Scope lapping absolutely necessary?

[gitrdun]

Originally Posted by Faststeel

absolutely necessary if you are using Ruger rings, actually they need to be reamed first then lapped.

If they require reaming before lapping, it is a sure indicator that the concentricity must be a quarter mile out at least. But, that wouldn't surprise me in the least.

In my trade as a millwright I've often had to deal with this sort of thing. This is why it carries over onto my dedication to lap. Both steam and gas fired turbines (jet engines) require close tolerances between the babbit bearings that support the rotating shaft front to rear. Once babbits were scrapped to allow at good oil wedge at each end, we had to ensure concentricity and alignment front to back. These rotors spin at 13,000 RPM. Any mistake or questionable overhaul would have your little discharge hole pucker up on start up. The best way to avoid that were good tolerance practises and record keeping. I carried that over to my personal scope mounting, and it had never let me down.

As of late, we've seen many threads from people asking why they had so much trouble getting their scopes on target, can't achieve consistency, ran out of adjustments on their turrets. Most replies and suggestions seem to blame the optics. Hogwash I say. Check your mounting practises and you'l likely find an issue right there. My two cents anyhow for what it's worth....

[Pathfinder76]

Originally Posted by DaleJ

Sinclair 2013-B catalog arrived. Bottom of page 211 has a "Sinclair Tech Tip" on scope mounting/lapping that suggests using the lapping tool to align rings before clamping rings to bases. Hmm? Then lap ring bottoms if you desire. (Or suffer from OCD)

I guess any microscopic irregularities on upper ring halves will have no effect on scope internal adjustments? Grind one half but not the other.

In theory top halves will seek their own level.

I'll add that since starting to mount rings with a bar I've quit lapping altogether.

[gitrdun]

Originally Posted by chuck

In theory top halves will seek their own level.

I'll add that since starting to mount rings with a bar I've quit lapping altogether.

Therefore any accuracy in the drilled reciever holes can simply be altered with bars? Sorry, but I under the impression that someone else did your scope mounting and gun works. You've changed your story so quickly that I feel an impending whiplash..should I tag your past post as a simple reminder?

[Pathfinder76]

Originally Posted by gitrdun

Therefore any accuracy in the drilled reciever holes can simply be altered with bars? Sorry, but I under the impression that someone else did your scope mounting and gun works. You've changed your story so quickly that I feel an impending whiplash..should I tag your past post as a simple reminder?

Sure. Do that.

[Duramaximos]

I'm a recent convert to Burris signature rings. After trying 3 other sets of rings I had to admit my receiver and/or scope are not perfect - the sig rings resolved the problem quickly.

Not to mention they seem to grip the scope better than the conventional rings I tried. Was also nice to add 20 MOA of elevation without using a rail.

Unfortunate they don't come in a "low" configuration.

[twofifty]

I recently used this mounting/lapping procedure on a Savage rifle and got good results:

1. confirm that the base holes in the receiver are in line with the bore & action.
I swept the receiver holes with a rotating laser. If the laser beam is in line with the bore centre and the centre of the action (tang safety), those holes are good to receive the base mounts. This Savage's holes were perfect.

2. I didn't check to see if the bases (2 pieces) were themselves centered to their own holes. I assumed they were and lucked out.

3. Mounted the lower ring halves onto the bases, mechanically centered the rear ring lower half with the windage screws, and final centered the rear half to the front half with 1" steel round stock. I didn't check to see how perfectly straight this Brownells bar was, but could have.

4. Lapped (maybe 15 light passes) the lower rings in place. There was very little metal to remove, so I probably removed some of the manuf's tolerances.
Lap kit -Brownells- was borrowed from a shooting buddy.

5. Very very lightly (2 or 3 passes) rubbed each upper half on their own along the lapping bar (i.e. not while they were fastened to the lowers), just to find & remove any possible high spots left by the manufacturer.

6. Ran the turrets all the way up-down-left-right and left them in the middle of their adjustment range.

7. Mounted scope in rings, levelled crosshairs to a plumbob string, tightened evenly with low strength Loctite while set at the proper eye relief with perfect cheek weld. I didn't use a torque wrench but would have if I owned one.


The end result was that I was 2" left at 25 yds on the first shot, and centered at 100 within five more shots. There's lots of adjustment range left in either turret.

Note: It was a gunsmith/machinist who told me that his practice is to lap the lowers, not the uppers.

[wally338]

One piece rings like those offered by Spuhr or Nightforce are usually dead straight but they are not cheap and are often too high for hunting type rifles.

[gitrdun]

Originally Posted by wally338

One piece rings like those offered by Spuhr or Nightforce are usually dead straight but they are not cheap and are often too high for hunting type rifles.

No matter how accurate rings and bases are made. Tey cannot compensate for inaccuracies in receiver drilling and tapping, now can they?

[wally338]

Originally Posted by gitrdun

No matter how accurate rings and bases are made. Tey cannot compensate for inaccuracies in receiver drilling and tapping, now can they?

