Max Dovetail depth on colerain 58 round bottom groove near breech

[HighUintas]

I'm going to put a dovetail near the breech of my 58cal colerain round groove barrel (1" across flats) for a peep sight. I'm wondering on max depth that would be considered safe.

0.580 bore / 2 = 0.290
0.016 groove + 0.290 = 0.306
0.500 half bbl diameter - 0.306 = 0.194 wall thickness

The dovetail of the sight I'm using is about 0.098 tall, which is how deep I'd need to make my dovetail if I want the sight to sit flat on the barrel.

As long as I'm in front of the breech plug threads, that would leave me about 0.096 barrel wall thickness.

Does my math check out and is that an acceptable wall thickness at the breech?

I can't remember what the breech thread max diameter is, but I'm thinking I would want to stay in front of that because I wouldn't have enough barrel wall material there, correct?

[rich pierce]

In my thinking the area of the barrel surrounding the breechplug is not under radial pressure so should be as safe a spot as one could find for a dovetail. Could be wrong.

[smylee grouch]

A 1" bore - .580 = .420 over 2 for .210 I think. Better check my math. 

[bluenoser]

Not addressing the safety question, but .098" seems to be a rather deep dovetail.  Could you not remove some material from the bottom of the dovetail on the sight to reduce the depth and then cut the dovetail in the barrel to match the now narrower sight dovetail?

[HighUintas]

In my thinking the area of the barrel surrounding the breechplug is not under radial pressure so should be as safe a spot as one could find for a dovetail. Could be wrong.

That's a good point. The thinnest material left if done over the plug threads would be 0.030 and would only be at the very top of the thread arc. No radial pressure and I would think that it wouldn't severely weaken the threads to a point of safety risk.

[HighUintas]

Not addressing the safety question, but .098" seems to be a rather deep dovetail.  Could you not remove some material from the bottom of the dovetail on the sight to reduce the depth and then cut the dovetail in the barrel to match the now narrower sight dovetail?

Yes I could! But was sort of wanting to keep the sight unmodified in case I don't like it an want to sell it somewhere down the line. But, I'd rather lose the money on that sight rather than risk my safety or screw up my barrel.

[Jim Kibler]

Cut the dovetail base down as suggested. Half the current thickness would work.

[Bob Roller]

The safety of any cut in a barrel like this is determined by what the barrel is made from and the intended loads and projectiles,ball or hollow base bullets.My first muzzle loader was an octagon 58 caliber barrel an inch across the flats with 8 grooves and a 1 in 44 twist.It was made from 1144 which is NOT certified for any gun barrels and the sight dovetails were .060x3/8 done with a milling machine.This barrel was the FIRST one Bill Large made in 1958 when he got his much bigger shop started.He gave it to me and it was a match and turkey shoot winner.
65 grains of DuPont or King's Mills powder and a .575 soft lead ball patched with surplus cleaning patches for the M1 Garand.
Bob Roller

[HighUintas]

That's a good point, Bob.

I don't know what the barrel steel is. It is whatever colerain has used the last few years.

It's a 1:66 or 1:70 58 round ball barrel. Hefty charges of 2f

[B.Habermehl]

If the sight base dovetail is not too wide you can inlet the dovetail in the tang adjacent to the breech. That will present no safety issue at all. Just be sure that any tang bending and file work is complete before cutting the sight dovetail. I will be doing something similar on my rifle that’s presently on my bench. BJH

[HighUintas]

If the sight base dovetail is not too wide you can inlet the dovetail in the tang adjacent to the breech. That will present no safety issue at all. Just be sure that any tang bending and file work is complete before cutting the sight dovetail. I will be doing something similar on my rifle that’s presently on my bench. BJH

I had thought of doing that, or drilling and tapping it for a different sight. But, I don't think it will work with the one I'm using.

https://skinnersights.com/products/universal-barrel-mount-peep-sight?_pos=1&_sid=b97df697a&_ss=r

I know... Blasphemy. I wouldn't ever normally do this to my flintlock, but I've got an elk tag I'll never have a chance at again, so I want to do all I can to improve my chances. I'll be stripping the blue off and aging it a bit to hopefully look a little better. Then remove it after. I'm also putting a Lyman 17 globe on the front with Lee shaver inserts. Double blasphemy  :/

[B.Habermehl]

If I’m not mistaken, the shank on those sights is 8-40. If this special tap is available, then the tang can be drilled and tapped for the sight shank. It will take some precision location to the centerline of the bore. BJH

[bluenoser]

If, as B H suggested, the sight body threads into the base, and if you have the ability, make a new base to suit your needs and mount the sight body on it.  That would give you more mounting options.

