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Old July 4, 2020, 05:24 PM   #1
Swifty Morgan
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Midwest .15" Offset QD Scope Mount: Lap or no Lap?

Now that I know a tiny bit about long range shooting, I am upgrading the brand-new duplex scope on my AR-15 to MIL-dot. I don't expect it to be a competition gun, but I should be able to decimate small targets up to several hundred yards, which would have been pretty hard with a duplex reticle.

I bought a Midwest Industries QD mount with a 1.5" offset.

Here's a question I have asked about elsewhere. Maybe people here will have different input. Should I lap the rings on this mount? It's pretty good quality, but it's not top-tier.

I'm thinking I could make a 34mm bar, cram it in the mount, and turn it a few times to see what the contact is like.

I'm a little reluctant to start out with abrasive paste. I would rather not scrape off the finish before I know I need to.
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Old July 4, 2020, 06:09 PM   #2
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I will assume you bought an AR integrated ring/mount with a 1.5 in height.

I have not looked at Midwest. IMO,a ringmount certainly offers the possibility of being line bored true.

Screwing two piece bases down on bolt gun receivers offers more chance for alignment problems.

Some of this stuff i precisely machined and black oxide finished or parkerised.

Those can fit the rail in a quite repeatable way.

Some have a layer of paint or powder coat. I'd be skeptical of the precision of my Hermann Schmidt Grinder vise if it was powder paint coated.

I have found the Burris ring mount seemed powder coated or painted some way.

I have found the moderately priced Rock River ring mounts to be a good choice. Cleanly machined,and not painted. Aesthetically,the rings seem a bit blocky/bulky.Till I realized with the rifle laying on its side,The rings would contact the deck before the ocular or objective bells would. I like that.

The finish insidethe rings will never be seen.I don't worry about it.Go ahead and turn your lapping bar. I suggest .005 under nominal,Every lapping compound will give you an overcut.If you make your bar nominal size,you will oversize your rings. A .005 under nominal on your bar should cut close to nominal with 320 grit. If that is too tight on the rings.240 will get it.

I suggest making a match mark on your ring caps so you don't lose orientation.

IMO,everything you check and confirm good is longer a nagging unknown,or a problem variable.
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Old July 4, 2020, 09:56 PM   #3
Swifty Morgan
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Thanks for the help. I'm not extremely concerned about repeatability, since I expect to zero at 100 yards every time. It would be very nice if I got perfect repeatability, but it's not the end of the world if I have to fire three or 4 shots.
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Old July 5, 2020, 11:22 AM   #4
Bart B.
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The scoped rifle and its ammo are much more repeatable for a zero setting on the sight than our position supporting, aiming then firing it. Rezeroing the sight corrects for our variables holding and firing the rifle.

Proof's the fact that several people will have a different zero shooting the same rifle and ammo.
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Old July 5, 2020, 11:52 AM   #5
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As Bart says, how you hold/support the rifle has more to do with it than lapped rings.

Along with body position and follow through.

And ring lapping kits are a better investment than spending your time trying to locate the correct diameter piece of rod.

Unless your using the mildot reticle for ranging, or hold overs, it's not any better than a fine lined duplex, or even a dot reticle.
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Old July 5, 2020, 12:11 PM   #6
Swifty Morgan
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I was actually going to make the rod myself, since I probably have something suitable in the scrap pile. It seemed to me that a prefab bar would become undersized pretty quickly, so I figured it would be best to use something free. Just guessing.

The reason I chose this scope and reticle is that it will work well with the kind of training I got at my long-range class, and the price is phenomenal.
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Old July 13, 2020, 03:37 PM   #7
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A machinist at our club made up 3 lapping kits and offered em for the raffle the club has every Memorial shot.

I ended up w/ one of them and have used it on about 5 scopes now, not all mine. We have all be extremely pleased w/ the lapping/mounting done w/ the kit. I recommend it for all mounts.

As on poster mentioned, make some kind of reference marks on the rings,
top/bottoms, so they get back together the way they were lapped.
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Old July 14, 2020, 09:28 PM   #8
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I always understood that lapping was about increasing the contact surface with the rings to reduce scope slippage under heavy recoil, not accuracy. Am I missing something?

Also, you are going to lose zero when you take the scope off... Even if its just a little bit you will lose it. in my mind QD mounts are for emergencies you can get the scope off and use the iron sights fast.
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