Using a military spec picatinny scope rail...

If ten rifles have the picatinny scope rail...

If one rifle has a properly mounted scope on it...

Can that scope be moved from one rifle to the next without adjusting the scope rings ?

Expect the scope will have to be sighted-in for each rifle, but will the scope rings have to be adjusted in order to fit the scope on the rifle ?

Hammer

quote:

Originally posted by Hammer:
Using a military spec picatinny scope rail...

If ten rifles have the picatinny scope rail...

If one rifle has a properly mounted scope on it...

Can that scope be moved from one rifle to the next without adjusting the scope rings ?

Expect the scope will have to be sighted-in for each rifle, but will the scope rings have to be adjusted in order to fit the scope on the rifle ?

Hammer

YES

Yes and no. It was standardized by the military for exactly that reason--to be able to swap stuff from rifle to rifle quickly and easily. Yes, it works.

However, if you're particularly concerned about lapping rings and stuff like that, like anything else there are tolerances, etc, that you'll want to account for to get a 100.000% perfect fit verses a 99% fit.

Keep in mind, there are many "picatinny type" rails out there that are not made to the Mil spec that may not be compatable.

It might not work at all, depending on the rings.

The tolerances for the picatinny rail is set betwen two groves and two lands.
But if you are manufacturing two picatinny rails where one is haveing maximum measurements withing the tolerance and the other one minimum.
In such case 5" farther down the rail where one rail have a groove the other one have a land.

The picatinny standard sucks and has to be restandardized.

So if your scope has rings with recoillugs in both rings, the swop betwen two rails might not work, but if you have only one recoillug it will work.

Regards

StenGun

Guys, what is the difference between "picatinny" and Weaver mounts?? Apart from the picatinnys often having one-piece bases, can Weaver rings be used on a picatinny base and/or vice-versa?? (Sorry to be thick, I rarely get in touch with military guns, and have been wanting to ask this question for a while).

Personally, I would have a hard time believing that scopes could be switched from rifle A to rifle B, even if both were mounted and sighted with picatinny mounts. You'd be surprised at how much difference in POI just minor adjustments in length of pull or stock configuration cause. Besides, even if all the rails were manufactured exactly the same, who says the screwholes in the receiver will position them exactly the same on various rifles??

- mike

The most common difference is that the crossslots in Weaver have rounded corners but the picatinny have square.
That means in most of the cases can a weaverring be mounted on a picatinny rail but not the opposite.
But as the standard is so bad there is exact rules.

Regards StenGun

In switching scopes from one rifle to the next...

Am not switching bases. Bases stay with rifle.

Rings stay with scope.

Expect to have to make scope adjustments from rifle to rifle.

Expect to be able to record adjustment, remove scope from rifle, and repeat settings without resighting in rifle.

Currently am playing with four scopes with one rifle.

Don't some high power 1,000 yard competitors do this when they go from an iron-sight match to an any-sight match using the same rifle ?

Hammer

There is a lot of people using high quality detachable mounts for using more than one optical sight per rifle.
But very few use more than one rifle per sight, and I think you should stay away from that as it causes a lot of potential problems.

When it comes to detachable mounts there is names like Apel, Recknagel, ARMS etc that makes good detachable repetable scopemounts.

Regards StenGun

quote:

Originally posted by StenGun:
The tolerances for the picatinny rail is set betwen two groves and two lands.
But if you are manufacturing two picatinny rails where one is haveing maximum measurements withing the tolerance and the other one minimum.
In such case 5" farther down the rail where one rail have a groove the other one have a land.

The picatinny standard sucks and has to be restandardized.

I think somebody's GD&T is even rustier than mine. You can't just go moving the datum plane from groove to groove such that you can add up tolerences--"tolerence buildup." The spec says the dimension applies between adjacent grooves, it doesn't say you move the datum plane J to a new groove every time you dimension another. The "Centered within .006 of datum J" box (I'm pretty sure that interpretation is correct, rusty as I may be) refers back to the first groove for exactly the reason of avoiding the problem you describe--all successive grooves are within that from the noted dimension from the very first groove, not just the last one behind it.

quote:

Originally posted by Hammer:
In switching scopes from one rifle to the next...

Am not switching bases. Bases stay with rifle.

Rings stay with scope.

Expect to have to make scope adjustments from rifle to rifle.

Expect to be able to record adjustment, remove scope from rifle, and repeat settings without resighting in rifle.

Currently am playing with four scopes with one rifle.

Don't some high power 1,000 yard competitors do this when they go from an iron-sight match to an any-sight match using the same rifle ?

Hammer

I have several rifles with Picatinny rails and I have never had a problem taking one scope off and putting on any other by just looseing the rings from the base and putting the scope on another rifle that has a picatinny rail

Jon A

I have compered picatinny rails where one have a groove there the another one have a land.

Simplified for picatinny 1913 http://www.biggerhammer.net/picatinny/

The full drawings:
http://www.biggerhammer.net/picatinny/1913_specs.pdf

Please have a look trough it and see if you can get someting else out of it than I did.

Regards StenGun

quote:

Originally posted by StenGun:
Please have a look trough it and see if you can get someting else out of it than I did.

I already have and I did "get something else out of it" as stated above. Did you not follow what the terms of the GD&T symbols mean?

What brands did you compare? Before you go blaming the spec, you ought to know enough to determine whether or not the parts were made to spec first. In order to do that you need to understand the spec.

John A is precisely correct. Perhaps the drawing markups that I made here below can help some. If these tolerances are met or exceeded, expecially those involving true position with respect to action and barrel, then this system works as designed. We often replace holes in action to allow us to improve mounting tolerances.

DCMI
That part of the Drawing is not the real problem, its the other part where you see the slots.
The measurement of the slots is just toleranced betwen two close slots but often you have 10-15 slots.
The problem as I did see it comes if two manufacturers are using minimum respectivley maximum tolerances then the slots will have different placement on the other end of the rail.
AS long as you have only one locking lug this will cause no problem but if you of siome reason have two lockinglugs on the item that should be attached to the rail then you will realize that one of the rails have a bar where the other one have a slot.

But Jon can be partly right in the aspect that the tolerances is maybe not followed by the manufacturers and this give mounting problems.

Regards STenGun

quote:

Originally posted by StenGun:
But Jon can be partly right

There's no partly about it.

quote:

The measurement of the slots is just toleranced betwen two close slots but often you have 10-15 slots.

Again, the measurement is between two slots. The tolerance is not.



The measurement is exactly .394 between the centers of successive slots with no tolerance applied. Each individual slot has a locational tolerance of .006 in the Maximum Material Condition (smallest slot size) in relation to Datum Plane J all the way back at the beginning, not the slot before it.

You're thinking after 10 slots you could be off by .060 if you're off by .006 on each one, putting it at .394 * 10 + .060 = 4.00" away from the first slot. If you are, the part does not meet the spec. After 10 slots, the 10th slot needs to be 3.94000000 exactly, then plus the .006 tolerance from the first slot meaning it will be placed as accurately in relation to the first slot as the second slot was--they both have exactly the same tolerance from the first slot.

Anybody who machines parts and sells them ought to be able to open up his copy of ASME Y14.5M-1994 to page 96 and follow along with a very nice example that makes this very clear. I do agree, however, that there are those out there selling parts who don't know how to properly read Engineering Drawings.

The above is simplified a bit as going into the minutia of slot size vs material condition, actual placement boundaries, etc, isn't needed for the important point to get accross.