Scope mounting problem.

[VSS]

Recently I bought a lovely scope, of a model I've coveted for some time, from a member on here.
Mounting a 30mm tubed scope on a P-H is a bit of a bother, but thanks to the generosity of another site member I was fully equipped with these:


With the result:


All good, so off I went to zero it.
I had centred the reticle before mounting.
As you know, zeroing is not my strong point, (OK, so I'm **** at it!), but this is how it went:

First, I boresighted at 25 yards and then fired a shot, which landed pretty close.
Next, with the rifle securely clamped, I moved the reticle to the POI.
Then I moved out to a longer distance and, after a few more shots and minor adjustments, I started to build up a fairly respectable (for me) group, more or less where I wanted.
Then, all of a sudden, one of my shots was 6" off. I fired a few more, and they were all impacting in the new place, creating a fairly tidy group, but not where I was aiming.

So, something had clearly moved. My first thought was that the scope had moved forward in the rings under recoil, but there isnt really any room for it to move anyway, so I doubt that's it (although it remains a possibility).

Closer inspection reveals that the mating surfaces of the new rear base and the top of the action don't quite mate. Their curvatures are marginally different. So there's a very slight gap either side, and the only point that they're making full contact is at the top where the screws pass through. The gap is very small, just enough to slide a fag paper into, but I've managed to catch it one side in the following photo (gap clearly visible on right hand side):

(The gap is the same both sides, but you can't see that in this photo).

I guess this is kind of to be expected when using components from different manufacturers, even if they are described as "compatible".

So, my first question is, is this the likely cause of my POI shifting?
And secondly, what to do about it?
Two suggestions have been made so far:
1) Bed the base on something like araldite to take up the slack.
2) File out the top of the curvature on the base using a half-round file so it sits in position better.

The first option seems a bit shoddy, but at least it's reversible. The second option sounds more secure, but is irreversible if it proves not to work.

Your comments and suggestions would be welcomed.

(Incidentally, the POI didn't move again. It stayed in the new position, with tidy grouping. That seems to point more towards the scope having moved, rather than a wobbly base).

(Edited to add: The POI shifted UP by 6", and LEFT by about 2.5", if that is of any significance?)

 

[Stalker-of-the-deer]

I would hazard a guess that thoes mounts are for a remmington 700 and not a PH /mauser 98.

Also check the mounts are the right way round as the action has a slight step in them from memory. Or spin them 180 degrees to see if that makes a difference

 

[VSS]

I would hazard a guess that thoes mounts are for a remmington 700 and not a PH /mauser 98.

Also check the mounts are the right way round as the action has a slight step in them from memory. Or spin them 180 degrees to see if that makes a difference

They're definitely the right bases. Not only does it say so on the packet, I checked the part number online.

The rear base can't be spun 180 degrees or it fouls the bolt. Every other P-H rifle I've seen with these bases has them fitted the way I have.

 

[Cyres]

Just because the packaging says its for your PH doesn't mean its the correct ones in the packaging.
I had those type mounts on my Remmy 700 and they were a perfect fit on the action.
When you fitted the rings were you perfectly happy that they cammed in correctly.?
I used Burris Zee Signature rings.
Really you should use Leupold rings with their bases and would match up the scope.
The rings used to come with a special tool to ensure you correctly fitted the rings to the bases did you have that tool.?
Seems to me that you didn't quite cam the ring(s) in correctly and they have bedding in after a few shots and hence the POI change which now has settled down.
D

 

[VSS]

Just because the packaging says its for your PH doesn't mean its the correct ones in the packaging.
I had those type mounts on my Remmy 700 and they were a perfect fit on the action.
When you fitted the rings were you perfectly happy that they cammed in correctly.?
I used Burris Zee Signature rings.
Really you should use Leupold rings with their bases and would match up the scope.
The rings used to come with a special tool to ensure you correctly fitted the rings to the bases did you have that tool.?
Seems to me that you didn't quite cam the ring(s) in correctly and they have bedding in after a few shots and hence the POI change which now has settled down.
D

The front ring appeared to.me to cam in correctly. The rear base is windage adjustable, so no camming required.
I believe that the bases had been purchased new by the person who I got them from, so I have no reason to suspect that they didn't match their packaging.

