Given an 18" rifle length gas barrel, what needs to go on the back end of the AR15?

Does it require an A2 buttstock with rifle tube and buffer?
Or can a carbine stock, tube, and buffer work as well?

Carbine stock, tube, buffer & spring will work just fine.

There is a range of rifle gas port sizes from around .093" - .108" as I recall. I also think I remember that the Crane standard is .096"

I'd advise starting with a carbine weight buffer & a standard spring & if necessary or you're able, go up in buffer weight if you think it's too fast or your brass is going to something less than 3 o'clock.

The only rifle gas gun that I have has an .096" port & I use a standard spring & a carbine (3.0 oz) buffer & it works fine on everything. I could likely go up to either an H buffer or a slightly stronger spring but probably not both together on full power ammo.

The larger the gas port size the more buffer weight and/or heavier spring you may be able to run.........depending on ammo.

Lower pressure .223 ammo may not function reliably on the setup that full power 5.56 will run on.

I also have an 18" gun set up with a mid-length gas system & an adjustable gas block & set up right, it's just as smooth as the rifle gas gun, FWIW.

MM

The Vltor A5 kit works well with that setup also. That's what I'd go with if I was doing it over again.

I looked at the Vltor A5. Is my understanding correct that you must use the A5 stock with that setup? IOW, it is not interchangeable with any other stock company product?

No, any mil spec diameter stock will fit.

Some won't close completely, because they tube is a little longer, but they'll all close to the first "click".

The A5 is the best option to get rifle gas to work correctly with a collapsible stock.

And why do you say that?

MM

What is the essential change/difference in the A5 spring+buffer system that makes it work better than other setups?

It looks like nothing special in a picture, so what is special about it?

Because the system was designed around a rifle spring and buffer, though most of the problems have been ironed out with collapsable stocks, there is no denying a rifle system offers better reliabilty, easier shooting, less felt recoil and increased parts life.

Though I have nothing but collapsable stocks and carbine buffer tubes, think of how many different combinations of springs, buffers, extractors extractor springs and o-rings, port sizes, adjustable gas blocks, are out there for collapsable stocks. All of these deviated from the standard rifle system.

If you're starting from scratch, why not start with the original design?

Weight and spring rate.

Not to start an argument, but for the sake of discussion.........maybe I'll learn something from other's comments.

The A5 kit was developed for the USMC & as such, was developed around a specific set of gun set-up parameters (port size, BCG weight, extractor spring, etc) & ammo. Having said that, since I've not used an A5, I don't know what the buffer weight or the spring length/weight in that kit is.

But as soon as those other gun set-up parameters are changed, then all bets are off regarding reliable function.....said somewhat TIC, as you do know what may have been changed & directionally how to adjust for it.

Starting with a carbine weight buffer & standard spring is likely never a bad place to start, while holding the other parameters fixed, including ammo. Knowing the gas port size is also a solid clue as to where to start.

In any case, IMO, it's relatively easy to make changes or adjustments based on how the gun performs to either a heavier buffer or spring or both if needed. Unless you're shooting suppressed, on a rifle gas gun, I don't see much need for an adjustable gas block.

As far as I know, the A5 was likely developed for the Crane designed guns with a gas port size of .096" & probably MK 12 ammo; if someone gets a barrel with a .108" port size, the A5 setup might well not be optimum for that gun.

Or even worse, a .093" port size & shooting anemic 55 gr .223 ammo.

I guess, IMO, unless you have a gun set-up very similar to a MK 12 & are shooting MK 12 ammo, beginning with an A5 is no better or worse than starting with another stock/buffer/spring setup & making adjustments as needed.......& the A5 is an expensive set-up besides.

I keep several buffer weights & spring weights available.............

In the end, I guess it just depends of what your goals are, how much you are willing to spend & how much dinking around you are willing to do.

MM

I'm certainly no expert on the A5 or anything else for that matter but here's my take on it.

It was the USMC that wanted to go back to the 20" rifle but wanted to keep the collapsable stock. Colt, FN and anyone else who tried could not come up with a system that was as reliable as the rifle system. Even though Diemaco had been using the C7's for years they still didn't meet the criteria so the A5 was designed and solved the issues.

It took over 10 years to get the carbine stock to work as well as it does but even to this date, shoot a tuned carbine and then shoot a rifle and you will feel the difference. The A5 just combines the best of both worlds while on a carbine, it broadens the operating parameters allowing it to work with both lower pressured ammo and high pressure ammo.

