6ARC gas systems and A5 buffer systems and factory ammo...what's the baseline?

[dms416]

While it's not always clear, and port size is always a factor...

Where it seemed like the jumping off point for one's preferences in 5.56 is, it SEEMS like the starting point for the 6ARC is the next step up in gas length AND down one weight in the A5 system.

For example: where I would traditionally run an unsuppressed 18" rifle with an A5h2 in 5.56.... for a 6ARC 18" on a rifle +1 with an A5h1 (or 0) seems a parallel operational envelope.

Am I about in the ballpark?

 

[zinny]

Ran into an issue with this recently, they make T0 weight buffers which are equivalent to standard T1 buffers at 3.8oz, for the A5 system. Id get one. Wolff also makes as 10% less power rifle length spring. If you're going to be playing with 6arc and A5 systems, Id make sure to get those to increase probability of making it run reliably after mixing and matching.

 

[dms416]

Ran into an issue with this recently, they make T0 weight buffers which are equivalent to standard T1 buffers at 3.8oz, for the A5 system. Id get one. Wolff also makes as 10% less power rifle length spring. If you're going to be playing with 6arc and A5 systems, Id make sure to get those to increase probability of making it run reliably after mixing and matching.

I'm not sure I'm tracking correctly on what you mean by T0and T1
A5H0 is 3.8oz already
A5H1 is 4.56
A5H2 is 5.33

 

[zinny]

Yeah, that the A5H0 is equvalent to a std carbine T1 at 3.8oz. So thats probably the best place to start.

 

[TonyAngel]

Unless this is going to be some sort of setup for gaming or you plant to shoot very few rounds between cleanings, I'd avoid going with any sort of lighter spring. As the rifle gets dirty you'll likely start having problems with the bolt not wanting to go all the way into battery during cycling or dropping the bolt on a fresh magazine.

Are you going to be running suppressed? If so, which can? If youre going to be running a higher back pressure can, all of the thought about how light you can go on the buffer will likely be wasted. In the event that you do need to go lighter than an A5H0, you can always replace some or all of the weights with aluminum.

 

[WeR0206]

Unless this is going to be some sort of setup for gaming or you plant to shoot very few rounds between cleanings, I'd avoid going with any sort of lighter spring. As the rifle gets dirty you'll likely start having problems with the bolt not wanting to go all the way into battery during cycling or dropping the bolt on a fresh magazine.

Are you going to be running suppressed? If so, which can? If youre going to be running a higher back pressure can, all of the thought about how light you can go on the buffer will likely be wasted. In the event that you do need to go lighter than an A5H0, you can always replace some or all of the weights with aluminum.

Yeah, good point on the type of can that he uses could completely mess up whatever tuning he does with buffer weights. I agree that if possible its best to avoid using weaker springs.

I’m actually in the middle of trying to fix a short stroking 18 inch rifle +2 6 arc upper (gas port is .093”) that came with a headspaced RCA bolt. I’m gonna try to use a slightly lighter RCA carrier (in place of an enhanced radian carrier) because right now it’s still not feeding or locking back with a carbine buffer weight and sprinco white (with a set screw or clamp on gas block). Next step if that doesn’t help is a buffer with 3 aluminum weights and then possibly a weaker spring.

I have a bcm MK2 buffer kit I was going to put on the 6 arc lower but not going near that until I can figure out how to get it to run on a carbine length buffer tube/weight in case that’s all that available for whatever reason and all my other lowers have carbine tubes.

 

[zinny]

A reduced power rifle length spring isn't the same as a springco reduced power carbine spring. Working with the A5 system, the reduced power rifle length spring is closer to a factory carbine spring in compression strength.

Like how WeR0206 is having issues in a standard carbine system, you'd be going to delrin buffers in such a case with stock rifle length spring.

 

[dms416]

No suppressor. Fucking Illinois

 

[TonyAngel]

No suppressor. Fucking Illinois

Oh, geez. I feel for you. In any case, I wouldn't burn too many brain cells on it.

Now, you really have to take what I say with a grain of salt. I've had to diagnose and repair MANY ARs in varying calibers, but I have zero experience with 6 ARC. I'm talking in complete generalities.

