Lapping Leupold aluminum rings on an AR15.

[MCMXI]

Six months ago I bought a Leupold Mark 4 3.5 - 10x FFP scope for my AR15. I bought Leupold Mark 4 super high steel rings since I have a DPMS flattop upper but I wasn't too happy with the weight of the rings ... a whopping 350 grams (12-1/2 oz)!! Recently I bought a pair of lightly used aluminum Leupold Mark 4 super high rings on Ebay weighing only 155 grams (5-1/2 oz). Since I didn't have to lap the steel rings, I hoped that the aluminum rings wouldn't need lapping either. I installed the lower half of the rings and torqued the nuts to 65 in-lb, then installed the 30mm Wheeler Engineering alignment bars with the top half of the rings and checked the alignment.

Side view - before lapping

Top view - before lapping ... WHOAA!!

Side view - after lapping

Top view - after lapping

Lower rings - after lapping

As you can see, the rings were WAY off, but after lapping the alignment was a lot better.

 

[DRYHUMOR]

It looks kind of like the torque of installing the lowers set them at an angle.

Good pics though, a lot of people have no idea.

 

[Horsemany]

Great example of why we lap rings. Most people would say that gun doesn't need lapping since the rings are mounted directly to the receiver. IMO any ring that is not vertically split should be lapped. I use the alignment bars and even if they are dead (*^ perfect I'll still lightly lap them. Why risk putting ring marks on a pricey scope? No torquing of the scope tube and more contact surface between ring and tube. The only way lapping could hurt would be to go too far with it and loose tightness. This would then be cured by lightly lapping the ears on the sides of the rings to allow them to come closer together.

 

[Chipperman]

Very nice pics.

 

[MCMXI]

It looks kind of like the torque of installing the lowers set them at an angle.

DRYHUMOR, good point ... that's possibly why the steel rings didn't need lapping.

Horsemany & Chipperman, thanks ... I can't imagine installing a scope now without checking the alignment first. I cringe when I think of the scopes I've mounted before I knew better.

 

[DRYHUMOR]

Maybe they weren't as lightly used as you thought.

I still catch myself overtightening screws on occasion, I really should invest in a torque screwdriver.

However, I do have several spare screw sets for my rings, a good idea for anyone.

 

[MCMXI]

Maybe they weren't as lightly used as you thought.

It's hard to say for sure but based on their appearance I think "lightly used" is a fair description. I was able to get them aligned so it's all good.

I still catch myself overtightening screws on occasion, I really should invest in a torque screwdriver.

I have Wiha torque screwdrivers. One is a 7-1/2 to 20 in-lb and the other one is a 20 to 70 in-lb. Leupold base mounting screws get tightened to 18 in-lb, ring screws to 28 in-lb and ring nuts (on Mark 4 rings) to 65 in-lb. I would advise against buying the FAT from Wheeler Engineering ... Wiha is the way to go in my opinion.

 

[9mmepiphany]

that's possibly why the steel rings didn't need lapping.

i ws taught to always lap rings...be they Al or steel...it isn't just the tolerences in the rings, but in the machining of the bases and the recieiver

 

[MCMXI]

i ws taught to always lap rings...be they Al or steel...it isn't just the tolerences in the rings, but in the machining of the bases and the recieiver

I always check the alignment of the rings using the Wheeler Engineering alignment bars. If they line up (which they did for the steel rings on the DPMS upper) then lapping is optional. I had to lap the rings on three Remington 700 rifles because as you mentioned, there are tolerances to consider in the receiver, bases and rings. I had Leupold Mark 4 two-piece bases on a Remington 700 in .300 Win Mag with Leupold Mark 4 rings. I lapped those rings to get good alignment and then recently, I "upgraded" to a one-piece Badger Ordnance base but still used the Leupold rings. When I checked the alignment, it was off so I had to re-lap the rings.

 

[no_problem]

Thanks for the great post!

 

[skinewmexico]

Good example of why I buy Burris Signature Zee rings.