6.8 SPC Forums banner
1 - 9 of 9 Posts

·
Registered
Joined
·
488 Posts
So there is a way?
Bluehaze2 recommended x caliber. It's the perfect one tbh considering they make a superlative arms piston specific barrel, and that's the gas system I'm using, but Jesus Christ it's almost $600 for a barrel with like 8 months lead time.
Have you considered the route I took? A road far less traveled. You could use my concept but tweak it in the other direction (for a lightweight 6.8 build). I wanted a heavy barrel without heavy barrel woes (meaning it's so heavy it's tiring, slow to present, front heavy etc.) and to increase overall system performance at the same weight.

So I paired my 16" Daniels S2W CHF CL 5R SPC II barrel with a JL Billet NANO Ultra Magnesium / Aluminum 15" handguard....the handguard with hardware is just 6oz!!! It's lighter weight than carbon fiber handguard setups in that length that clock in at 8oz total. They also make a 13" version that's even lighter yet if you don't need full coverage of a 15".

A standard 6061-T6 15" handguard will run north of 15oz-16oz even with an aluminum barrel nut like the Geissele 13.5" SMR on the SF's new URGI. BCM's 12" m-lock handguard still clocks in at 11oz despite being considerably shorter as well.

So my 16" Heavy barreled 6.8 SPC upper weighs the same as a 16" gov profile 5.56 upper with a standard 15" 6061 T6 m-lok handguard....actually the balance is even better with my setup as more of the total weight is back at the receiver due to the S2W profile and mass bias of the handguard. I've not seen ANYONE explore this concept.

The only use cases I've seen for AZ61A alloy is on ultra lightweight builds where the idea is "light as possible everywhere". No one has used it to off-set the weight of a heavy barrel to make an "standard weight" high performance upper that punches well above it's weight class.

So, what if you paired an ultra lightweight handguard with a standard scout profile 6.8 SPC barrel? That would give you a lightweight 6.8 SPC setup without compromising thermal related accuracy loss associated with pencil barrels and the faster throat erosion that also accompanies those profiles. Throat erosion is directly related to heat, the hotter it gets, the softer the steel and the faster the rate of wear on the lands, the issue is worse with nitrided steel vs. chrome lined.

JL Billet's handguards will fit the SA piston gas system if your bent on that still, but I stand by synopsis to avoid it. I think your better off using DI NiB bolts and NiB carriers in a traditional DI system if your concerned about maintenance time as they are pretty easy to clean and all your going to do is shift the cleaning from the receiver to the gas block / piston assembly.

Short stroke tappet piston setups make the most sense in heavy full auto applications where heat can become a real issue. For a typical infantry AR use, LE or even military, DI with modern plating and good mags is very reliable even if you don't clean it, just keep it wet! BCM ran a mil-spec DI upper for over 30k rounds....not cleaned even once. They just kept dousing it with lube...Fail Zero with their Nib setup has run over 50k rounds through their test upper WITHOUT lube...that's a couple barrels at least...

Here's the weight breakdown difference for illustration (adjusted barrel weight for a 16" gov profile, not the 14.5" used on the actual URGI to give an apples to apples comparison):

URGI (Upper Receiver Group Improved, modified with a 16" gov profile vs. 14.5" gov profile for an apples to apples):
Geissel 13.5" SMR M-Lok Handguard 14.9oz
Daniels 16" Gov profile mid-length 556 Barrel 27.2oz
Total: 42.1oz

6.8 URGHB (Upper Receiver Group Heavy Barrel, this is my implementation):
Handguard 6oz
Barrel 36.9oz
Total: 42.9oz

Difference 0.8oz...and more of that weight is at the back of the receiver where the weight matters a lot less than out front. But I have a barrel in a more powerful caliber and in a heavy profile....my 6.8 URGHB would massively outperform their brand new URGI at nearly the same weight and handling.

6.8 URGSCOUT:
JL Billet NANO Ultra Mag / Alu 15" Handguard 6oz
ARP 16" Scout Barrel 28.6oz
Total: 34.6oz

Or if you pin the gas block AND if ARP still has them:

6.8 URGSCOUT14.5:
JL Billet NANO Ultra Mag / Alu 13" Handguard 5.8oz
ARP 16" Scout Barrel 25oz
Total: 30.8oz...that's a pretty lightweight barrel / handguard config for 6.8 SPC.

Even my 5.56 Daniels Light Weight CHF CL barrel clocks in at 24oz...and that's a pencil profile I use for a training upper / CQB upper for an alternate caliber to my 68 that's a primary.

Gas piston system will also add more weight than a DI gas system, even the SA one (lightest piston system of them all) is 3oz more total weight mostly out front than a low profile gas block (1.3oz) and gas tube (0.6oz) in a DI gas system. Carriers are the same weight. So if your weight conscious, go DI. And this coming from someone who ran AA's also reasonably lightweight piston system for years....

69693

Note that I have since replaced the bulky picatinny mount surefire pressure pad with sure fire's smaller tape version and magpul m-lock mount plate for a lower profile and cleaner design, no rubber bands or zip ties, but at the time of the photo worked reasonably well still, even if a bit ghetto, I was using what I had at the time of the initial build. That's a heavy barreled 6.8 barrel with JL's mag / alum handguard.

Handles like the oh so typical 16" 556 gov profile / 6601 15" m-lok handguard combo but shoots in a league of it's own comparatively.

