rifle length gas system on dissipator 16 brl AR

M

Meljobin

Inactive
Hi guys long time lurker first time poster.

Well iv finally decided to bight the bullet and build an AR. Iv decided to build one since living in California your options tend to be limited as far a just purchasing one outright without being over $1000.

I have decided I really like the look of a dissipator style but I also really dont want a carbine length gas system. Ideally I would like a mid length system that has a low profile gas block then an aditional sight at the end of the barrel. While looking for inexpensive solutions I have found that many Dissipator uppers are using a rifle length gas system.

I would love to hear back from people who have experiance with a rifle length gas system on there 16 inch barrel and if they have had any problems. I know manufacturers like Del-ton recomend ussing hot rounds but I also want to be able to run steel case ammo as I am on a continual tight budget.

Also if anyone knows where I can find a complete upper dissapator style with a mid length gas system in the $600s or less I would be greatly apreciative.
 
I can't speak of a rifle length gas tube on a 16inch barrel. I run a mid-length on a 14.5 inch barrel with a normal carbine buffer and spring and it works great.

Did you ever consider running the mid length system... and just putting a rifle free float rail over it, and using a flip up front sight such as Troy or MI? Or did you specifically want the F marked front sight gas block?
 
I have thought of going that route but it seems like by the time I start adding up all the parts to make a mid lenght kit into a dissipator style things start getting more expensive. Since I would really like the sight mounted on the barrel as i like to use a sling, and have heard that using a sling and sight on the handguard can through things off.

but thanks for the feedback about your midlength on the 14.5 inch
 
The one issue with using a sling on a AR is the fact that yes it can throw things off. Whether it's like you stated with the sling and sight attached to the rail, or the military type gas block... with the front sight post and sling attachment.

Shooting with a sling as a brace in either scenario is going to put stress and change things. However I personally do not know which one would do it less. Hopefully someone else comes along and can clear that up.

Personally on my 14.5 middy upper... I didn't free float it, and it uses the mil-spec front sight gas block... and I have a flip up rear that co-witness's through an EOtech. 99% of the time my rear sight is flipped down, and I run a single point sling if a stage needs a sling. So I don't normally shoot my AR for group size... so I can't comment on if a sling on a non free-float throws it off that much.
 
Yes, the sling throws it off, but the Marines who shoot it that way seem to have little trouble. The trick is to have consistent pressure every shot - then the deviation is controllable.

In combat, you don't use the sling. In fact, I was taught in the Infantry to remove the sling entirely in the field. The weapon is then held at the ready, and never carried by that handle on top.

I built a dissipator, the issue with gas length is really simple - it's about TIMING, not looks, shoot the correct gas length regardless. On 16", that's mid. Then install the handguard of choice behind the FSB (and if it's got BUIS on a rail, it's arguable that its' not a dissipator at all.)

The mechanical difficulty is getting the FSB to mount forward on an area on the barrel where the ID of most sight bases and the OD of the barrel are not the same - like a .750 or .625 on a .700 barrel. That's why you see a lot of medium contour barrels with .750 out to the muzzle, it makes it a no brainer for the vendor to assemble.

If you stumble into the mismatch after you bought parts, there are solutions. You don't have to ask, I've been working on this last step for three months. Basically, you get a clamp on or set screw FSB (Armalite NM,) and fabricate a bushing to take up the slack. That bushing may need to slide over a .725 bulge - another complication - and then the entire affair has to cinch down firmly to prevent the sight base moving. I'm using a short piece of 5/8 copper tubing split lengthwise to fit, and since the handguard cap came from an HBAR, I can bend small tabs over to retain it against the sight. Lots of holes to lighten it, although anyone will tell you, using an FSB itself is the heaviest item on the barrel, aside from the contour.

That's precisely why most builders don't attempt dissipators, and why they aren't offered much, aside from lack of demand, but like they say, observe the masses, and do the opposite. Carbines were just too short for gas or handguard length.
 
Thanks for the feedback you have helped to finally convince me to do it right rather than taking the easy way of ordering a premade dissipator kit.

And thank you for the advice about the barrel OD, I never would have thought of that. And while fabricating a shim is not to complex, I would much rather know that I may be doing something like that BEFORE the parts dont fit.

I am going to order a mid length setup, barrel mount the front sight, and mount the sling on the the free floating hand guard to minimize its effects
 
I had a 20" "match" barreled gun that shot pretty crappy to say the least. Soon, I grew out of my fondness for the long barrel anyway, so I had it cut down to 16" and built a 'three gun' type rifle out of it. At 16" it is more accurate and I am much happier, and it has never skipped a beat reliability wise. I used the same gas tube that was on it originally.
 
There are rifle gassed 16" barrels out there that seem to work OK for those shooters.

The issue of gas length is really seen backwards by many. Gas for the AR is actually measured from the muzzle, as the distance from port to muzzle is what times the action to unlock. Carbine gas on 16" - which was never meant as a working solution - has a longer "dwell time, " allowing high gas pressure into the tube early, and unlocking the bolt early against high barrel pressure against the case. Carbine gas was for 14.5" or LESS, not 16", something gun buyers seem to insist on regardless that it didn't work best.

Measured from port to muzzle, gas length is actually all about the same, 5 to 7 inches, and thats optimum. Most builders understand a dissipator shooter won't restrict themselves to just one kind of ammo - milspec only, and that's always loaded hot for power and to cycle the action - so running the optimum gas to work with varying ammo pressures is preferred. That's why most of the dissipator market is midlength, not rifle.

Just makes since to prevent Customer Service issues before the guns are even shipped.
 
You must log in or register to reply here.
Back
Top