# Lapping aliminium.



## Fat ferret (4 Nov 2016)

Hi all. Bit of an odd one but maybe someone can help. Not a usual topic on here but it's still metal working. Will try to explain clearly for those not familiar with rifle shooting.

I am trying to zero an air rifle. The pellets strike the target low and the scope has run out of "up" adjustment. I want to try adjusting the scope mount which looks like this. 

https://www.google.co.uk/search?q=s...S7AOIQ_AUIBygC&dpr=1.55#imgrc=Hk_-YHpdOcSitM: 

I know I could end up wrecking the mount but want to try anyway.

My idea was to get a piece of 1" round steel bar, same diameter as the rifle scope. Jig the bar so it is rubbing against the front cradle of the mount and apply some cutting paste and rub the bar back and forth over the scope mount thus wearing away some metal mostly from the front cradle and a little from the back cradle. This will make the scope look "lower" where the pellets are striking. 

I know there are other answers like shimming the rear cradle, which I have tried but still not enough. Adjustable mounts are available but for various reasons I don't want to use them.

If you didn't understand don't worry, you can still help  . I need to know what lapping paste to use on the aluminium to cut it slowly that will work in conjunction with the round steel bar. 

Thanks.


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## woodpig (4 Nov 2016)

As far as I am aware what you suggest is exactly what some folks do in America on Full bore rifles. The only grinding paste I've seen commonly available is the stuff used for lapping inlet and exhaust valves for engines. This comes as a double sided tin with coarse paste one end and fine the other. This should be ok for the job I would have thought but it may take you a while. Halfords or other motor factors should still sell it, they used to. If not, I have some aluminium oxide blasting powder I could send you but you'll need to mix it with some grease or something. Not sure how well that would work.


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## Harbo (4 Nov 2016)

You could also wrap some coarse wet and dry paper around the steel rod.

Rod


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## woodpig (4 Nov 2016)

That would work Rod but the thickness of the paper means it could cut over size a little on the width unless you're careful.


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## novocaine (4 Nov 2016)

don't remove material, add it, by removing material you will induce other errors as you enlarge the clamp including bending the scope. use film as a shim on the rear mount, you can also us beer tins if you don't have film. if a shim isn't enough then the amount of material to removed is going to be the same and you'll have to take off a large amount. what happens if you turn the mount round?
as you've normally got about 18" of adjustment in a scope at 30 yards I'd suggest you need to look at what the issue is, as it's striking low it sounds like you are underpowered but it maybe that mount isn't sitting flush on the dovetail, hence turning it round. you can also shim under the mount on top of the dove tail if need be.


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## Fat ferret (4 Nov 2016)

Hi woodpig found the American sites but I note the special bar costs $50 and I would need to import one. I see your valve grinding paste on Ebay and it's around £5. Don't mind if it takes a while as I don't want to grind too much. Should work. Thanks very much.

Harbro I did think of that but unless I use an undersize bar it will be oversize. Thanks anyway.

Novocaine I am not underpowered the rifles running at 24ft/lb on ticket. Recoil is not bad but noticeably more than a 12ft/lb rifle. I can't turn around the mounts as they have an arrestor at the back that fits into the rifles dovetail stops. I can't buy an adjustable mount as I can't find one that fits my dovetail stops and want these to cope with the recoil. I have tried shimming the rear mount but still not enough. At 30yards I am just about have enough adjustment with some pellets I tried but far from ideal. If I shim any further I think I will run into problems with bending the tube. The problem is caused by the barrel pointing down but the lock up is solid. The barrel is not bent it's the breech causing the droop which is common enough even with top brands like hw.

I understand what your saying about other errors but have thought of this. My jig will mean the bar starts grinding at the front edge of the front cradle and I will slowly remove material until I have removed a small amount on the rear cradle and a little more of the front one. I only anticipate removing maybe 1mm from the front of the front cradle tapering to almost nothing from the rear of the rear cradle.
So the mounts should slope down. Then I can screw on the tops of the mounts. If the front one wont tighten up I may need to file it's feet very slightly. There is enough play in the screw holes that the top part wont bend the tube if I'm careful.


