Smacking an ACOG after adjustment - is it really necessary?

[Eurodriver]

I have spent a lot of time using the ACOG, and teaching Marines to use the ACOG. I have been told from day one that in order to properly zero an ACOG you must smack the optic after any adjustment to "reset the prism". So naturally, I told everyone they must smack it as well.

Yesterday, I put this to the test by shooting two current USMC inventory (Bible verse scratched off and everything) TA31s. One was a TA31RCOM4 and the other an A4. The procedure was to fire both rifles from a rest at 100 yards and perform a box drill on a target. Each box was 12" apart, corresponding to 36 clicks of windage and elevation. I stayed behind the rifle holding it steady and looking through the optic while a buddy made the adjustments. I could physically see the reticle moving with the clicks and ending exactly where it was supposed to. After resetting on the original target, I found absolutely no reason to smack the ACOG as the rounds impacted exactly where they should have.

I am beginning to wonder if there is something going on internally that I am unaware of at the user level, or I spent several years wasting people's time on the KD range...

Does anyone have any information on this? How did this get started?

[markm]

How did this get started?

Strikes me as a classic USMC myth. I've never even heard of it.

[nimdabew]

Grunts need a reason to hit things.

[scoutfsu99]

Strikes me as a classic USMC myth. I've never even heard of it.

I've seen it stated in the Triji manuals to do it. Helps seat the prism apparently.

[Kain]

Have a TA01NSN, yeah not the USMC model, but I have noticed on a occasion when zeroing that if not tapped with some degree of authority that adjustments would not occur and you would end up in the situation where you are chasing zero if you are not careful or have the first round sitting way the hell away from the rest. Tapping the turrets or shooting a second group to verify that the first wasn't just wonky is my usual MO in that type of situation. I chalk it up to a quark of the gear. Not like everything else doesn't have its weird quarks.

[Eurodriver]

Not always needed with the COG, but often enough that its worth it to make sure your stacked failed adjustments don't send the shooter on a wild goose chase.
I have witnessed failures of the optics to adjust.
My experience is based on RCOs acquired between 2005 and 2009.
It is possible that then new models were susceptible to the issue, and possibly with use the stickiness clears up, or that the design has been corrected, but I can say without a doubt that it was an issue.

No doubt that at some point it is an issue, and whether time has loosened them and/or the new ones are fixed it still makes sense to continue the practice as it is cheap insurance.

Do you know if they have been fixed? I think the ACOGs I used were manufactured around 2011. Not brand new, but certainly not Fallujah vintage

Strikes me as a classic USMC myth. I've never even heard of it.

That's interesting, because from where I'm sitting I can't imagine how you wouldn't hear about it. It's that prevalent (much more than typical USMC Scuttlebutt), but it certainly explains some of the looks I get when I smack my ACOG on civilian ranges now!

[Failure2Stop]

Do you know if they have been fixed?

I do not.
I have buddies at Trijicon, guess I could just ask, but I don't want to put them on the spot by asking them to potentially cast doubt on their products.

I did alternate between staring at a 31 I have in the safe, my work bench, and my bit kit this morning though...

[bullitt5172]

Has what been fixed? The need to smack them or fire a round off target? That hasn't changed, the design of the ACOG is the same. For some reason we removed it from the manual but it doesn't hurt either way. There is no "need" to smack the optic, just speeds up the process.

[Failure2Stop]

Has what been fixed? The need to smack them or fire a round off target? That hasn't changed, the design of the ACOG is the same. For some reason we removed it from the manual but it doesn't hurt either way. There is no "need" to smack the optic, just speeds up the process.

That pretty much answers that.
For those that don't know, bullitt5172 works for Trijicon, and is therefore the final authority on the matter.

RE: Chem-Light batteries:
http://www.kriana.com/aa-krill-lights

[Failure2Stop]

Found this diagram: