OK Guys,

Got my 9,3x62 VZ.24 back today. It had spent a month with a 3rd party smith my barrel guy uses to do things like drilling and tapping.

The third party was supposed to drill and tap the receiver for steel Weaver two piece mounts so that the slots for QRW rings were a specified distance apart ... I had even provided a drawing. The third party did everything wrong :

1) I cannot find any place that measures the distance given him for the slot separation. My plan to have two rifles that I could share scopes with ain't gonna happen. Even much, much worse:

2) One of the mounts appears to be rotated some so that the flats on the mounts are not coplanar.

Will put it on a mill vise and hit it with a dial gauge to determine which mount is screwed up, but I think it is the back one.

So now I have a rifle that needs to be bedded (which I can do), but cannot be shot until the mess is fixed.

I am terribly disappointed to say the very least.

I suspect the correct way to fix it is to TIG up the holes, redrill them straight and in the right place on the back mount, and have the receiver reblued.

Any other ideas before I go off and do something stupid?

Thanks!

Tigging shut holes always makes one squeemish.....but there's nothing wrong with it on the rear bridge.

Just install threaded plugs and tig them in, file the surface contours again and re drill and tap them where they need to be!

Getting them aligned to the front ones may require some mill work however.

Share the 3rd party smith's name with us so we can steer clear of his work.

Guys,

I do not know the smith's name ... will get it for sure.

I flipped the rear mount around 180 degrees and the amount of deviance dropped significantly. Now I am wondering if the one side can be shimmed enough to make it flat. Obviously, something isn't symmetrical.

I will put the thing in a mill vise and put a DRO and dial gauge on the thing to see how far out it really is. I can see it, but I'm told I have a sensitive eye for such things.

Thanks for the PMs. I'd like to wait just a little while to make sure I understand what's wrong here.

Thanks!

If its not too bad you might correct the holes by drilling 8 x 40 properly centered. I've seen that fix offset 6 x 40 holes once or twice.

Are all of the screw holes in-line with each other? The dimensions on the action itself could be a little off, causing the mounts to appear skewed as well. An easy fix for the problem is Burris signature rings with the polymer inserts. They are available in a Weaver cross-slot version.
Also, is there a height difference between the front and rear bases? I've had a couple of VZ-24s that didn't work with the standard Weaver 45 and 46 bases, it seemed like the rear base was too high, or the front wasn't tall enough. I used a #419M base for the front, which is a little taller and was a much better match for one of my rifles. The other one has Signature rings with offset inserts.

Some measurements with the receiver in a mill vise take with a dial gauge:

1) Looking at the back of the receiver, the right side of the rear mount is 0.012" lower than the left side (an approximate run of 1/2"). The front mount is flat +- 0.001" across.

2) Looking at the side of the receiver, the back of the front mount taken as zero ... the front of the rear mount is 0.042" taller than the front mount.

Now ... I do not know what the tolerances are for this kind of thing. I would think the slope of the rear mount is not good and the difference in height between the two mounts is unacceptable.

Is my analysis correct?

Also noted that the left side of the rear mount has an air gap between it and the receiver. Could make up for the slope on the top surface.

Anyone know what the curvature radius of the bridge of a VZ.24 measure out to be? I think it might be possible to recut the bottom of the mount and make it fit properly. The height of the rear needs to come down some anyway.

Thoughts?

Thanks very much for reading and cogitating my problem!

Particularly if you plan to remove a scope and install it on another gun, I would suggest that you switch to a one-piece mount. That insures that the front and rear rings are co-planar. Weaver aluminum bases don't do much for me in the way of either aesthetics or function.

Just opinion -- no charge......

Clemson

Bases are steel, but your point is taken. I don't know what the hole spacing is in one piece mounts, so I may already have commited the unsaveable sin as they'd not fit.

Did you take the mounts off and look at the holes? Did "third party" screw it up?

Is the charger hump removed?

Charger hump was ground off with a surface grinder. The rear holes appear to be on a straight line that is ever so slightly off to the right of the line formed by the front holes. It would take so little to get the deviation I am seeing that it would be hard to see.

Smith may have only marginally screwed up on the angle of the holes and the mount may be the major problem. What blows my mind is that the mount was visibly off and the smith did't notice or didn't say anything about it.

