I have an AR with a 14.5" barrel and a flattop upper
with an ACOG TA01 mounted on it with an ARMS #19S
mount.

That being said, here is the concern.

The scope moves a bit on the upper.
Not side to side, just front to rear, just a hair.
Not much at all,  just a hair.
I know it is not the scope to mount interface, as I
used blue locktite on it.  The mount just slides a bit
on top of the rail.

I was wondering if this is just the nature of the beast
for a quick detach mount, or if my upper receiver is out
of spec or something.   Could the rail itself, be undersized
and causing this, or am I just paranoid ?

The rifle still shoots great groups, so I guess it dosen't affect
accuracy.  I took the 4 day practical rifle course at Front Sight
and earned Distingushed Graduate honors with the rifle,
so I guess it dosen't affect accuracy,  Hell I can even shoot 1.25"
groups with it at 100yds when I do my part, but I am still a bit
concerned.

Thanks for any help you can provide.

Scott

shouldn't move at all IMO.  what kind of mount do you have lever or screw down ?

Quoted: shouldn't move at all IMO.  what kind of mount do you have lever or screw down ?

#19S  Throw lever

most likely its the pressure plate on the arms throw lever but if its just moving a hair front to back i wouldnt worry too much

#19S Throw lever

Imagine that.... One of the many reasons I have left all of my ARMS stuff in the dust!  

KAC is the way.

i have started using larue tactical

Shouldn't move at all and mine shoots 1/2 MOA all day long.  Not bad for a rifle meant for IMGA/USPSA 3-Gun and NOT for bench shooting.

Check your levers and it wouldn't hurt to check some dimensions on the receiver.

SPC Richard A. White, Senior Medic
249th MP Detachment (EACF)
Camp Humphreys, ROK

the pressure pad under the throw lever wears out and that could cause it or it could be the variance of different manufactures anodizing

What brand of upper are you using?

The problem with the ARMS mounts is that they are made to fit ONLY on in-spec uppers.  If yours is a second or third tier manufacturer it may not be in-spec.

You could try a Larue mount, as they have some adjustability to mate better to out-of-spec uppers.

I was thinking it could be the pad also, as it really dosen't look to
me to be a very secure mounting system.
BTW it is a upper I got from J&T Distributing.

It has no marks on it at all, but is seems to be a good one.
Perhaps I will try another mount and see what happens.

Are the GG&G mounts for this optic good ones ?

Regards,

Scott

I had the exact setup and problem on a Bushy upper.  There was just a slight fore and aft movement, but it wasn't really hurting accuracy.
I went with the Trij thumbscrew mount and there is no problem.

I had the same Upper / ARMS mount wobble.

The receiver was out of spec, so used a LARUE mount instead

The ARMS fitted only a true spec receiver; The LARUE fitted both........

The rifle came from Sabre Defense, the lower was PWA, yet the Upper and barrel remain a mystery!

ARMS mounts are not adjustable at the throw lever.
All upper receivers are a little different..read different sizes.

ARMS mounts are made to fit ARMS rails..  
ARMS rails may not be the same size as a Colt, Bushy, LMT or CMT rails.

Use a QD mount with a throw lever that is adjustable.  

It does matter if your mount moves!

LaRue Tactical = Solution

Quoted: What brand of upper are you using? The problem with the ARMS mounts is that they are made to fit ONLY on in-spec uppers.  If yours is a second or third tier manufacturer it may not be in-spec. You could try a Larue mount, as they have some adjustability to mate better to out-of-spec uppers.

what would you consider "mil-spec" and who would fall into second or third tier?

I had the same problem with my M68 mount on a Bushy upper.

Tryed it on a Colt, two RRAs, and an Oly.  It was only tight with no movement on the Oly.

Since then, I changed to Larue.