[Scota4570]

A peep sights needs to be near the eye to work properly.  I put peep sights on the tang.  The tang can be replaced and is much cheaper than the barrel. I would not cut a dove tail in the breech section.  I would not buy a gun that has one. 

Here is an alternative. I have been happy with this sight that made out of a junk drawer 22 sight.  It require no modification of the rifle.  Put a little rosin on the leather washer and it will stay put. 

IF you make your sight out of steel you can soft solder it to the tang.  The installation will be fully reversible and very strong. 

[HighUintas]

If, as B H suggested, the sight body threads into the base, and if you have the ability, make a new base to suit your needs and mount the sight body on it.  That would give you more mounting options.

I could do that, but it's more time than I have available so I'm looking to install something pretty quickly and easily. I also want it to be as sturdy as possible and the skinner seems to fit that bill. I'm not worried about a dovetail at the breech, I just don't want to go too deep.

[HighUintas]

A peep sights needs to be near the eye to work properly.  I put peep sights on the tang.  The tang can be replaced and is much cheaper than the barrel. I would not cut a dove tail in the breech section.  I would not buy a gun that has one. 

Here is an alternative. I have been happy with this sight that made out of a junk drawer 22 sight.  It require no modification of the rifle.  Put a little rosin on the leather washer and it will stay put. 

IF you make your sight out of steel you can soft solder it to the tang.  The installation will be fully reversible and very strong. 

The peep for me is just to help align sight picture more than anything. I thought about making something, but as I mentioned above, just don't have the time to make something that would be reliable enough.

I'm ok with dovetailing my barrel at the breech and I'll very likely grind the dovetail on the sight in half so that my barrel dovetail isn't as deep.

 I do like your sight design though. I thought about going with something like that but it would be susceptible to getting knocked out of alignment with just a single anchor point. I'd have to put a pin or screw in to a mortise in the tang after sighting it in.

[HighUintas]

I guess one option would be to dovetail a base for the sight and solder that onto the barrel, instead of dovetailing the barrel.

[Scota4570]

I use that sight for load testing.  I coat the leather washer with rosin solder flux.  The flux's solvent evaporates.  The rosin holds the sight firm under the screw's pressure. 

IF I wanted to make a sight that was to be permanently installed I'd solder it to the tang.  A much shorter base would be fine.  IT would not have any adjustability.  That is not a problem because you have to the old rear sight to line it up on.  Once it is soldered in the correct place the old rear sight would be removed. 

[HighUintas]

I cut the dovetail on the sight down to about 0.055. then I royally screwed up my barrel dovetail. I somehow went to deep (0.060) and the corners of the dovetail were not cut sharply... There was a slightly higher spot in the corner. I think it may be due to the particular side of my file I was using (3 square w 1 safe side ground in). One side of it has the teeth angles down and the other angled up. I remember from the last time I cut one that one side is better than there other and I think I used the wrong side. Possibly the teeth angles down side.

So I had to put a shim underneath and luckily the sight has a set screw from the top you can tighten down if the dovetail is too big. Not ideal, but it will work. It is ugly. At some point, I may patch it by soldering in a mild steel piece the. Then recut the dovetail slightly offset.

Tried the sight out this morning and it's great! I'll have to "age" it a bit. I still need to get it regulated though. I had some odd issues with stuck balls loading, which is odd. Need to troubleshoot that.

[bluenoser]

Bummer about the screw up.  You are not the first one to have a project go sideways
You might be able to solder a thin shim to the bottom of the sight dovetail and then clean up the dovetail in the barrel, but that would not tighten up a loose dovetail without leaving a gap at the barrel/sight interface.  Lightly tapping down the sloped edges of the dovetail in the barrel can tighten things up a tad. Feeler gauges make good shim stock.

[Dphariss]

I'm going to put a dovetail near the breech of my 58cal colerain round groove barrel (1" across flats) for a peep sight. I'm wondering on max depth that would be considered safe.

0.580 bore / 2 = 0.290
0.016 groove + 0.290 = 0.306
0.500 half bbl diameter - 0.306 = 0.194 wall thickness

The dovetail of the sight I'm using is about 0.098 tall, which is how deep I'd need to make my dovetail if I want the sight to sit flat on the barrel.

As long as I'm in front of the breech plug threads, that would leave me about 0.096 barrel wall thickness.

