A guide/warning on used scopes.

 I’m taking the time to write this because I care about this sport. 

I see newcomers confused & give up. I see highly experienced firearm folks laugh.

I’ve seen guys that understand math, physics, firearms more in depth than I do not understand this test. I learned from reading EVERY post YRRAH in OZ ever wrote. All of R. Sterne’s posts, though I admittedly don’t comprehend it all. Most of all I learned from typing one word into a search & reading for days on that subject. Also anyone else who’s proved they can shoot better than I can by holding off & over. I do NOT click. I zero for a given distance. 20-32 for 8-12 ftlb .177 springers. 32-38 yards for mid power spring or PCP, & as far as 60 to 100 for higher power air guns. The furthest I’ve ever shot a PCP is 316 yards. Ever notice changes in POI from a PCP in no wind at close to far? Yes, cant is to be taken into consideration but let me start with my main problem of “LNIB” used scopes.

When you 1st get a scope of decent quality this is what you should do before buying if possible. Get a 2-3” compact make up mirror depending on bell size or if scope isn’t mounted (better because torque, not a true bend could be at fault) you want to go to brightest lit mirror in home. 

A scope bell end should be truly flat. If you have filters, honey comb, anything like such on bell, take off. Turn magnification as low as possible. Turn AO, adjustable objective if on scope to ♾ infinity. Now, place bell flat against mirror & tell me what you see. What you normally SHOULD see is a reflection of your reticle & a COMPLETE FULL CIRCULAR VIEW OF BELL! If you see 1/4, 1/2 of a bell ocular ⭕️ circle, your scope tube is most likely bent. Over tightened, torqued beyond specs, & most likely not repairable by most. If you see anything along these lines, it’s bent.🌙 

Now, if you see a perfect circular view with reflection of reticle, GREAT! Chances are you’ll notice the reticle is not in-line with its reflection. Adjust turrets to do this so you see ONE reticle. Perfection is reached when reflection is hidden behind the actual crosshairs or etched glass image. That is called optically centering your scope & very few I’ve ever tested are perfectly aligned along with dividing your click range in half. In fact you should try that & compare the calibration. A good 100% tracking scope can be clicked until the 🐄’s come 🏡 but I, am NOT a clicker. I will rezero if need be for extended range but I usually have everything set so I can simply adjust to lower magnification with 2nd FP scope & use more hold over. I don’t like shooting on high magnification unless I’m in a gun vice F-Class rest, lead sled, bags. Even a bipod, breathing, your pulse makes your reticle jump around at higher powers. I honestly shoot better than most people I’ve shot with at ranges when I use fine buckhorn sights, or scopes that are at 1-10x, preferring 6x the most & with Diabolo pellets going beyond 150 yards I must use 3-4x to even have enough holdover & 🎯 in sight.

Now do us all a favor. IF you’ve taken the time to read this, then test a, or all scopes & please report back as to what you’re findings are. I’ll cover adjustable rings, shimming properly & setting a scope up correctly at next step should their be inquiries of interest. I’ll give you some hints.

Most guys new to air gunning over tighten their rings & ruin their own new scopes. You don’t use the long part of Allen wrench for massive leverage. You shouldn’t have to tighten rings beyond inch pounds if proper procedures are taken. This is PCP’s we’re talking about. Not springers which require more preparation, scope stop pin, buffer, a quality one piece adjustable mount like B-Square, 90% rubbing alcohol on dovetail, possibly preparation of mating surface with 1200 grit wet/dry sand paper & for goodness’s sake quality scope friction tape. Shims, inch pound wrench, feeler gauges are your best friends as is a indoor bench with the right color, thickness string, and background contrast. You’ll also need quality torpedo level & several calibrated tiny bubble levels out of their holders. They should roll across glass silently. You may have to clean, prep them also. Perfection isn’t quick but let us hear how many bent scopes you’ve bought first. 

Thank you if you’ve stuck with me over the past 12 years & if you’re a friend, let’s build this forum into the best it can be. I know there’s some here from older forums that I know but I may not know your handle here. That being said, The Enoch Brothers just were spoken of highly to me last night by a long time collector & I agreed I miss David’s contributions & his Brothers machining skills.

Be safe & be blessed. Let’s hear about your scopes true condition & see if we can’t get you newcomers fixed up so you don’t give up. The pay off in trigger time is priceless. 
 
Thanks for the post-It's very timely as I seem to be noticing a change in POI from near to far with my used Aeon scope. In addition to the POI shifts I notice another POI shift when I dial down to low power for offhand shots. I will get my mirror out and try your diagnostics on it.

I personally find if I'm changing from high to low magnification that I need to decrease my hold over to hit on target.

I recently ran across this long range shooting video on Youtube and found it helpful-my Aeon passed the tall target test when I held over with the reticle.

https://www.youtube.com/watch?v=12Wf0Cuwwi8

Regards,

John
 
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Note a feeler gauge is used to evenly space ring gaps when tightening. The top picture may require several stacks of feeler gauges & not all scopes have flat bottoms but as shown, it can be confusing as it’s not true according to feeler from mount to scope bottom. What is true is a level on that springers barrel block & matching crosshairs to free hanging plum bob. 
 
James, really good write up. As far as feeler gages go in the application of checking the gap between top and bottom rings, is .010 the typical gap? If not, what is the rule of thumb, besides using math along with calipers, in using feeler gages to make sure the gaps at each side are even? 

Or are you using this gap as a form of “torque to” ?
 
It’s normal to have to hold over more or less with magnification changes & a 2nd FP scope. 

This is a big reason FFP scopes are more popular now among air gunners. I like them, but the reticle is too small for me to split it into 1/4’s let alone 1/10 mils when on 1-4x.