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## woodpig (4 Nov 2016)

Silver steel rod is accurately ground to size so you could use that. Shouldn't cost more than about £20 for a 1 inch diameter rod.


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## Rorschach (4 Nov 2016)

If you can't fix it by adding a 1mm shim at the back, then you won't fix it by filing away 1mm at the front.


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## woodpig (4 Nov 2016)

Lapping has been an excepted way of doing it for many years and won't risk bending the scope if done correctly, especially on a one piece mount. Adding shim material on the other hand is not a good method and can result in a bend if you're not lucky. The alternative is an adjustable mount.


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## Fat ferret (4 Nov 2016)

Agreed, I have already shimmed as much as I dare and it's still low. 1mm is too much to shim whereas I could lap as much as 2mm off and not compromise the mount or scope. 

As woodpig stated the alternative is an adjustable mount but I can't get one that fits my rifle properly and don't trust it not to adjust when I don't want it to.


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## monkeybiter (4 Nov 2016)

Have you tried different diameter pellets, you can get [as you probably know] different sizes within a nominal calibre, the difference in performance can be quite stunning.
Another thing to consider is pellet weight. Lighter pellets will get to the target quicker, before they've had chance to fall as far from the aim point.
Many years ago I had an unexpected drop from aim which turned out to be the scope drifting rearwards due to recoil and causing deflection of the rear mount [solved by an arrestor] perhaps your rear mount/arrestor could do with a check?

If you do end up altering your mounts, I would suggest doing a calculation first based on the discrepancy in aim/impact with the scope centrally adjusted to give you an idea of the amount to be removed, you could then remove the majority with small files before lapping in.


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## Fat ferret (4 Nov 2016)

Hi Monkeybiter, using a one piece mount with arrestor built in and not shifting.

Yes I'm working my way through all the common pellets. Can't shoot lightweights but middleweight JSB's are the best so far with 1 1/2" 10 shot groups at 30 yards which isn't too hot but hoping this will improve as the rifle beds in. With these pellets I am just able to aim dead on but right at the edge of the scopes adjustment which isn't good. 

I know I could wreck the mounts but don't mind taking a chance. Will buy some paste and give it a go. Thanks all.


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## Inspector (4 Nov 2016)

My very limited experience with lapping has the compound imbedding in the softer material and wearing the harder. I would think the aluminum will pick up the abrasive and wear the steel bar unless the bar is softer. Am I out to lunch?

Pete


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## woodpig (4 Nov 2016)

Some useful information here on lapping Alloy scope rings.

http://www.24hourcampfire.com/ubbthread ... /3645701/2

I've done it as well and it does work.


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## novocaine (4 Nov 2016)

Well as you are set on doing it (not trying to be insulting) then use a wooden dowl and put the top clamps on. You want the same angle on those as the lower. Lapping paste, id use 220 grit to remove material then 600 to finish. bore lapping paste will be fine. Not a fun job and one ive only had to do once because of a bent barrel (note, never let a friend borrow anything). You are right not to shim more than you have although id be tempted to do both to save on work required. nothing wrong with film shims, its how we were taught to do it.


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## Walney Col (4 Nov 2016)

woodpig":2p4wyjpq said:


> That would work Rod but the thickness of the paper means it could cut over size a little on the width unless you're careful.



if you want to lower your front mount (say 0.02") then take your 1" bar and turn or emery it down to 

1" - 0.02" - the thickness of the wet and dry you're going to lap it

with and you'll still have a 1" diameter mount when you've finished.

Col.


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## Eric The Viking (4 Nov 2016)

I'm amazed: If you've already shimmed it and it's still off, something else is (seriously) wrong, especially at that power -- the trajectory should be relatively flat. Have you got any idea why it's so badly off?