The beauty and danger of the AR platform is that you can muck with just about every aspect of it to change one thing or another. For every gas system length in each caliber, there is an ideal dwell time at which the system will be the most forgiving. Each gas system length will typically get more and more finicky as you decrease dwell time from whatever the ideal dwell time is.

In this case, I really don't know what effect going +1 on the gas system length will have. Still, in the present case, dealing with an A5 buffer system, I wouldn't go below an A5H0 buffer weight and a standard rifle spring in any system, if reliability is high on the list of priorities.

If you put the rig together and it won't run on the base minimum A5H0 and rifle spring, I would increase the gas port size by 3/1000 and see what that gets you. An alternative to going to that extreme (I'm calling it extreme, but I do it pretty often) is to stack about 8 quarters (3/4 of an inch being sure that you bolt carrier isn't banging into the receiver) and go with a carbine spring and buffer. This will give you a bit more tuning ability.

Just be aware, your rig with the +1 gas system length may be finicky; meaning tune it for the ammo you plan to run all of the time. It would suck to tune to some cheap ammo and then when you're done, discover that it won't run on what you want it to.

The following isn't advise, I'm just sharing what I do at this point. I tune my rigs, regardless of caliber in the AR15 platform, to run on an A5H2 buffer with a green springco spring. I've found that tuning the gas system to run that amount of buffer weight has the setup running with a wide operational windows. It will be the least sensitive to ammo and environmental changes. If the setup won't run this, I increase gas port size 3/1000 at a time, until I get to where I want to be. Tuning to an A5H2 will leave you the headroom to either go up to an A5H3 or A5H4 or down to an A5H1 or H0 should the need arises.

OR, you can get to where you want to be on the gas port then go 3/1000 over and run a Riflespeed gas block. This is what I do on my suppressed rigs. Very flexible and reliable.

 

[TonyAngel]

Oh, as for messing with the differing buffer weights. The best deal I've seen is to just buy an A5H4 buffer from KAK. This way you'll have 4 tungsten weights and its the cheapest way to get tungsten weights that I've found. You can just cannibalize steel weights from whatever cheap carbine buffers you have laying around.

 

[WeR0206]

Oh, geez. I feel for you. In any case, I wouldn't burn too many brain cells on it.

Now, you really have to take what I say with a grain of salt. I've had to diagnose and repair MANY ARs in varying calibers, but I have zero experience with 6 ARC. I'm talking in complete generalities.

The beauty and danger of the AR platform is that you can muck with just about every aspect of it to change one thing or another. For every gas system length in each caliber, there is an ideal dwell time at which the system will be the most forgiving. Each gas system length will typically get more and more finicky as you decrease dwell time from whatever the ideal dwell time is.

In this case, I really don't know what effect going +1 on the gas system length will have. Still, in the present case, dealing with an A5 buffer system, I wouldn't go below an A5H0 buffer weight and a standard rifle spring in any system, if reliability is high on the list of priorities.

If you put the rig together and it won't run on the base minimum A5H0 and rifle spring, I would increase the gas port size by 3/1000 and see what that gets you. An alternative to going to that extreme (I'm calling it extreme, but I do it pretty often) is to stack about 8 quarters (3/4 of an inch being sure that you bolt carrier isn't banging into the receiver) and go with a carbine spring and buffer. This will give you a bit more tuning ability.

Just be aware, your rig with the +1 gas system length may be finicky; meaning tune it for the ammo you plan to run all of the time. It would suck to tune to some cheap ammo and then when you're done, discover that it won't run on what you want it to.

The following isn't advise, I'm just sharing what I do at this point. I tune my rigs, regardless of caliber in the AR15 platform, to run on an A5H2 buffer with a green springco spring. I've found that tuning the gas system to run that amount of buffer weight has the setup running with a wide operational windows. It will be the least sensitive to ammo and environmental changes. If the setup won't run this, I increase gas port size 3/1000 at a time, until I get to where I want to be. Tuning to an A5H2 will leave you the headroom to either go up to an A5H3 or A5H4 or down to an A5H1 or H0 should the need arises.

OR, you can get to where you want to be on the gas port then go 3/1000 over and run a Riflespeed gas block. This is what I do on my suppressed rigs. Very flexible and reliable.