He definitely screwed up the spacing of the mounts. He missed what I spec'ed by 0.280"

Without seeing it to take my own measurements it'shard to say exactly. But, as this is a vz24 and since you have an air gap between the base & rear bridge, part of you problem could be the way the rear bridge was contoured. Maybe nbot a problem per se but if the bridge contour doesn't match the base contour you can have issues.

Assuming it is just the bases, then you can probably solve your spacing problem by having custom bases made. That way you can put the cross slot where it is needed so the scope can be switched.

A lot of bases have a "air gap" and make contact on the sides.

Mike,
Sorry this happened to ya. The rear bridge is no problem to tig up and have a better smith do it.

or open to 8x40, using a 3mm endmill to make the pilot holes, and tap.. if it's only "off a little"

jeffe

quote:

Originally posted by GSP7:
A lot of bases have a "air gap" and make contact on the sides.

Then this is doubly bad, ain't it? The air gap in this case is on the side.

In most cases where I've seen this it is due to the rear bridge having been cut wrong. I'm not saying that's the case here. Occasionally it is due to the holes being drilled at an angle.

Have you tried centering up the barreled action, then rotating it, with a dial indicator checking the profile of both the rear and front receiver rings? From this distance it sounds like it may not be the smith's work in doing the drilling and tapping, but might be minor errors and/or tolerance stack in both the receiver profiling and the base profiling.

In the old days, when I opened my first shop, fitting bases quite often required careful filing of the bottom of the bases to fit the profiles of the receiver rings. It sounds to me as if that still might be the easiest, neatest way to resolve your situation.

If you like Weaver bases, it is often possible to get bases of the same hole pattern, but that are thicker than the ones you have. With thicker ones, you can file on both bases to get the thickness & fit you want.

Mike

It sounds like your problem is in the rear bridge or base. Check the angle on the rear bridge and make sure it is the same. It is usually 30%. Check the height from side to side. It may have been ground to a different height from side to side. With the differences that you quote I would recommend that you buy a blank base and machine to fit. You can also get the spacing that you wanted.

James

I think this problem has a solution but the errors are two-fold. There is no excuse for the spacing you specified not being done correctly. The rear bridge appears to be the problem, not the base. I have surface ground a number of receiver rear bridges in the past and found that the angle on the top of the bridge varied from side to side by as much as ten degrees. Normally it is a thirty degree angle, but not always.

The solution to your problem would be to have custom bases made to match the holes already in your receiver. The cross-bolt slots could then be cut to the correct spacing.

"The solution to your problem would be to have custom bases made to match the holes already in your receiver. The cross-bolt slots could then be cut to the correct spacing"

this is correct

A valuable lesson to be learned !.

What was the 3 Rd. party involved for in the first place ?.

I would steer far and wide of Party 2 as well !!. What were they thinking of allowing it to happen !??.

It's obvious neither one are Smiths !.

A professional does not make mistakes a client or customer knows about !. It never should have left their hands unless it was near perfect !!.

I'm sure I have insulted several professionals on several levels in my day !. By asking for " References ". Some just tell you to put it where the sun doesn't shine !.

The others which are " True Professionals " are all to happy to show their skills . Those are MY SMITHS !!. ...

If the holes are 6x48 the action can be set up on a cnc and new holes for 8x40 screws can be interpolated on the centerline of the action and tapped 8x40,if 6x48 are no to far off, the new holes will have to be where the old holes are fore and aft on the receiver, which steps out of your design perameters. Once the bases are in the center of the reciever, new weaver bases with no slots could possibly be purchased from weaver, the new blank bases could then be mounted to the receiver and the slots be cut where you need them, or if blanks are not available from Weaver some could be made to fit your ring tops.
The main reason the back base ends up off center is the guy who did the D&P did not have a fixture to hold a 98 and he vised on the front ring, which does not gaurantee the center of the rear bridge. To get centered, the action must be on a fixture plate in the vise, then a mandrel that fits the bore of the action must be inserted thru the action, then the portion of the mandrel that protrudes out the front of the action needs to to have it's center located, with that done, the same needs to be done for the portion of the mandrel that proturdes out the back of the action in the rear bridge area At which point refering back to the dro on the machine will tell the machinist the amount of deviation he is dealing with and can make adjustments to the setup to get the centerline of the receiver in line with the x axis of the machine. In the case where a cnc is in use the machinist can simply program the holes in the rear bridge to match the centerline of the rear bridge for the holes in the rear bridge, negating any need to manually manipulate the part or the fixure, the only thing you really need to know here how much to offset, which is easily figured out with an edge finer and refering back to the DRO
Note: mark the mandrel with a felt marker so you can come back to the same place on the mandrel when checking all this out, don't be satisfied with the first batch of numbers you come up with either check it out a number of times until you are sure you know extactly where you stand, then you can make an accurate move and do the work.
Timan

