Gas port size 16” 308

[Flying Fish]

Gents,

I’m new here and have built a few AR15’s, now preparing to build an AR10 in .308. I’ve searched the forum and can’t find an answer to my particular build. Main thing here is barrel selection and gas port size. I’ve seen gas port sizes range from .072 - .083 and trying to figure which one is correct. Here’s a run down on my thoughts.

- Rifle that is a shooter and will run, I dont care if it’s a bit over gassed and will run a suppressor when I feel like it
- Midlength gas
- A5 tube with H2 buffer and green spring
- Ballistic Advantage 16” Hanson stainless with .073 gas port
- NON adjustable pinned gas block
- Planned build will be a reliable shooter for animals and defense that will eat all ammo. Don’t care about punching paper but accuracy still
matters.

Anything I’m missing?

Thanks

 

[TonyTheTiger]

Sounds like you're getting an .073 regardless of any replies.
A mid gas 308 with no provisions for gas adjustment in conjunction with occasional suppressor use sounds like a not great idea though.

 

[Flying Fish]

Sounds like you're getting an .073 regardless of any replies.
A mid gas 308 with no provisions for gas adjustment in conjunction with occasional suppressor use sounds like a not great idea though.

Well that’s why I came here and all barrels are still on the drafting table, BA seems like the best value.

What do you recommend?

 

[msgriff]

Gas port diameters on .308 barrels are generally the same as .223 barrels of the same length, gas journal diameter, gas system length, or dwell. The increased pressure of the .308 compensates for the higher operating system mass and required extraction force. Running suppressed will change things up, especially with high back pressure cans.
Here's a data set for gas port diameters of various barrels. I believe that I have another set that I'll post that includes large frame barrels.
Gas Port Diameters Spreadsheet

 

[BCP]

I've built a lot of AR10s and now the only one I have is a sig 716i that I bought used for a grand. There's nothing wrong with your setup on paper but it'll likely kick kinda hard and not be very fun to shoot long strings with.

My suggestions would be armalite spring, with the A5 tube you can swap in regular carbine buffers h1 h2 whatever, longer gas system, barrel with matched bolt from a decent company (criterion for example). An adjustable gas block is highly recommended.

 

[Flying Fish]

Gas port diameters on .308 barrels are generally the same as .223 barrels of the same length, gas journal diameter, gas system length, or dwell. The increased pressure of the .308 compensates for the higher operating system mass and required extraction force. Running suppressed will change things up, especially with high back pressure cans.
Here's a data set for gas port diameters of various barrels. I believe that I have another set that I'll post that includes large frame barrels.
Gas Port Diameters Spreadsheet

One heck of a data set, thanks for sharing.

 

[Flying Fish]

I've built a lot of AR10s and now the only one I have is a sig 716i that I bought used for a grand. There's nothing wrong with your setup on paper but it'll likely kick kinda hard and not be very fun to shoot long strings with.

My suggestions would be armalite spring, with the A5 tube you can swap in regular carbine buffers h1 h2 whatever, longer gas system, barrel with matched bolt from a decent company (criterion for example). An adjustable gas block is highly recommended.

Man, I really don’t want another failure point and have to dick around with adjusting gas.

 

[TonyTheTiger]

Well that’s why I came here and all barrels are still on the drafting table, BA seems like the best value.

What do you recommend?

At least an intermediate if not rifle gas 16" for your application. No matter what, you're going to have a tricky operational window to have it work well both suppressed and unsuppressed without a way to regulate gas.

 

[Jsp556]

My can is still in jail so I can’t comment on how they run suppressed but the 16” rifle gassed 308 and 6.5 Creedmoor Criterion barrels I have function fine so far. They’re fun to shoot and neither strings shots when they’re hot. The gas block on the 6.5 is wide open and the 308 doesn’t have an adjustable gas block. That may change with a can but I won’t mess with either unless it’s bad. I’d rather have a little extra gas than keeping it on the ragged edge of reliability.

 

[BCP]

If he assembles the rifle properly and sticks with normal milspec ammo he'll 99% be fine the suppressor is the biggest variable.

 

[Cascade Hemi]

Well that’s why I came here and all barrels are still on the drafting table, BA seems like the best value.

What do you recommend?

It isn't a good value once you factor in your time and ammunition. Criterion sells reasonably priced barrels that are guaranteed to shoot.

