Aftermarket Barrel/Handguard Compatibility with DPMS G-II 308 Rifle

[TehLlama]

I'm looking at putting together a .308 light precision do-everything unicorn rifle (basically do 90% of what the SR-25ACC does at under half the price by using an aftermarket SS barrel and accepting that barrel life compared to the KAC offerings is going to suck).

I'd like to run a URX3.1 handguard if possible (but building up an Aero Precision M5 receiver set into an SR25ECC knockoff would have the installed handguard alone at 40% of the cost of the rifle for me), so the DPMS G2 is an appealing prospect.

I realize that the threading is odd (unsure if it's an outright different thread pitch, different diameter, or what the deal is, all I can ascertain is that the DPMS nut is 'the' nut, and it so far only works with a few handguard options). Has anybody tried making this work, or have any other insight?
I would actually have the ability to try make (and talk my shop into making a run) of DPMS G-2 threaded KAC URX 2/3/3.1 units if that's physically possible, but I don't even know if that really is workable, let alone the fact that making a 7075 billet barrel nut isn't exactly a cost-saving move in low quantities.

Finally, would it make sense to try any of this stuff, since that platform still seems to be having minor niggles with feeding and Gen3 PMagLR's, primer and firing pin channels, and no particularly good TDP-like spec reference for gas port? I still figure the whole market is liable to change if a big player got involved significantly (DD, BCM; Noveske returning, or LMT making a Defender LR308), and if the winner is ironically enough the older AP4/Gen1/LR-308 spec then I'll have committed a ton of resources into a 7.62mm betamax. Thoughts?

[caporider]

Are you talking about using an AR15 URX rail? Because that's the only one that would line up with the GII's receiver height. The SR25 rails would step up very noticeably over the height of the receiver.

MI and Samson are making dedicated GII barrel nuts for their GII rails. I'm hearing V7 Weapon Systems is developing a Ti GII nut for the BCM KMR handguards. It would be cool if someone were to develop GII barrel nuts for popular AR15 handguards... (hint)

[TehLlama]

Are you talking about using an AR15 URX rail? Because that's the only one that would line up with the GII's receiver height. The SR25 rails would step up very noticeably over the height of the receiver.

MI and Samson are making dedicated GII barrel nuts for their GII rails. I'm hearing V7 Weapon Systems is developing a Ti GII nut for the BCM KMR handguards. It would be cool if someone were to develop GII barrel nuts for popular AR15 handguards... (hint)

Yeah, that's exactly what I was looking at doing - but it would only make sense if it's a money making venture [my shop is busy trying to remake a bunch of satellite parts since the parts we made for a dozen of them got blown up on launch a couple weeks back].

[LRRPF52]

The GII's barrel nut is in between the diameter of an AR15 and an AR10, but the AP4 and MOE models use a nut that can be torqued with a standard AR15 armorer's wrench. I suspect the same is true of the free-float models, but don't have them in hand.

On the GII captive handguard nuts, they fluted the outside to coincide with the gas tube alignment, while keeping ID's larger, and overall OD of the barrel nut shaft itself larger, so they could fit over the enlarged upper receiver extension threads.

They used radiused lugs on the bolt and extension like the old Professional Ordnance Carbon 15, which is what many now are familiar with on the KAC E3 bolt and extensions designs. The GII also used alloys with this combination to increase strength over 8620, which has been used on AR10 bolts since the 1950's.

These are some of the design points under the hood that allowed them to reduce the receiver height, weight, and overall profile, while maintaining Factors of Safety for the hoop stress of the 7.62x51 NATO and .308 Winchester cartridges, with substantial chamber wall thickness.

It really is an aggressive and interesting approach to the design, and gets back to what an AR10 should really be for weight and balance.

The URX has female threads inside of the handguard, with a barrel nut that simply sleeves over the barrel, and male threads to engage the inside of the URX, then placing force against the barrel extension flange.

The URX might be one of the easiest handguards to adapt to the GII, as long as the barrel nut can slip over the barrel. It might need to be bored to increase the ID of the URX nut, but I don't have any of these in hand to determine if this is doable or not. It definitely would make a slick set-up. The handguard threads will need to be opened up for the GII's upper receiver thread pattern. Not sure if you would want to leave aluminum in the white after that.

I would also pull the barrel, get a Bartlein, have it reamed concentrically to the bore, with a gas gun reamer spec'd to your preferences, locate the port where you want, with the port diameter that will handle your intended diet of fodder, and make very slick little blaster with a premium pipe. You could also get the barrel nitrided if you are concerned about barrel life, by a shop that specializes in AR15 and AR10 barrels. .308 barrel life is one of the best in center-fire rifle cartridges.

One thing will be getting a GII barrel extension installation/removal tool, since it is not common to anything in the industry right now.