Advice on Tuning a "Precision" AR15

[Deleted member 113831]

Can somebody explain some of the nuance in balancing spring strength and buffer weight? I'm trying to fine tune some AR's and am wondering if there is benefit to strong spring/lighter buffer vs. standard spring /heavier buffer.

I have a hodgepodge of rifle length, carbine length, and mid-length gas systems.

I have some Wolff extra power springs and the following buffers on hand: standard buffer (3oz), H1(3.7oz), H2(4.5oz) and H3(5.7oz) buffers on hand.

I realize adjustable gas blocks are the current trend, but I have a number of rifles to deal with, and I'm hoping to have some success without spending $80-$100 a piece on adjustable gas blocks.

 

[Lil Casino]

Tagging in to learn as well

 

[ChitownCopper]

You can get a adjustable gas key for like 30 bucks if you want to go the cheap way to adjustable gas

 

[Matches Malone]

It has nothing to do with the gas. The concept of tuning the buffer and spring if you have a quality barrel that is ported properly, is timing. If you are under or over gassed, are using a oem buffer and spring, then you have a gas problem. Often because the manufacture of the barrel made to big a hole for gas port. This is where the quality comes in.

while you CAN use a really light spring and buffer for short stroking or vice versa for over gassed, it doesn’t really fix the problem, and again, might fix the intial problem, just to run into poor timing and dwell of the bolt cycle.

So going back to what I said before about barrel manufactures, a lot of these barrels from full assembled uppers are usually over gassed for reliability purposes. Hence why people like to recommend the H and sometimes H2 buffers.

Your springs that are 12 3/4 in are for the rifle length
and carbines are 10 1/2. I forget the coils.

Unless you have another reason to go heavier, like suppressor, your closest to 5 ounce is ideal for rifle length, and your 3 oz for carbines.

 

[natdscott]

Do you handload?

If you handload, I can assure you that a truly good AR can shoot very nearly 1/4 Minute groups with a regular rifle spring, and full weight buffer.

I use a TUBB spring so that I can basically forget about maintenance.

 

[Deleted member 113831]

Do you handload?

If you handload, I can assure you that a truly good AR can shoot very nearly 1/4 Minute groups with a regular rifle spring, and full weight buffer.

I use a TUBB spring so that I can basically forget about maintenance.

I do handload, and I typically load 69's and 75's. All my guns are over gassed.

I have never seen 1/4 moa groups out of any of these guns, but then again, I'm not a 1/4 moa shooter. I also test my loads using 10-20 rnd groups at 200 yards...so there is that to consider.

Really just trying to figure out if an extra power spring equals say, 1 tungsten weight?...maybe 2?

Is there an aspect I may be missing?

 

[2aBaC̶a̶]

Is there a goal in mind? Do you want it to do something different?

Usually tuning is about correcting an issue or achieve a desired goal like changing the cycling rate or reducing recoil.

Keep in mind that overgassing tends to be more reliable as you can feed it any off the shelf ammo. If you tune it for your specific hand loads it might not cycle other ammo reliability.

 

[Deleted member 113831]

Is there a goal in mind? Do you want it to do something different?

Usually tuning is about correcting an issue or achieve a desired goal like changing the cycling rate or reducing recoil.

Keep in mind that overgassing tends to be more reliable as you can feed it any off the shelf ammo. If you tune it for your specific hand loads it might not cycle other ammo reliability.

The goal is to improve or retain current accuracy, while better facilitating follow on shots and reducing stress on brass and components.

 

[natdscott]

I do handload, and I typically load 69's and 75's. All my guns are over gassed.

I have never seen 1/4 moa groups out of any of these guns, but then again, I'm not a 1/4 moa shooter. I also test my loads using 10-20 rnd groups at 200 yards...so there is that to consider.

Really just trying to figure out if an extra power spring equals say, 1 tungsten weight?...maybe 2?

Is there an aspect I may be missing?

Is the rifle braked? What muzzle device do you have, if any?

