Model 99 scope mounting problem

[banshee1]

So my father wants a new scope for his '54 99R. The problem is the guy who mounted the weaver pivot mounts did a poor job and the scope points left or right by several inches at 200yds compared to being right on at 100. Part of the reason for new scope is because the Tasco is at least 40yrs old with horrible glass and he needs the scope brought back over an 1" to get eye relief correct and cant do that with current mounts.

So I put a 1pc Leupold mount on it with an extended front ring thinking it would allow me to move a scope back and to get the scope parallel to barrel using rear windage screws. Well it didnt because the front ring mount is in front of screws so it just barely puts front ring behind the weaver flip mount. Also noticed that with just the 2 front screws in the base the back of the base is not on center of the receiver and rear screw hole doesnt line up with front hole of 2 piece mount in the left to right direction when looking from back. It's dead perfect front to rear though. Assuming I modify the base so I have all 3 screws in it, are the windage screws strong enough to pivot the front rings and hold them there? I would use a long steel dowel pin to pivot the mounts to get them parallel to barrel as best as I can, but will the front pivot mount stay in place when I remove steel pin to mount scope or will it return to center upon removal? Forcing the scope tube to realign front ring when it is clamped to rings and possibly how ever slightly bend the aluminum tube of a new scope.

Now at a quick glance it looks like that if I use just the front and rear screws in the base it should make it parallel to barrel, but be off center. I could then elongate the middle hole so I can use all 3 screws. Will I still have a problem with the poi being 3-4" off from 100yd to 200yds if scope isn't dead center left to right or would it only be an inch or so different? 1" or less my dad could probably live with.

The eye relief of his Tasco only seems to be 2" or less, so maybe with new scopes having greater eye relief I wont have to deal with moving scope back.

My other option is to buy the weaver #14 & 19 bases and order a set of extended Burris Z rings with plastic sleeves and hope I can get scope on center and parallel to bore. The weaver bases look to have the slots between the screws so extended rings would allow me to bring the scope back roughly an inch further then it is now and with greater eye relief scopes this could work better for my father.

What is everybodies opinion on fixing my issues? Any other ideaa?

Mike.

[J.Baker]

Honestly, I think you're pretty well screwed in this case with the mounting holes being off-center. Nothing you can do is going to allow you to zero at one distance and not be off left or right at another distance.


Not sure if the rings linked to below will work with the Leupold base, but if they will they'd probably be your best option along with elongating that middle screw hole. With +/- offset inserts installed with the seams at 12 and 6 o'clock rather than 3 and 9 o'clock in both rings you could effectively move the scope closer to being directly over the centerline of the bore. Probably not enough to make it perfect, but should make the horizontal difference at 200 yards a fair bit less.

https://www.midwayusa.com/product/1548332714

You might be able to accomplish the same thing with the Weaver bases you mentioned and the Burris Signature Zee rings + inserts installed as noted above.

[Big Al1]

Sounds like the holes were drilled off center. If the offset rings don't work ( sonds like a good idea) Brownells sells a base blank. A good gun smith could mackine it to fit and drill the mounting holes off center to match the existing holes!! Just a thought!!
https://www.brownells.com/optics-mou...-prod9851.aspx

[banshee1]

Thanks for the replies guys. Now let me ask you this, if I wanted to d&t new holes in the receiver what is the best way to make sure the holes are on center of the barrel? Is picking up the center of the receiver good enough or is there a better method?
Been a machinist for 25yrs and make aerospace, defense and parts for medical industry so plenty capable. Now before you guys say anything I'm not actually going to add holes, but once I pick up centerline I can measure location of every hole and then modify the leupold base so it can actually be put on center and straight to barrel. Would this work as long as I can be sure the base will stay put after modifying?

Thanks.

[Big Al1]

If you have a way to monut securely on a milling machine, you can find dead center by measuring from side to side of the receiver, divide in half and rotate head to center. I have a special fixture that mounts the barrel in V blocks, and the jug is automatically dead center. Like this one!

https://www.brownells.com/gunsmith-t...-prod6638.aspx

Look at the fixture it may give you some ideas!

[banshee1]

If you have a way to monut securely on a milling machine, you can find dead center by measuring from side to side of the receiver, divide in half and rotate head to center. I have a special fixture that mounts the barrel in V blocks, and the jug is automatically dead center. Like this one!

https://www.brownells.com/gunsmith-t...-prod6638.aspx

Look at the fixture it may give you some ideas!

That's pretty much how I was thinking about going at this. I was thinking about finding centerline of barrel and receiver and split the difference. Although if theres a big descrepency (more then .005") not sure what I'd do.

Since I'm not super knowledgeable in scope building, maybe you guys can answer this. When adjusting the crosshairs are they actually moving like they are mounted on tracks (linear motion) or are you just pivoting the housing containing the crosshairs? If its the former it wouldn't matter if scope is on centerline perfectly just as long as it's close enough that you dont use all of the lateral adjustment of the crosshairs correct? The only critical part really is just that the scope is parallel to the bore right?

