To Lap or not to Lap

[RustyRick]

I'm contemplating the purchase of lapping bars. My quandary is with the ability to put a man on the moon and bring him back again. Is the engineering on our modern rifles and scopes not true enough to not need lapping? Especially on our better rifles.

How often in 10 off the shelf rifles need lapping to be done to mount true?

 

[Hairtrigger]

I have found NASA has tighter tolerances than the gun industry
Lapping bars are well worth the cost and time

I'm contemplating the purchase of lapping bars. My quandary is with the ability to put a man on the moon and bring him back again. Is the engineering on our modern rifles and scopes not true enough to not need lapping? Especially on our better rifles.

How often in 10 off the shelf rifles need lapping to be done to mount true?

 

[J E Custom]

I'm contemplating the purchase of lapping bars. My quandary is with the ability to put a man on the moon and bring him back again. Is the engineering on our modern rifles and scopes not true enough to not need lapping? Especially on our better rifles.

How often in 10 off the shelf rifles need lapping to be done to mount true?

It is rare to buy any rifle that has 90% lug contact, much less 100%.

Most are at best 50%.

Just lapping is not all that is necessary, the bolt and the receiver need to be trued/squared first,
then lap to make the surfaces smooth to aid in bolt lift.

J E CUSTOM

 

[RustyRick]

R you talking about lapping the scope rings? Or something else?

 

[WapitiBob]

The chances of getting a set of rings, concentric, cylindrical, and planar within say .002 when screwed to a one piece base are just about zero. Getting rings that close when screwed to individual bases, screwed to a factory action, are a whole lot less. Checking the accuracy of those componants with a $1500 piece of thin wall aluminum tube ie; scope body, isn't something I care to do. I bed the base then lap the rings.

 

[sable tireur]

RustyRick,

I think your comparison is a little out of range.

The cost to develop and produce most of the technology for space has cost trillions of dollars. The cost to develop a rifle and mounts is maybe a million from concept to final production.

Scope mounts, bases and rings are relatively inexpensive when compared to the cost of actions and barrels. Generically speaking, of course, like Leupold, Burris, etc. But consider the lack of alignment given Leupold's 'twist in' base and rings. Or the Burris plastic inserts used to affect the range of adjustments. Then add in the fact that everything gets attached with tiny little screws into holes that have been barely aligned in manufacturing. Heat treat the action after machining and watch the dimension move. That's why most of the top custom action makers heat treat before machining and the actions cost more.

Can all the foibles be eliminated? Sure, with a ton of additional cost of manufacturing. The makers are not going to give away any profits they're achieving now so any additional improvements will cost more money.

In your situation, the lapping bar will achieve the desired results by eliminating most of the misalignment and rings being out of round. You will be rewarded with proper alignment as long as you do your part in the mounting process and no ring marks on your scope tube.

If you want the best, get a custom action with an integral Picatinny rail and buy Spuhr rings. Be sitting down when you see the prices...

Regards.

 

[J E Custom]

R you talking about lapping the scope rings? Or something else?

Sorry , I misread the post.

I though he was talking about the action not the scope rings.

I have a scope ring reamer but have never used it because if a set of rings are bad enough to need reaming, I simply replace/exchange them.

Most of the time improper installation is the problem with rings that are misaligned and marking the scope.

J E CUSTOM

 

[RustyRick]

Sable - you got my point. It shouldn't be that hard to set up the CNC machines and engineer receivers to ensure that scope bases lie on a flat planer surface and that the screws mount the rings to ensure that the front and rear scope rings perfectly align the tube.

You may use a scope ring lapping tool, but that still doesn't ensure that the center line (bore sight) is exactly parallel with the line of sight of the scope. And there is no way to measure that.

My question still stands - if I pull 10 rifles off the shelf in the store, and mount the same set of good rings on all 10. How many time would the lapping bars NOT line up?

I have a hard time imagining that it would happen often? But I don't know.

 

[WapitiBob]

Screws threads don't perfectly align anything.

 

[Kennibear]

If you were to mount everything and then machine the scope beds in the rings the rings would line up. Just torquing the rings to the base can introduce a small amount of misalignment. It is not so much that each item and attachment is so far out but that the tolerance stack up and that is cumulative.

My experience with lapping rings is that very little is removed. I have not measured it but I use magic marker to check the progress and not very much is removed.If you keep the rings cinched down and never take the scope off it may not matter but I always lap the rings to remove any unwanted stress as I believe all stress is a potential misalignment or accuracy fail some time down the line. Just like prepping your brass consistency pays accuracy dividends.

KB

 

[markopolo50]

I alway lap the rings, or I have been for the last few years. I was surprised how bad some of them are and it sure saves the scopes from getting the witness marks. I usually don't check bases but just remounted a one piece Leupold base on a Remington model 7, after Remington replaced the barrel( another story). The base was not nesting on the receiver like it should so I Acraglassed the one end and it fit like a glove then. Lapped the rings and all is good.

 

[Clark]

If I bed the mounts to be in line, coplanar, and parallel to the bore, then the rings should be concentric.
This is a procedure with two scope bases and most people starting out should just use a one piece base.

If I buy a rifle and someone has lapped the rings, I take them off and throw them away.

But I will lap bolt lugs, reluctantly, if I have to.... not grumpy enough to throw the bolt away.

 

[Hired Gun]

My question still stands - if I pull 10 rifles off the shelf in the store, and mount the same set of good rings on all 10. How many time would the lapping bars NOT line up?

The rings will lay different on every rifle. No two are exactly the same. A one piece base will flex to follow the contour or angle of the action it's bolted too. A perfectly stress free scope mount would be nice but whether they are lapped or not the tube will be stressed as soon as the screws are tightened up. If even the most perfect rings are over tightened where the erector assemble pivot is it will cause the scope to have accuracy issues.

Lapping rings is always a good idea but not always necessary.

 

[Hairtrigger]

I only left the Rings if the scope I am using I do not want to put a dent in.

OK I lap all my rings. It is surprising how many rings have less than 50percent contact