Whose barrel do you have, what twist, what chamber, how many rounds on it?


Set up your springs as normal.

Look to your loads for the difference.

-- Load at something-reasonable-powder-charge... make sure the primers are flat, but not cratering or mushroomed.
--Seat primers -0.003-4" under the case head. Squaring pockets is fine, but not essential. Uniforming flash holes is fine, but I've shot 3/8" with Lake City from the bag.
--Consider weight sorting brass, if you're gonna be beyond 3-400 yards.
--FL Size the brass to -0.003" from fired dimension. Size the neck to generate 0.002" tension. Do not CLEAN the necks to "spotless". some graphite left in there is a good thing, and some have even lightly included a little lube.
--Seat bullets with a good seating die (Forster BR, Redding Match with slding sleeve). Make sure TIR is under 0.005"
--Weigh powder. Or don't, if you feel like your powder measurement method is pretty good. By pretty good, I mean within a tenth. At Long Range, it better be closer than that. But even at 300 yards, my rifles shoot better with the powder at least "quick weighed" to eliminate the high/low spots that the measure/me kicks out... and I use a Harrell BR....

--Load 7 rounds of the SAME thing, at 2.250", 2.240", and 2.230" COAL.

Shoot them on a target at 100 yards, with the impacts in a black sheet of paper such that you cannot SEE the group forming.

ONE of those groups will be smaller, hopefully significantly.




What powder are you using, what casings, and what primers?

 

[Deleted member 113831]

Is the rifle braked? What muzzle device do you have, if any?

Whose barrel do you have, what twist, what chamber, how many rounds on it?


Set up your springs as normal.

Look to your loads for the difference.

-- Load at something-reasonable-powder-charge... make sure the primers are flat, but not cratering or mushroomed.
--Seat primers -0.003-4" under the case head. Squaring pockets is fine, but not essential. Uniforming flash holes is fine, but I've shot 3/8" with Lake City from the bag.
--Consider weight sorting brass, if you're gonna be beyond 3-400 yards.
--FL Size the brass to -0.003" from fired dimension. Size the neck to generate 0.002" tension. Do not CLEAN the necks to "spotless". some graphite left in there is a good thing, and some have even lightly included a little lube.
--Seat bullets with a good seating die (Forster BR, Redding Match with slding sleeve). Make sure TIR is under 0.005"
--Weigh powder. Or don't, if you feel like your powder measurement method is pretty good. By pretty good, I mean within a tenth. At Long Range, it better be closer than that. But even at 300 yards, my rifles shoot better with the powder at least "quick weighed" to eliminate the high/low spots that the measure/me kicks out... and I use a Harrell BR....

--Load 7 rounds of the SAME thing, at 2.250", 2.240", and 2.230" COAL.

Shoot them on a target at 100 yards, with the impacts in a black sheet of paper such that you cannot SEE the group forming.

ONE of those groups will be smaller, hopefully significantly.




What powder are you using, what casings, and what primers?

I really appreciate your willingness to help, but this isn't a reloading question. It is a gas management question.

Stated again...Is there a discernible difference between adding more spring resistance vs. more buffer weight?

 

[natdscott]

It IS a reloading question, at least to me. I have not noticed a difference between more spring force and more weight. Don't think it matters...it's gonna batter things either way. Holliger, for example, is COMPLETELY against the Carrier Weight System. He says it breaks things and whatnot. Dunno..mine works fine.

But uou asked for same accuracy, while "...better facilitating follow on shots and reducing stress on brass and components."

Brass and components are affected the most by being used poorly by hot rounds. Or any rounds, really.

Setting up your reloads the way they should be is how this is best done. Drill the port to 0.093", run rifle gas, run a good spring, and move on with tuning the ROUNDS for how much they beat up your system.