Thanks guys.

[J.Baker]

You can make (or buy) yourself a simple fixture like this that would fit over the receiver.

[J.Baker]

Since I'm not super knowledgeable in scope building, maybe you guys can answer this. When adjusting the crosshairs are they actually moving like they are mounted on tracks (linear motion) or are you just pivoting the housing containing the crosshairs? If its the former it wouldn't matter if scope is on centerline perfectly just as long as it's close enough that you dont use all of the lateral adjustment of the crosshairs correct? The only critical part really is just that the scope is parallel to the bore right?

Thanks guys.

The reticle and several lenses of a scope are mounted in what's called the erector tube. It's a smaller tube mounted inside the scope. When you turn the adjustment dials for windage and elevation, you're basically pushing that erector tube to the left or down. A spring (usually mounted at about the 7:30 position, though some scopes have two springs at 6 and 9 o'clock) keeps the erector pressed firmly against the contact points for the turrets when making adjustments.

Here's a couple fairly decent pics to give you a visual...

[banshee1]

The reticle and several lenses of a scope are mounted in what's called the erector tube. It's a smaller tube mounted inside the scope. When you turn the adjustment dials for windage and elevation, you're basically pushing that erector tube to the left or down. A spring (usually mounted at about the 7:30 position, though some scopes have two springs at 6 and 9 o'clock) keeps the erector pressed firmly against the contact points for the turrets when making adjustments.

Here's a couple fairly decent pics to give you a visual...

Thanks for the info Baker. So the whole tube slides and not pivot on a fixed point? Wouldn't have thought that.

Thanks again.
Mike

[J.Baker]

Thanks for the info Baker. So the whole tube slides and not pivot on a fixed point? Wouldn't have thought that.

Thanks again.
Mike

It pivots. If you look at that second cutaway photo under the magnification ring you will see a black square ring. That's a rubber seal/bushing that holds the rear of the erector tube in place at the back end and allows enough give to allow the movement needed when the front of the erector tube is pushed left/right/up/down by the turret screws/spring(s).

The only part that slides is that rear section under the magnification ring. When you turn the magnification ring it moves the rear lens of the erector assembly (one with crosshair in it) and it's inner sleeve forward and back. This change in distance between that lens and the lens stack in the forward part of the erector tube is what causes the change in magnification power.

[Model24]

I had exactly the same issue. Fixed the alignment with a hand built front base and Burris Signature Zee Rings. As for eye relief, I use a Bushnell Banner 3-9x40 "Muzzleloader" scope with 5 inches of eye relief. It's the only one I've ever been able to find with that eye relief.

[banshee1]

It pivots. If you look at that second cutaway photo under the magnification ring you will see a black square ring. That's a rubber seal/bushing that holds the rear of the erector tube in place at the back end and allows enough give to allow the movement needed when the front of the erector tube is pushed left/right/up/down by the turret screws/spring(s).

The only part that slides is that rear section under the magnification ring. When you turn the magnification ring it moves the rear lens of the erector assembly (one with crosshair in it) and it's inner sleeve forward and back. This change in distance between that lens and the lens stack in the forward part of the erector tube is what causes the change in magnification power.

Thanks for answering my questions Baker. I saw that ring but wasnt sure exactly what its purpose was, now I do.

So did a little more investigating this weekend and the front 2 holes are what seem to be really off. Determined this by mounting the Leupold 1pc mount with just the front screw and the back of base was nowhere near centered on the back of receiver. Used the back single screw on the base and it fits the back of receiver pretty good and the front radius of base fits good on the front of receiver nice, but the 2 front holes are off roughly .02/.03".

I've read that the back of the receivers can be fairly hard and difficult to tap, but after buying the leupold base I think it would be best to enlarge the threads and buy the #14 and #19 bases and modify them for larger screws.

What I dont like about the Leupold base is that with the one I got the rear ring doesnt sit on the base, it's off the base at least .005" and this is with a piece of straight shaft and I dont want to force a new scope to get it tight to base. That and with the ext. base the ring isn't any further back then the original weaver flop over rings. With the #14/19 bases to looks line the extended front Z ring will be further back from what I can see from online pics. Still not 100% confident even the Z rings wont bend the scope if rings arent perfectly in line and different offsets are used, but I think I can minimize the need for large offsets.

Thanks again for the helps guys.

[banshee1]

I had exactly the same issue. Fixed the alignment with a hand built front base and Burris Signature Zee Rings. As for eye relief, I use a Bushnell Banner 3-9x40 "Muzzleloader" scope with 5 inches of eye relief. It's the only one I've ever been able to find with that eye relief.

Is it truely 5-6" eye relief and is that the only difference between that and the center fire version? Wouldn't have to worry about extended rings with that scope.

[Model24]

Yup, it really is 5 - 6 inches, and that is the only difference. I just looked at it on Optics Planet and Midway, and they’re not even calling it a muzzle loader or shotgun scope anymore. Just long eye relief.