Rifle length gas and an AGB will go a long way toward a rifle that works.

 

[Flying Fish]

I just looked at Criterion barrels and price isn’t too bad although they are a little heavier. Might go this route and trade off a little heavier barrel if they are that good.

Was originally planning on an Aero BCG but maybe not. How’s the head spacing with these barrels and do certain BCGs work better?

 

[Norther]

After trying a mid-gas 16” .308, I had it cut to 12.5”. It still functions without issue. Then I bought a rifle gas 16”.

 

[Cascade Hemi]

I just looked at Criterion barrels and price isn’t too bad although they are a little heavier. Might go this route and trade off a little heavier barrel if they are that good.

Was originally planning on an Aero BCG but maybe not. How’s the head spacing with these barrels and do certain BCGs work better?

I don't have an Aero BCG but they get OK reviews. I have a couple of other low end LFAR BCGs in my parts bin and don't think much of them. Rubber City makes an OK mid grade BCG. ToolCraft gets ok reviews too.

 

[LRRPF52]

Gents,

I’m new here and have built a few AR15’s, now preparing to build an AR10 in .308. I’ve searched the forum and can’t find an answer to my particular build. Main thing here is barrel selection and gas port size. I’ve seen gas port sizes range from .072 - .083 and trying to figure which one is correct. Here’s a run down on my thoughts.

- Rifle that is a shooter and will run, I dont care if it’s a bit over gassed and will run a suppressor when I feel like it
- Midlength gas
- A5 tube with H2 buffer and green spring
- Ballistic Advantage 16” Hanson stainless with .073 gas port
- NON adjustable pinned gas block
- Planned build will be a reliable shooter for animals and defense that will eat all ammo. Don’t care about punching paper but accuracy still
matters.

Anything I’m missing?

Thanks

You basically want a stock DIY AR-10 with 16” MLGS barrel from BA that will run reliably unsuppressed and suppressed with all ammunition.

This plan will not work for a number of reasons, the biggest ones being roll the dice with BA barrels and the variability of factory .308 and 7.62x51 ammunition.

7.62x51 has gone through a number of Mil-Std and NATO standard iterations with chamber and gas port pressure specs at certain lengths, starting with the M14 and FAL. The original AR-10 was set up to run on those specs as well, with a similarly-located gas port.

With MLGS 16”, the port is a bit closer to the chamber.

The FAL has a closer gas port location, but it also has an excellent gas regulator and bleed-off design to be tunable to ammunition and conditions. It is the most prolific rifle with an adjustable gas system in the world.

What I would consider is the Bootleg Adjustable Gas Carrier for LR-308, which just came out recently.

It gives you 4 positions that are adjustable through the ejection port with a small flat head, very easy to use.

You might also consider a dual ejector bolt with smaller firing pin aperture.

I’ve been down this path over the past 30+ years and chose to go to AR-15s chambered in 6.5 Grendel instead.

I still have 2 large frame AR-10s in .260 Rem and .308, and 1 Medium-Small frame in .308, but don’t shoot them.

 

[Jsp556]

I don't have an Aero BCG but they get OK reviews. I have a couple of other low end LFAR BCGs in my parts bin and don't think much of them. Rubber City makes an OK mid grade BCG. ToolCraft gets ok reviews too.

I know you weren’t asking but the OP should be aware that the phosphate Aero 308 BCG does not have a chrome lined bore or gas key.

 

[Cascade Hemi]

I know you weren’t asking but the OP should be aware that the phosphate Aero 308 BCG does not have a chrome lined bore or gas key.

Aero makes decent receivers and LPK. I'd skip the rest from them. Frankly, I'd spend the money on a JP BCG. Low end is exactly that.

 

[Flying Fish]

You basically want a stock DIY AR-10 with 16” MLGS barrel from BA that will run reliably unsuppressed and suppressed with all ammunition.

This plan will not work for a number of reasons, the biggest ones being roll the dice with BA barrels and the variability of factory .308 and 7.62x51 ammunition.

7.62x51 has gone through a number of Mil-Std and NATO standard iterations with chamber and gas port pressure specs at certain lengths, starting with the M14 and FAL. The original AR-10 was set up to run on those specs as well, with a similarly-located gas port.

With MLGS 16”, the port is a bit closer to the chamber.

