AR15: Is this possible?

[turnerdye1]

I have been wanting to extend my hand guards for awhile now. The only way I knew how was to get a lo pro gas block and get a free float rail. After finding the rail and gas block I wanted it was going to run me around 200 dollars. A little much for me as a college kid.

I thought about doing this though. I just want to know if its possible before I buy the stuff. I currently am running a MOE carbine length hand guard with a Yankee Hill gas block/flip up front sight combo. As seen below.

Here is my plan. Buying a MOE hand guard in the mid-length variety and a lo pro gas block. Could I put on the lo pro gas block and then put hand guard over that gas block and then use my gas block/flip up front sight to hold my hand guards in place? In theory I could see this working and saving me $150 bucks in the process.

 

[mvician]

Yes it will work. It is the same thing they do to make a "mock dissipator", just at the mid length instead of rifle length. You will need a way to secure the hand guard retaining cap to keep it from wanting to rotate.

 

[IndianaResident]

Without cuts in the barrel for drift pins it seems like a good way to end up with a canted front sight after some rough use, but that's just conjecture.

 

[phylodog]

You will need a way to secure the hand guard retaining cap to keep it from wanting to rotate.

My BCM Kino upper had a screw through the cap and into the gas tube hole of the FSB to keep it from rotating. Seems like that would work in this application since the hole isn't being used for the tube any longer.

 

[turnerdye1]

Yes it will work. It is the same thing they do to make a "mock dissipator", just at the mid length instead of rifle length. You will need a way to secure the hand guard retaining cap to keep it from wanting to rotate.

My BCM Kino upper had a screw through the cap and into the gas tube hole of the FSB to keep it from rotating. Seems like that would work in this application since the hole isn't being used for the tube any longer.

Could I JB weld the hand guard retaining cap to the front sight? That way I dont completely mess up my barrel? Or would it be easier to just thread the old gas port hole and get a screw for it? I just thought of this as well. Couldnt I just get another gas tube and roll pin? Cut off the current gas tube just long enough to go into the hand guard retaining cap. Then flair the end of the gas tube holding it in place?

Without cuts in the barrel for drift pins it seems like a good way to end up with a canted front sight after some rough use, but that's just conjecture.

My current front sight post isnt pinned. It's just held in by the four screws. It should be just as sturdy shouldnt it? The gas tube is the only thing that isnt connected to it anymore.

 

[paddling_man]

In theory.

Something to think about though... the gas tube is thin. The gas block is several magnitudes more in sheer metal, which would make it more of a heat sink. It would stand to reason that the gas block itself would be hotter. I've done no testing to confirm that but I've got a carbine length gas lo-pro under an 11" Troy Alpha and a factory noveske lo-pro midlength gas under a 11" troy trx. My gut is that much more heat comes from the specific area of the gas block - which stands to reason - than the gas tube.

So... do you really want plastic (moe) over the top of a gas block?

It honestly may not be an issue but I would rather save for a metal free-float intended to be mounted over a gas block than attempt to jerry-rig a mount for a plastic mid-length hand guard that might be compromised from heat. Just my two cents and you can't buy anything for $0.02 anymore. Heck... I don't even have a "cents" symbol on my keyboard anymore. When did that happen??

 

[mvician]

Dissies have had plastic handguards covering the gasblock for years....the MOE isn't going to melt from it.

 

[evsnova74]

Lol a "mock middy". Love it.

 

[paddling_man]

Excellent point, mvician. I suppose it isn't an untried idea.

MOE handguards have no heat shield on the upper half, right? Classic AR plastic do, I think.

 

[mvician]

if this is your goal, then yes the plastic/polymer handguard of any AR will catch fire.

How To Set Your AR-15 On Fire « Vuurwapen Blog

If normal shooting conditions apply....they will not catch fire.

 

[turnerdye1]

Excellent point, mvician. I suppose it isn't an untried idea.

MOE handguards have no heat shield on the upper half, right? Classic AR plastic do, I think.

I just checked and you are correct. The handguards do not have a heat shield on top.

if this is your goal, then yes the plastic/polymer handguard of any AR will catch fire.