My 1,000 yard ammo is as hard on an AR-15 as you can possibly be... full auto at least is ball ammo at NATO pressure usually, where that stuff is WAY "not-NATO". I had to run a full-weight Tubb CWS to make it work, and it still beats up the bolt stop, bolt, etc...in a barrel that was extremely-specifically set up for that task. There's just only so much that the platform can do, and I'm about 300 yards past that. My bolt stop in that lower can probably rock back and forth 10-degrees, though it has never broken.

And don't use 8208 with heavy bullets, RE-15 with 55's.... etc. Match powders well, and the rifle will function better.

Also: start tuning your loads at 100 yards. It shows what it needs to show, without showing wind's effect on elevation and windage. I get the "10-20 rounds thing". I've had groups of as many at 10-15 in ~1.5" at 300. Sling prone.



The answers to some of my other questions might help me guide you more. Your call.

 

[Deleted member 113831]

It IS a reloading question, at least to me.

You asked for same accuracy, while "...better facilitating follow on shots and reducing stress on brass and components."

Brass and components are affected the most by being used poorly by hot rounds. Or any rounds, really.

Setting up your reloads the way they should be is how this is best done. Drill the port to 0.093", run rifle gas, run a good spring, and move on with tuning the ROUNDS for how much they beat up your system.

My 1,000 yard ammo is as hard on an AR-15 as you can possibly be... full auto at least is ball ammo at NATO pressure usually, where that stuff is WAY "not-NATO". I had to run a full-weight Tubb CWS to make it work, and it still battered the bolt stop, bolt, etc.

And don't use 8208 with heavy bullets, RE-15 with 55's.... etc. Match powders well, and the rifle will function better.

Also: start tuning your loads at 100 yards. It shows what it needs to show, without showing wind's effect on elevation and windage. I get the "10-20 rounds thing". I've had groups of as many at 10-15 in ~1.5" at 300. Sling prone.



The answers to some of my other questions might help me guide you more. Your call.

7 different rifles.

I don't even remember what barrel is on them. I built them years ago.

LC brass
AA 2460
Sierra 69's and Hornady 75's

 

[natdscott]

2460 is a little fast for those weights. Do you have RE-15 or Varget on hand?

Those are two great bullets. My X-count record was held by the 69 for a long time.

And the ONLY truly 1/4 Minute upper I ever handled was a muzzle-weigted 16" Krieger 7.7" 4 Groove with a CLE. Of all things, it wouldn't shoot Sierra less than 3/4".... but ohmygawd those 75 BTHP.

I don't shoot Hornady, but that rifle sure did. At least at 100 and 300.

 

[ken226]

There's a significant difference.

A change in spring force and rate has a different effect than a change in buffer mass, although there is some overlap. The biggest difference is in the timing.

A change in spring force/strength, most significantly, changes both the rearward and forward acceleration rates of the bolt carrier during firing. Less significantly, it somewhat changes the bullet dwell/unlock timing.

Changing the mass of the buffer, most significantly, changes the bullet dwell/unlock timing, and less significantly changes the bolts velocity during firing.

So, to have the most significant effect on dwell/lockup timing and initial acceleration rate if the bolt, changing the mass of the buffer, or peak pressure with an adjustable gas block, gets the most bang for the buck.

To have the most significant change on the bolt velocity later in the cycle, say when the bolt is about 1/3 or more of the way rearward, changing the spring rate would have a more significant effect.



Basically, if the gun is unlocking early and damaging extractors or damaging the rim of cases, you'll get the best results by increasing the buffer mass and/or reducing the peak pressure inside the carrier with an adjustable gas block.

If there's no issue with the dwell/unlock timing, but it's short-stroking, a lighter spring and would be most helpful.

If there's no issue with the dwell/unlock timing and the bolt is cycling with too much energy, that can be mitigated with a heavier spring.



Confusion and unintended results can occur if the wrong thing is changed to fix an issue. For example if the dwell/unlock timing is fine, but your bolt velocity is too high, and you then decide to significantly increase the buffer mass to slow the bolt down, you may fix the bolt speed issue while screwing up the dwell timing.

