Lapping a used scope

[mconwa951]

So i have a nikon 5-20x44 monarch that i had mounted on my .308 i had it mounted by a gunsmith however i do not think he ever lapped it like i asked him to. Now that i have a new rifle i want to mount it on a savage .300wsm i want to mount it on should i lap it now before i mount it or is it to late.
Thanks guys

 

[Hookturnr]

You lap the rings, not the scope itself. As for parking it on a new rig, I'd lap the new rings just like i do on all of my rifles.

 

[mconwa951]

I meant to say that the rings are going with the scope to the new rig. and from what i understand by not lapping it can affect the accuarcy of the scope by not being aligned in the rings properly ie binding and such.

 

[LouBoyd]

So i have a nikon 5-20x44 monarch that i had mounted on my .308 i had it mounted by a gunsmith however i do not think he ever lapped it like i asked him to. Now that i have a new rifle i want to mount it on a savage .300wsm i want to mount it on should i lap it now before i mount it or is it to late.
Thanks guys

It's not to late. It's not a static situation.

If the point of impact seems to be moving with shooting then lapping the rings may help accuracy. Think about what the problem really is. The scope base can cause similar problems. Check both before doing anything. Bedding is adding material while lapping is removing material on mating surfaces. Both have the objective of eliminating gaps and warping when the surface are clamped together. You need to choose which will work best for each mating surface.

Lapping anything with an anodized or blued surface will reduce it's value. Lapping is usually done on the least valuble surface if it's practical. Bedding is usually applied so it's permanent to the least valuable surface and removable from the other.

The purpose of lapping or bedding is so the scope line of sight and bore don't change their relative angle when the gun is in use. Firing does two things. It flexes all of the the component (action, base, rings, and scope) slightly and they should all return to the same positions. If they don't fit well then can return to a different position with any shot. The action also heats and expands from each firing and cools between firings. So does the base, rings, and scope, but not at the same time or achieve the same temperature. Aluminum expands 2-3 times as much as steel for the same temperatures, but rifle components aren't exposed to the same temperatures. The two main heat source while shooting are heat conducted from the propllant though the case and action and direct solar energy. Either can be larger. In Arizona I've had rifles get too hot to touch without shooting them. The scope can be hotter than the action. Likewise In winter the scope can stay cold while the action heats from firing. Lapping and bedding does not eliminate the stress of recoil or the thermal stresses, but good symmetrical fits will minimize the angular offset between the scope and bore.

 

[mconwa951]

If a scope is binding or bending then lapping the rings >may< reduce the binding and bending. Think about what the problem really is before doing anything. Bedding the scope base may be a better solution if it's binding or bending too. Check both before doing anything. Lapping anything with an anodized surface will reduce it's value. Rings are usually the least visible wen lapped, easiest to lap, and least loss of value when they are lapped. Bedding usually doesn't need lapping on the same mating surfaces. Lapping the bluing on a rifle action or the anodizing on a scope may fix a problem but it can really hurt resale value.

I dont notice any binding or anything right now basically what i am wondering is would it do anygood to lap it now or if it hasnt been done to this point is it pointless to do it now.

 

[42769vette]

personal opinion here, but 20 years ago i lapped every set of rings i got. now i think machining tolarances have gotten good enough that its not required. that said it cant really hurt so if you want to do it go for it

 

[LouBoyd]

I dont notice any binding or anything right now basically what i am wondering is would it do anygood to lap it now or if it hasnt been done to this point is it pointless to do it now.

I don't know what binding you might expect to notice. The question is if all of the mating surfaces when the bases, rings, or scope are properly torqued are in good contact. If they aren't in good contact they may change positiion from recoil or temperature changes. The scope will always have some stress on it and under recoil or large temperature changes the forces can be many pounds (or ft-lbs) either linear or as torque. That is normal.

How do you tell if the sufaces are properly mated when torqued? I use this type of material to check mating surfaces:
Prescale™ Pressure Indicating Film
There are several comparable brands. You can find this sort of film at most machinist supply stores.
Just cut a piece to the area you want to measure, Assemble and apply whatever pressure is to be measured, and disassemble it. The color intensity shows the peak pressure with good dimensional resolution and decent pressure resolution.
If there are areas of low or high pressure , particularly if they're asymmetrical and could warp the base or wobble, then bedding or lapping should give a better match and make the scope to bore alignment more stable.

Is it pointless to do it now?
It is very difficult to do it in the past. Procrastination is easiest.

 

[mconwa951]

Thanks Lou that is the advice i was looking for.