The amount of variables, tolerance issues, etc. that one can run into in the AR system is quite mind-boggling. Although there are some known accepted good specs for certain things like gas port sizes and others stuff each gun is almost its own unique fingerprint as far as what it needs to run properly.

For example, in my short stroking issue before I switch to a lighter carrier or start playing with my buffer weights more I actually found that there was a good amount of drag between my bolt and my carrier (I’m doing a mix and match build) and I think this is actually the main cause of my short stroking. Currently When I’m done shooting only 50 rounds and I’m taking the bolt apart to clean it, it’s almost carbon locked in the carrier (using lucas CLP or EWL30). Im going to switch to some polished one piece JP enhanced rings to see if they help then go from there.

Oh, as for messing with the differing buffer weights. The best deal I've seen is to just buy an A5H4 buffer from KAK. This way you'll have 4 tungsten weights and its the cheapest way to get tungsten weights that I've found. You can just cannibalize steel weights from whatever cheap carbine buffers you have laying around.

That’s pretty much what I did as well as buy some aluminum weights from them. They also sell a nice buffer tuning kit for around $45. I ended up kinda just making my own kit that I put in a little plastic organizer box.

 

[Bantam1]

I'm running a Proof carbon 20" with an A5 with the rifle weight buffer. I have zero issues running factory Hornady 108 ELDM ammo. Before I went to the A5 system I ran it with a regular AR rifle buffer and spring. Also zero issues.

 

[zinny]

Proof is rifle+1? What buffer weight are you running. 20" definetly would be more forgiving compared to 18" with the same gas length.

 

[JR1200W3]

@WeR0206

Without knowing all the details of your rifle and the short stroking, which could be caused by other things than simply being undergassed, and barring it being a gas ring issue like you mentioned..... to the theoretical point of base line buffer systems for 6ARC:

Instead of reducing buffer weights and spring rates, I would recommend just opening up the gas port. Instead of biasing the operating system to one extreme and with specialty springs and buffers in order to compensate for an incorrect gasport size. I would rather baseline the buffer weight and spring with a conventional and middle of the road back end, and then just make the gassing correct. Like just keep a rifle length, green springco and an A5 H2 or H1. So you have a little bit above and a little bit below to select from when you change loads. And then work the gas port to get it to operate reliably with a solid buffer system.

Talking about drilling out a gas port scares a lot of people but it is a pretty easy task. You just need to make sure that you don't over penetrate. And there is potential to clean up burrs or a little bit of port erosion with a fresh cut larger hole. You can order a #41 or a 2.4mm bit to step up from .093". This is exactly how my gunsmith gassed my custom 6.5CM barrel, albeit with a mill instead of a drill press or hand drill. I set up the SCS in the buffer weight and spring color I wanted (middle of the road configuration) and we just went up in bit size, firing into a clearing barrel with a proven load, until it locked back. Then you can fine tune, adjust a buffer weight up or down to account for cleaning, changes in powder and loads, etc.

 

[dms416]

Well...

A5H1 w/ milspec rifle spring on the Rifle +1 18" seems to good, but approaching the line. 120 rounds deep and 0 failures to cycle but only 1 failure to hold the bolt open (shooting mostly 5-shot strings) with an 8 round Geissele out 15+ lock backs and I was alternating between a Geissele 8-rounder and a Duramag 20.

 

[WeR0206]

@WeR0206

Without knowing all the details of your rifle and the short stroking, which could be caused by other things than simply being undergassed, and barring it being a gas ring issue like you mentioned..... to the theoretical point of base line buffer systems for 6ARC:

Instead of reducing buffer weights and spring rates, I would recommend just opening up the gas port. Instead of biasing the operating system to one extreme and with specialty springs and buffers in order to compensate for an incorrect gasport size. I would rather baseline the buffer weight and spring with a conventional and middle of the road back end, and then just make the gassing correct. Like just keep a rifle length, green springco and an A5 H2 or H1. So you have a little bit above and a little bit below to select from when you change loads. And then work the gas port to get it to operate reliably with a solid buffer system.