That is essentially what I was saying only you used more words. A CNC would be nice in this case but everyone does not have access to one. It is a simple matter to locate the off-center holes and fit a new steel base to the action, front and rear. Brownells sells a steel base made by B-square that will accept the weaver rings. This is a blank base and the holes can then be done with the base in place; a simple matter to indicate in the old holes and with the DRO, transfer that to the base. I would simply make the bases to match the receiver first and then super glue them in place and transfer the DRO measurement to the rings. Simple eh!

I have drilled and tapped lots of VZ24s and bought more at gun shows with the scope mounts screwed up, taken them home and fixed them.

Here are 9 of my VZ24s drilled and tapped.
Sorry Z1R, I know you are tired of me posting this same pic.



I am obsessed about getting the Weaver mounts co- planar and co- linear.

I do not TIG weld up holes that are off center.
I live with them.

If the holes in the receiver are too far off, I put the Weaver mount between 2 V blocks and open the through hole and counter sink into oval shapes so I can move the mount into position on the receiver.




Then I put the mounts on the rifle and the rings on the mounts and a scope in the middle of it's vertical and horizontal adjustment range in the rings.

I bore sight.

Then I shim and dam until the scope is parallel with the bore.

Then I put oil on the screws and put the mounts on the receiver loosely with wet Devcon Steel Putty epoxy between the mount and the receiver. I put the scope and rings on the mounts tightly. The scope acts as an alignment fixture for the mounts. I verify that the bore and scope align on the same target while the epoxy is setting up. I can only glass mounts during the day.

When the epoxy is hard, I remove the screws and clean the holes and screws with alcohol. I put blue Loctite® on the screws. I tighten the mount screws.

Here is the seat of the pants tolerance stack up:
1) Bore....nice and straight
2) Bore to receiver....co axial and rigid
3) Receiver to mount.....poor fit, has gaps, flexes, and twists. 5 of 6 degrees of freedom are problematic. A ham fisted gunsmith can drill the holes anywhere.
4) weaver Ring manufacturing tolerance... very accurate alignment of Weaver dovetail to ring bore
5) Scope body tube...very round and straight


Everything goes to hell in 3).
It is the mount to receiver fit.
I put epoxy between them and then clamp them with a fixture that forces them into alignment.

When the epoxy hardens, I take the fixture off, and any rings put on that rifle seem to have already been lapped.

When I am done, the mounts should be aligned with each other and aligned with the bore.
My scopes with Weaver rings should be able to move from rifle to rifle and be on the paper, and my rings never need any lapping.


I would like to say I invented this, but lots of people invent this process out of necessity.
This is how Boeing aligns fixtures.
This is how Pacific Car and Foundry aligned Mercury switches in the pendulum that senses the fall line of the hill to balance a 20 ton gun barrel.

tnekkcc,

Sorry for the dumb question ... but ...

What do you mean by dam in "shim and dam"?

I love the modified v-block clamp!

Thank you for the thorough explanation.

See a " Real Smith " not only explains it but shows you as well !. Three Cheers " tnekkcc " old boy !. ...

quote:

Originally posted by mstarling:


What do you mean by dam in "shim and dam"?

Between the mount and receiver I put narrow layers of masking tape that act as "shims" to make the mount the right height. It is thin so there is lots or area for the epoxy to make the compressive strength between mount and reciever.

If the epoxy were thin, a strip of tape would be needed around the periphery of the mount outline on the receiver to keep the epoxy from leaking. This would be a "dam".

More tape is put on the receiver where no epoxy is wanted, and this is a "mask".