How is any sporterized rifle with a 2 piece scope base accurate?

T

Technologist

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I have an old Sako M98 built on a civilian production FN reveiver. The screws for the two piece bases broke (I think it was the forward ones but I don't remember) a long time ago. I've finally received the replacements in the mail but I wonder, how was this ever a good setup?

The two scope bases are mounted on a surface that as far as I know was never intended to be used as a platform for mounting optics. What are the tolerances as far as parallelity of the forward and rear reveiver rings? There is nothing ensuring the alignment of the bases as they are screwed to the receiver, except a minute cone shape on the bottom of the screw heads. In most other applications one would have added guide pins (two per base) to ensure that the bases go on straight relative to each other.

In our days of mil/mil scopes, full length top rails and very accurate factory rifles, we take scope mounting for granted.

How do I put the bases back on the rifle the best way? I know a lot of people recommend just screwing them on there and then grinding the scope rings with a kit. It seems backwards to me to correct the scope rings, that most likely, since they were actually designed to hold a scope of a specified diameter, have tighter tolerances than the surfaces on the receiver.

Is there some way to get bedding mass or some other goo in between the bases and the receiver? If I'd mount a scope on there while it sets, wouldn't that ensure that the bases are mounted well relative to each other?

I assume that the scope is straighter than the receiver, because the straightness of the scope is likely ensured by a tighter tolerance than the surfaces on the receiver, which was designed long before this kind of bases was a thing.
 
I have heard of people putting a skim layer of JB weld and then screwing the bases on. Doing this will stop any rocking or movement that could ever occur.

What I would then do, is get a set of Burris Signature rings. These have the nylon ring inserts that you can play around with for elevation, but by turning a pair of offset ring inserts, you can also correct R>L or L>R skew.

And the Burris rings won't mar your scope. I cannot figure out why more people don't like them. The idea that the plastic inserts are unable to hold the scope is unfounded.
 
ShtrRdy said:
I would permanently bed/bond them onto the receiver with the scope tube holding them in alignment.
Click to expand...
Since the rings often cover up the screws, that approach usually won't work in my experience. Once you have put the scope on the bases/rings, you cannot screw the bases down. And I would not trust just epoxy bedding to hold the bases.
 
I have plenty of experience milling and setting up bases on Mauser '98 actions. Why you use a 2 base set-up is for the sole reason to have WINDAGE adjustment on the rear base and ring. You can also use a single one piece base, but again the rear ring has WINDAGE adjustment.
Most base screw holes are machined using a jig, even at the factory, and others are CNC milled, mistakes happen on production items.

You are overthinking this, even today, actions are milled off centre for scope base holes. My own Win Model 70 EW 338WM is out, it was a warranty job, milled it true from 6-32 to 8-40 and fixed it, then the customer decided he didn't want to buy more bases, which wasn't actually necessary, and sold it to me half price. It was brand new…

Cheers.
 
I like that the 2 piece base preserves access to the ejection port. A picatinny rail across the action is not an option for me, on this rifle.

What I don't like is that this rifle has three plugged holes on the side, from a previous owner (my grandfather) who used a side mount to put some archaic fixed power scope on there. My uncle wanted a modern scope, so he plugged those holes and had a smith mount the two piece bases.

To be honest, I'd prefer to have the top holes magically disappear and reopen the side mount holes. If I could get a hold of some one piece mount for a modern scope tube diameter that would be amazing.
 
I had a sporterized 1903 springfield I ran a giveaway for and donated it to a young hunter . And had a very similar problem it had 2 piece bases . I think weaver as they were popular for this . Took the rifle in and had a 4x12 scope mounted as I was making it a ready to hunt package . It went to Axis Works for a muzzle break back before Eric knew what I was going to do with the rifle so it was outa my pocket. That rifle kicked my but for 3 months and a few new vortex scopes before I took it in and had it looked at . The bases were not even close to level and all 3 scopes had bent tubes because of this. I had Keith at Phoenix custom rifles take a look and we went egw one piece bases. You'd think problem fixed but nope . Still fought the scope vortex are junk in the few hundred dollar scopes so I put on a Leupold and had a go . It was on at 50 put I couldn't find my hit at100 so as I'm at the range another guy and his dad complemented me on the rifle as it was beautiful . As I explained it was being donated in a few days and I still couldn't get it to group the dad said maybe it's you . So he shot and I called hits and we walked it in . Problem solved and the rifle went to a deserving young hunter. I still do the giveaway I just use new guns to make sure they give the best results. If you need to run a one piece it definitely helped me just make sure your two piece are level . Had I done my own checks I'd have saved probably 100 rds of 06 ammo.
 
Assume the rings are for 1 inch scope. Do not use a scope to validate mechanical alignment. Go to your local hardware store and buy round metal stock in 1 inch diameter and at least 18 inches long (36" good too as you can see obvious errors). With a steel wool <Brillo> pad (fiber leaves fewer filings) smooth and clean the aluminum stock smooth. Care not to take off too much, but enough to not damage rings. The round stock is perfect as a bar to twist rings into base and to get rear base alignment screws centered as a good starting point. With this round stock you can put base bedding, shims, JB Weld, or other attaching devices without ruining your scope. Similar refined stock was sold years ago in scope mounting tool kits.
 
I have had several custom built M98s. I use Conetrol rings and bases. They have always been good. Interesting how they are made, and I have never had to lap them. They are different! They have windage is in the bases screws, too. Once you get the scope into the rings, the caps have got to be correctly aligned and once you do, you can hardly tell they have parts; they appear as one piece. I have only done the one inch rings and honestly don't know if they make 30mm.
 
Help me understand your purpose. You have a rifle designed 130 some years ago, made in 30 some countries. I see you are from Sweden, When it was drilled for a side mount it may have been for any number of available scopes with diameters from 3/6 to 26mm many of which did not have windage adjustments. The mounting holes on the top of the action may or may not be aligned which should probably be addressed along with the height. Note the popularity of 20 to 50 moa bases. This is what we used to call Ga. precision machining,
"measure with a micrometer
mark with chalk
cut with a chain saw"
Decide what your objective is and then how much you are willing to spend to get there,
kind regards
 

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