Some are using Springco's green spring for even better results with the A5 across the board, even suppressed. So my take is if it's available, why not use it?

That said, I've used nearly every buffer and spring combo out there and have yet I still think a rifle is smoother shooting but I deal with my standard carbine tubes cause I ain't starting over, can't afford to.

If one was starting over on rifle gas 18" barrel, what stock, spring, buffer would you guys go with?

What about just standard plain old A2 equipment?

Well, since I have no need or desire for an A2 stock, that only leaves me with a carbine stock...........and I have 2, 18" guns.

One is a factory Knight's rifle with a Kreiger barrel & rifle gas with an LMT SOPMOD carbine stock; it has a .096" gas port, a 3.0 oz carbine buffer & and a standard carbine spring as configured by Knight. It eats everything from .223 factory ammo, to Mk-12 factory ammo to my handloads similar to Mk-12.

Ejection is perfect & the gun has never hiccuped a single time.

If I were to only shoot the Mk-12 or equivalent ammo, I'd likely fool around with an H buffer or a slightly heavier spring, & I may still do that as that is mainly what the gun is intended to shoot.

There are lots of factory built 18" factory rifles built with carbine stocks & rifle gas; IMHO, there is no big deal to getting that combination to work.

Also nothing wrong with starting with a Viltor A5 if you so choose.

On the other hand, I just built another carbine stocked 18" rifle recently & I went with a mid-length gas system & an adjustable gas block for more flexibility on a WOA barrel.

I spoke extensively to both WOA & to Compass Lake & both advised & said they preferred a mid-length gas on an 18" barrel & in fact, that is Compass Lake's standard offering on their Bartlien & Kreiger barrels.

The new gun works just fine & will run a wide range of ammo, with an H & an H+ (between an H & an H2) and a Sprinco standard weight carbine spring............same as my 16" mid-gas guns do, (but with a slightly stronger spring). I cannot tell much, if any difference in smoothness compared to the rifle gas gun, either.

So, it's really up to what you prefer for a stock, in both styling, fit & cost.

You can make the carbine stocks work just fine if that's what you want, w/o going to an A5 stock................there is plenty of documentation available to show that & it's also validated by all the factory built 18" rifles with carbine stocks.

But, I also think that with an 18" rifle, you get more flexibility with a mid-gas system..........18" is kind of an in-between-er.

Move up to a 20" barrel, & then a rifle gas system is the strongly really preferred system.

JMHO, JME, YMMV.

Lots of ways to skin the cat; don't over think it..........given all the availability of springs & buffers, it's not that hard.

MM

Did Knight move away from the intermediate gas system on 18" barrels? The 18" Noveske comes with it and at one time I thought KAC did too.

I'm not positive about Knight's current MOD2 18" version, but yes, I think it is still rifle gas.

Mine is a MOD1 and they actually made it up for me after the official end of the MOD1 run a couple of years ago as they still had some parts available, & yes it is rifle gas length on an 18" barrel.

KAC does some different & sometimes special or limited run stuff from time to time so it's very possible that they have 18" guns in the field with mid-gas systems on them.

I also have a couple of their 16" guns & those are mid-length systems on them that they call "proprietary".

MM

From many reports the A5 system is more forgiving than standard length systems. The buffers are available in heavier and lighter weights and are able to be disassembled if needed.

I've shot 10.5, 14.5, 16, and 18 guns back to back with a standard and an A5 lower and several shooters noticed a difference. The difference is more noticeable on over-gassed systems, which most are. But it's still noticeable on my 18" rifle gas BCM barrel, who typically ports their barrels fairly conservatively.

The proprietary KAC gas is longer than mid. It's essentially an intermediate gassed 16" barrel.

Yep, it measures about an inch & a quarter or so longer than my true mid-length guns, shoots a bit softer & does fine with a 3 oz. carbine buffer........my true mid-length does better with a 3.8 oz H buffer.

What barrel length are you shooting now in your 3-gun comps?

MM

I'm shooting a match this weekend with a 16" mid-length gas gun. It's got adjustable gas and an aluminum carrier.

18" guns can be too cumbersome a lot of the time. I think a 14.5" middy would be ideal for what I want to do, but I haven't wanted to mess with pinning one and this 16" has been so good to me that I'm hesitant to jinx myself by doing something else.