The FAL has a closer gas port location, but it also has an excellent gas regulator and bleed-off design to be tunable to ammunition and conditions. It is the most prolific rifle with an adjustable gas system in the world.

What I would consider is the Bootleg Adjustable Gas Carrier for LR-308, which just came out recently.

It gives you 4 positions that are adjustable through the ejection port with a small flat head, very easy to use.

You might also consider a dual ejector bolt with smaller firing pin aperture.

I’ve been down this path over the past 30+ years and chose to go to AR-15s chambered in 6.5 Grendel instead.

I still have 2 large frame AR-10s in .260 Rem and .308, and 1 Medium-Small frame in .308, but don’t shoot them.

Great info, thanks. I might just have to change my idea and use an adjustable gas block or look into the adjustable gas carrier. Are the adjustable systems ever a common failure point?

 

[BCP]

Great info, thanks. I might just have to change my idea and use an adjustable gas block or look into the adjustable gas carrier. Are the adjustable systems ever a common failure point?

Not really.

Also take a look at this thread, palmetto has been having sales on the Armalite 308s:

Armalite AR10A TAC 18

I’ve never really been one to do reviews. If you’re expecting @bigjake83 , @LRRPF52 , or @sinister level info or details you’re gonna be disappointed. I don’t take a lot of pics, the ones I take are crappy, and I have poor grammer. So any time people ask about large frames I usually recommend...

www.snipershide.com

 

[smoooth1]

Gents,

I’m new here and have built a few AR15’s, now preparing to build an AR10 in .308. I’ve searched the forum and can’t find an answer to my particular build. Main thing here is barrel selection and gas port size. I’ve seen gas port sizes range from .072 - .083 and trying to figure which one is correct. Here’s a run down on my thoughts.

- Rifle that is a shooter and will run, I dont care if it’s a bit over gassed and will run a suppressor when I feel like it
- Midlength gas
- A5 tube with H2 buffer and green spring
- Ballistic Advantage 16” Hanson stainless with .073 gas port
- NON adjustable pinned gas block
- Planned build will be a reliable shooter for animals and defense that will eat all ammo. Don’t care about punching paper but accuracy still
matters.

Anything I’m missing?

Thanks

I didn’t read all of the above comments, BUT I just went through this with the exact same setup and an Adjustable Gas Block is the correct answer here!

AGB for flawless function!

Good luck!

 

[Flying Fish]

Not really.

Also take a look at this thread, palmetto has been having sales on the Armalite 308s:

Armalite AR10A TAC 18

I’ve never really been one to do reviews. If you’re expecting @bigjake83 , @LRRPF52 , or @sinister level info or details you’re gonna be disappointed. I don’t take a lot of pics, the ones I take are crappy, and I have poor grammer. So any time people ask about large frames I usually recommend...

www.snipershide.com

That‘s one heck of a deal for a factory rifle. wonder why they are selling at such a deep discount?

 

[LRRPF52]

Great info, thanks. I might just have to change my idea and use an adjustable gas block or look into the adjustable gas carrier. Are the adjustable systems ever a common failure point?

Tiny set screw AGBs tend to carbon-weld in one position that is extremely difficult to adjust afterwards.

I like blocks that have more of a mechanical advantage with a large knob or regulator, or the Bootleg carrier. The Bootleg really does work though and is great for switching between ammo that is hotter at the port, suppressed, and unsuppressed.

Of all the .308s I’ve had, I really like what Savage did with the MSR-10. It has all the features you could ask for in a factory gun and more:

* Smaller frame size so it feels like an AR-15 with a medium-heavy contour barrel.
* A5 RET with rifle spring and AR-15 carbine buffer
* Smaller Bolt Carrier mass, hard-chromed
* Forged tower gas system with pinned sleeve instead of a carrier key
* Sprung firing pin
* Dual ejector bolt
* 2-Stage trigger, appears to be NiB or polished chrome, very crisp like a Geissele or LaRue 2-stage
* True free-floating upper-to-handguard mate-up with seamless fit/feel like a pipe flange
* Fluted barrel
* Adjustable gas with regulator that can use cartridge tips to turn, vs tiny set screw mess
* Slim but full MLOK handguard with 12 o’clock rail
* Muzzle brake

The MSR-10 would be really slick in a 12” suppressed configuration. I’m thinking about chopping it from 16” to 13.7” with P&W, but it isn’t anywhere near my priority list right now.

