Is this normal?
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Old 10-29-2011, 07:08 PM   #1
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Default Is this normal?

On my brand new, as yet unfired other than the factory, LMT CQB MRP 16" I have noticed a "loose" sound when fondling...I mean handling it.

I thought it was the empty metal 10 round mag rattling in the mag well.

Today, since my wife and kids have all gone to the stables to ride, I got some YouTube video's going on AR takedown so I can familiarize myself with the basics at least.

This is when I noticed the "rattle" or loose sound, is coming from the fit of the upper into the lower. It is specifically at the area of the rear take down pin.

If I hold the lower firmly, either by the grip or the stock, I can move the upper side to side a goodly amount. I threw a vernier across it, holding the upper all the way Left and then all the way Right in relation to the lower....the vernier jaws between the outside of the forward assist and the frame of the weapon lower, right at the area of the barrel nut. Not perfect but it gives me an idea of the play. I got a difference of about .3mm.

I converted this and the best I can tell is that this is about .011".......somewhere around 1/64" I think. I was raised on metric so my small inches increment knowledge is a bit strained. I can "see" 12 thousands though because that is what motorcycle points used to be adjusted at. About the thickness of a matchbook cover.......this is consistent with what I see in movement side to side. A tickle less.....011" makes total sense to me, going by what my eye sees.

It is like a semi auto handgun with a loose fit of the slide to the rails.

I gotta tell ya, I don't like that. I know I did not buy a match grade weapon, but that model is still a more expensive type offering and I would expect tolerances to be tighter.


Not only that but surely that amount of slop will translate to a much greater amount out at 100yds or more? Won't the weapon slamming in and out of battery not have a tendency to return to a different spot each time?

So, is this a normal amount of wiggle or does it seem like a lot? How much do your weapons move side to side at that point? I don't expect you to measure but is it noticeable.....can you make it rattle if you shake the gun?

Maybe it is normal or something stupid I am overlooking being as I am new to the platform but I'd appreciate some feedback.

BTW, you folks have been extremely helpful so far.

Thanks.

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Old 10-29-2011, 07:31 PM   #2
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It is pretty normal. But if you want to get rid of the slack, here you go

Accurizing Wedge AR-15

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Old 10-29-2011, 08:06 PM   #3
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Whoa....way cool and cheap too. I might just buy a whole bunch and give them as Christmas presents to my AR totin' buddies. Thanks trip.

So that is normal huh? I would have expected tighter on a more expensive firearm. Kinda like you'd expect a higher end Colt 1911 to have a very good slide fit.

I sent LMT an E mail. I will see what they say also. My bro in law checked his and going by what he said over the phone he said it was not as loose. His Stag had a tiny bit of slop, he said it was even tighter when he first got it.

Come to think about it, isn't it always like that?

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Old 10-29-2011, 08:06 PM   #4
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i got worried with my first build and found it to be two things, the fireing pin and the weights in the buffer its self, remove both the fireing pin and buffer and reassemble and u will see what i mean.

but yes, the $3000 build as well as my $600 build both do just that

let me guess if u hold the rifle level and tip the muzzle down then tip it up you hear some thing moving right

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Old 10-29-2011, 09:25 PM   #5
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Not sure about that nathantc.....this seems more like the upper receiver sloppy side to side. I will look though.

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Old 10-29-2011, 09:45 PM   #6
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Yeah the only ones I haven't seen do that was when my unit got the brand new FN herstal M16A4's. They had no slop to them at all; However, within about 3 hours, probably 50% of them had plenty of slop.

BTW, I've seen folks just stick a strip of cardstock (like a business card) on either side of the receiver, in between the upper and the lower, and that tightened it up just fine too.

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Old 10-29-2011, 11:30 PM   #7
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Granted I am just a civilian operator, but it feels totally weird holding the weapon say at my side as one would advance when not threatened.....and you can feel the weapon "bend" at that joint....ie pivot off the pivot pin....sideways.

The only way I can describe it is like an air rifle with a break barrel that has side to side slop.

It is minuscule LOL...... .011".....but now that I know it's there it bugs! Yeah the thickness of a business card is exactly what I am talking about. That card stock seems similar to a bookmatch cover in thickness....roughly .012". Makes sense.

I wonder why the extra tolerance? Expansion when super hot? Just so it comes apart easy?

Even my rear take down pin came out super easy, from the very 1st time. I just pressed lightly and through it went. I was expecting to have to use something to press it through.

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Old 10-30-2011, 12:15 AM   #8
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Quote:
Originally Posted by Fumbles View Post
Even my rear take down pin came out super easy, from the very 1st time. I just pressed lightly and through it went. I was expecting to have to use something to press it through.
Check the rear pin spring and detent to make sure they are properly installed. Sometimes the detent gets loose if the stock has been removed. This loosens the fit and eliminates the necessary tension, the pin should not just come out but should need a bit of force until the detent releases.
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Old 10-30-2011, 05:17 AM   #9
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I don't have a way to make such precise measurements but the side to side movement is normal and won't effect the operation or accuracy of your rifle.

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Old 10-30-2011, 05:43 AM   #10
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Thanks guys. Jpyle, I'll take a look at that. Thanks.

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