Long COAL .223 Gas Gun

[swhiteh3]

So I was thinking today that most gas-guns are limited in bullet selection (and in some parts powder capacity) mostly by magazine length, and that really limits what a .223 AR15 can do compared to a comparable bolt gun. (Yes, I know that the gas system robs gas volume, barrel length is typically shorter, cycling mass moving in the rifle affects some inherent accuracy, etc and all those things matter too).

So my thought was that as we start seeing more and more small-frame .308s, why could we not adapt some of that design work to build a .223 gas gun, still in a small frame size, that would take a .308 length magazine (or at least one that's longer than the current 223 ones available). Certainly there would be some design work required, and production of that magazine would require some engineering, but is the idea doable?

I'd love a gas gun that could run my bolt gun loads! (Even if they were a little slower and less precise.)

 

[Molon]

(Yes, I know that the gas system robs gas volume,

The amount of relative muzzle velocity lost due to the cycling of the AR-15 gas system is inconsequential.

Observations On The Velocities Obtained From A Direct Impingement Gas System AR-15

Compared To A “Single Shot” AR-15​

I conducted a simple test that consisted of a comparison of the velocities obtained from an AR-15 using the direct impingement gas system with a standard sized gas block, to that of the same barrel with no gas system at all; that is, I completely clamped-off the gas port, turning the AR-15 into a "single-shot" rifle.


The ammunition used in this test was hand-loaded 69 grain Sierra MatchKings. I fired three 10-shot strings of this ammunition in a row over an Oehler 35-P chronograph, with proof-screen technology. The center screen of the chronograph was positioned 21 feet from the muzzle. The test vehicle was a 16” barreled AR-15 with a carbine-length direct impingement gas system and a standard sized (0.75”) Larue Tactical low-profile gas block.


After firing the three 10-shot strings from the upper using the direct impingement system, I let the barrel cool and then removed the gas tube. Next, I removed the low profile gas block from the barrel, flipped it 180 degrees and reinstalled it on the barrel, thereby completely clamping off the gas port on the barrel. This gave me a single-shot AR-15 in which I had to manually load and eject each round using the charging handle, thus giving me the means to determine the amount of velocity that is lost due to the auto-loading function of the direct impingement gas system of the AR-15.


Following the same procedure as previously used, I fired three 10-shot strings of the same hand-loaded 69 grain Sierra MatchKings over the Oehler 35-P chronograph positioned 21 feet from the muzzle using the single-shot AR-15. The results are show in the table below.


As you can see in the table below, there was a small (but statistically significant) difference of 23 FPS between the grand averages of the velocities from the direct impingement gas system and the single-shot (gas port clamped-off) system.

Atmospheric Conditions

Temperature- 63 degrees F

Humidity - 34%

Barometric pressure – 30.20

Elevation - 960 feet above sea level

Skies – sunny, Jupiter aligned with Mars

 

[TheOE800]

Because STANAG magazine well.

 

[swhiteh3]

Because STANAG magazine well.

I'm talking about a lower with a .308 sized magwell, and a custom magazine.

 

[swhiteh3]

The amount of relative muzzle velocity lost due to the cycling of the AR-15 gas system is inconsequential.

The whole point of my listing those things was so that we DIDN'T get side-tracked. :-(

 

[TheOE800]

I'm talking about a lower with a .308 sized magwell, and a custom magazine.

Exactly. Won’t happen because STANAG magazine well.

 

[swhiteh3]

Exactly. Won’t happen because STANAG magazine well.

Can you expand on that? I don't see why a company could not utilize the .308 magwell with a custom magazine to fit it. Of course, it won't be compatible with the standard magwell on other AR15s. Am I missing something?

 

[simonp]

Can you expand on that? I don't see why a company could not utilize the .308 magwell with a custom magazine to fit it. Of course, it won't be compatible with the standard magwell on other AR15s. Am I missing something?

Id venture one guess, not enough demand to justify the tooling up to create the modified receiver and to build new magazines.

Most folks shooting gas guns looking to shoot long COAL just use a sled or a standard magazine and single feed. How many are going to need or want to load a 20 round magazine with long rounds?

 

[Mike_in_FL]

If this is what you desire it makes more sense just to build a bolt gun. Ten round magazines are already available versus trying to deal with feeding from .308 length magazines with incorrect, for cartridge, followers.

 

[6.5SH]

Getting magazines made without a known demand would be a huge hurdle.
I've seen a few people use modified PRI magazines and even cutting the front of the mag well to use longer bullets like 75gr ELD-M in AR-15 size lowers. It would be a very expensive niche.

