000

Re: AR adjustable gas blocks
« Reply #15 on: April 14, 2022, 09:44:45 AM »
PMC bronze .223 is well known as being one of the lighter pressure/recoil loads. So that is what I tune all my 5.56 gas systems to function fully with that ammo. And then I mostly shoot XM193 and M193
Same for me.  I have shot a lot of PMC bronze over the years, but at least one of my ARs with mid-length gas had some malfunctions with it.  One was an LMT, which was supposed to be "targeted" for 193 and 855.  I've had other mid-lengths that were more generously gassed and chewed up the PMC just fine.

Tula is another notorious for being underpowered.  I bought a PSA upper, that is known for being generously gassed, specifically to test and eventually shoot a lot of the cheaper steel cased ammo, many which are typically underpowered.  Since then, the pricing of steel cased ammo were trending close to brass, so haven't bought steel cased much. 

drck1000

Re: AR adjustable gas blocks
« Reply #16 on: April 14, 2022, 09:49:10 AM »
So building ur own one and an unforseen problem of it cycling. Next step to get an adjustible gas block and adjust as needed.

Right?

Sent from my SM-G991U using Tapatalk
YMMV, but I consider an adjustable gas block close to last on the list of "as needed". 

changemyoil66

Re: AR adjustable gas blocks
« Reply #17 on: April 14, 2022, 09:56:02 AM »
I never said that.

"The rifle might be working now, but that doesn't mean it can't work better."

I was asking another general question to try to understand due to my lack of knowledge about the topic.  But this is going above my pay grade now.

*edit
And I'm starting to highjack the thread. Sorry OP. If I have further questions I'll google or post here.
« Last Edit: April 14, 2022, 10:01:08 AM by changemyoil66 »

robtmc

Re: AR adjustable gas blocks
« Reply #18 on: April 14, 2022, 10:43:30 AM »
Sorry to highjack, why would u want to adjust it when not using a supressor? 1 or 2 points. Anything more and its above my grade.

My AR shoots any range ammo.

Sent from my SM-G991U using Tapatalk
Can you or have you driven a manual transmission car?   If so, do you pop the clutch to get moving?   That would do the trick, but needlessly batter the vehicle. 

Same same for gas operated firearms.  Just enough gas to operate makes life easier on parts, disturbs the sight picture less, etc.    Makes for a more pleasant shoot as well.    I was a .308 AR shooter for a long time.  There is a big difference in that and the mouse gun.   Settling it down by reducing gas makes a major difference.

edit:  Oh yeah, I got into adjusting the cycling after first building my .308.  Violent ejection in every direction.   Sometimes not feeding correctly.  Read up on it and was classic over-gassing.   Now drops cases with in inches of each other at 3:30.  Gas port sizes and operating gas length are all over the map, so it is good to understand how to adjust for the sweet spot.
« Last Edit: April 14, 2022, 10:57:21 AM by robtmc »

Flapp_Jackson

Re: AR adjustable gas blocks
« Reply #19 on: April 14, 2022, 12:12:25 PM »
Can you or have you driven a manual transmission car?   If so, do you pop the clutch to get moving?   That would do the trick, but needlessly batter the vehicle. 

Same same for gas operated firearms.  Just enough gas to operate makes life easier on parts, disturbs the sight picture less, etc.    Makes for a more pleasant shoot as well.    I was a .308 AR shooter for a long time.  There is a big difference in that and the mouse gun.   Settling it down by reducing gas makes a major difference.

edit:  Oh yeah, I got into adjusting the cycling after first building my .308.  Violent ejection in every direction.   Sometimes not feeding correctly.  Read up on it and was classic over-gassing.   Now drops cases with in inches of each other at 3:30.  Gas port sizes and operating gas length are all over the map, so it is good to understand how to adjust for the sweet spot.

Exactly.  I look at it like a teen first learning to drive.

If the driver always floors the accelerator when they start off, they'll usually get where they are going, but you'll be a nervous wreck during the trip.

If the driver "adjusts" the amount of gas they give the car to the bare minimum needed to get moving at a comfortable speed, not only does that treat the machine more gently with less stress (wear & tear) on the parts, it also makes the ride more pleasant for everyone. 

The cycling of a semi-auto firearm is a violent reaction.  Reducing that to the least-violent force needed just makes sense.
Truth, when not sought after, rarely comes to light.  -- Oliver Wendell Holmes, Sr.

I need some new conspiracy theories. All my old ones turned out to be true.

Hamburger Helper only works if the hamburger really wants to be helped.