No they sure can't, never said they could. What's your point?

[twofifty]

His point is that lapping can correct some of those inaccuracies.

My own bases & rings were Leupold, not top of the line.

[Bolete]

Originally Posted by Rusty Joots

Can I throw those on a weatherby vanguard?

They will fit any Weaver style base.

[Pathfinder76]

Originally Posted by gitrdun

No matter how accurate rings and bases are made. Tey cannot compensate for inaccuracies in receiver drilling and tapping, now can they?

Do me a favor. Take out one of your rifles. preferably one with a two piece base on it. Pop the scope off it. Loosen the base screws one turn. Then push them from starboard to port. Now push the front base starboard. Tighten. Then push the rear one port side. Tighten. Now lap them concentric. Good luck. Now back the screws off and let the front base seek its level. Tighten. Now loosen the rear base. Lay a concentric one inch bar in the rings. Apply some force and tighten at least one of the rear base screws. Remove bar. Tighten the other screw. Now lap if you like.

I have already mentioned here that bridges and receiver rings can be a mess and that base holes can be out of alignment. So much so that more than just a lapping bar and valve grinding compound will fix it. In SOME cases holes need to be opened up and receivers need to be altered. There is a reason why some of the best gunsmiths in the world do things like this.

[gitrdun]

No need to do that Chuck, not only do I get it but I happen to agree with you. When you mentioned that 3 people had laughed at you for following this procedure, I'll go out on a limb here and say that it likely wasn't I.

[Dean2]

Here is a picture of a front ring (1st picture) and a rear ring. This is after about 10 minutes of lapping. When I started, the only contact point on the front ring was a small band at the front of the ring, much smaller than the light band on the rear side of the front ring now. It is now starting to get good contact front and back. The rear ring is much better for overall contact but still has a ways to go. When I started it had contact in one small area at the front of it as well.

These are Leupold quick detach rings for mounting on a weaver rail or bases, and cost $65 a set. Thus even quality rings need to be lapped for an exact fit on the receiver they are mounted to as any small angle on the base or receiver yields rings with poor contact. You can choose to have your rings only contact the scope on a small patch in the front of each, I prefer mine to have bite on at least 75% of the tube and 100% is better.

Click on the picture for an expanded view.

IMG_00000030resiz.jpg

IMG_00000034 resiz.jpg

[260 Rem]

Some food for thought:
First: Given the apparent lack of precision machining with recievers, bases, and rings --- is there any reason to have confidence in the "straightness" of the scope tube or consistency in its diameter ?? Or, perish the thought, the true of the lapping tool
Second: Would it make more sense to "lap" the bases so they were in perfect alignment?

[DaleJ]

Dean2,
Leupold rings are among the worst for being cock-eyed. Try a pair of dual dovetail and you'll lap those puppies for days. One piece Leupold bases with front dovetail and windage gizmo rear rings are bad too. For hunting rifle applications the Burris Signature Zee rings eliminate the need to lap, and if they were built to tip off scope bases would the ultimate ring made. If I had rings as bad as yours I'd take them back. The thought of grinding excess metal from rings directly above the trigger assembly is a concern.

[Dean2]

DaleJ

I do have to agree with you on the Leupold rings. The last few sets I have bought have not been great and took a lot of lapping. Unfortunately there are a couple of issue, if you want a QD type ring there aren't very many choices and of the others I tried to date they were as bad or worse than the Leupolds. Ruger factory rings are abysmal. Warne works well on the Ruger but I don't particularly care for the ridge that is on the top of their somewhat unusual two piece rings.

http://warnescopemounts.com/product/ruger-rings/#

p_947005332_1.jpg


The Burris are a good option in the right application but no QD in the signature series (the one with the inserts) and poor selection of ring heights for some guns. There all steel rings aren't as tight tolerances as the Leupolds and take even more lapping.

http://www.burrisoptics.com/sigrings.html

I would love to find rings and bases that fit as wide an array of guns as the Leupold rings and bases and are better built.

[gitrdun]

Originally Posted by 260 Rem

Some food for thought:
First: Given the apparent lack of precision machining with recievers, bases, and rings --- is there any reason to have confidence in the "straightness" of the scope tube or consistency in its diameter ?? Or, perish the thought, the true of the lapping tool
Second: Would it make more sense to "lap" the bases so they were in perfect alignment?

You should have some level of confidence in some of the components, surely the scope tube and especially the lapping bars. If one lacks trust in the lapping bars, that is easily checked. The scope tube? expecially a quality scope that hasn't been dropped or damaged by any means, I suppose you'll have to take it for granted.

As far as lapping the bases, I don't see that as being easily done without a surface grinder. But, tolernances in the receiver, plus the bases, plus the rings all accumulate to be seen in the ring bore. Thus lapping the ring bore seems logical to make up all of the inaccuracies in the components below them.