 

[TonyTheTiger]

I've done quite a bit of silliness to shoot 2.41" OAL ammo in a small frame AR. Ballistics wise it is a huge step up from mag length 223. The problem with a company designing and producing a proprietary lower to accommodate this is that it only makes sense to about 42 weirdo handloaders. It does nothing for the factory ammo buyer, which is most of the market.

 

[redneckbmxer24]

Or just run a 224V since that’s the whole point of it and all…

 

[TonyTheTiger]

Or just run a 224V since that’s the whole point of it and all…

Yeah, there is that.
Not that 224V couldn't be further hotrodded by more OAL allowance.
When I was dicking around with long 223 loads 224V didn't exist yet, and even if it did I probably would've still done it. Partly because I like to avoid adding cartridges to reload for, but mostly out of stubbornness. Either way, it's all handloader stuff and uninteresting to most people.

 

[TheOE800]

If only someone would make metal Six8 magazines.

 

[TonyTheTiger]

If only someone would make metal Six8 magazines.

Or if they sold stripped receivers.

 

[TheOE800]

Or if they sold stripped receivers.

They do. Lipseys had them in a month or two ago.

 

[msgriff]

There's a member here who just made a 0% large frame lower that uses short action AICS mags. Similar intent to get a bit more length for his 300 WSM and 6.5 PRC uppers. You could gain 0.200" COAL if someone did the same for an AR-15. Minor upper modification might be all it takes after that.

 

[TheOE800]

There's a member here who just made a 0% large frame lower that uses short action AICS mags. Similar intent to get a bit more length for his 300 WSM and 6.5 PRC uppers. You could gain 0.200" COAL if someone did the same for an AR-15. Minor upper modification might be all it takes after that.

Gonna need 20rd AW mags stat. ARs feed from both sides anyway…

 

[Ernest 5.56]

 

[MarshallDodge]

@swhiteh3

We are on the same page, and I had the exact same idea when the SFAR came out. If you could get a 223 AR to chamber an 80 grain VLD type bullet, that would be a fun project. I would be building one in 223AI, and it would only be half a step be behind a 224 Valkyrie.

In this day and age with metal 3DP coming online, prototype mags would be easy to make.

 

[swhiteh3]

Just work within the confines of the platform and learn to shoot better. If this is a 1% AMU shooter, I'll retract that statement. If it's just another new guy with a "new to him" idea, I stand by it.

I’m brainstorming the idea to help win national level team matches, like Mammoth, where 223 is often a requirement and gas guns provides a large advantage in certain scenarios. I train a lot. (Not as much as I should, but a lot LOL!!)

 

[swhiteh3]

@swhiteh3

We are on the same page, and I had the exact same idea when the SFAR came out. If you could get a 223 AR to chamber an 80 grain VLD type bullet, that would be a fun project. I would be building one in 223AI, and it would only be half a step be behind a 224 Valkyrie.

In this day and age with metal 3DP coming online, prototype mags would be easy to make.

Funny, I do aerospace level 3DP for a living.

I do wonder about the 6ARC platform. I need to learn more about that cartridge (base diameter, coal, etc) to see if using that as a stepping off point might make sense.

For this project, I can not use 223 AI as much as I might like to. Must be 223 but freebore is open.

 

[swhiteh3]

Magazines will cripple you. It is much more difficult to mass produce reliable magazines than people think. The bigger feat isn't designing a new platform that shoots .223 in an AR10 length magwell in a AR-15 sized gun. It's making a reliable, custom, small batch of magazines. For a person to go through all that they're going to have to commit a decade of pouring money down the drain.

How bad do you want to win those matches and how sure are you that secret weapons are the key to winning vs just learning to be a better shooter? That's the calculus of your question.

No doubt! But I think there are manufacturers who might take on that job if there was a clear plan. If I was trying to keep this "secret", I would not post it here. But I think there are enough people who would like to be able to shoot a more ballistically capable .223 gas gun that it would be popular if it was figured out. Regardless, those are things to let the market figure out.

But as far as existing magazines, I'll bet an existing metal 224 Valkyrie AR-10 magazine (if one is made) could be made to feed 223 with some modifications - at least to prove the concept. Polymer, of course, are a lot harder to modify.

I wonder about a BCG for an AR10 with a .223 bolt face. The barrel is the easy part.

 

[Ernest 5.56]

No doubt! But I think there are manufacturers who might take on that job if there was a clear plan. If I was trying to keep this "secret", I would not post it here. But I think there are enough people who would like to be able to shoot a more ballistically capable .223 gas gun that it would be popular if it was figured out. Regardless, those are things to let the market figure out.

But as far as existing magazines, I'll bet an existing metal 224 Valkyrie AR-10 magazine (if one is made) could be made to feed 223 with some modifications - at least to prove the concept. Polymer, of course, are a lot harder to modify.