Does my math check out and is that an acceptable wall thickness at the breech?

I can't remember what the breech thread max diameter is, but I'm thinking I would want to stay in front of that because I wouldn't have enough barrel wall material there, correct?

.580 + .032 =0.612   1-.612=0.388.  Divided by 2 = .194  I would not cut deeper than .040 anywhere. But in the waist I would solder on the under lugs even with a 1137 barrel.  I make them from brass sheet with a pretty large contact area for the solder. Why? Because when you proof the barrel you will find loose spots at every dovetail cut in the high pressure areas. Even with 1137. Cutting .100” dovetails in a barrel made of low quality steel is not safe.  They look ugly and certainly are not historic. You can file the bottom the the rear sight to thin it to something acceptable or just buy a more suitable rear sight. There is no reason to cut a dovetail over the breech threads. But this area has no internal pressure anyway.

[Dphariss]

For a peep sight attach it OVER the breech plug with 6x48 scope mount screws. This will not effect the strength of the breeching to any extent and you can drill and tap into the breech plug even. But just make sure you know EXACTLY where the end of it is. I.E. debreech and LOOK. Alternative is into the breech tang right behind the barrel. This rifle as 1 1/4” barrel so wall thickness is not an issue and its 4150 GB quality. The idea with the sight shown is to keep the base on the same plain as the bore. Silly maybe but it works. But its not a store bought sight either.

[HighUintas]

Good suggestion, bluenoser.

Another thought for fixing my screw up is having my stepson weld in a patch, and then I can cut the dovetail again. That would be stronger than soldering in a patch.

Any thoughts on that, other than it not being historically correct?

[Scota4570]

You asked.  Please do not think I am being mean.  We all grow from our mistakes.  I have made plenty.   : )   

One guideline is to work on the cheap replaceable part whenever possible. 

If you weld in a patch you will have non bonded metal in the middle of the patch.  When you try again you will not have accomplished anything.  IF you fill it up with weld, TIG I hope, it will get hot enough to scale the inside of the bore?  Run argon thought he bore?  Distort the plug threads?  Will the filler finish the same color as your leaded steel barrel? 

My advice is to stop digging.  Make a sight that fits the dovetail you already did?   

This exact kind of problem is why I suggested not cutting a dovetail in the barrel.  Dovetails are difficult.  Even with a milling machine I am only about 90% at making them perfect. 

I'd make a patch that fits the existing dovetail perfectly.  I'd do that  by making the filler piece slightly tapered and driving it in and out until it is a 100% interference fit.  I would then glue it in place with Loctite shaft sealant.  Solder will show.  Then cut the ends off a little proud.  Then peen the end to fill seam completely.  Then dress off and refinish. 

After that I'd make a sight that goes on the tang, where it belongs : ) .  Putting peep sights on the barrel is not the way to go for optical reasons. 

Good luck,
Scot

[HighUintas]

You asked.  Please do not think I am being mean.  We all grow from our mistakes.  I have made plenty.   : )   

One guideline is to work on the cheap replaceable part whenever possible. 

If you weld in a patch you will have non bonded metal in the middle of the patch.  When you try again you will not have accomplished anything.  IF you fill it up with weld, TIG I hope, it will get hot enough to scale the inside of the bore?  Run argon thought he bore?  Distort the plug threads?  Will the filler finish the same color as your leaded steel barrel? 

My advice is to stop digging.  Make a sight that fits the dovetail you already did?   

This exact kind of problem is why I suggested not cutting a dovetail in the barrel.  Dovetails are difficult.  Even with a milling machine I am only about 90% at making them perfect. 

I'd make a patch that fits the existing dovetail perfectly.  I'd do that  by making the filler piece slightly tapered and driving it in and out until it is a 100% interference fit.  I would then glue it in place with Loctite shaft sealant.  Solder will show.  Then cut the ends off a little proud.  Then peen the end to fill seam completely.  Then dress off and refinish. 

After that I'd make a sight that goes on the tang, where it belongs : ) .  Putting peep sights on the barrel is not the way to go for optical reasons. 

Good luck,
Scot

I appreciate the feedback, Scott.

Your proposed issues with welding a patch in are why I asked. I don't know much about welding and my boy doesn't know much about rifles, so we wouldn't know what issues could be present. My thoughts was that it may provide a stronger patch but didn't know if it could cause other issues.

I'll use it as is for a bit and see how well it will stay in place. If it works, I'll fix it properly and think about a different peep/aperture set up for the future.