Author Topic: fixing a sloppy barrel/sight dovetail  (Read 11124 times)

4ster

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fixing a sloppy barrel/sight dovetail
« on: December 07, 2012, 08:33:51 AM »
In this instance I have this problem on a modern (well, late 1930's vintage) gun but it could easily be on on a LR during a build if I got too aggressive with a file when cutting a dovetail.  I would like to repair it as a skill building exercise to bank for future LR builds.  The gun is probably not in condition where it makes sense to pay a gunsmith to fix the problem.  But it has value to me since is was my dad's gun.

The rear sight on this gun is like one on a Winchester, where a buckhorn sight is on spring steel and is mated to a dovetail key.  On this one elevation changes are made with a screw instead of a stepped captured slider as on a Winchester.  Windage is adjusted by drifting the sight in the dovetail on the barrel.

The trouble is that if the gun was built with a 3/8 dovetail cut on the barrel, its not 3/8 anymore.  I've tried other sights and they are all loose.  You can tell by inspection that previously someone has tried to remedy this by peening the tops of the dovetail on the barrel, but the gap is just too large to fix this way.  I can see daylight in the dovetail slot and the sight is loose enough to "adjust" with finger pressure only.

I am thinking of soldering a sheet metal plate to the bottom of the sight using some steel banding in my scrap pile and low temp solder.  I could then file this to fit the dovetail on the barrel.

Is there a forehead slap solution I'm not thinking of?


Offline KLMoors

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Re: fixing a sloppy barrel/sight dovetail
« Reply #1 on: December 07, 2012, 02:50:47 PM »
I was thinking of the shim method you mentioned. This is assuming that if you slide the sight into the dovetail, you can't lift it straight up and out.

Another possibility- really good welders can weld amazingly small pieces without damaging them. You might have somebody add some material to the sight base so you could file it back to fit.
« Last Edit: December 07, 2012, 02:51:10 PM by KLMoors »

Offline Chris Treichel

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Re: fixing a sloppy barrel/sight dovetail
« Reply #2 on: December 07, 2012, 03:46:12 PM »
Why not just make a new longer/larger base for the sight? 

4ster

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Re: fixing a sloppy barrel/sight dovetail
« Reply #3 on: December 07, 2012, 04:05:39 PM »
Why not just make a new longer/larger base for the sight?  

This one is all one piece.  I do have another sight that is two piece and the leaf spring screws into the dovetail key, but it has other issues.  The gun hits point of aim with this one when the sight is in the right spot.  

I hadn't thought about putting a spot of weld on the bottom.  I don't know if I have the dexterity and skill to do it with my equipment but I have a local shop that could do it.  

However, I don't think an eighteenth century gun smith had access to TIG welding equipment.  I am asking what a period gun smith would have done here.  (That keeps this question relevant to this group.)
« Last Edit: December 07, 2012, 04:12:01 PM by 4ster »

Offline rich pierce

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Re: fixing a sloppy barrel/sight dovetail
« Reply #4 on: December 07, 2012, 04:26:05 PM »
Pretty sure the 18th century gunsmith would just make a new sight.
Andover, Vermont

Offline TMerkley

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Re: fixing a sloppy barrel/sight dovetail
« Reply #5 on: December 07, 2012, 04:29:31 PM »
A period blacksmith solution would probably do as they call "upsetting"  where the pieceis laid on it side and struck with the hammer which will cause the metal to push up an down rather than flatten out.  It would not requre alot.  Strike one side then the other to keep it even.  It will still require some touch up filing to keep it looking nice.  It may work and then again, It might make it look like a ten year olds repair.  The other option is to strike the dovetail downward with the flat edge of a screw driver and then "stake the corners in place around the sight.  Then dress up your marks with a swiss file.  Not sure if this has been done already as you said it had been peened.  

Just an idea.  I have tried stuff like this in the past usually it works.  Play with another piece to practice first.  

Offline Long Ears

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Re: fixing a sloppy barrel/sight dovetail
« Reply #6 on: December 07, 2012, 06:29:10 PM »
I'm with  Rich on this one. A PC 18Th century gunsmith would make a new non adjustable sight in an hours worth of work with a file. He wouldn't have to worry about the little Leaf Spring like on a Winchester. However it sure is nice to make those rear sights on my mill! :D

Offline Jerry V Lape

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Re: fixing a sloppy barrel/sight dovetail
« Reply #7 on: December 07, 2012, 07:13:24 PM »
I think starting with your suggestion to silver solder a shim to the existing base and then filing to fit would be the first thing to try.  If it doesn't work you can remove it and try the welding suggestion. 

Offline kutter

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Re: fixing a sloppy barrel/sight dovetail
« Reply #8 on: December 08, 2012, 12:45:41 AM »
I've fix a lot of loose sights by using a shim made from a piece of discarded hacksaw blade.

Heat the blade first to get rid of it's temper so you can work with it easier.

I make the shim to fit one of the sides of the dovetail,,not onto the bottom of the dovetail base.