I wonder about a BCG for an AR10 with a .223 bolt face. The barrel is the easy part.

What overall length do you need?

No idea if these will feed 5.56 but they are available along with the oversized recievers


The new Magpul [6.8 SPC] mags will allow for an OAL of 2.32"
https://defensereview.com/magpul-pm...ci-m6-8-uciw-ultra-compact-individual-weapon/

 

[bfoosh006]

22 Creedmoor ?

 

[TheOE800]

A metal Six8 magazine would be awesome, as it is the plastic Magpul ones are still fairly COAL limiting aren’t they?

 

[Ernest 5.56]

A metal Six8 magazine would be awesome, as it is the plastic Magpul ones are still fairly COAL limiting aren’t they?

These are the special ones for Saudi with non standard dimensions that require a special receiver set.

 

[TheOE800]

I know, I own a Six8… You think 2.32” is more sufficient over 2.26”? The plastic Six8 mag is not a huge advancement in that.

 

[TonyTheTiger]

Especially when stainless ASC mags will get you to 2.31" in a standard small frame.

 

[Ernest 5.56]

Especially when stainless ASC mags will get you to 2.31" in a standard small frame.

Wow not much to gain at all. Didn't realize you could get so much with a stainless mag

 

[Ernest 5.56]

Sounds like you could maybe get there with a custom bolt and barrel extension and a 3d printed mag lol

I assume you could use a 22 blank and have it reamed??

Just thinking out loud

 

[TonyTheTiger]

Wow not much to gain at all. Didn't realize you could get so much with a stainless mag

I think they'll actually get to 2.316" or so if we want to get really specific.

 

[TheOE800]

Wow not much to gain at all. Didn't realize you could get so much with a stainless mag

Why I said a stainless Six8 mag would be cool, but no one’s dedicating the resources to that when the receiver sets are hardly ever available or in circulation and the production rifle isn’t even popular. No market.

 

[Ernest 5.56]

Why I said a stainless Six8 mag would be cool, but no one’s dedicating the resources to that when the receiver sets are hardly ever available or in circulation and the production rifle isn’t even popular. No market.

There are these receiver sets available not sure of the quality though.

Designed to use the LWRC SIX8 magazine

C-6.8 Slick Side Billet Upper

 

[TonyTheTiger]

There are these receiver sets available not sure of the quality though.

Designed to use the LWRC SIX8 magazine

C-6.8 Slick Side Billet Upper

NFA makes good stuff.

 

[carbonbased]

I’m no engineer, but guns seem much more like hand-made mechanical watches than most plug-play-it-works-or-it-doesn’t modern-day devices.

Seems easy to underestimate the importance of the small bits that make both mechanical watches and firearms function (and easy to underestimate the effort needed to discover & produce those small bits).

John Moses Browning etc. were more like watchsmiths that created entire new watch movements (like rifle actions), if you will. No small task.

But I could be wrong. Perhaps @swhiteh3 can solve the issue he faces with less effort than some think.

 

[Benroe1000]

I was having trouble getting the accuracy I wanted using Barnes bullets for hunting at standard mag length so I cut the front of the mag out so I could seat the bullets long where my gun likes them. Others here have pictures.

 

[Ernest 5.56]

Cavity back was selling a modifed pri 5.56 and 6.8 but looks like they are sold out


https://www.cavitybackbullets.com/product-p/cb-pri-mod-5.56.htm

 

[Pappasniper]

I can dig what you are saying because I like my Tikka TX3 varmint bolt gun bc I can run 88 ELD's with it. I have to single feed them but that is a breeze with a Mountain Tactical mag. Mag length has always limited us on .223 and 308 for that matter.

PB

 

[Kinked_Chrome]

I have also cut the front my mags, my mag well, upper and barrel extension. I load 75gr elds to 2.42oal and shoot them at 2750 from an 18in gun with a modest load of cfe223. Its like they are in a different league vs mag length 77smks. Factory imi 77gr would do 2650 from this gun.

I wouldn't exactly consider it go to war ready/reliable, but it lets me shoot long range matches a cheaper than my large frame guns. Midway has the 75s eld seconds from time to time, but even full price 75 elds are pretty affordable.

I have a 24in barrel i think that ill modify next and put in that upper which should give me an extra ~100fps over the 18in. If i could get to 2900 and keep them 1moa with cfe223, id be pretty happy.

 

[MarshallDodge]

I have also cut the front my mags, my mag well, upper and barrel extension. I load 75gr elds to 2.42oal and shoot them at 2750 from an 18in gun with a modest load of cfe223. Its like they are in a different league vs mag length 77smks. Factory imi 77gr would do 2650 from this gun.

