Originally "Anyone got a photo of a lightened DCM tube?"

Arfcom archives and elsewhere haven't been kind to my searching. I've got a plot for six 0.75" holes and one 1" hole spaced 0.5" apart per side, but my memory recalls bigger holes.

Currently a BCM M4 receiver, FN A4 barrel, Rock River Arms DCM barrel nut and tube weighs 4.3lbs on the old grocery scale. So add a pound for BCG and sights to make an assembled upper.

Sinister posted one a few years ago.

B

Yep yep.

Attached File

I got a line to borrow a vertical mill tomorrow.

According to the old grocery scales, the tube itself weighs 1.2lbs. The handguards weigh 0.4lb. The barrel nut assembly is probably another 0.3lb. Altogether about 2 pounds. I expect about 5oz shaved off.

Is the whole idea to get under the weight for a Modern Military rig?

I don't own one but have borrowed rigs to shoot that CMP game.

ETA: http://bulletin.accurateshooter.com/2021/01/sunday-gunday-7-5-lb-ar-for-cmps-modern-military-discipline/

No. Just floating an A4 upper. Don't wanna spend another $200 on QRF12 yet, but 2lbs is ridiculous for a featureless handguard.

Sketching out the side holes.
Attached File


Roughly indexing centers for the 5/16" vent holes.
Attached File


Attached File


Expanding the pilot holes in the sides to 3/4". I wanted 7/8", but the next size bit he had was 1" which was too much.
Attached File


Blue, orange/gold, and silver colored chips.
Attached File



15oz tube. The gas tube slot wasn't milled quite far enough for standard tubes. Meh. I was being conservative.
Attached File


Attached File


I think I'll do 4 flats and a dimple eventually.
Attached File


Attached File



8.5lbs. Still front heavy, dammit. About the same as the carbine with light, BUIS, and TR24.
Attached File

I broke the upper in yesterday.

Weather: 90-100*F, sunny with a some cloud patches over 2nd relay, occasional 5 mph gusts. It sucked, but wasn't unbearable.

I did just about everything to sabotage my mental game in the morning, but still pulled out a win amongst a majority field of M1, M1A, and M1 Carbines.

Load: 25gr IMR 3031/Hornady 55gr FMJ/2.255".

Standing: 77/100
The sighters beforehand weren't close to call. I had decent sight pictures and trigger presses, but they just didn't go in the middle. I worried there might be ammo/fresh throat dissonance and considered DNFing. I wasn't feeling good anyway. For the last 3 shots, I switched to Offhand and snapped them out. They were a typical 4 MOA left, but elevation was good and about 10-ring size. I used stock notch #5 of 6 for A2 length.

Sitting "Rapid": 93/100
My pants were too tight. Couldn't get my elbows on the front side of my knees. Wobble was a 9-ring CCW circle; I sent them at 12:00 when the post touched the bottom of bull. I recall the group being decently round at 11:00. Two notches longer than Prone with an M1907 sling still works well, but I might've been better off with 3 this day.

Prone "Rapid": 89/100-2x
Prep time was looking and feeling good until the end when my right hip/lower back started to cramp. So I rotated my position CCW about my waist and straightened my legs, more Euro style. 5 shots in the middle, 5 shots out left. Considering I tried 5+5 mags for the first time in more than a decade, I think I might have failed to place the stock or right elbow in the same spot.

Prone Slow: 188/200-4x
I had some difficulty with stock and  elbow placement, but mostly fought sliding glasses. It was heckin' hot. No spotting scope - just sent 'em.
Attached File



Aggregate: 447/500-6x.

A week had gone by and I felt guilty about not paying homage to the barrel gods with an abbreviated proper break-in.

I lightly scrubbed the bore with Hoppe's #9 and JB paste. The only green I saw was in the crown and flash hider. Maybe moly just masks it well. I wanna get the borescope in just to see how little 65rds did.

5oz.

How much does it make weight by?  You have room for tungsten weights in the pistol grip hole.

Nice shooting.

Why not any number of free float rails?

I kinda wanna switch to an A2 upper receiver. Kinda wanna buy another QRF12, a Meopta 3-18x, and 1913 adapter for my VersaPod to make something SDMish.

The barrel, receiver, and bolt are new, but have sat since autumn. I had the urge to tinker and break-in the barrel, so I pulled the DCM tube out of the parts bin for shakedown. Save money til a plan is more set.

Whose plug do you use? Will it fit a spare bolt?

I think it's this one from Missouri Tactical off amazon.  I have two different types (one I got off Commercial Row -- I don't know who made it).

Yes, there's plenty of room for a spare bolt.



This is the improved Ergo from Midway:


I built a flat-top like you describe.  QRF-12 on sale from Primary.

Attached File

You gonna paint over the bare metal? What size and spacing did you use?

Yeah, I have to get something on that bare metal. Holes .75 & .2 spacing... Removed approx 4oz.