Home Forums Hunting & Shooting Hunting Optics 'P.O.I.T.' syndrome

Al
I bed under the base even under pic rails, and lap the rings, but have not bedded a scope in lapped rings. Do you see a big difference by bedding the scope?
All my issues have gone away by just bedding the base and lapping the rings.

Al:

Thanks for the answer. The rigs I experienced scope movement in Talley LW on were a Weatherby ULW in 7mm WM and a lightweight 338 Win mag. Both have significant recoil that is very sharp in nature. The scopes involved were Leupold 2.5-8's, so not even as much inertia as you'd experience with the heavier scopes more commonly in use these days.

The light 338 in reference has killed a few scopes and broke a few iterations of mounting/ring set ups. I credit it with greatly enhancing my scope and mounting systems durability knowledge; had to keep researching and trying different things to get something that would hold up on it.

Seems manufacturing processes on guns and scope mounting accessories are getting much better these days. I still check alignment of everything with a lapping bar, but I rarely have to grind anything. I do use a lot more rails these days, which obviously helps with alignment.

Good luck out there. Let us know how the job worked out.

Al:

What type of bedding compound do you use for the bases (and the rings, I assume). Also, if you want to change bases and/or rings (i.e. for a scope change), how difficult is it to break the bedding bond and what can be used to remove the bedding material itself?

So, Al...have you tested the rifle in the OP to verify that the scope mounting was the root cause of the problem?

I guess it depends on how far out the rings are. A quick pass with the lapping bar will give a good indicator of where things are at. l simply bed all the rings at this point. No work and a little bit of time and then you know stuff is right. I'm not much on guessing or hoping stuff is right.

Here's some recent before/afters for example:

Interarms Mini Mauser:









Sako A1 single shot 22PPC:







Kelbly/Davidson BR 3/8" dovetails get the same treatment:

I tested the scope from it on one of my other guns and it checked out fine.

One of my test scopes is on the gun now...just to make sure. Will swap scopes at the range if that looks good. -Al

For bedding the bases, I use Pro Bed 2000. But I've also used other brands in the past with good results. I'd advise not using anything with a metallic component, though. The bases are not epoxied to the receiver....the epoxy simply makes for a perfect mating surface between the bases and the receiver.

For the rings, I like Acra Glas Gel or Pro Bed. Don't use anything too 'hard'...like Steel Bed, for example.

Hope this helps. -Al

Here's the 'problem target' shot after the new scope and mounts were installed.

This is three, 3 shot groups at 200 using the same aiming point (center of target) for all three groups. Everything strung out vertically at random. This is from a gun and load that routinely shoots 1/2" three shot groups at 100 and and a bit over 1" groups at 200 with 180 Accubonds.



With my handmade 150gr. flat based BR bullets, it's scary accurate!

Looks like that rifle's a shooter for sure, Al, but what I'd like to know is whether that second pic is a target shot after working over the mounts and rings...or have you not shot for verification yet?

I'm interested for my own purposes, not to pick nits.

The .253 group is from when I did the initial load workup after putting the rifle together....posted to show that the gun is a known-good rig. My Dakota B-1 150 gr. flat bases are what I use as a 'standard' when initially working with a mid to big-ish .30 cal. hunting rig. If a gun won't show you something with these, it's got problems!

This where I ended with for a hunting load and what's been shot in the gun ever since....180 Accubonds over 61 gr. of H4350 and a Winchester LRM primer. Solid mid -1/2" three shot groups are pretty routine with this load in any sort of decent conditions. This load is what was shot on the 'problem' target posted above.



Will get it out tomorrow and see what happens. Load will be the same 61.0 H4350 and 180 Accubonds.

Good shootin'. -Al

I'm guessing the gun in question is not a really light weight gun.....if it is not why would you run cheaply made aluminum one piece rings and bases on it ?

This morning, the winds were 16-18 mph from the 10 o'clock position with a bit of gusty tossed in. Set out wind flags at 10 and 70 yds. and hung a target at 100. With one of my test scopes on it, a three shot group measured .521.

Took my test scope off and mounted the Swarovski 3.5-18 on it. This was the new scope that was mounted with new rings and bases that led to the issues. I had previously tested the Swarovski on one my own rifles and it performed fine. After bore sighting and a couple to center things up, target #1 was shot. Let the barrel have some cool down time, gave the scope 1 click 'up' and fired target #2.



This is as good as the rifle has ever shot with this H4350/180 Accubond load.

To to close the loop on this, everything is the same except that the scope and mounts have been properly done to ensure 100% contact and to eliminate any stress.

Was this an extreme example? Yes...by all means. But it was as good a time as any to document this approach. Quite honestly, I initially suspected the scope as I didn't see any way the mounting setup could be so bad as to cause that kind of change. No need to name the maker of the bases and rings that were initially installed....they are a quality product. It's a bad mounting job and not paying attention to details that caused this. No doubt the original mounting system, properly done, would have done a very good job.

And things don't have be this extremely wonky to still give problems and give opportunities for improvement. Given that the scope tracks well and holds POI, a rifles accuracy and POI ability to hold zero are all about consistency. For the serious hunter and rifleman, bedding bases and rings simply gives you that extra bit of consistency.

Good shootin' -Al

P.S. The Swarovski 3.5-18 has great glass and big sweet spot of parallax correction. One annoying thing is that the w/e adjustments are close to 1/2" at 100 yds., despite what the turrets say. That's been an Swarovski tendancy on every one of their scopes I've been behind, including a prototype 36X BR scope that had close to 3/8" of movement rather than 1/8".

Again, good stuff Al. Thanks for taking the time to post the info.

Good write up and photos, thanks for taking the time to do this.
I have bedded bases for years and lapped rings but never bedded the scope. Something new to look at.

Early on, I'd bed the scope I was going to use in the rings. As things evolved, I began mic'ing scope tubes and found that 1" tubes ran the gamut from .995 to 1.003. I've since settled on bedding the lapping bar. If you do this and use a bedding compound that isn't too 'hard' (relative term), the scopes rings become universal for any scopes in that family of tube size. That's why AcraGlas Gel is my go-to for bedding rings.

The late Norman E. Johnson put me on to checking tube diameters. At first I was skeptical but after checking a couple dozen I found out he was correct. Norm was one of the first guys doing this and writing about it. His work on this and also on properly bedding the action was very, very helpful to a young guy like me looking for guidance.

Good shootin'. -Al

Al,
Any comments on the practice of using rubber cement inside the rings?

Some good info here.Thanks for taking the time to give us a tutorial!!
Maybe the Bossman could make it a sticky.

I've only done it twice on a couple of bigger guns. One was a .338 Mag. Model 70 and the other as 700 Custom Shop 375 H&H. Both had bedded and lapped Leupold Dual Dovetails and the rubber cement was insurance for slippage since both have gloss Leupolds on them. Neither had issues...which may or may not say anything about the rubber cement. -Al

Thanks for sharing this info. I will definitely start going a little deeper when I’m scope mounting.

Ditto. Thanks Al.