P.S. sorry for the uber lengthy post, but there was a lot of technical reasoning to my suggestions. I've tried MANY configurations over the last 10 years and I've really honed in on what works and what doesn't, what's the best and what's marginal. I'm always after overmatch, not just in caliber selection, but rifle design, so I roll my own as they say.
 

·
Registered
Joined
·
488 Posts
Looks pretty cool, never saw the JAG before, but it looks like they are for competition applications. My concern would be that the thermals are going to SUCK big time. There's no airflow and carbon fiber is an insulator...while it may not heat up the handguard as much for a short while (just wear gloves), it's going to trap a lot more heat in the barrel which will start to saturate much faster. That robs you of accuracy and barrel life.

Skeletal handguards allow a for a lot more convection cooling and AZ61A has very good thermal conductivity (better than 6061 T6) making it a giant thermal dissipater. You might think intuitively that high thermal conductivity in a handguard is bad, but what it does is dissipate the heat it absorbs more quickly and the skeletal designs convection cooling keeps the barrels cooler longer and allows for faster cool off when they do heat up. The JL Billet isn't a super slim design either, so there's a decent clearance around the barrel (some really get as close as possible for the smallest diameter).

Installation looks pretty standard though: Handguard_Installation.pdf (shopify.com)

But I'm sure it works well for a competition gun, would probably be a good choice for lightweight hunting upper or even a fast deploy truck gun.
 

·
Registered
Joined
·
488 Posts
I painted mine with rattle can, I don't mind it looking worn etc. as the paint rubs off in contact areas, primary function of the point job is just to visually brake up the outline of the gun which it accomplishes, even when worn. I believe from the factory they are all cerakote in either black or FDE.
 

·
Registered
Joined
·
488 Posts
Maybe that's the regular 6061 variant I was thinking of. They make them in 6061 T6 as well at a lower cost but I do believe those are painted black by default or maybe it was a heavy type 3 phosphate. Either way, I just remember one I ordered didn't require a color selection, but don't remember which one that was.

I run the magnesium one on my heavy barreled 6.8 upper that's sporting the Razor HD gen 2-E 1-6x + 45 RDS on a badger C1 1.70" mount (lower 1/3), but the 6061 version is on my 556 upper with the Daniels Lightweight profile barrel that just has an RDS, figured why spend the extra $50 when that barrel and optic combo are already pretty lightweight.
 

·
Registered
Joined
·
488 Posts
The 16" ARP 3R I had and 16" DD 5R I now have were / both very accurate. Both are MOA or better with several factory loads and Druid Hill custom loads. I really like JP's receiver vice clamps for swapping barrels. It does an excellent job of proper holding and supporting the upper receiver. Using a crows foot and calibrated torque wrench, it's not a difficult process at all.
 

·
Registered
Joined
·
488 Posts
Handguards. I paired a heavy S2W profile 16" DD barrel clocking in at a hefty 36.9oz with a 5.8oz Magnesium Alloy handguard (15", that weight includes barrel nut and screws). A typical 6061 T6 15" handguard (MLok) weighs 15oz with barrel nut. Something like the Daniels Defense RIS II non-FSP 12.2" in picatinny used on the Block II M4A1's is a whopping 17.7oz. The 14.5" socom 5.56 barrel weighs 30 oz.

Do the math:

My Setup
36.9 + 5.8 = 42.7oz

ARP 16" Scout + 15" M-Lok Handguard (6061 T4, something like the Geissele SMR 13.5" or run of the mill 15")
28.6oz + 15oz = 43.6oz

ARP 16" Scout / Bison 16" Recon + JL Billet Mag-Alloy 15"
28.6oz + 6.5oz = 35.1oz

ARP 16" Scout / Bison 16" Recon + JL Billet Mag-Alloy 13"
28.6oz + 5.8oz = 34.4oz
 

·
Registered
Joined
·
488 Posts
Good info there. I went a similar route:

ARP 16" 3R-11 Scout 28.6 oz + Jag 13.5" Ultralight Carbon Fiber 4.1 oz = 32.7 oz total.

Love that carbon fiber too. It doesn't get hot to the touch, or feel cold in the winter. Amazingly solid for the weight.
I almost went carbon fiber, but decided not to for one reason. Abrasion. Once you loose the protective coating, it's exposed to UV light and will start to break down.

Carbon fiber is an awesome material, but my use cases are pretty hard on the rifle, typically half the gun is exposed to bare metal after just a year or so of use due to being knocked about, dropped, scraped against gravel etc.

I was a concerned that I would run into that issue at some point due to wear, but maybe I'm just paranoid. If I build a new system, maybe I'll give it a try and see how it holds up. But I think that would be a really good option for hunting rigs or home defense.
 

·
Registered
Joined
·
488 Posts
One of the reasons I chose magnesium alloy is that it's highly corrosion resistant but 33% lighter than 6061. AZ61A is about 13% less yield strength than 6061-T6, but that's pretty close. ZK60A magnesium alloy is actually 20% stronger tensile strength than 6061-T6 but the same density as AZ61A. I've been looking for one made in ZK60A but have not found any. I think that would be the ultimate balance between weight vs. strength as it's as light as what I have now but 20% greater material strength than 6061-T6.
 
1 - 9 of 9 Posts
Top