It may be that whatever moved has now settled down, as you say. But I'd like to know what moved, and how to stop it moving again.

 

[Stalker-of-the-deer]

They're definitely the right bases. Not only does it say so on the packet, I checked the part number online.

The rear base can't be spun 180 degrees or it fouls the bolt. Every other P-H rifle I've seen with these bases has them fitted the way I have.

I mean swap the front for the back and the back to the front rather than the actual mount 180 degrees. My bad English.

Looking at the bases on the Internet and from memory the front of the receiver is a slightly diffrent profile to the rear plus a slight step. Its hardly noticeable.

I would guess the slight slop in the mounts is what's causing zero shift. Takes hary anything

 

[bullet chucker]

Why not ensure all screw and attachments are now fully tight, then adjust your scope to point of aim then leave well alone.

BC.

 

[8x57]

Looking at your photograph it appears that the rear base is not fitting flush to the receiver. You are aware that not all K98 receivers are identical and that a different base may be required.
Even if you have achieved a zero now, that may change if you are simply relying on the screws to hold the base tight as with time and under recoil those screws will slacken off or even shear if the base is not a close fit. I would suggest that when on your travels you pop into Norman Clark in Rugby and either get a proper fitting base for your actual rifle or get the base bedded in expoxy.

 

[8x57]

I might be on the wrong track here but looking at the packaging it looks like you have bases for a FN Mauser. You may need the bases for a K98 large ring Mauser.

 

[Freeforester]

Looking at the pictured result, without proper mating between surfaces, there is always going to be room there for ‘doubt’, which of course is rather unsatisfactory. Risking a wounded deer-type outcome is never desirable. Peace of mind is a valuable commodity, and there are limits to what we amateur tinkerers can achieve; I see in the scenario the following options:

1) take steps to remove aforementioned doubt, or

2) live with the unexplained shift in POI and ‘hope’ that it does not happen again.

It is clear that there will be a cost either way, psychologically or/and in financial outlay, beyond this it will come down to your personal choice of which path you choose, but making certain (ie removing the ‘doubt’ element) would be my advice, as it will take but one mishap when used in earnest to destroy any further confidence in the kit you are already clearly striving to achieve.

I’d look upon any additional expense incurred as to be a worthwhile (business) investment in achieving the aforementioned peace of mind. Someone will know exactly why there is daylight or a scintilla of same where there ought not to be, and how best, as well as the next best means of addressing the problem; try to find, or even become that person.

A specialist’s advice is going to be worth more in this matter than encouragement from well meaning but possibly less experienced contributor/s; full disclosure — I know little to nothing about these matters, beyond the general knowledge that anything that involves the mating of bases to curved actions has significant potential for getting it wrong, as well as introducing other critical aspects ie reliance on tiny grub screws, nail varnish, Loctite or similar thread locking compound and perfect mating of machined surfaces of differing origin, even when done correctly, as for example when compared to an action with either machined dovetails of sound design principles (eg Sako, Tikka, Ruger etc, or proprietary solutions such as the Blaser or more recent Mauser solutions.

Best of luck with getting the issue satisfactorily addressed, Tim.

 

[Jagged77]

On the subject of bedding bases, it can be done easily to a high standard using Devcon 10112. I’ve done several R700 rails and providing the clean up is thorough you can achieve a very fine result. Once done loctite blue for the screws (not the most forward screw though if it’s tapped over the barrel threads!).

I would wax the receiver and screw holes with neutral shoe polish, apply the Devcon to the underside of the bases then screw down lightly (coat the screws in wax also). Then clean up with WD40 and ear buds.

 

[VSS]

I mean swap the front for the back and the back to the front rather than the actual mount 180 degrees. My bad English.

That can't be done. The front and rear bases are completely different.

Why not ensure all screw and attachments are now fully tight, then adjust your scope to point of aim then leave well alone.

BC.

That’s basically what I've done so far.

Looking at your photograph it appears that the rear base is not fitting flush to the receiver. You are aware that not all K98 receivers are identical and that a different base may be required.
Even if you have achieved a zero now, that may change if you are simply relying on the screws to hold the base tight as with time and under recoil those screws will slacken off or even shear if the base is not a close fit. I would suggest that when on your travels you pop into Norman Clark in Rugby and either get a proper fitting base for your actual rifle or get the base bedded in expoxy.

