Exactly. While *I* have found that for *my uses* the FF on 0.625" OD barrel makes a difference, someone not shooting braced off of object much may not. Or, may find another workaround that works better for them.Originally Posted by Jay Cunningham
My BCM dissipator (which is a 16", A2 profile barrel with rifle-length handguards) seems much less susceptible to POI shift on the 9-hole for whatever reason.
Sounds like a lot of work, but you may be on to something here.
The carbine as pictured (no magazine, empty chamber) weighs 7 lbs. 9 oz.
At 100 yards off of the bench I kept 7 of 10 rounds inside the black of a bull on the obverse of a VTAC target with iron sights. The rounds favored left and the three outside the black were a little high and left; pretty good rough zero at 25 yards. I threw one extra click of right windage in and will check it again next time.
The above was with the Aimpoint detached. I went ahead and stuck it back on and dropped the dot straight down onto the top edge of the front sight, then I folded down the rear and shot a group.
Five rounds hit 4" left. I dialed in some windage and put five for five in the black. I then switched to a 12"x12" steel square at 200 yards. I initially placed my dot on the top edge of the target but wasn't getting results, so I simply held dead center: hit - hit - hit, etc. The old "boring regularity" thing.
So no hard data for this post besides the weight. The carbine functioned just fine and I won't mention function again unless I need to.
So far I'm happy, but more to come.
I got my 6720 in 05/2010 or so, and it was one of the first 500. It came with the Matech sights, two 20rd PMags, H-buffer, and the GI-type stock. When received, I did a quick once over but no detailed inspection. I then lubed it up and threw it in the back of my GOV for about a week. At the end of that week, I fired 2053 rounds in three total hours, over two range sessions (~1300 or so and ~700) without stoppage. Since, it's been to classes, quals, and accrued several thousand more rounds. I changed the bolt rings once, and I think I'm due for an action spring. I've had the same Matech BUIS on it since the beginning, but broke the crossbolt once and replaced it. That's pretty common. I've been running the same T1 (LT mount) as well.
This 6720 is my EDC and duty rifle, and is commonly used as an exemplar in demonstrating and justifying LW rifles for patrol rifle programs. My wee ones, ladies, and IBOs can run it with great effectiveness.
In a recent work-up of differential POIs, an assortment of duty and training loads (most 55gr) all shot within 4" from a monopod prone on a B8 bullseye at 100yds. A few of the better loads with this gun will consistently come in under 2". When heated up, they open up a bit but not as much as you would predict. This included some crappy low end stuff, as well as TulAmmo and Herters-Tula. I did NOT sling up or introduce any barrel stresses or forces. (I'm away from home and can't be more quantitative than that right now.) I do know that I ran a stack of magazines of some 55gr training ammo on steel torsos at 200yds. While the forearm was hot hot hot, I could still hit COM on the torsos without issue. Accordingly, this gun meets my needs. This gun also functions with low-impulse handloads, frangible and green ammo, and some non-commercially available ammo that is iffy in some others.
I have considered a FF and quad rail, but don't have need to mount other tools/accessories. My next modification will be a new light mount and an updated light (Fury), but other than that it will remain as pictured for the foreseeable future.
Someone asked about the barrel profile.
Skintop,
What light mount are you using on that 6720? (I noticed two different light mounts in your photos actually, and I'm curious which one you recommend at this point.)
I like your setup - no BS, no frills. How do you like the ARC mags? I've been very happy with mine, and have found them to be more reliable than the first production run of Lancer Advanced Warfighter Mags. This thread has me pricing 6720's online...... Like I need another AR.....I got my 6720 in 05/2010 or so, and it was one of the first 500. It came with the Matech sights, two 20rd PMags, H-buffer, and the GI-type stock. When received, I did a quick once over but no detailed inspection. I then lubed it up and threw it in the back of my GOV for about a week. At the end of that week, I fired 2053 rounds in three total hours, over two range sessions (~1300 or so and ~700) without stoppage. Since, it's been to classes, quals, and accrued several thousand more rounds. I changed the bolt rings once, and I think I'm due for an action spring. I've had the same Matech BUIS on it since the beginning, but broke the crossbolt once and replaced it. That's pretty common. I've been running the same T1 (LT mount) as well.
