Please explain buffers/buffer tubes in relation to gas system?

[swampcrawler]

So after years of threatening to do so, I finally picked up a spikes lower last night, and am ready to begin my first build. At this point all I'm really sure of is that I want a 18 inch barrel with a rifle length gas system.

I have my tools on the way, and will be ordering a PSA lpk minus fire control group, and an ssa trigger friday. Where I'm running into confusion is the buffer/stock area. What exactly do I need here for the 18 inch/rifle combo? The vltor A5 seems to be highly regarded, but I believe there are different length tubes for the different gas systems?

What should I order to help insure proper reliability, durability, and a smooth shooting rifle? I'm even open to fixed stocks if they offer advantages.

Thanks for your patience with the newbie questions!

 

[Robert]

Do you want to run a rifle or carbine stock? Kits are available that include everything you need for either set up. So it really just depends on wither you want a fixed rifle stock or an adjustable stock.

 

[Mike C2]

Rifle stocks use rifle buffer tube and carbines use a carbine tube.


I think you are confusing gas tube and buffer tube. Pistol, carbine, mid-length, and rifle length gas tubes are available and need to match where the gas port is drilled in your barrel.

18" could be rifle length or mid-lenghth. Most likely a mid but you need to verify with vendor or with a tape measure.

 

[NWcityguy2]

With the buffer tube, either will work as long as it is supplied with the appropriate spring and buffer. There are two types of buffer tubes out there, commercial and mil-spec, and each one needs to be supplied with the matching stock. These days, almost all buffer tubes being sold in kits are mil-spec. Just make sure to order a mil-spec stock as well.

I don't think fixed stocks offer any advantage over adjustable stocks if you are going to be using standard buffers and springs. If you want to get into competitive products though, such as adjustable gas blocks and low mass carriers, then fixed stocks become an advantage because there are more accessories available to go with them. But those are expensive and make a rifle operate within a very slim window of tolerances.

 

[Olympus]

Your barrel will dictate your gas tube length. As for buffer and tube, you can use a carbine buffer and tube with a rifle gas system or you can also use the rifle buffer and tube. Your stock selection will generally dictate your buffer and tube size. Collapsible stocks are almost certainly going to require a carbine tube and buffer.

 

[Tirod]

Why 18" with rifle gas?

It's not the correct length for that, and it implies that the 18" barrel has some quantifiably superior reason for the extra length over 16". In terms of accuracy there is no guarantee a longer barrel will be more accurate. All you get is slightly higher FPS and an incrementally longer effective range for the extra speed. Conversely - it loses energy and speed compared to a 20".

18" barrels use "intermediate" gas - because the location of the gas port is based on it's set back from the muzzle, which is 4-6" for the most part, regardless of how far back the chamber is located. It's an action timing function more than anything, and getting it closer or further from the muzzle out of it's optimal location means it's being exploited for an incremental advantage. That always means there is an accompanying disadvantage.

Carbine gas = 14.5"
Midlength = 16"
Intermediate = 18"
Rifle = 20"

The combinations that cross one with the other are the ones historically that created issues, like, carbine on 16', which caused a lot of makers some Customer Service issues. While not "milspec" they not only invented midlength but marketed it as being the better way to handle a 16" barrel.

What specific advantage is their in pushing the port closer to the muzzle? I ask because that will likely have more affect on reliability than what buffer you use. You can tune it by using a heavier buffer, but you can't tune it easily by moving the port back to it's optimal site.

 

[taliv]

my favorite rifle to shoot is an 18" with rifle length gas. it is a good compromise and shoots almost as smooth as the 20" guns. i think i have 5 or 6 of them. never had cycling issues with any of them.

i vaguely recollect hearing some noise about people having problems with them, but i'd like to hear if there is a systemic issue.

 

[swampcrawler]

Ok, that clears things up! Thanks guys!

By the way I actually decided to go with the noveske 18 inch barrel with intermediate gas and the vltor a5 system

 

[ClemY]

my favorite rifle to shoot is an 18" with rifle length gas. it is a good compromise and shoots almost as smooth as the 20" guns. i think i have 5 or 6 of them. never had cycling issues with any of them.

i vaguely recollect hearing some noise about people having problems with them, but i'd like to hear if there is a systemic issue.

Concur. Love my 18" Rifle length gun. I use an H3 buffer with a MilSpec Magpul CTR stock.

 

[HammsBeer]

Any barrel and gas length can use any buffer system. You need to match the buffer weight to the gas port bushing.

If I hadn't already installed a carbine buffer on my AR's, I would have used the A5 buffer (they are about $100 to retrofit). It uses a rifle weight buffer, but in a buffer tube almost as short as a carbine buffer. The purpose of heavy buffers is to slow down the unlock speed of the BCG and to stop bolt bounce upon chambering. There is also a bias spring in the A5 that is supposed to keep the internal weights forward.

