AR15 Barrel Length Q

[Mainsail]

Ok, this is hard to explain. I’m building an AR15 and just finished the lower. I would like to use a 16” barrel. Now, here’s the tricky part. I want the length between the end of the barrel and the bayonet lug to be ‘normal’. With the short barrel and short hand guard, a bayonet would not mount in the proper place; in fact it looks like only a couple inches would be protruding beyond the end of the barrel. With a short barrel and a long hand guard I would have the opposite problem, the bayonet would be hanging precariously off the end by only the lug.

So what I want is a 16” barrel with the front sight/bayonet lug correctly positioned to allow a bayonet to engage the lug and the flash suppressor. Yes, I know I’ll never need to mount a bayonet, but I want it that way for aesthetics.

Will a 16” barrel and mid length hand guard put the bayonet lug in the proper place? If so, does anyone have pictures of this configuration, possibly with the bayonet in place?

 

[rcmodel]

I understand what you want to do, but I'm not sure if you can do it.

The problem with moving the front sight/lug that far foreword on a 16" barrel is gas port location. The port gets too close to the muzzle, and bullet dwell time past the port may cause functioning problems.

I'm sure folks have done it, but it may cause functioning problems well beyond what it is worth.

Have you considered just using a clamp-on bayo lug that mounts far enough forward on the barrel to use a bayonet with the standard gas block location on a standard 16" barrel?

PS: Woops, here is how to do it so it works, but it might take an 18" barrel to put the bayo lug in the proper place?
http://www.bushmaster.com/catalog_xm15_BCWA3S16D.asp
The shaved gas block is in the standard carbine place under the hand-guard. The front sight gas block is just a dummy and the barrel is not drilled for it.


rcmodel

 

[SnakeEater]

Go look at these pics, they might help. LINK

 

[Zak Smith]

Just use a mid-length gas system. Many vendors sell complete MLGS 16" barrels and complete uppers.

-z

 

[Mainsail]

Have you considered just using a clamp-on bayo lug that mounts far enough forward on the barrel to use a bayonet with the standard gas block location on a standard 16" barrel?

That would be ugly. The reason I want this configuration is because I cannot buy the 14½” barrel with the short hand guard, the configuration of an M4. So for aesthetic reasons I am trying to duplicate the look of the 14” barrel in 16”.

Looking at the link you posted, that configuration won’t work either, the bayonet ring would not be anywhere near the flash suppressor:

 

[Zak Smith]

16" with MLGS

 

[Mainsail]

Thanks Zak, that looks like it would work. Now, if the flash hider is screwed on, the barrel must be no shorter than 16”, right? If the flash hider is welded on, the barrel can be cut shorter by the length of the flash hider, also correct? I want to think that welding it on gives me some wiggle room to get the length just right, so that the ring on the bayonet engages the ring behind the flash hider.

 

[Zak Smith]

You're overthinking this. A MLGS 16" has the same muzzle to lug distance as a 20" A2. It'll "just work" with no changes. The ring on the bayonet will be about 1/2" forward on the A2 flash-hider from where it would be on a 20" rifle, but it will work fine.

This thread has photos
http://www.ar15.com/forums/topic.html?b=3&f=118&t=340794

The only way to make it exactly the same would be to have a custom barrel made which is approx 1/2" longer.

 

[usp_fan]

Yep, the mid length system is what you want. Listen to Zak--he is never wrong!

The added advantage is the increase in gas system length over the standard carbine. The gas impulse to the bolt is slightly delayed--making it more like the rifle length system.

 

[Mainsail]

OK, thanks Zak! I will go that route with the project then. Oh, one more thing, where can I get some extra money to finish this quickly?

 

[usp_fan]

If you take a look at Zak's toys in his pictures--you may want to take his advice on where to find $$$.

 

[HorseSoldier]

Or just get a 14.5" barrel with a welded flash hider that gets it to 16" overall length.