Talking about drilling out a gas port scares a lot of people but it is a pretty easy task. You just need to make sure that you don't over penetrate. And there is potential to clean up burrs or a little bit of port erosion with a fresh cut larger hole. You can order a #41 or a 2.4mm bit to step up from .093". This is exactly how my gunsmith gassed my custom 6.5CM barrel, albeit with a mill instead of a drill press or hand drill. I set up the SCS in the buffer weight and spring color I wanted (middle of the road configuration) and we just went up in bit size, firing into a clearing barrel with a proven load, until it locked back. Then you can fine tune, adjust a buffer weight up or down to account for cleaning, changes in powder and loads, etc.

View attachment 8727753

Thanks for the tip re: drilling out the port hole. I was curious what type of bit people used for that. I will keep this in mind if fixing the bolt drag doesn’t resolve the short stroking.

I agree its best to not resort to super weak springs or super light buffer weights etc to get it to run if it can be avoided. Itd be nice to still be able to use my other 2 lowers on the 6 arc upper without too much tweaking.

The other option besides drilling the gas port (if polished JP one piece gas ring doesn’t fix the issue) is a low mass bolt carrier from JP, Rubber City, etc paired with a standard spring/buffer weight.

 

[WeR0206]

Well...

A5H1 w/ milspec rifle spring on the Rifle +1 18" seems to good, but approaching the line. 120 rounds deep and 0 failures to cycle but only 1 failure to hold the bolt open (shooting mostly 5-shot strings) with an 8 round Geissele out 15+ lock backs and I was alternating between a Geissele 8-rounder and a Duramag 20.

Hmm…maybe bump down to A5H0? How spicy was the ammo you were shooting?

 

[dms416]

Hmm…maybe bump down to A5H0? How spicy was the ammo you were shooting?

factory 108 and 105. I don't reload

I might try an A5h0 eventually for grins; however, this is just fine for the time being getting use to this gun/cartridge.
I also don't have the utmost faith in short, stubby mags anyways compared to their standard capacity counterparts and sheer spring length/tension dynamics.

If it starts failing to lock back on a Duramag 20 or higher capacity Geissele, that's more of a concern.

 

[JR1200W3]

While it's not always clear, and port size is always a factor...

Where it seemed like the jumping off point for one's preferences in 5.56 is, it SEEMS like the starting point for the 6ARC is the next step up in gas length AND down one weight in the A5 system.

For example: where I would traditionally run an unsuppressed 18" rifle with an A5h2 in 5.56.... for a 6ARC 18" on a rifle +1 with an A5h1 (or 0) seems a parallel operational envelope.

Am I about in the ballpark?

I'm mildly interested in how the long stroke BCG designs with their peculiar buffers and springs, like the Griffin or Surefire solutions might do in cartridges with a lot of case volume and gas pressure for 5.56 components

 

[dms416]

I'm mildly interested in how the long stroke BCG designs with their peculiar buffers and springs, like the Griffin or Surefire solutions might do in cartridges with a lot of case volume and gas pressure for 5.56 components

Funny you mention that, I just got a promo email today in that Primaryarms(maybe) is selling the Surefire BCG's again...even though they looked like they were gone for quite a while and not talked about.

I remember there was the AROC that had it's own proprietary extension while the Optimized bcg for surefire was drop-in(ish)

MDM 17 - SureFire Advanced Rifle Operating Core | Soldier Systems Daily

SureFire's new Advanced Rifle Operating Core is a system consisting of an enhanced Bolt Carrier Group, Barrel Extension, Buffer and Spring. Because ARO ...

ssdaily.tempurl.host

 

[JR1200W3]

Y

Funny you mention that, I just got a promo email today in that Primaryarms(maybe) is selling the Surefire BCG's again...even though they looked like they were gone for quite a while and not talked about.

I remember there was the AROC that had it's own proprietary extension while the Optimized bcg for surefire was drop-in(ish)

MDM 17 - SureFire Advanced Rifle Operating Core | Soldier Systems Daily

SureFire's new Advanced Rifle Operating Core is a system consisting of an enhanced Bolt Carrier Group, Barrel Extension, Buffer and Spring. Because ARO ...

ssdaily.tempurl.host

Ya, I got an announcement email from Surefire and then the flyer from PA. All the delayed stuff in ARs kind of interest me, within their own niche applications. Like what Broad River Tactical is doing with the CMMG radial delayed 9 mm PCCs. Griffins gas pocket BCG has the Kspec stuff going on, plus a long stroke delayed response if paired with their bolt and buffer/ spring for short barreled suppressed applications.