Another thing I’m gonna point out is a rock solid gun vice is as important as a chronograph. An etched glass reticle is a big help. If you’re in a good gun vice, and can see your reticle move off target when you adjust the front AO bell, side focus, or eyepiece (I see that one move A LOT of the time) then it’s time to either buy new scope or set and forget until you can buy a better scope. 

Look at scopes like Leapers, UTG, CenterPoint. Great for springers. I suggest setting eyepiece so reticle is clear as day as soon as you look. Not wait for eye to try & focus on 3 different things. Set it, don’t move it again. I’ve seen scopes with threads, must be close to 72tpi for eyepiece. They, aren’t going to move on you. I still prefer etched glass but; I recently found a guy who restores old scopes to factory condition including Nitrogen 
 
Hey B.R.,

I wouldn’t say 0.010” is a standard in gap of top/bottom ring at all. Some rings will have no gap at all and not be over tightened. Some rings could use a lap job. Some rings may seem to need a lap job but scope tube just isn’t true.

Manufacturers have specs. Good luck getting an engineer on the phone that knows and forget asking a certain company called Remmy, Worthington? Something like that. 

Midway sells a good ring lapping kit, inch & ftlb torque wrenches & screwdrivers, all good gunsmith tools you could ever need. 

I recently got a John Thomas tuned HW30. He’s started using some type of very sticky Vibra-Tight or Loc-Tite. I’m not sure what it is but the rings weren’t overly tightened, that stuff works great though as I can see it stopping any walking/backing out.

Your question to 0.010” being standard, no. Center & level as described. Once that’s done tighten down both sides as equally as you can. Start at back ring. If you have a 20moa rail & rings that don’t tilt do NOT try to get front flush tight. Do back first & front second only tight enough to hold according to manufacturers specs and REMEMBER these rings if not for air guns maybe going off of recoil from a 06 or bigger. No need at all for that on a PCP. 

Just center & level. Tighten with a vibration tite thread locker just enough so it stays put. I’m personally not picking any rifle up by its scope.
 
I have a .270 with a 2.5x8x40 Bosch and Lomb scope, and I noticed the higher the power on the scope, the higher the bullet went over the aiming point. 4x was about 3” over and 8x about 7 or so. I zeroed it at 100y on 2.5 (it shoots 1cm under a real tack, I used it to see true bullseye at that distance). On 4 it hit a quart beer bottle at 200 plus yards.

So I thought that’s how it worked, use the magnification to move the bullet up for longer ranges. Now I think my scope is bent in the best way possible. I wouldn’t change it, it never misses. 
 
Mr james and I may not see eye to eye on clicking vs holdovers (I personally don’t give a poop about optical center as I like to click).

But he taught me the mirror method and it is a VERY good thing to check on every scope (new/used) and will tell you alot about the quality/condition of the scope.

thanks for the write up james, very nice

https://m.youtube.com/watch?v=3L4eO16rKvQ

You’re absolutely correct about not using hold over when it comes to certain types of shooting. I, don’t participate in any of those types. Thus no need for top tier glass as I’m not hunting in low light conditions, nor will I ever shoot even the custom .243 or .257 I build past 500 yards at absolute maximum. That would actually be pushing it for me. 

When I do get it all done I basically wish to be able to know what power my mils are absolutely true at. Then set it somewhere so I can simply divide 6’,12’,18’,24’ and that’s about as far as I’d ever care to plink. Don’t want any expensive 300-600moa riser or Ivey rings. 

If I WERE actually shooting for a serious group at say 300 yards, yes, I would definitely zero my scope for that exact distance. It’s just with what I shoot the most, 18.13 & 22.14 Baracuda Match 5.52 I know the drop and landmarks from my bench. Competition, hunting, unfamiliar ground or any target over 100 yards with more than a 3* angle, I’d be missing. 

I hope I didn’t break any rules by linking this fellow but like I tell them, Airguns can teach you a lot. Well so do good sites like Rimfire Central & LRS. Good bunch of guys and I’m mainly there to learn what I can with slugs at long range in sub sonic range. 
 
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JamesD.,

I'd like to do your mirror test with a scope I'm having suspicions about -- however, I don't seem to understand how to do this.

If I place the scope objective against the mirror, all I see is BLACK, because there is no light between the objective and the mirror -- the objective sits on the mirror not letting any light in.

So, plz, help me out here, how can I do this mirror test? 😊

Thanks,

Matthias
 
James, really good write up. As far as feeler gages go in the application of checking the gap between top and bottom rings, is .010 the typical gap? If not, what is the rule of thumb, besides using math along with calipers, in using feeler gages to make sure the gaps at each side are even? 

Or are you using this gap as a form of “torque to” ?

Your question of the feeler gauges.

I would say once all is level you torque all down evenly to snug but not torqued.

I wouldn’t tighten the back to torque specs, then the front. I’d try to torque evenly.

A PCP needs hardly any pressure at all. A springer is going to. Any variation in dovetail, rings, scope tube, or torque on any screw will change things ever so slightly. The slightest difference in face/eye placement, cheek weld, could equate to 1/4” variations at even 30 yards. 

Add ammo variation, temp, reg, all things and tolerance stacking can soon make a sub .5 moa gun a 1.5-2 moa gun. 
 
Thanks for the tips. One of the best tools I’ve purchased since being introduced to better scope is the Wheeler torque wrench. I tighten the screws as per the manufacturer specs for the rings.

Very good purchase. Most common 1” & 30mm rings are tightening down to foot inches, not pounds. 
A great solution I’ve seen for springer rings and screws is PTFE anti seize. That thick hoop kills vibration of them working their way out.