[DSM]

http://www.ar15.com/forums/topic.html?b=2&f=28&t=197902

For your inner tabulated data nerd I posted this info up over there.

 

[DSM]

Completed stats.

I'm waiting on my ACR barrel to come back from ADCO. I requested the barrel be profiled forward of the gas block, cut back with an AAC Phantom mount pinned to legal length. I don't have delusions that it will null out six pounds of weight but I want to bring back the added length and weight of the can. I've seen where folks ask about weights before/after so I took some measurements and figured I'd post 'em up if anyone else might be interested. I took the weights of different flash hiders I had around for comparison so that if you'd rather use a different muzzle device you'd have something to compare to by subtracting the weight of the AAC I used and then adding the appropriate numbers. It'd be a matter of ounces but for the sake of completeness. I only did the ones that would compare to the same length of barrel. They are listed in metric (kilograms [kg] or grams [g]) and standard (pounds [lb] and ounces [oz]).


ACR barrel (complete), 16", w/ A2 flash hider
1.175kg // 2lb 9 3/8oz

ACR barrel, modified as above
1.081kg // 2lb 6 1/8oz


Flash hiders

AAC 18T Phantom mount
98g // 3 1/2oz

AAC 18T Blackout mount
124g // 4 3/8oz

Vortex
88g // 3 1/8oz

YHM Phantom
64g // 2 1/4oz

YHM 5C2 Phantom
59g // 2 1/8oz

 

[cjt50]

Just curious, did it "feel" like the CG was moved aft?

Do you have any pictures, love to see the finished product (profile forward of gas block)

I have always like the thin profile barrels, (forward of the gas block) Robarms light 556 barrel, FNH SCAR and the old Colt A1 profile to name a few examples.

 

[DSM]

It's subjective of course but I think it made a lot of difference in how the rifle shoulders.

 

[losman]

I was just on the Remington Defense website, sister company BUSHMASTER (and where hopefully all of the ACR production will move to after Bushmaster closes down their FAB in March). I saw REM is showing there ACR with a 16 DMR barrel. Does anybody have any info on this?

 

[DSM]

Just realized there wasn't a photo to go with the thread. You can see where Adco turned down the M4 profile and re-park'd the barrel. It makes it have a couple different tones of black from the different textures but that's all cosmetic. I suppose if you asked them to at least shave the entire length you would have a more even finish.

It still rings the steel w/o effort out at the range at 200 and 300yds with regular M855 style reloads. This is a worthwhile modification to the ACR. Looking at the stats above, and assuming you're not in need of a host mount, the YHM Phantom 5C2 gives the greatest weight savings overall, a touch more than a 1/4 pound.

 

[jivem]

DSM, could you mail me and/or post a tighter close-up pic of the barrel work? (I can't IM you since my post numbers aren't above 15 yet) I'm sending mine to Adco shortly for the same work and I want to see how they profiled the barrel just before the flash hider. I might have the same done, or slightly different.
Thanks,
jivem

 

[cjt50]

Adco, hmmmmmm.....

Now that I see the picture the profile looks good. Shame it just didn't come that way. Thanks for posting the picture.

 

[DSM]

DSM, could you mail me and/or post a tighter close-up pic of the barrel work? (I can't IM you since my post numbers aren't above 15 yet) I'm sending mine to Adco shortly for the same work and I want to see how they profiled the barrel just before the flash hider. I might have the same done, or slightly different.
Thanks,
jivem

I'll try and get to it later today. But basically they turned a small shoulder for the muzzle device to seat against. It's not the same size shoulder as a regular LW, it's smaller, but entirely functional for what it needs to do. I had considered asking them to mirror the M4 notch bevel but just kept it simple for everyone's sake.

 

[DSM]

Geez, I never get around to doing anything anymore. Not enough time in the day! Here's a pic of the Adco work on the barrel. Profiled, then cut back and pinned. Really makes a difference. If you do nothing else to your rifle then this is something I would whole heartedly recommend. For aesthetics sake you could ask them to give the entire length forward of the gas block a touch with the bit for when they re-park it so it'll match if you worry about such things.


Now I don't have a problem with it or think that the ACR is an ultra heavy rifle but when I took that pic above it got me to thinking about what one could do to shave even more weight off of the front of the rifle. I like my gear to be light and that means everything not just the rifle (my days of humping an M60 around made an impression on me!). Below are my notes on what I might look into doing on my next barrel. Each little thing by itself is trivial but added up they should cut it down even further.

A: 3/16"-1/4" hole drilled through top of piston guide. Reamed of burrs of course
B: 1/4"-5/16" hole drilled through both sides of the piston guide.
C: Shorter shoulder and turned down to smaller diameter.
D: Barrel fluted inside of gas block "window".
E: Bottom of gas block opened and barrel fluted.
F: Shorter journal with taper flush w/ gas block.
*G: Something could be done with the gas block, maybe turn down the fins or possibly shorten it. Light flutes could be milled into the main body behind the regulator.

Going from the factory M4 profile to the first pic was about 1/4 pound. Starting from factory to the above specs will put you maybe around, or just under, 3/8 pound removed.

If the effort involved to do so is worth the result is entirely up to you.

 

[cjt50]

Thanks for sharing the pictures. I am assuming that the CG has moved aft. Does the rifle feel more CG nautral? I think you mentioned earlier it did, just don't remember. Wife says I suffer from CRS (can't remember sh#t )

 

[DSM]

Yes, not by much of course but the change was noticeable enough, well worth the investment. It still has superb accuracy.

 

[SDDuc996]

Darren, not to get off subject but are you runningTroy Micros and the LaRue mid-height Micro mount?

What kind of cheekweld are you getting? I thought the ACR used standard height sights.

 

[DSM]

lol! Yes to both. I stole them from my XCR initially until I got an extra set and the Midway sale on the R1's a little while back. You can definitely use standard sights but they seem to sit just a little extra high on there. The micros are perfect for me.

 

[bigdog2003_99]

+1 i like my micros, i run a hk mount t-1 and it works great with them

 

[DSM]

Good comparison pic of the reworked barrel next to a stock factory barrel (thanks bigdog!)

 

[cjt50]

Good comparison pic of the reworked barrel next to a stock factory barrel (thanks bigdog!)

That picture tells alot, thanks. I want to keep the stock barrel assembly intact at the moment so I gotta wait on barrel parts or another full assembly.

 

[bigdog2003_99]

Good comparison pic of the reworked barrel next to a stock factory barrel (thanks bigdog!)

Any time Darren!!

 

[SDDuc996]

So there is somebody willing to do all the relief cuts to the barrel, just nobody (officially) that will do the op-rod cut?

 

[DSM]

So there is somebody willing to do all the relief cuts to the barrel, just nobody (officially) that will do the op-rod cut?

For a carbine length barrel?