Norman Clarke is a good shout. I pass Rugby fairly regularly.

I might be on the wrong track here but looking at the packaging it looks like you have bases for a FN Mauser. You may need the bases for a K98 large ring Mauser.

You're correct.
But the packaging also states that they're P-H compatible.

Looking at the pictured result, without proper mating between surfaces, there is always going to be room there for ‘doubt’, which of course is rather unsatisfactory. Risking a wounded deer-type outcome is never desirable. Peace of mind is a valuable commodity, and there are limits to what we amateur tinkerers can achieve; I see in the scenario the following options:

1) take steps to remove aforementioned doubt, or

2) live with the unexplained shift in POI and ‘hope’ that it does not happen again.

Agreed. That's exactly where I'm at with this.

On the subject of bedding bases, it can be done easily to a high standard using Devcon 10112. I’ve done several R700 rails and providing the clean up is thorough you can achieve a very fine result. Once done loctite blue for the screws (not the most forward screw though if it’s tapped over the barrel threads!).

I would wax the receiver and screw holes with neutral shoe polish, apply the Devcon to the underside of the bases then screw down lightly (coat the screws in wax also). Then clean up with WD40 and ear buds.

That's helpful info, thanks. Bedding it is definitely something I could do myself, before resorting to more expensive options.
I might PM you for more detailed instructions, if thats OK?

 

[Ronin]

On the subject of bedding bases, it can be done easily to a high standard using Devcon 10112. I’ve done several R700 rails and providing the clean up is thorough you can achieve a very fine result. Once done loctite blue for the screws (not the most forward screw though if it’s tapped over the barrel threads!).

I would wax the receiver and screw holes with neutral shoe polish, apply the Devcon to the underside of the bases then screw down lightly (coat the screws in wax also). Then clean up with WD40 and ear buds.

If the bases are correct then this is the way forwards

 

[Dunwaters]

Maybe try shimming the bases to take up the slack?
A strip of aluminium beer can works and is easily sourced.

 

[VSS]

Here are the exact same bases etc, mounted on the previous owner's P-H and shown in an earlier thread.
Thought it might help to show what they look like in situ but without a scope.



I believe that @Gorgon bought them brand new.

 

[VSS]

If the bases are correct then this is the way forwards

Thank you.

 

[Ronin]

Thank you.

This is only if the bases are correct

The bedding will take up the voids

Personally I would obtain another set for Mauser and try those as well

You can’t re radius the existing mount to the reciever without doing both front and rear which will alter the clearance for scope objective and ocular on barrel and bolt when open

 

[Klenchblaize]

Start by gathering the key components but if at all uncomfortable with execution of the process, have a competent person undertake the job:

* Plasticine/Blu-Tack
* Preffred bedding compound. (A two-part epoxy will suffice if you wish to be spared the cost of steel loaded Devcon.)
* Medium grade production paper
* Masking or sparks tape
* White spirit and rag (For de-greasing and cleanup.)

Good luck!

K
Ps: Somewhat ironically, I'm in the process of modifying a set of Mauser 98 bases, using steel-loaded epoxy, to fit a flat bed air-rifle receiver!

 

[8x57]

The photos in post #15 show a commercial Mauser, possibly a FN receiver or a Parker Hale Santa Barbara receiver. Before resorting to the Santa Barbara action Parker Hale used ex military K98 actions. Is your Parker Hale one of these (usually identified by the thumb cut out on the left receiver wall)?

I'm with Ronin "Personally I would obtain another set for Mauser and try those as well".

I think the part number you may need is 52370 and not 50026 that you have.

 

[VSS]

The photos in post #15 show a commercial Mauser, possibly a FN receiver or a Parker Hale Santa Barbara receiver. Before resorting to the Santa Barbara action Parker Hale used ex military K98 actions. Is your Parker Hale one of these (usually identified by the thumb cut out on the left receiver wall)?

I'm with Ronin "Personally I would obtain another set for Mauser and try those as well".

Yes, mine has the thumb cutout.