 

[LRRPF52]

Honestly, if there was a builder’s kit off that Savage MSR-10 Smaller Frame with different barrel options, pistol configuration, with support, it would be ideal for anything based on .308-sized cartridges.

That isn’t Savage’s business model though. The rifles themselves are really feature-rich and shooters. My buddy’s shoots bug holes out of the gate. He thought he was off-target or something, so went to go check and had a tiny bug hole with 6.5CM. Mine in .308 Win.

The bolts and barrel extensions are normal AR-10 sized, whereas the carrier is smaller but a bit longer than an AR-15 carrier.

 

[Cascade Hemi]

That‘s one heck of a deal for a factory rifle. wonder why they are selling at such a deep discount?

Despite what some think, Armalite has always been a mid to lower tier company. The ABC's were BS and Armalite is/was consumer grade at best. That rifle is cheap because Armalite probably cut ever corner they could.

 

[BCP]

Armalite are very mid tier and that’s perfectly fine. There’s nothing bad about their barrels, triggers or components and they have a few small touches that make them an improvement over an aero or whatever else you’d pick in the same price range. I wouldn’t spend 2k on one but at 1200-1300? I’d 100% buy.

 

[Flying Fish]

Armalite are very mid tier and that’s perfectly fine. There’s nothing bad about their barrels, triggers or components and they have a few small touches that make them an improvement over an aero or whatever else you’d pick in the same price range. I wouldn’t spend 2k on one but at 1200-1300? I’d 100% buy.

The Aero Build I’m considering will come out to $2200 and really considering this Armalite. After reading these forums I’ve learned that AR-10‘s can be very finicky. Might just grab this if it’s built correctly right out of the gate and use the extra grand towards an optic. Seems like a it will fit the intended role I need.

 

[LRRPF52]

Despite what some think, Armalite has always been a mid to lower tier company. The ABC's were BS and Armalite is/was consumer grade at best. That rifle is cheap because Armalite probably cut ever corner they could.

ArmaLite AR-10s spank most of the higher-end large frame gassers when you look at quality of the BCG, quality and fit/feel/finish of the receivers, accuracy, small parts, but most importantly-reliability.

I don’t have brand loyalty, but just from all the SR-25s, AR-10s, and imitation AR-10s I’ve seen over the past 30 years, most of the market has not caught up to the level of parts quality and engineering on those 1990s-2000s AR-10s.

 

[Cascade Hemi]

ArmaLite AR-10s spank most of the higher-end large frame gassers when you look at quality of the BCG, quality and fit/feel/finish of the receivers, accuracy, small parts, but most importantly-reliability.

I don’t have brand loyalty, but just from all the SR-25s, AR-10s, and imitation AR-10s I’ve seen over the past 30 years, most of the market has not caught up to the level of parts quality and engineering on those 1990s-2000s AR-10s.

Nah. I had an AR10B. It was over gassed, poorly fit, and had the same cheap furniture as every other Armalite of the time. It was a 90's vintage AWB era gun. The M14 mags sucked compared SR25 mags too. That gun didn't spank anything, good riddance.

I think you have a bad case of the nostalgias. There's 100X more AR10 guns available today and I think the lower tier quality colors your opinion of the past. Hardly anyone owned an AR10 25 years ago, let alone end users building them at home.

 

[LRRPF52]

Nah. I had an AR10B. It was over gassed, poorly fit, and had the same cheap furniture as every other Armalite of the time. It was a 90's vintage AWB era gun. The M14 mags sucked compared SR25 mags too. That gun didn't spank anything, good riddance.

I think you have a bad case of the nostalgias. There's 100X more AR10 guns available today and I think the lower tier quality colors your opinion of the past. Hardly anyone owned an AR10 25 years ago, let alone end users building them at home.

I’m talking about samples of scores of guns, not single samples from the mid-1990s.

In just a 30-day period over 20 years ago, I transferred 86 SR-25s one year, had my own AR-10T from 2002 manufacture to compare, and then have kept my finger on the pulse of large frames all along since then.

Additionally, I’ve seen and used a lot of large frames in competition and training, to include in the US and in Europe. The Finns took a liking to the ArmaLite AR-10s and I’ve seen and shot them a bunch in training events there throughout the weather cycle, which gets down to -30˚C in the winter.