How To Set Your AR-15 On Fire « Vuurwapen Blog

If normal shooting conditions apply....they will not catch fire.

Thankfully I dont plan on shooting like that ever...


The whole reason I am wanting to do this is to get more arm space. Im a 6'4 200lb guy that has some pretty long arms. The carbine MOE system just doesnt give me enough room to shoot doing the thumb wrapped over the top method that I like shooting with. So in theory I should be alright doing the mock middy right?

 

[mvician]

Yep

 

[Yeah]

You needn't shoot as much as the video to get warm. I don't know what MOE handguards are made from, Zytel HTN maybe? So can't know their melt temp or glass temp.

During the AR Build Spree in spring 2012 the heat protection afforded by tube type rails was scrutinized by several friends and I. My claim that a man's hand will become acclimated to a boiling hot handguard by repeated exposure fell on deaf ears, so we shot a whole lot of different rifles a whole lot and took photos of the proceedings. The earlier post suggesting the gas block can get hot, is correct.

That is a Noveske stainless upper after a single 30 round mag fired over the span of 10 seconds or so, and the gas block is roughly 90F hotter than the barrel. The gas tube is as well but after about 5 seconds it has cooled to barrel temp, owing to less mass per surface area than the block. The block stayed above 150F for a couple of minutes.

Of course the muzzle end gets quite a lot hotter than everything else.

Temp differences stay about the same the more mags you put through the gun without stopping to let it cool, but I'm not able to locate the subject photos at the moment. If MOE guards are indeed Zytel or something similar they should retain their plasticy stiffness easily though a couple of rapid mags. Somewhere shortly beyond that I can see them getting soft as the gas block would be near their 290ish F glass transition temp.

We did fry the overmoulding loose from a Hogue tube that day, for reference.

 

[paddling_man]

^^ That's one of the coolest sci-geek posts I've seen in a long time. Very, very cool! ^^

 

[subtlesixer03]

You could just get it converted to a middy gas system. Or do what I did and hit the classifieds for a midy free float. I have yhm rifle over a lo pro carbine gas system. I got it for $100

 

[turnerdye1]

You needn't shoot as much as the video to get warm. I don't know what MOE handguards are made from, Zytel HTN maybe? So can't know their melt temp or glass temp.

During the AR Build Spree in spring 2012 the heat protection afforded by tube type rails was scrutinized by several friends and I. My claim that a man's hand will become acclimated to a boiling hot handguard by repeated exposure fell on deaf ears, so we shot a whole lot of different rifles a whole lot and took photos of the proceedings. The earlier post suggesting the gas block can get hot, is correct.

That is a Noveske stainless upper after a single 30 round mag fired over the span of 10 seconds or so, and the gas block is roughly 90F hotter than the barrel. The gas tube is as well but after about 5 seconds it has cooled to barrel temp, owing to less mass per surface area than the block. The block stayed above 150F for a couple of minutes.

Of course the muzzle end gets quite a lot hotter than everything else.

Temp differences stay about the same the more mags you put through the gun without stopping to let it cool, but I'm not able to locate the subject photos at the moment. If MOE guards are indeed Zytel or something similar they should retain their plasticy stiffness easily though a couple of rapid mags. Somewhere shortly beyond that I can see them getting soft as the gas block would be near their 290ish F glass transition temp.

We did fry the overmoulding loose from a Hogue tube that day, for reference.

Wow thats impressive!! Thank you very much for that. I'll probably end up saving for a free float rail. I really want a MI Gen2 SS free float rail which runs around 180 lol

You could just get it converted to a middy gas system. Or do what I did and hit the classifieds for a midy free float. I have yhm rifle over a lo pro carbine gas system. I got it for $100

Ill have to keep my eyes peeled. That and on AR15.com I browse alot too

 

[phylodog]

I ran a MOE mid-length hand guard over a low pro gas block on my Kino upper for several months and never had any issues. I don't do mag dumps but I train realistically with the rifle so depending upon your intentions it could work fine.

 

[subtlesixer03]

F.Y.I. The man above really knows his stuff and if it works for him it will most likely work for you. He builds things that from what Ive seen and heard not only are they gun porn instant orgasmic but are proven life saving tools.