Carry Handle Marking Upper Receiver

[vingrjoe]

Hey guys,

I've got another question that may seem out there, but here it goes.

On my A3/A4 Flat Top Receiver I have a detachable carry handle. I usually do not remove it because I have no optics as of yet. I removed it the other day and discovered that the ends of the steel clamp on the handle had dug a little into the aluminum of the upper receiver. See the photos below.




Now I'm okay with marks from usage, it's going to happen eventually. However, I am concerned about possible reaction over time of the dissimilar metals touching. Specifically from the bare aluminum touching the metal of the carry handle clamp. I've read about galvanic corrision from dissimilar metals, especially in regards to the barrel nut and upper receiver. That subject prompted me to wonder if my situation should be of any concern.

I'm guessing I may be letting my OCD run wild again, but I'd like to hear from some of you with long time experience with the AR15 platform.

Is galvanic corrosion even a possiblity here at all ?

Thank you for taking your time to read this and to any responses.

[Quib]

I wouldn’t worry about corrosion.

If you want to prevent the possibility of further wear, you might dress up any sharp edges of the carry handle clamp where it digs into the upper receiver, and then re-finish those areas of the clamp with cold blue.

ETA:

[Quentin]

I sure wouldn't worry about galvanic corrosion. While you never can say never, the AR-15 has been around since at least 1959 with millions in use yet few complaints of problems of steel contacting aluminum except normal wear like enlongated pin holes, etc. And only after heavy use.

The carry handle clamps down tight and nicked the receiver but that's normal wear. I doubt it'll become a problem.

[vingrjoe]

Thanks for the replies guys. I didn't think that it would be a problem, but still the same, I was looking for some reassurance

I love those cartoons you post Quib, they are enjoyable and informative.

BTW Quib, what would you recommend for smoothing down the edge of the clamp ?

[Quib]

BTW Quib, what would you recommend for smoothing down the edge of the clamp ?

I’d probably hit it with a small file, then some Crocus or Emery Cloth. Just break any existing sharp edges.

[Quentin]

So the old Sarge in the cartoon doesn't recommend tightening the thumb screws with a quarter?

Oh yeah, they're called thumb screws!

[Doc Safari]

I tried to find an old thread where this was addressed, but this is the only one which seems to contain a relevant discussion to begin with.

There is an ongoing debate as to how much to tighten the thumb nuts on a carry handle:

1. Thumb tight (that's why they're called "thumb nuts")
2. 1/4 turn or thereabouts past thumb tight with a quarter
3. Tightened down as far as the thumb nuts will go with a quarter and a pair of pliers. "Spend the quarter" is the motto here as you will probably bend the coin out of shape using this method.

The $64,000 question is whether overtightening is necessary to keep the sight from loosening, and whether excessive overtightening damages the carry handle or receiver.

The answer to all questions is "yes".

This is anecdotal evidence, but it has happened to two rifles (one Colt once BCM) and two quality carry handles.

One carry handle had been torqued 1/4 turn past thumb tight with a quarter. One had been tightened until it wouldn't move any further with a quarter clamped in a pair of pliers.

Here is the damage observed:

1. Both AR upper receivers sustained a minor "mark" in the form of a disturbance to the finish, and a tiny, almost imperceptible indent where the carry handle had clamped the receiver. The indent was roughly the width of a line on a piece of paper and had a depth that was only noticeable under a bright LED light at certain angles under a magnifying glass. This appears to be mostly cosmetic since it happened to a solid part of the rail. It did not get any worse with removal of the carry handle for installation of other optics. The other optics both had quick-detach clamps. The indent would not have even been noticeable in normal use, i.e. unless a person were looking for it under an extremely bright light, it was barely visible.

2. Both carry handles, on the other hand, sustained damage to the little "gasket" that goes up inside the thumb nut. Overtightening the thumb nuts harms this gasket. When the carry handle that has been overtightened is removed and then replaced, these "gaskets" on both carry handles shredded into strips as the thumb nuts were tightened a second time. This damage to the "gaskets" inside the thumb nuts did not prevent the thumb nuts from tightening down adequately, but in all cases the nuts were tightened past witness marks placed on them during the first tightening for reference.

The BCM rifle with the overtightened thumb nuts had fired between 6,000 and 7,000 rounds after the carry handle was installed, with no loosening of the carry handle or any additional scoring or other damage to the receiver rail. I always put a drop of nail polish or black paint on the top of the thumb nut bolts (thumb nut side) to prevent loosening from vibration.

Other rifles in which the thumb nuts were only hand tight suffered from loosening of the thumb nuts after less than 500 rounds (I did not take an exact round count; it could have been as few as 100-200 rounds before I noticed the loosening).

Conclusion: overtightening does appear to damage both the receiver rail and the thumb nuts, but in the case of the receiver rail it appears to be largely cosmetic. The damage to the thumb nuts probably necessitates overtightening that carry handle from then on since the inner "gasket" sustains quite a bit of damage from overtightening.

My take: I plan to use a large flat blade screwdriver or quarter to overtighten "just beyond" hand tight. A person with substantial hand strength may be able to get by with truly "hand tight". I have never had thumb nuts on an optic that did not eventually loosen when left just "hand tight", so if you plan to go that route then re-tightening the thumb nuts occasionally becomes part of the necessary equipment check.

Personally, I have decided if I need a rifle with strictly iron sights, I will seek out an AR with a fixed carry handle and avoid the hassle altogether.