I wonder if the delayed unlocking would at the very least help treat your brass a little better. Maybe spread some recoil out, and potentially, maybe/ maybe not even reduce some of the gas blow back coming down the barrel into the action.

 

[dms416]

Y

Ya, I got an announcement email from Surefire and then the flyer from PA. All the delayed stuff in ARs kind of interest me, within their own niche applications. Like what Broad River Tactical is doing with the CMMG radial delayed 9 mm PCCs. Griffins gas pocket BCG has the Kspec stuff going on, plus a long stroke delayed response if paired with their bolt and buffer/ spring for short barreled suppressed applications.

I wonder if the delayed unlocking would at the very least help treat your brass a little better. Maybe spread some recoil out, and potentially, maybe/ maybe not even reduce some of the gas blow back coming down the barrel into the action.

There was a fella that did a whole bunch of high-speed camera work showing the merits of the A5 system in various guns and his vids with the HK416 and the A5h4 are what sold me on the idea.

I very much would like to see the same on the Surefire done in the same fashion...and with various calibers.

 

[zinny]

Slight hijack of this thread, had a 18" 6arc barrel from a well known manufacturer, gas port was canted. I tried to run it thru a match and it was just not cycling. Sent it back, asked for a refund.

Well two weeks later they send me back the same exact barrel, same extension on the barrel too. but it looks like gas port is now better timed. That kosher, especially for a match system?

Just got a UPS notification I was getting a package, which was recieved today, no reply back or even a note in the package.

and yea ditto on the benefits of the A5 system, SOLGW did a video on it and sold me on the system.

 

[JR1200W3]

Gas port? Or gas block? Your barrel has two gas ports now?

 

[zinny]

Gas port, it was crooked at the 11.5 O'clock or so previously. Enough that you could clearly see the gas tube touch the ejection port side of the upper reciever, when its supposed to semi free float in the middle.

Its the exact same barrel, same barrel extension too. So have to assume they messed with the extension to time it. Which doesn't sound like a good thing to do to a match barrel.

 

[JR1200W3]

Gas port, it was crooked at the 11.5 O'clock or so previously. Enough that you could clearly see the gas tube touch the ejection port side of the upper reciever, when its supposed to semi free float in the middle.

Its the exact same barrel, same barrel extension too. So have to assume they messed with the extension to time it. Which doesn't sound like a good thing to do to a match barrel.

Semantics but maybe it was just the extension that was mistimed. I think the gas port gets drilled first, then the tenon is threaded, then the chamber is cut to headspace on the bolt/ extension. So if the timing offset was on the lucky side, they just had to cut the shoulder in the tenon back, extend the threads, and deepen the chamber to headspace. If that was the case, I don't think it's a bum barrel.

I had a very expensive 6.5CM barrel made and the extension wouldn't feed 140 Hybrids. We found a custom extension made for 22 Creedmoors and verified it would feed. My Smith had to cut .011" back to clock the extension to the gas port. It's a hammer of a barrel.

I would give it a chance and do my best to shed the natural, subconscious bias.

 

[dms416]

Well, the lock back issue was not gas system related but in relation to the Geissele follower and my catch.

I will not be going any lower or lighter…if anything I’ll bump things up and see

 

[Bantam1]

Proof is rifle+1? What buffer weight are you running. 20" definetly would be more forgiving compared to 18" with the same gas length.

Yes it is Rifle + 1 gas length. I think the standard A5 weight was 5.3 ounces, same as the rifle buffer.

 

[WeR0206]

Yes it is Rifle + 1 gas length. I think the standard A5 weight was 5.3 ounces, same as the rifle buffer.

Depends on what your definition of standard is (all steel weights, etc). FWIW, from chatgpt, A5H2 would be closest to 5.3 oz.

Edit: I removed the chart AI spit out bc it had A5 buffers only using 3 weights instead of 4 so I don’t trust anything else in it

 

[Bantam1]

Depends on what your definition of standard is (all steel weights, etc). FWIW, from chatgpt, A5H2 would be closest to 5.3 oz.