Even the 16” MLGS ArmaLite carbines were always reliable, didn’t skip a beat in extreme cold in high-volume courses we did with them present.

When you look at the internals of those ArmaLites from the 2000s vs even the $2000 - $3000 large frames today, there aren’t many of the modern ones that compare well. Machining and chrome-lining of the carrier bore were as good or better, and they all had sprung firing pins.

Most modern large frame assemblers don’t even use a sprung firing pin and skirt manufacturing costs by going with nitrided carriers. They cover it all up with billet receivers, coatings, and some type of other differentiation for brand identity, but short-cut some of the critical core formula that make the ArmaLites so reliable and accurate.

 

[Cascade Hemi]

I’m talking about samples of scores of guns, not single samples from the mid-1990s.

In just a 30-day period over 20 years ago, I transferred 86 SR-25s one year, had my own AR-10T from 2002 manufacture to compare, and then have kept my finger on the pulse of large frames all along since then.

Additionally, I’ve seen and used a lot of large frames in competition and training, to include in the US and in Europe. The Finns took a liking to the ArmaLite AR-10s and I’ve seen and shot them a bunch in training events there throughout the weather cycle, which gets down to -30˚C in the winter.

Even the 16” MLGS ArmaLite carbines were always reliable, didn’t skip a beat in extreme cold in high-volume courses we did with them present.

When you look at the internals of those ArmaLites from the 2000s vs even the $2000 - $3000 large frames today, there aren’t many of the modern ones that compare well. Machining and chrome-lining of the carrier bore were as good or better, and they all had sprung firing pins.

Most modern large frame assemblers don’t even use a sprung firing pin and skirt manufacturing costs by going with nitrided carriers. They cover it all up with billet receivers, coatings, and some type of other differentiation for brand identity, but short-cut some of the critical core formula that make the ArmaLites so reliable and accurate.

Amazing how few slam fires there are with how few companies use firing pin springs in the AR10. Also amazing how irrelevant Armalite has become despite how good you think their product was. I don't think the market place agrees with you; as soon as the AWB went away so did Armalite. You're certainly entitled to your opinion though.

 

[LRRPF52]

Amazing how few slam fires there are with how few companies use firing pin springs in the AR10. Also amazing how irrelevant Armalite has become despite how good you think their product was. I don't think the market place agrees with you; as soon as the AWB went away so did Armalite. You're certainly entitled to your opinion though.

ArmaLite had a ton of growth after the AWB expired. They took a while to do the AR-10A with SR-25 mag compatibility, but did it in the early 2010s. A lot of guys prefer the M14 pattern steel mags because they allow longer COL and they work. I just think ArmaLite didn’t keep up with the modern forms of advertising to the hipster crowd with paid YouTube promotions/reviews on the big channels, but still has been shipping product all this time. They were also bought by SAC in 2013.

I did notice that Savage, KAC, and LaRue all went to sprung firing pins in their .308s/.260s/6.5CM large frame rifles. Hk started out with a sprung pin design from the get-go on the 416 and 417.

I’m just looking at this dispassionately from a design, production, and performance standpoint based on 28 years of watching what Eagle Arms/ArmaLite did with the AR-10. It isn’t personal or based on emotions.

They pioneered the “A5” RET length for their 16” AR-10 carbines, which is now the standard for the companies that care about reliability and action spring longevity. In fact, they are the first one to make a reliable 16” AR-10 in production. I love the KAC guns, but KAC will be the first to tell you they went through headache-after-headache trying to get 16” SR-25s running well.

Look how many companies today can’t even make a 20” RLGS .308 run reliably. What I’ve seen is a lot of focus on things that don’t matter like furniture, ambi selectors, or whatever charge handle someone prefers, while the critical core parts get overlooked. Anyone can change ancillary parts on the gun, but getting the barrel, barrel extension, chambering, bolt, bolt carrier, extractor, ejector, carrier key, gas port, gas block, action spring, RET, receiver datum relative to the bore is more important. None of the outside is worth a crap if the gun doesn’t work or shoot well.

 

[Flying Fish]

Well I did a complete 180 from my initial thoughts and bought the Armalite AR10A TAC 16. I couldn’t pass up a factory build for $1200 and it seems to get great reviews for the price point. Rifle should arrive next week and all I’m going to do is add a Nightforce 1-8 ATACR and Harris bipod then hopefully call it done.

Thanks for everyone’s input.