I have read a few reports of poor cycling in 18" with rifle gas during very cold weather. 18" with intermediate gas should be fine. I would recommend you start with the standard 5.3oz A5 weight, listed as an A5 H2.

 

[CapnMac]

Hammsbeer has the right of it.

It's not the length of the buffer tube that matters; it's the weight of the buffer within it (and it's return spring).

 

[Onmilo]

I have an 18" rifle length gas system FN Barrelled rifle using an adjustable carbine stock extension tube.
I use a Colt H2 buffer when shooting heavy bullet loads of 62-77 grain weights and i use a standard carbine buffer when shooting 55 grain stuff.
This is especially important when shooting steel case 55-62 grain stuff as all of it is not strong enough to fully cycle the action using the heavier buffer.

I have had the same issue in my 20" barreled rifles using both adjustable stocked lowers and fixed stock lowers.

While you can regulate the carbines using a lighter or heavier buffer, fixed stock rifles use one weight of buffer and in these you must regulate the gun using a stronger or lighter action spring.
I use a Wolf reduced power action spring when shooting steel case ammunition in fixed stock rifles.
Some people have found the slightly more resilient chrome silicone action springs work very well in fixed stock rifles for toning down the action when shooting the heavier 68-77 grain ammunition.
I myself have not found the C.S. springs as necessary but certainly won't knock anyone for choosing one.

Rifle length fixed stock buffers weight about 6.5 ounces

Carbine length adjustable stock buffers are roughly weighed out as,
Standard 4.5 oz
H buffer 5 ounce
H2 6.5 ounce
H3 7 ounce
Most shooters will never need a 7 ounce H3 buffer unless they are lucky enough to own a select fire weapon and especially lucky enough to pair that rifle with a suppressor and the average semi auto shooter may find the heaviest buffers actually cause reliability and function issues in their weapon.

I have also found that the H buffer works best with all types of ammunition in my 14.5" barrelled M4aClone.
Most shooters using 14.5-16" barrelled adjustable stock carbines will also realize similar results.

As an added bonus to my testing, by following these results, I have never stuck a steel case in the chamber of any of my rifles even when firing the stuff from dirty and cooled barrels.
HTH

 

[d2wing]

I had a Dissapator meaning a rifle length gas system on an 18 inch barrel. It would only cycle with hotter loads. It had a carbine stock on it. I decided to swap it for a full rifle and am glad I did. For a small weight gain I got more velocity which is important in a .223 and as it happens better accuracy. If you have the right loads and buffer and springs a Dissapator works but they are more reliable in a mid-length gas system. Just my two cents.

 

[shotgunjoel]

I just finished an almost identical build today. I used the Vltor A5 system, the one that's 6 position instead of 7. You'll only get all 7 positions on the longer one if you use a big stock like Vltor offers. I contacted Vltor and told them the gas system length, barrel length, gas port diameter and bullet weights I wanted to use and they recommended the 0 or 1 weighted buffers. I bought the 1 and a generic carbine buffer so that I could scavenge the lighter weights if needed to go to a 0.

 

[taliv]

(dissipator usually means the "front sight block" is in a rifle position but isn't actually acting as a gas block, and there's a real gas block in the carbine position underneath the handguards, which means carbine pressure and a heckuva lot of dwell time)

 

[Caliper_Mi]

I had a Dissapator meaning a rifle length gas system on an 18 inch barrel.

I'm used to the Dissipator style being a rifle length gas on a 16" barrel. I've never heard a 18" barrel called a dissipator.

What Taliv describes has been called a "mock Dissipator" by many retailers to denote that the sight is at rifle placement but the gas block is something shorter than rifle length. I've got one set that way with midlength gas and a small gas block under the handguards. Very fun rifle.

 

[Caliper_Mi]

18" barrels use "intermediate" gas - because the location of the gas port is based on it's set back from the muzzle, which is 4-6" for the most part, regardless of how far back the chamber is located. It's an action timing function more than anything, and getting it closer or further from the muzzle out of it's optimal location means it's being exploited for an incremental advantage. That always means there is an accompanying disadvantage.

Carbine gas = 14.5"
Midlength = 16"
Intermediate = 18"
Rifle = 20"

I get the gas port placement in relation to dwell time and action cycling, but this is the first I've heard of intermediate gas as something different than midlength. I assume that like midlength on a 16" barrel, intermediate on an 18" barrel would be the correct placement to allow mounting a bayonet properly? (not that I base my decisions on that, it's just a standard distance)

I've got an 18" rifle length gas barrel from Rainier arms that cycles just fine. I chose the combo because I had heard that it cycles with no troubles and fairly gently to boot. I also like front sights closer to the muzzle from a practical and asthetic standpoint. And because I needed an excuse to build another rifle.

 

[taliv]

i could be completely wrong on this but i think intermediate is something KAC made and its what ran on all their SR-25 308win rifles. i think they started using it on their SR15s later