So, relationship between the peak gas pressure inside the bolt carrier, the mass of the buffer/carrier and the overall pressure dwell time (distance between the gas port and muzzle) have a much more of an effect on lock/unlock timing than the spring. The spring has its most significant effect on the bolts velocity at the more rearward portion of its travel, and most significantly on the closing/feeding portion of the cycle of operations.



I hope this helps.

 

[Deleted member 113831]

2460 is a little fast for those weights. Do you have RE-15 or Varget on hand?

Those are two great bullets. My X-count record was held by the 69 for a long time.

And the ONLY truly 1/4 Minute upper I ever handled was a muzzle-weigted 16" Krieger 7.7" 4 Groove with a CLE. Of all things, it wouldn't shoot Sierra less than 3/4".... but ohmygawd those 75 BTHP.

I don't shoot Hornady, but that rifle sure did. At least at 100 and 300.

I have 24lbs of 2460 and am trying to load bulk for all those rifles and use it up.

 

[FishDr]

There's a significant difference.

A change in spring force and rate has a different effect than a change in buffer mass, although there is some overlap. The biggest difference is in the timing.

A change in spring force/strength, most significantly, changes both the rearward and forward acceleration rates of the bolt carrier during firing. Less significantly, it somewhat changes the bullet dwell/unlock timing.

Changing the mass of the buffer, most significantly, changes the bullet dwell/unlock timing, and less significantly changes the bolts velocity during firing.

So, to have the most significant effect on dwell/lockup timing and initial acceleration rate if the bolt, changing the mass of the buffer, or peak pressure with an adjustable gas block, gets the most bang for the buck.

To have the most significant change on the bolt velocity later in the cycle, say when the bolt is about 1/3 or more of the way rearward, changing the spring rate would have a more significant effect.



Basically, if the gun is unlocking early and damaging extractors or damaging the rim of cases, you'll get the best results by increasing the buffer mass and/or reducing the peak pressure inside the carrier with an adjustable gas block.

If there's no issue with the dwell/unlock timing, but it's short-stroking, a lighter spring and would be most helpful.

If there's no issue with the dwell/unlock timing and the bolt is cycling with too much energy, that can be mitigated with a heavier spring.



Confusion and unintended results can occur if the wrong thing is changed to fix an issue. For example if the dwell/unlock timing is fine, but your bolt velocity is too high, and you then decide to significantly increase the buffer mass to slow the bolt down, you may fix the bolt speed issue while screwing up the dwell timing.

So, relationship between the peak gas pressure inside the bolt carrier, the mass of the buffer/carrier and the overall pressure dwell time (distance between the gas port and muzzle) have a much more of an effect on lock/unlock timing than the spring. The spring has its most significant effect on the bolts velocity at the more rearward portion of its travel, and most significantly on the closing/feeding portion of the cycle of operations.



I hope this helps.

I've been wondering this for a long time. This is an explanation that I understand (I think).... Thanks for writing it out.

 

[2aBaC̶a̶]

As stated above changing each part has it's own effect on the others. You'll have to play with combinations to find the right one

Basically your tuning mass and inertia.

It doesnt sound like your interested in changing out your BCGs or gas blocks so your left with buffer and spring combinations. If you have adjustable gas blocks it will better help dial in your combo.

Lighter buffer makes cycle rate faster and is harder on brass. Think race gun.

A heavier buffer will slow things down and is typically easier on brass and other components.

Your spring has to fall somewhere between not allowing the buffer to smack the back of the tube and being able to travel far enough to lock on the empty mag.

If @padom is around maybe he can chime in.

 

[Bantam1]

I played with buffer weight in one of my AR's. It is a 14.5 Mid length gas system. It is not over gassed but I didn't like the recoil impulse. I could feel it just wasn't right. I had some buffers in carbine, H and H2. I swapped them and shot them for feel. H was ok but H2 was too much. So I bought an H3 buffer and took it apart along with the H and weighed all the weights inside. I make my own fishing lures so I have tungsten powder to balance the baits or make them heavier.

