Upper receiver - BCM or Daniel Defense. I haven’t verified it, but I believe the MUR is heavier than a standard upper receiver so that is out. I’m not sure what advantage M4 feed ramps are in a semi-auto rifle, but the barrel I’m using has them so my upper might as well.
Barrel - AR15 Performance 16" 1:11.25" 5R, QPQ, mid-length gas. I haven’t been able to find a hammer forged, chrome-lined 6.8 SPC barrel, this seems like the next best thing. Pure accuracy isn’t terribly important here, a 2 minute rifle would be perfectly fine, but this barrel is probably capable of much more than 2 MOA. I had thought about cutting it down to 14.5, but I don’t know how well that would work. I’m aware that there are 14.5" mid-length 6.8 barrels out there, but I don’t know the gas port sizing differences nor how well those rifles actually run. I might have Marvin ball mill/dimple it under the hand guard.
Gas block - DD Mk 12, pinned.
Bolt carrier - LMT or BCM auto carrier.
Bolt - Undecided, probably LMT.
Hand guard/rail - Knight’s Armament URX III or URX 3.1. KAC Micro 300m rear and Micro front (if 3.1). Does anyone know what the URX 3 and 3.1 weigh?
Muzzle device - Undecided. Another reason for the 16" barrel, I can change this should I desire to (I don’t yet have a registered lower).
Charging Handle - BCM Mod 4.
I’d rather this not end up being any heavier than my DD M4V5 when mated with a lower. Thanks for any input.
A lot of what you’re asking can be answered via searching this forum and Google, but I’ll try to get you started.
The MUR with forward assist (MUR 1A) is 10 oz versus a standard forged upper at 8 oz. Get an upper with feed ramps as this will help when using PRI mags and these mags/combo can accommodate slightly longer rounds.
ARP’s Scout profile barrel is very light and wouldn’t need any dimpling. IIRC, the barrel I weighed was 27 oz. I’m a big fan of Marvin’s work, but it’s really not necessary for this profile and wouldn’t save you much weight. I had one of these barrels and it was pretty accurate. Below is a five shot group from 50 yards with SSA 110 gr Nosler Accubond. This barrel was good for ~ 1 MOA at 100y. I wouldn’t recommend cutting the barrel and you wouldn’t want to do that with the profile I recommended anyway.
DD is coming out with a HF, CL barrel, but I have yet to see it in stock anywhere.
Those are fine, but I’d recommend getting a headspaced bolt from Harrison at ARP and using a BCM or equivalent carrier. The MK12 gas block is slightly thicker and wider than VLTOR’s standard block on the bottom and “may” need to be modified when using some narrow or low profile rails.
The URX 3 weighs 13.6 oz with their barrel nut. The 3.1 is 14 oz, but I’m not sure if that’s with the barrel nut (which is probably only an ounce or so). I’ve three of the URX 3s and if I had to do it over again, would probably opt for something else given the installation hassle as well as the weight. The profile is nice, however, but if you’re looking to save weight the TRX and MI rails are lighter as is Noveske’s new NSR.
Good idea re: the 16" BBL. I’ve used a VLTOR VC-302, but there are plenty available now for the 308/6.8.
I have a handy spreadsheet I used to calculate weights. Using:
[ul]
[li]standard A4 upper receiver
[/li][li]ARP barrel I mentioned
[/li][li]VLTOR VC-302 FH
[/li][li]VLTOR set screw GB
[/li][li]middy gas tube
[/li][li]Standard BCG with ARP bolt
[/li][li]BCM GF CH
[/li][li]NSR 13.5 rail
[/li][li] DD front and rear sights
[/li][/ul]
The upper should be very close to 65.9 oz or 4.1 lbs (I don’t know what the DD M4V5 upper weighs, but I’d guess it is nearly the same). Without the sights, the upper will be approx. 3.94 lbs.
Mate that with a standard lower with a H buffer, carbine RE and VLTOR IMOD stock and you’re looking at a 6.5 lb rifle with the sights and 6.35 without.
I have heard of this mythical DD CHF/CL 6.8 SPC barrel, but I’ve never seen it. It’s out of the equation as far as I am concerned. It would be nice if that were to change, but I am not optimistic.