This 6720 is my EDC and duty rifle, and is commonly used as an exemplar in demonstrating and justifying LW rifles for patrol rifle programs. My wee ones, ladies, and IBOs can run it with great effectiveness.
In a recent work-up of differential POIs, an assortment of duty and training loads (most 55gr) all shot within 4" from a monopod prone on a B8 bullseye at 100yds. A few of the better loads with this gun will consistently come in under 2". When heated up, they open up a bit but not as much as you would predict. This included some crappy low end stuff, as well as TulAmmo and Herters-Tula. I did NOT sling up or introduce any barrel stresses or forces. (I'm away from home and can't be more quantitative than that right now.) I do know that I ran a stack of magazines of some 55gr training ammo on steel torsos at 200yds. While the forearm was hot hot hot, I could still hit COM on the torsos without issue. Accordingly, this gun meets my needs. This gun also functions with low-impulse handloads, frangible and green ammo, and some non-commercially available ammo that is iffy in some others.
I have considered a FF and quad rail, but don't have need to mount other tools/accessories. My next modification will be a new light mount and an updated light (Fury), but other than that it will remain as pictured for the foreseeable future.
Someone asked about the barrel profile.
They should be the same light and mount? Not sure what other pic you're referencing.
It's a VTAC mount on a rail section, Surefire G2, Malkoff drop in. Cheap, simple, functional. I'm going to look at some other options in mounts, and will almost certainly change that light out to a SF Fury.
I like the ARCs and have great luck with them, including the earliest production. The ones pictured above are v1 and some transitionals.
Of all the days to forget to wear my contacts...
I made a quick trip to the range after work today with the sole intention of firing a group from the 6720 and a group from my recce/gamer/whatever rifle under similar circumstances. The temperature was 84 degrees F, the winds were calm, and humidity was 33%. The range faces west and I shot between 1600 & 1700 and was getting glare from the setting sun in my face.
I planted a VTAC target out at 100 yards and shot 10 rounds through the Colt first, with a minimum 30 second interval between shots. Optic was a 4 moa Aimpoint and ammo was generic 62 grain greentip.
I then removed the optic and installed it on my recce/gamer/whatever rifle. This rifle has a BCM barrel with the following characteristics:
Features
M4 Feed Ramp Barrel Extension
Mid Length Gas System
1/8 Twist Rate
5.56 NATO Match Chambers (USMC SAM-R Chamber)
410 Stainless Steel
Mid Weight Contour Profile Barrels
Button Rifled
Hand Lapped Rifling
HPT (High Pressure Test) Barrels
MPI (Magnetic Particle Inspected) Barrels
So, pretty fancy. It also has a Geissele Super Semi-Automatic (SSA) trigger and a DD free float M4 Rail 12.0. So with the exception of the aforementioned gadgetry, I shot the same ammo at the same rate at the same target with the same atmospheric conditions with the same optic off the same benchrest position... I do not "sling up" at the bench.
So here were my results:
Colt 6720 10 round group max spread: 4.875"
Fancy BCM barrel 10 round group max spread: 3.75"
Colt 6720 nine round group (worst "flyer" deleted): 3.5"
Fancy BCM barrel nine round group (worst "flyer" deleted): 3.0"
If you disagree with my methodology, I'm cool with that. I have never been nor will I ever be a numbers guy. I figure as long as my methodology (such as it is) is consistent it should be good enough.
My take away from this was that inside 100 yards with a 4 moa 1x optic and decent (but certainly not match) ammo and a light firing schedule, the actual benefits from fancy barrels, triggers, and free float tubes is minimal. It's there, but maybe you're buying yourself a half moa. I will note that shot group "density" seemed tighter with the BCM barrel. I had three holes touching in this group; the Colt group did not have holes touching.
My next little test will involve a more demanding firing schedule... and also eyewear so I can actually see the damn target.I also plan on shooting closer to midday to eliminate glare from the sun being in my face.
As long as you are testing, it would be interesting to work 3 things into the mix:
1) some ammo with a rep for shooting well.
2) some magnification to help tease ou what is the rifle/ammo accuracy versus ability to see the target.
3) either slinging or bracing, that might show up the difference between free float and standard hand guards.
Yeah I have some of that already planned.
You PF members are so helpful!
;-)
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