ACR barrel install question

H

HawkWei

CGN Regular
Rating - 100%
35   0   0
Location
Canada
Hi there got a quick question regarding to my ACR and hope someone can help a bit.

Recently I did a full clean with my ACR.
When reinstalled the barrel, there are no more crisp clicking sound from turning the barrel lock lever

Upon closer look there are some wear on the barrel retain knob on the reciever, which explain the lack of sharp clicking sound

Is this normal from use or is there a safety concern? Cheers. The barrel itsself is not moving at all and shoots fine but just wondering.
 
Best practice do not wear out that plunger and the ratcheting mechanism that it rubs on is to always hold the handle of the barrel "wrench" down all the way when turning so that the plunger is disengaged fully. You technically shouldn't be hearing the ratcheting sound if done correctly. You can also use your left thumb to Aid in this process
 
Lesson learned! but since there is no more sharp clicking sound, safety concern? I think there is a tiny bit of wear on the plunger
 
I don't think I'd be too worried about it especially if you cant rotate the aforementioned barrel wrench without depressing the plunger. Even if the barrel was just Loosely installed I cant see it posing a major safety concern. It would just likely cause increased wear and tear on things if it would even go into battery and fire.
 
onetwentyish said:
I don't think I'd be too worried about it especially if you cant rotate the aforementioned barrel wrench without depressing the plunger. Even if the barrel was just Loosely installed I cant see it posing a major safety concern. It would just likely cause increased wear and tear on things if it would even go into battery and fire.
Click to expand...

Thnaks mate, after checking around on the net you are correct!
 
/Rant/
That QD mechanism is such a crutch. If you're swapping barrels it loses zero. If the barrel isn't screwed on tightly it loses zero. If you rely on the system for "DMR" it has wandering zero.

I hated the ACR barrel mechanism and wish they went for just a standard trunion and a more finely threaded barrel nut system. (Templar makes this actually but cost quite some money)
 
I had a similar issue/concern with my ACR QD Barrel and Trunnion arrangement. As stated, first and foremost do NOT "ratchet" the system when installing the barrel. You need to pull down fully on the Handle Then crank it around until tight. There should be no clicking/ratcheting sound as you crank the Handle around to tighten the Barrel against the Trunnion. If you don't pull down fully on the Handle before cranking it down, the Trunnion Plunger will wear against the matching indents on the Barrel Locking Ring. This is what makes the "ratcheting" sound that you wish to avoid. Tightening the Barrel against the Trunnion should be a silent affair. Just release and fold the Handle in the stowed position once you have the barrel tight against the Trunnion. This will allow the pointed Trunion Plunger to contact the corresponding indent on the Barrel Locking Ring, thus "locking" the Barrel. You wear down the interface between the Trunnion Plunger and the Indents on the Barrel Locking Ring at your own peril if you insist on "ratcheting" the parts...

My paricular problem is that the Trunnion in my ACR is such that the Handle has to be cranked past center to tighten the Barrel down. Then when I fold the Handle upwards it interferes with my after-market RPM MLOK Forend near the Handguard Mounting Pin. The Handle has to be centered in order for the handguard to mount to the Rifle. Big problem, as my barrels are loose in the Trunnion when the Handle is centered as it is not fully cranked down tight. This problem is common to all 4 of my ACR barrels, which is why I say the problem lies with the Upper Reciever's Trunnion and not with the Barrel Locking Ring(s). The solution for me was to create a shim that I insert between the Barrel and the Trunnion before I crank the Handle of the Barrel Locking Ring over to tighten everything down. The shim takes up just enough space that the Handle now reaches the sweet spot for tightness right at the center point underneath the Barrel. The Handguard fits and prevents the Handle (and Barrel Locking Ring) from loosening for any reason as the rifle is handled and fired. The "shim system" works very well to resolve my particular problem. The shim itself was made by cutting out an appropriately-sized, "U"-shaped piece of aluminum Soda Can. The thickness of the material was perfect for the job. Accuracy from my 18.5" 5.56mm Barrel went from a "meh" 3 MOA before the shim, to 1.5 MOA with 62 Gr PMC X-Tac ammo after installation. Another win for the Wiley Coyote School of Gunsmithing (WECSOG)!
 