View attachment 8728867

When I bought the A5 kit they only offered one weight at the time. I am not up to speed on all the other buffer weight versions they off and the naming conventions for them. The 3 kits I have were all purchased when they released them years ago. Also the A5 buffers have 4 weights inside I think. I took one apart to adjust the weight. I think it's 4 weights and a short spring. It's been many years since I did it. I thought they were all steel but I could be mistaken.

 

[dms416]

When I bought the A5 kit they only offered one weight at the time. I am not up to speed on all the other buffer weight versions they off and the naming conventions for them. The 3 kits I have were all purchased when they released them years ago. Also the A5 buffers have 4 weights inside I think. I took one apart to adjust the weight. I think it's 4 weights and a short spring. It's been many years since I did it. I thought they were all steel but I could be mistaken.

This is correct. The chart is flawed.
The “h” refers to the number of tungsten weights be it 0-4.

 

[WeR0206]

This is correct. The chart is flawed.
The “h” refers to the number of tungsten weights be it 0-4.

Haha just noticed that. Thanks for pointing out the chatGPT fucked up the number of buffer weights for A5. Fucking AI…smh

Here’s a new and corrected version from the AI. It only took me about 15 fucking iterations for it to get everything correct I think.

System	Buffer Type	Approx. Weight	Spring Strength	Spring Length	Insert Combo (Steel / Tungsten)	Recommended Use Case
Carbine	Carbine (All Aluminum)	1.7 oz	Light	Carbine	N/A	Low-recoil race guns, short-stroke tuning
Carbine	Carbine (Standard)	3.0 oz	Light	Carbine	3 / 0	General use, OEM configuration
Carbine	H1	3.8 oz	Light–Medium	Carbine	2 / 1	Mid-gas or overgassed setups
Carbine	H2	4.6 oz	Medium	Carbine	1 / 2	Suppressed or hotter loads
Carbine	H3	5.4 oz	Medium–Heavy	Carbine	0 / 3	Heavily overgassed, suppressed SBRs
Carbine	XH / HSS	5.7–6.5 oz	Heavy	Carbine	0 / 3 + spacers	Full-auto, extreme suppression
A5	A5H0	3.8 oz	Medium	Rifle (A5)	4 / 0	Lightweight tuning, precision builds
A5	A5H1	4.6 oz	Medium	Rifle (A5)	3 / 1	Balanced DMR or 16–18†rifle builds
A5	A5H2	5.3 oz	Medium–Heavy	Rifle (A5)	2 / 2	Suppressed or hotter ammo in A5 systems
A5	A5H3	6.1 oz	Heavy	Rifle (A5)	1 / 3	Suppressed, full-mass precision or SBR
A5	A5H4	6.8 oz	Extra Heavy	Rifle (A5)	0 / 4	Full-auto A5 or extreme suppression tuning

 

[dms416]

Haha just noticed that. Thanks for pointing out the chatGPT fucked up the number of buffer weights for A5. Fucking AI…smh

Yeah...ya gotta watch out for that. Sometimes I like to read the AI for a laugh myself.

 

[zinny]

When I bought the A5 kit they only offered one weight at the time. I am not up to speed on all the other buffer weight versions they off and the naming conventions for them. The 3 kits I have were all purchased when they released them years ago. Also the A5 buffers have 4 weights inside I think. I took one apart to adjust the weight. I think it's 4 weights and a short spring. It's been many years since I did it. I thought they were all steel but I could be mistaken.

Odin makes an adjustable buffer system for standard carbine length buffer, I wish they'd make one that was A5 length, honesty if they made a custom buffer bumper that was longer, thatd probably do it. But yeah A5 has 4 weights vs 3 for std

 

[hlee]

Odin makes an adjustable buffer system for standard carbine length buffer, I wish they'd make one that was A5 length, honesty if they made a custom buffer bumper that was longer, thatd probably do it. But yeah A5 has 4 weights vs 3 for std

All you need is a hard spacer to take up the extra space. Quarters will work in a pinch. JP provides a delrin spacer with their SCS so that one part can be used with both carbine and rifle extensions. I had an unused JP SCS spacer and cut it to fit my application. Not rocket surgery.