AR-15 cold weather issue, anyone ever have problems?

[THE COOP]

Long story-short version, was in a 2 day carbine class this weekend and I was using my personally built LMT upper, SLR-15 lower with a full auto BCG, I put 400 rounds through it on Saturday with no issues and 100% reliable, that night I cleaned it up a little and lubed it well with CLP, Sunday morning start of the class the mags were having issues seating all the way in and when I forced them lock in the BCG would jam every round, most of the time the face of the BCD wouldnt pick up the round? Borrowed another rifle for a few hours and at lunch I wet to a friends and borrowed his Spike tactical lower I built for him a few months ago, put it on my upper and it ran fine all day. After the class I inspected my upper and lower also compared them to my friends upper and lower, I did see a few issues with fit on my upper and lower and seemed to have loosen up the fit between the upper and lower, a lot of play side to side and a noticeable gap between them. But as the rifle warmed up in the house it started to function normally which leads me to think the weather on Sunday, 30 degrees may have something to do with it and was 10 - 15 degrees cooler then the day before. So I'm looking for some info on cold weather AR or if anyone else has seen this kind of issue before? COOP

[MacGyver]

Could be the lube you were using. Different viscosity at lower temperatures slowing things down?

[Guest carbonarcher]

After dealing with all of the extremes in the the northeast. We all bedded our upper to our lower.. we used epoxy under the rear take down pin. first you need to gap it with some feeler gauges. after you get the right thickness... put a small pea shaped ball under the rear pin. remove any excess, ensure that you can get the pin in and out. (ensure you grease it good) also ensure that you grease up the upper lug that sets in the lower right behind the pin. let sit for a couple of hours. you will have a rock solid upper that is like being glass bedded for a bolt action rifle. I have had no issues with this set up going from cold to hot, hot to cold an humid. Worst case.... you can remove it very easy.

Just my two cents...

oh, cost me two cents to do it too!!

[Guest carbonarcher]

P.S. I am no Gunsmith!

This was just what I learned from the local and stated police armorers and the military. I don't know, but...... I think if you read this you are all going to say..... HUMMMMMM... how come I didn't think of this!

No more of those little red rubber things!

[Mike]

The clp is gelling up and causing the BCG to slow down most likely. What weight buffer are you using?

Carbonarcher, what benefits does having the upper and lower "bedded" give you?

Mike

[THE COOP]

Definately not the lube, I changed lowers so the upper stayed the same and all the lube just a defferent lower. I went by the local Gunsmith and we took some measurements and here is what we found, if you look into the magwell the lower is off set in one direction by more than .020 so there is a lip on one side where the lower meets the upper and not on the other side. Rocking the upper side to side on the lower causes a .020 gap and we can get feeler guages in the gap. The P mags fit pretty tight with only .002 gap in a 75 degree room so I wouldnt be surprised if a 50 degree drop in tempreture would close up a .002 gap on the mag. So next question, what is the maximum gap inbetween an upper and lower? I've had AR's that were so tight you had to tap the take down pins in and out with and my upper fits on other lowers much better that my current lower. COOP

Edited December 7, 2010 by THE COOP

[Kenstaroni]

I ran about 300 rounds through my Ruger SR556 on Sunday in the snow. Ran 100%. It's about the coldest weather I've shot the gun in and had no issues of any kind. I can't recall any issues with any AR's running poorly in the cold weather. I would recommend inspecting everything...even disassembling the lower and bolt carrier to make sure everything is right.

Good luck!

Edited December 7, 2010 by Kenstaroni

[Dolomite_supafly]

The clp is gelling up and causing the BCG to slow down most likely. What weight buffer are you using?

Carbonarcher, what benefits does having the upper and lower "bedded" give you?

Mike

Some people say it helps with accuracy. It definitely makes the gun feel more solid or robust. I can see it helping with accuracy providing the material used to take up the space doesn't change with temp. The rubber wedges would have to change with the temp so the harmonics of the entire gun might change as well leading to an inconsistent gun. I personally have tried wedging the upper and lower and saw no increase in accuracy but it definitely made the gun feel more robust.

There are uppers out there that have holes drilled and tapped for a setscrew so you can tighten up the two halves. The hole coincides with the bottom of the upper's lug. When you tighten the setscrew this forces the upper up and binds it against the takedown pin.

Personally I think most of it is to make the gun feel better than make the gun more accurate but again I could be wrong.

Dolomite

[Mike]

It won't affect accuracy one bit. The sights are on the upper, so having the lower move won't change the sight/barrel relationship. I've seen all kind of doodads inside ar receivers. Most all of them do nothing but make it hard to take apart and put back together.

Mike

[Guest carbonarcher]

Mike,

Your right, I just like to reduce the amount of "wiggle" between the upper and the lower. I made sure that when I did mine, it was tight but not so tight that I could not get my pins out.