ACRO Mounting Question

[ssc45]

Background:

Bought another Glock 45 MOS. Mounted a FCD ACRO plate approximately 4 months ago. ACRO arrived last week. Mounted ACRO to plate pursuant to Aimpoint instruction. (Push sight forward and snug down cross bolt and then give it another twist to tighten. Check after 50 rounds etc.)

I didn't use any loctite. I marked the bolt with a paint pin. The ACRO was rock solid. Shot 200 rounds last week and checked paint mark--no movement. The ACRO was solid. Shot another 200 rounds 2 days ago. Paint mark--no movement. Took it out yesterday to dry fire. All was good with the paint mark. Checked the ACRO and it was rocking fore and aft.

I then tightened the cross screw which was loose. It turned just shy of a 1/4 turn. The ACRO is again solid and I reapplied another paint mark. I didn't use loctite.

Questions:

1. Should I use blue loctite?

2. How did the cross bolt become loose with no movement of the screw? Cross bolt stretch? Break in? Shit happens?

Thank you for your response.

Cheers, Steve

[SoCalDep]

When the thing you do doesn’t work… don’t do that thing again.

You should use Loctite, and degrease all interacting surfaces before you apply the Loctite and mount. Aimpoint instruction is 26 in/lbs but I’d make sure there is Loctite (I like 248) is on there while I torque to 26 in/lbs with that FCD steel plate. If I were using the C&H aluminum plate, which I don’t recommend right now, I wouldn’t go more than 15 in/lbs.

Background:

Bought another Glock 45 MOS. Mounted a FCD ACRO plate approximately 4 months ago. ACRO arrived last week. Mounted ACRO to plate pursuant to Aimpoint instruction. (Push sight forward and snug down cross bolt and then give it another twist to tighten. Check after 50 rounds etc.)

I didn't use any loctite. I marked the bolt with a paint pin. The ACRO was rock solid. Shot 200 rounds last week and checked paint mark--no movement. The ACRO was solid. Shot another 200 rounds 2 days ago. Paint mark--no movement. Took it out yesterday to dry fire. All was good with the paint mark. Checked the ACRO and it was rocking fore and aft.

I then tightened the cross screw which was loose. It turned just shy of a 1/4 turn. The ACRO is again solid and I reapplied another paint mark. I didn't use loctite.

Questions:

1. Should I use blue loctite?

2. How did the cross bolt become loose with no movement of the screw? Cross bolt stretch? Break in? Shit happens?

Thank you for your response.

Cheers, Steve

[ssc45]

Thank you for the response. I edited to say thanks. I will remove the cross bolt and use loctite and torque to 26inLBs.

Cheers, Steve

[1Rangemaster]

@SoCalDep leads the way here; he has the art of mounting down to pretty much a science.

Just to reinforce, thread locker is critical on all fasteners-degrease, etc.
The other specific that’s changed over the past couple of years are the torque specs. For some manufacturers we didn’t initially have them.
Almost all of the “failures” my dept. has had over the years are mount, not sight failures.
Best of luck!

[HeavyDuty]

I’m not sure if not using threadlocker really explains why it got loose with no fastener movement, though. I’m thinking something wasn’t fully seated the first time.

[Wayne Dobbs]

I have a set of ACRO mounting notes if anybody wants them, but SoCalDep (who is past being an SME on all this now) nailed the first step: DEGREASE the slide screw holes and plate screws. The OP's experience with the optic cross bolt holding is exactly what we expect and have seen over and over on many pistol/ACRO combinations. I've never used thread sealer on the crossbolt at all. As for Locktite, I really like the 248 version, which is a semisolid and lots easier to work with. It looks like a big Chapstick!

[SoCalDep]

I’m not sure if not using threadlocker really explains why it got loose with no fastener movement, though. I’m thinking something wasn’t fully seated the first time.

I agree with you. I don’t think it was a threadlocker issue. It probably wasn’t fully seated and torqued.

That said, there are several ways an optic can become loose and we wouldn’t want to fix one thing just to have something else make the optic come loose again, thus the degrease-threadlocker-proper torque recommendation.

[Pnut]

One thing I learned on this site was the importance of bedding the mounting plate if your set up uses one. People here recommended using a product called E6000 to bed the plate to the slide. This solved a lot of problems with my STI/SRO setup where the plate was constantly working loose, even with thread locker

[TC215]

I were using the C&H aluminum plate, which I don’t recommend right now, I wouldn’t go more than 15 in/lbs.

Can you expand on this? I’m planning on installing an Acro tomorrow using the C&H plate because I couldn’t find an FCD plate in stock anywhere.

[SoCalDep]

Can you expand on this? I’m planning on installing an Acro tomorrow using the C&H plate because I couldn’t find an FCD plate in stock anywhere.

I’m glad you posted this because I do need to clarify… I don’t have experience with the C&H ACRO plate for Glocks. They may be great. Their 509T plate has worked great for me.

In my response I was thinking of their plate for the ACRO/M&P optic ready slide. Those have been sketchy along with the 509T M&P plates. They are working on it and I’m not trying to talk crap because they are trying to accommodate needs and they are being super responsive to our input. I’m optimistic they’ll be good-to-go soon.

So again, it’s the M&P plate, not the Glock.