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PC Carbine M-LOK Problem

This is a discussion on PC Carbine M-LOK Problem within the Ruger Semi-Auto forums, part of the Rifle & Shotgun Forum category; Got a Streamlight flashlight with a tape switch that mounts on a 4” segment of M-LOK rail from Bravo Company. Installed the light on the ...


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Old December 16th, 2019, 08:30 AM   #1
 
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Angry PC Carbine M-LOK Problem

Got a Streamlight flashlight with a tape switch that mounts on a 4” segment of M-LOK rail from Bravo Company. Installed the light on the right side (3 o’clock) and put the tape switch on the top (12 o’clock) so I could activate it with my left thumb while holding the carbine.

Went to the range to zero my MRO and got it just about dialed in when the section of rail with the tape switch rail came loose. Removed it and the flashlight, then shot again and was way off from the almost zero. Checked that the MRO was not loose. Went to put the section of the rail back in place and realized the M-LOK screws hit and slightly depressed the barrel. There were small scratches on the top of the barrel from the M-LOK screws. The barrel is not centered in the handguard but higher and close to the 12 o’clock position if looking at it end on. From the side one can also see there is not much room between the underside of the hand guard and the top of the barrel.

It appears the location hand guard over the barrel precludes use of the top set of M-LOK slots.



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Old December 16th, 2019, 08:45 AM   #2
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WoW that sure didn't take much to throw that barrel out of wack. Almost seems impossible, but I guess not.
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Old December 16th, 2019, 02:22 PM   #3
 
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Can you file the screws down a little or get shorter ones for top of barrel Mlok use?
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Old December 17th, 2019, 02:03 PM   #4
 
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Quote:
Originally Posted by MountainHunter View Post
Can you file the screws down a little or get shorter ones for top of barrel Mlok use?
I presume that Bravo Company makes their M-LOK attachments according to the MagPul specifications. They certainly look just like the screws that came on the MagPul sourced angled fore grip that I mounted at 6 o’clock. And these screws come coated with a yellow form of a thread locker. Otherwise it might be worth buying a shorter screw.

I could try to shorten them my else’s, but how do I know how much is enough so that the barrel doesn’t hit them when it whips as fired? If you have ever watched a high speed camera replay in slo-mo, there is significant barrel whip. The whole point of free floating to give room for that. Anything that interferes with barrel harmonics can interfere with accuracy or consistency.
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Old December 17th, 2019, 02:28 PM   #5
 
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Paul, would you mind posting a photo? Having trouble visualizing this (sorry, I do better with pictures than descriptions!)
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Old December 17th, 2019, 04:15 PM   #6
 
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Here is a photo from the left side, muzzle just out of picture to the left.

Rail on top for tape switch with screws impinging on top surface of barrel.

Below is angled fore grip with at least one attachment screw visible inside the hand guard.
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File Type: jpeg 49103F98-8BF4-48A5-BDDC-85F17D9F8A30.jpeg (2.34 MB, 55 views)
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Old December 17th, 2019, 04:19 PM   #7
 
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Second photo has top rail removed showing minimal clearance between top of barrel and underside of hand guard. In contrast there is a lot of space between the bottom of the barrel and the bottom of the hand guard. All because the barrel is not centered in the hand guard.
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File Type: jpeg 00BCDDEC-1800-44F0-98EF-A4EF1EAE440F.jpeg (2.18 MB, 38 views)

Last edited by Paul49; December 17th, 2019 at 04:20 PM. Reason: Clarity
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Old December 17th, 2019, 04:42 PM   #8
 
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Just sent Ruger an online customer support request. Will update when they respond.
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Old December 17th, 2019, 05:00 PM   #9
 
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Thanks for the photos, that did help! Looking forward to Ruger's response.
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Old December 23rd, 2019, 10:29 AM   #10
 
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Ruger wants me to send the PCC in to them. I counter-offered that they tell me the normal gap between the top of the barrel and the underside of the hand guard. I don’t want to send it in only to find it is built to specifications.

I measure the gap as about 3.4 mm.

Anyone else here able to make that measurement to see if mine is similar?

Ruger won’t be getting back to me until after Christmas at the earliest.

Thanks!!
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Old December 24th, 2019, 04:56 AM   #11
 
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Quote:
Originally Posted by Paul49 View Post
Ruger wants me to send the PCC in to them. I counter-offered that they tell me the normal gap between the top of the barrel and the underside of the hand guard. I don’t want to send it in only to find it is built to specifications.

I measure the gap as about 3.4 mm.

Anyone else here able to make that measurement to see if mine is similar?

Ruger won’t be getting back to me until after Christmas at the earliest.

Thanks!!
The Ruger handgaurd is mounted eccentric for cosmetic reasons. It’s known to be a clearance issue on the top rail.

I have the Midwest Industries handgaurd and just tested a Mlok mount and the screws do NOT touch the barrel. The rail is also eccentric.
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Old December 24th, 2019, 06:50 AM   #12
 
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Maybe this comparison explains the design decisions?
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Old December 24th, 2019, 09:43 AM   #13
 
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Quote:
Originally Posted by Paul49 View Post
Maybe this comparison explains the design decisions? I measure the gap as about 3.4 mm.
Love that picture of side by side. Thank you!

I measured the bottom of the Midwest Industries rail to the bottom center of the top flute ~0.352”=8.9408 mm. Did you measure to the bottom of the flute?

Last edited by MountainHunter; December 24th, 2019 at 09:50 AM.
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Old December 24th, 2019, 02:21 PM   #14
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I like that the PCC looks like the suomi. I would like someone to offer a wood stock for that reason. I rrally enjoy the PCC
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Old December 27th, 2019, 12:24 AM   #15
 
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You might want to consider mounting the tape switch to the forend using cable ties or a section of bicycle inner tube, only. There may be no real need for a rail on top.
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