E.


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## Fat ferret (4 Nov 2016)

Inspector, you may be right. If I use a wooden dowel it should work as the dowel would be softer.

Novocaine, your not insulting. I'm set on doing it because I can't think of anything else to do. I can't shim any further. I could buy an adjustable mount for £30 but it wouldn't fit my arrestor slots so would need a separate arrestor block. Would rather try modifying what I have. Don't think you will damage the scope unless you over tighten. 

On another note a friend had a long barrelled HW35E which was bent down. I solved the problem for him by bending it up. It was a 15mm barrel in 22 so not a great amount of metal and I just took it off the gun and bent it over a padded sawhorse. It was still very accurate.

Anyway lots to think about. Thanks all.


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## Fat ferret (4 Nov 2016)

Wayney coll, could do that. Might work better with a wooden dowel which is the option I'm leaning towards.

Viking, its a break barrel. The barrel points down in relation to the cylinder where the scope is mounted. Not by much but it's noticeable and makes all the difference at longer ranges. The breech lock up is solid just points the barrel down slightly.


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## woodpig (4 Nov 2016)

Get yourself a nice PCP. :lol:


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## Fat ferret (4 Nov 2016)

Heathen! :x


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## novocaine (4 Nov 2016)

Thats what I did woodpig. lol love my wobley rider. Love my bsa airsporter too though, different horse for different course)
You want a skinny barrel try a crosman 1077. Like a peashotter. Clad in a curtain rail. You could bend it over your knee. Waste of space chunk of plastic. It didn't last long with me, was only bought for a laugh. Wasn't funny. Do have 1 plastic gun still but thats a joy to use. 

Have you changed the breach seal? I've seen where a new seal makes it all feel solid but drops the barrel considerably because its not seated or to fat, often becuase its an old rifle with a modern metric seal in it). A light skim with an emery board to flatten the top was all it took to sort. (fairly sure it was a webley, cant remember)


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## woodfarmer (4 Nov 2016)

There are a lot of issues here. My feeling is the break lock may just be pointing too low instead of straight. if the rifle is under warranty may pay to take it back and compare it with another.
From there get it chronoed, as [power might be down. You could also try a lighter pellet as it will be faster.
also, maybe try turning the mount end for end.
as a last resort, bore the front mount ring say 3mm and have a bush made with the hole eccentric. the bush could be made from a bit of industrial black plastic such as acetal or nylon.

hope this helps


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## Harbo (5 Nov 2016)

What rifle is it and if you are breaking it in it must be new.
Also at 24ft/lb that's a powerful gun for this country - needs to be licensed


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## monkeybiter (5 Nov 2016)

Fat ferret":hceigd4w said:


> the rifles running at 24ft/lb on ticket.


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## woodfarmer (5 Nov 2016)

Fat ferret":3utaltcv said:


> Hi woodpig found the American sites but I note the special bar costs $50 and I would need to import one. I see your valve grinding paste on Ebay and it's around £5. Don't mind if it takes a while as I don't want to grind too much. Should work. Thanks very much.
> 
> Harbro I did think of that but unless I use an undersize bar it will be oversize. Thanks anyway.
> 
> ...



Sorry I did not see this post before I wrote my previous answer...


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## Fat ferret (8 Nov 2016)

Gave it a go.

Shot a group at a 10 meter target with the scope optically centred. 4" low and 1" to the right. 

Got a fine file and filed a bit off the front cradle. Then used a 10" strip of 120 grit wet n dry wrapped round a length of 20mm copper pipe to smooth it off front and back twisting it round and round in the mounts. Remounted scope and the group moved an inch up. Repeated a few times and when it was an inch low I used some 240 grit wet n dry to finish it off. Had to file the front cradle arms slightly too. 

Mounted scope is now shooting groups on target well within it's range of adjustment at 30 yards. The mount and scope tube meet up perfectly well.