If you put a piece onto the bottom of the dovetail base, it pushes the entire sight upwards. If it's quite loose to begin with, it can look kind of odd with the leaf sitting far up and off of the surface of the bbl flat.
If you're working with a rear sight style that doesn't have a leaf extending back, or a flat portion that needs to sit flat onto the bbl, it's really not an issue however.

The tiny shim to fit the side of the dove tail is filed out but not cut off of the hack saw blade, Makes handleing it easier.
Clean up the bbl dovetail (both sides) for a fresh start and then trim till the sight base along the shim can be barely  knocked into position on the bbl.
You'll have an easier time pushing the sight in from one side and holding the shim in from the other as the long 'handle' of the hacksaw blade won't be in the way.

When it ready to go,,soft solder tin the shim and sight base contact surfaces.
Use a soft lead pencil (graphite) to coat the surfaces on the shim, the sight and especially the bbl dovetail itself that you don't want solder to stick to.

A tiny touch of flux to the surfaces to be joined,,,hammer them into position in the bbl dovetail itself.
When your satisfied that the shim is positioned right and it should only go in one way if it's tight,,sweat solder the two pieces together right on the bbl.

The pencil graphite will keep the assembly from soldering itself to the bbl and solder from creeping up onto the sight itself.
When it's  cooled off. Tap it back out of the dovetail, cut the excess shim off and file to contour.
Cold blue or brown to match. Clean up any residue on the bbl surface and reinstall the sight.

That's pretty much a permanent fix to the problem. I've seen many fixed using the same idea but the shim is just driven in along with the sight and trimmed off. Nothing soldered. That'll usually hold too, but will move with windage  sight adjustments and may not return with the sight if it's wacked in the other direction. Many are crude repairs to say the least, done after the obligatory hammering of the dovetail edges and usually some burrs turned up in of the bottom of the dovetail.

If the dovetail is just totally trashed and oversized, the entire area can be cut out squarely and a new piece soft soldered in place. The new tight fitting dovetail then cut in that piece. The newly inlaided piece does not have to be overly large, just enough to remove the damage. The rear sight often covers  solder joints from above and the any joint on the sides are up high enough so as not to be so noticable around the sight. 50/50 or 60/40 lead solder will darken with age anyway and a nice tight sweat solder fit will help matters from the start.
« Last Edit: December 08, 2012, 12:51:44 AM by kutter »

Offline rsells

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Re: fixing a sloppy barrel/sight dovetail
« Reply #9 on: December 08, 2012, 09:29:09 AM »
I have an original half stock in my shop now for stock repair that has the rear sight dove tail tightened up like Kutter suggested.  The smith made a shim to set against the side of the dove tail to make the fit tight.  The old guys had to deal with the same issues we do today.
                                                                            Roger Sells

Offline Pete G.

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Re: fixing a sloppy barrel/sight dovetail
« Reply #10 on: December 08, 2012, 04:43:58 PM »
I have put a cold chisel just aft of the slot and give it a whack. That will upset enough metal to tighten the slot and it leaves a "decorative" molding line behind the slot. Looks like it was filed in on purpose.

caliber45

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Re: fixing a sloppy barrel/sight dovetail
« Reply #11 on: December 08, 2012, 07:38:09 PM »
A quicker fix (though not historically correct) is three or four layers of heavy-duty aluminum foil, unless the gap is wa-a-a-ay deep.

4ster

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Re: fixing a sloppy barrel/sight dovetail
« Reply #12 on: December 09, 2012, 03:45:06 AM »
Hey, thanks everyone!  I haven't decided yet which way I'll skin this cat.  This helps a lot.

tyro

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Re: fixing a sloppy barrel/sight dovetail
« Reply #13 on: December 12, 2012, 05:15:17 PM »
another way is to take a prick punch and raise a couple lines of metal or a square in the bottom of the dove tail or on the bottom of the sight base and this raised metal will hold it tight enough to keep your shots all in the V ring... adjust gently with file as always when installing..TY

Offline Dphariss

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Re: fixing a sloppy barrel/sight dovetail
« Reply #14 on: December 12, 2012, 05:31:03 PM »
Pretty sure the 18th century gunsmith would just make a new sight.

Depends on how loose the sight is and what the sight base is like.
Is is possible to pean or otherwise make the sight large enough?
The BEST way is a new sight then set the other one aside for another rifle.

Dan
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tyro

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Re: fixing a sloppy barrel/sight dovetail
« Reply #15 on: December 14, 2012, 06:50:09 AM »
something i didn't think about til just now..you can flip the sight over , clamp it in your padded vise and drill a blind 1/16"hole in all four corners of the sight base fill them a little proud with soft solder and tap it into the sight dovetail it should trim the solder dots flush as you tap...you describe the looseness as "loose enough to adjust with thumb pressure" so peening the base or raising metal with a punch should do the trick, but if it's too lose for that this may work and you cant see it once it's installed..TY