Last edited:
Bartok5 said:
My paricular problem is that the Trunnion in my ACR is such that the Handle has to be cranked past center to tighten the Barrel down. Then when I fold the Handle upwards it interferes with my after-market RPM MLOK Forend near the Handguard Mounting Pin. The Handle has to be centered in order for the handguard to mount to the Rifle. Big problem, as my barrels are loose in the Trunnion when the Handle is centered as it is not fully cranked down tight. This problem is common to all 4 of my ACR barrels, which is why I say the problem lies with the Upper Reciever's Trunnion and not with the Barrel Locking Ring(s). The solution for me was to create a shim that I insert between the Barrel and the Trunnion before I crank the Handle of the Barrel Locking Ring over to tighten everything down. The shim takes up just enough space that the Handle now reaches the sweet spot for tightness right at the center point underneath the Barrel. The Handguard fits and prevents the Handle (and Barrel Locking Ring) from loosening for any reason as the rifle is handled and fired. The "shim system" works very well to resolve my particular problem. The shim itself was made by cutting out an appropriately-sized, "U"-shaped piece of aluminum Soda Can. The thickness of the material was perfect for the job. Accuracy from my 18.5" 5.56mm Barrel went from a "meh" 3 MOA before the shim, to 1.5 MOA with 62 Gr PMC X-Tac ammo after installation. Another win for the Wiley Coyote School of Gunsmithing (WECSOG)!
Click to expand...

That sounds very interesting... Can you post some pictures of what the shim looks like and where exactly you installed it?
 
Bartok5 said:
snip
Click to expand...

Cool stuff! When I still owned my ACRs, I unscrewed and remove the handle, put a rod through the trunion bottom holes, and put that on a vice. Next I use a rubber mallet to hammer(rotate) the barrel nut to apply extra torque to tighten it one more notch. I got sub MOA consistently with 77otm.

However with how hard it is to secure spare parts, I ultimately ditched all 3 of my ACRs and opted for some other “NR” option with widely available, “lego” parts.
 
Here are a couple of photos, as requested. The first shows my soda-can shim, which is an admittedly fragile and delicate piece of thin aluminum. Although they are cheap to fabricate, they do take care and time to get right. But for my particular problem of a loose Barrel lock-up when the Locking Ring Handle is centered, it works perfectly. In fact, it is almost scary what a difference it makes to my rifle's accuracy to have the Barrel held tightly to the Trunnion.

Photo 1: The Shim itself. Approx 3 cm x 3 cm, 2 mm wide, cut from a soda can with a razor knife.


20210926-234408.jpg



Photo 2: The Shim placed on the Trunnion prior to installing the Barrel. The Flange on the Barrel Extension will sandwich the Shim between the Barrel and Trunnion, thus ensuring that the Handle is centered beneath the rifle when the Barrel is cranked down at its tightest.


20210926-234758.jpg
 
Bartok5 said:
Here are a couple of photos, as requested. The first shows my soda-can shim, which is an admittedly fragile and delicate piece of thin aluminum. Although they are cheap to fabricate, they do take care and time to get right. But for my particular problem of a loose Barrel lock-up when the Locking Ring Handle is centered, it works perfectly. In fact, it is almost scary what a difference it makes to my rifle's accuracy to have the Barrel held tightly to the Trunnion.
Click to expand...

Thanks for sharing the pics. Looking at it, its shocking and amazing to hear what that little piece of a soda can does for your rifle.
Where did your handle used to be when cranked without the shim (in reference to your last picture). Was it around the 7 oclock position?
 
Yup - the Barrel Locking Ring Handle was at 7 o'clock when tightened without the shim. As a result, my RPM Handguard would not fit over the Handle skewed to the side.
 
Goes past 6 o'clock on every one I've seen thats been tightened properly. You remove it or bend it to work wRPM or the plastic handguard (on dmr barrel). If you don't tighten it enough you will have bad groups. With it tight enough a DMR barrel is more than capable of MOA. Also like the others have said, you're supposed to be depressing the plunger.

Cheers
 
You must log in or register to reply here.
Back
Top Bottom