Bit extreme but I now have mounts that have the arrestor system my rifle uses and look downwards a bit too. Not particularly difficult if you take your time. Thanks for all help and suggestions.


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## monkeybiter (8 Nov 2016)

Excellent result, well done!


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## woodpig (8 Nov 2016)

Nice job, glad it worked out ok. ccasion5:


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## novocaine (9 Nov 2016)

excellent. obviously without pictures it didn't happen, but we'll believe you this time.


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## Fat ferret (9 Nov 2016)

Did think of taking pictures but really not very exciting. Scope in place it looks like an ordinary scope mount. 

Never lapped anything but as I removed around a mm of metal it would have took a while if I had .


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## novocaine (9 Nov 2016)

was more interested in seeing the grouping to be honest. lol


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## Fat ferret (9 Nov 2016)

Still searching out pellets as it's a bit more choosy being FAC power. Best so far are JSB, 1 1/2" @ 30 yards. Going to try JSB heavy which are 18.2 grain and have some on order.


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## novocaine (9 Nov 2016)

have you tried crosman premier ultra magnums, they are a heavy weight pellet that should suit (think a .22 is 14.3 grain so not as heavy as the JSB). nicely pressed without any flack, I use them in .177 (10.5 grain) and they've suited everything I own excluding the airsporter (not enough punch for weight). I like them enough to have bought 2 boxes of 1250 pellets instead of in tins.


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## Fat ferret (23 Nov 2016)

Ok here's a 45 yard 10 shot group of JSB exact 5.52. 9 shots went into 3/4" one had to go and spoil it. Could have been a damaged pellet, bit of lube burning off or just operator error!

[url=https://flic.kr/p/NiUdMx][img]...com/6/5573/30394980593_385c360494_m.jpg[/img]DSCF5393 by fat ferret, on Flickr[/url]

Zeroed at 30 yards shooting bang on target with plenty of adjustment left. I shot groups from 10 yards out to 45 to get an idea of trajectory now the gun is shooting at 20ft/lb. Shoots flat to 35 yards an inch low at 40 and 2" low at 45. Nothing comes close to JSB 5.52 for accuracy.


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## Wildman (23 Nov 2016)

Fat ferret":hk0yiuq2 said:


> Hi all. Bit of an odd one but maybe someone can help. Not a usual topic on here but it's still metal working. Will try to explain clearly for those not familiar with rifle shooting.
> 
> I am trying to zero an air rifle. The pellets strike the target low and the scope has run out of "up" adjustment. I want to try adjusting the scope mount which looks like this.
> 
> ...


the easiest way is to just shim the scope mount. A cigarette paper is .0015 thou, (1 1/2 thousandth of an inch) maybe try a sliver of a coke can first. Save the accuracy of the mounts.


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## monkeybiter (24 Nov 2016)

Wildman":36b6lfdp said:


> A cigarette paper is .0015 thou, (1 1/2 thousandth of an inch) maybe try a sliver of a coke can first. Save the accuracy of the mounts.



0.0015" = 1.5 thou. Sorry, I can be a pedant at times.


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## Fat ferret (24 Nov 2016)

Wildman, In my original question, which you have quoted, I said I had already tried this but it wasn't providing enough adjustment. I don't mean to cause offence by pointing this out but maybe you should read the thread if your interested? Then again I doubt you have read my response so hopefully no offence will be taken.


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## novocaine (24 Nov 2016)

JSB are a mighty fine pellet and you only go to prove that. 
I found that the s200 was picky about them though and would occasionally send a flyer, where as with the crosmans both the AA and the wobley were happy as larry. I'm putting the exacts through the airsporter at the moment, waste not want not.  everyone has there preference when it comes to pellets. (the hw40 is a picky little thing but then it's only got a tiny barrel)

not a bad grouping you've got there, as usual though, 1 has to go and spoil it, only takes one breath and off it goes.


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