I made a buffer that weighs between H and H2 by adding a little tungsten powder. I did remove some of the rubber spacers to give it a little room for the powder. I do not remember the exact weight. The end result worked and it took a little bit of time to get it where I wanted. I did it all by feel in my shoulder. The result of being single and bored led to experiments like this.

The rifle is really flat now. Everyone that has shot it makes comments about how smooth it cycles and flat it is.

 

[Deleted member 113831]

I took some of them out yesterday. H3 was too heavy for them. The H1 was workable, but the H2 felt best in them.

The extra power springs did change the recoil pulse considerably, but need to test some other loads to make sure reliability is still there.

Incidentally, I didn't see an obvious difference in accuracy with any of them.

 

[Snuby642]

Been testing the same things.

One lower with a decent trigger was running a 16inch carbine with h2 buffer and standard spring.
It did not run suppressed without damaging brass.

Then I put a new 6.5g 20 inch upper on it. Tore hell out of brass almost looked overpresure.

Got a seekins precision flat wire spring.

It quit smashing 6.5g brass but that upper has an agb waiting to calm it more. It was opening to soon and all false overpresure signs are gone.

The 5.56 carbine got a agb and now will run suppressed or not and not tear up brass. Accuracy improved.
The 5.56 lower will go back to a new standard spring soon to alleviate occasional feed problems running unsuppressed.

I will get another lower put togeather to further fine tune.

Not a definitive solution but a look at what my recent tuning did in my overgassed uppers.

 

[Bantam1]

I guess someone is making a tune-able kit now...


https://www.kakindustry.com/shockwave/ar15-buffer-system

 

[MontanaMan]

I took some of them out yesterday. H3 was too heavy for them. The H1 was workable, but the H2 felt best in them.

The extra power springs did change the recoil pulse considerably, but need to test some other loads to make sure reliability is still there.

Incidentally, I didn't see an obvious difference in accuracy with any of them.

What your playing with it not much of a factor in accuracy.

In a carbine gas system an H2 & occasionally an H3 buffer with a Sprinco Blue (extra power) srping alwasy works over a big range of ammo.
In a mid length gas system, an H2 with the Blue Spring
In a rifle length gas system, a carbine buffer & a standard (white) spring

Assuming anywhere near "standard" gas porting; the above gets you to a reasonably well functioning gun across ammo from 223 55 grainers to 5.56 spec 77 grainers. I've used those setups in a goodly number of guns.

But in almost every case, the buffer /spring control system is some level of compromise/

But if you really want to "fine tune" a gun, there is just no substitute for an adjustable gas block or some other means of controlling gas; this goes double for attempting to use a lightweight BCG...............it more or less gives infinite gas control that, if desired, can be tuned to each specific load.

Or you could start with a small gas port & ope it up in tested increments..................but that's just not practical.

JMHO, YMMV

MM

 

[MontanaMan]

I guess someone is making a tune-able kit now...


https://www.kakindustry.com/shockwave/ar15-buffer-system

You'll still end up with some level of compromise, absent an adjustable gas block or some other method of controlling gas.

MM

 

[Snuby642]

I fought getting an agb for a very long time.

I am king of hard headed.

Even with many spring and buffer combinations sometimes suppressed to non suppressed is a compromise if you want to save brass or shoot a decent group .

Eventually I had a problem upper and gave in.

 

[Nimothy]

Kak sells an adjustable buffer kit. Sure makes things easy setting up a rifle just bring the kit and a small punch and hammer to the range with you. They also have differ t color bumpers so you don’t forget which buffer goes to what. It’s very reasonably priced. Plus it’ll probably give you enough weights to make 3 h1’s out of carbine buffers

 

[David4570]

I’m setting up a new Criterion 14.5” mid-length setup. I will be using a flash hider without a suppressor. I was planning on using a JP polished recoil spring with a Knights HH buffer As I have these on hand. I really don’t know what Criterion does with their porting, although I’m sure I can find out.
Does anyone have experience to share regarding the “proper spring/buffer setup” for this barrel?