I wouldn't exactly consider it go to war ready/reliable, but it lets me shoot long range matches a cheaper than my large frame guns. Midway has the 75s eld seconds from time to time, but even full price 75 elds are pretty affordable.

I have a 24in barrel i think that ill modify next and put in that upper which should give me an extra ~100fps over the 18in. If i could get to 2900 and keep them 1moa with cfe223, id be pretty happy.

I would like to see pics of your modifications if you care to share.

 

[TonyTheTiger]

I have also cut the front my mags, my mag well, upper and barrel extension. I load 75gr elds to 2.42oal and shoot them at 2750 from an 18in gun with a modest load of cfe223. Its like they are in a different league vs mag length 77smks. Factory imi 77gr would do 2650 from this gun.

I wouldn't exactly consider it go to war ready/reliable, but it lets me shoot long range matches a cheaper than my large frame guns. Midway has the 75s eld seconds from time to time, but even full price 75 elds are pretty affordable.

I have a 24in barrel i think that ill modify next and put in that upper which should give me an extra ~100fps over the 18in. If i could get to 2900 and keep them 1moa with cfe223, id be pretty happy.

When I did that same thing I was getting just a bit over 2900fps from a 22" barrel and TAC or 8208 XBR. It was a polygonal barrel which is always touted as being faster than conventional rifling but I never saw evidence of that. Also the only throat I've destroyed in 3k ish rounds.

 

[Kinked_Chrome]

I would like to see pics of your modifications if you care to share.

Its not pretty but it works, and I was able to do it all with a die grinder and file. I may do another like this and next time ill do it a little more proper. I could load all the way to 2.45oal, but thatd be in the lands for this chamber. I think right now im .020 off or so.

When I did that same thing I was getting just a bit over 2900fps from a 22" barrel and TAC or 8208 XBR. It was a polygonal barrel which is always touted as being faster than conventional rifling but I never saw evidence of that. Also the only throat I've destroyed in 3k ish rounds.

Thats encouraging. My 24in is just a Ballistic Advantage discount special, seems to shoot ok for the price though.

 

[Ernest 5.56]

When I did that same thing I was getting just a bit over 2900fps from a 22" barrel and TAC or 8208 XBR. It was a polygonal barrel which is always touted as being faster than conventional rifling but I never saw evidence of that. Also the only throat I've destroyed in 3k ish rounds.

Who made the barrel?

 

[TonyTheTiger]

Who made the barrel?

Black Hole Weaponry

 

[Ernest 5.56]

Black Hole Weaponry

Wow that's crazy sounds like some sort of metallurgical defect

 

[TonyTheTiger]

Wow that's crazy sounds like some sort of metallurgical defect

It's not unheard of for Highpower shooters to junk 223 barrels under 4k rounds, but this thing was smoked. I still have it in my pile of old barrels, it's fun when people ask me what it means or how I know when a barrel is toast. I just drop a loose 55fmj down the bore and show them that it's 1.5" past the end of the chamber before it hits rifling and stops. Funny enough it would still shoot a great 4 shot group with 77 SMK's, but that fifth one was always sideways in a different area code.

 

[Benroe1000]

That's a wild mod. I'm definitely not that committed lol

 

[DHDeal]

The Cavity Back magazine is easy to do yourself if you just have to try it and like to tinker. I suspect everyone knows they use a PRI mag as it's welded front and back. Not sure what my exact max OAL for them are as my notes are in the shop, but 2.35"ish is doable if your magwell will allow. Juice might not be worth the squeeze but for me it was. I know I can seat a 70/75 VLD out there and they like it.

Did the same with a PRI 6.8 magazine for one of my Grendel's and it was also a success. My definition of success is closer to lands, more powder (within reason), and very good accuracy.

I haven't been brave enough to hog out the front of the magwell and scoop out the barrel extention yet.

The problem, if you want to consider it one, is that ammo loaded long becomes pretty specific to that rifle. Unless you have 2 rifles with twin chambers that is. I'm a hoarder and more MTM boxes labeled for specific rifles is right down my alley...

 

[jLorenzo]

It's not unheard of for Highpower shooters to junk 223 barrels under 4k rounds, but this thing was smoked. I still have it in my pile of old barrels, it's fun when people ask me what it means or how I know when a barrel is toast. I just drop a loose 55fmj down the bore and show them that it's 1.5" past the end of the chamber before it hits rifling and stops. Funny enough it would still shoot a great 4 shot group with 77 SMK's, but that fifth one was always sideways in a different area code.

Tac and 8208 XBR both double base powders, when run hot will smoke barrels faster.