Barrel Wall Thickness Under Dovetail?

[Tacksman45]

Hey everyone,

I was wondering how many hundredths of an inch should be in between the bottom of a dovetail and the wall of the bore of an octagonal rifle barrel?

Note: I am asking about dovetailing a lug rather than soldering. The barrel I am thinking about is .54 with a .80 waist

Thanks!

[P.Bigham]

I believe  100 thousands is recommended. May depend on the type of steel used.  If concerned you could solder them on.

[B.Habermehl]

It depends on the wall thickness of the barrel. A weight barrels I soft solder all the lugs. B weight, the middle two. If a lug lays out near the waist of a swamped barrel I’ll usually solder it. I allways use soft solder. BJH

[Tim Ault]

When your measuring take into account the depth of the rifling not just the bore size . Let’s say it’s a colerain 50 cal the rifling is .016 I believe  so you have a hole that’s actually  .532” .

[Tacksman45]

I believe  100 thousands is recommended. May depend on the type of steel used.  If concerned you could solder them on.

Thanks for the response!

[D. Taylor Sapergia]

I usually make my own dovetailed tenons for my rifles, and I use .040" thick metal, usually steel, but occasionally, brass.  By the time I dress them ready for installation, the metal is around .032" thick.  I cut my dovetails 1/32" deep and I use dovetails on all octagonal barrels, no matter what weight or calibre.  I only solder tenons on round barrels.  I have never had a rifle where the barrel was ruined, dimpled or bulged because of a dovetail.  Take your time, and make your dovetails 1/32" deep, with confidence.

[Dphariss]

I believe  100 thousands is recommended. May depend on the type of steel used.  If concerned you could solder them on.

Thanks for the response!

.100” is WAY to deep. A “B” weight swamp in 50 caliber. Figure .520” groove diameter for .010 deep grooves. Bigger with .016” round grooves.  It might be OK in small bore brass suppository guns with high strength barrels. But you dovetail even a 1137 ML barrel a little too deep with a fairly thin barrel wall like B weight swamps and after proofing you may feel the dovetails with a short bearing surface jag. I never exceed .040 for dovetails.
One other thing. ANY cut in a bar of steel is a stress riser and can cause issues with brittle alloys. Be it a dovetail or “wedding bands”. There is no need for a dovetail more than .040”. I could cite a factory letter from the 1870s  about dovetails in thin wall barrels but its about a brass suppository rifle.

[Dphariss]

 Some B weight swamps are .730-.735 in the waist. .732-.525 / 2 = .103 wall thickness. Even a .040 cut leaves .063 wall and this is assuming the bore is in the center of the barrel. Sometimes they are not. I have seen a T/C Hawken barrel back in the 70s that split in the bottom of the deep (.100” I am sure) under lug dovetail.

[Bob Roller]

I believe  100 thousands is recommended. May depend on the type of steel used.  If concerned you could solder them on.

Yes.
Bob Roller

[Birddog6]

I do .030 to .040  on underlugs. And I know For Fact that 1 installed correctly will suspend
a 240# man, as I tested  it.

[silky]

Evening,

I've had the same question and there are some good threads with lots of info and considerations; the discussion about the dropping bore pressure as the ball travels toward the muzzle is especially relevant, I think.  My takeaway: minimum thickness depends upon where on the barrel the tennon is installed.

https://americanlongrifles.org/forum/index.php?topic=51051.0
https://americanlongrifles.org/forum/index.php?topic=23011.msg220625#msg220625

I'm very much a novice in gun building, but with some care and practice, .03", or even thinner if required (like in the waist of a lighter barrel), isn't difficult to achieve and plenty strong. 

- Tom

[Tacksman45]

I do .030 to .040  on underlugs. And I know For Fact that 1 installed correctly will suspend
a 240# man, as I tested  it.

Thanks Keith! I am wondering about putting a .04" dovetail into a barrel with a .80" barrel waist.

[Tacksman45]

I usually make my own dovetailed tenons for my rifles, and I use .040" thick metal, usually steel, but occasionally, brass.  By the time I dress them ready for installation, the metal is around .032" thick.  I cut my dovetails 1/32" deep and I use dovetails on all octagonal barrels, no matter what weight or calibre.  I only solder tenons on round barrels.  I have never had a rifle where the barrel was ruined, dimpled or bulged because of a dovetail.  Take your time, and make your dovetails 1/32" deep, with confidence.

Thanks so much for your reply! When you say .032" thick you mean the thickness of the barrel wall between the bottom of the dovetail and bore?

[flehto]

I've made many Bucks County LRs w/ .50 cal. "B" weight bbls and have never gone more than .035 deep for 2 of the bbl lugs.....the lug at the waist is always soft  soldered on. Why even take a chance when soldering is so easy? Because of the 1/16" thick web of wood near the breech, a different design of bbl lug is used which is also soft soldered into the dovetail. The front sight dovetail is .045 deep and the rear sight dovetail is only .035  but the angled sides are upset w/ a dovetail  chisel and the raised steel is filed into moldings....the total depth of the moldings is approx. 1/16". The dovetail chisel is also  used on the {2} .035 deep bbl lug dovetails and the raised steel is peened for a tight fit w/  the bbl lug and then filed smooth......Fred

[D. Taylor Sapergia]

I usually make my own dovetailed tenons for my rifles, and I use .040" thick metal, usually steel, but occasionally, brass.  By the time I dress them ready for installation, the metal is around .032" thick.  I cut my dovetails 1/32" deep and I use dovetails on all octagonal barrels, no matter what weight or calibre.  I only solder tenons on round barrels.  I have never had a rifle where the barrel was ruined, dimpled or bulged because of a dovetail.  Take your time, and make your dovetails 1/32" deep, with confidence.

Thanks so much for your reply! When you say .032" thick you mean the thickness of the barrel wall between the bottom of the dovetail and bore?

By the time I file my tenons, they are only 1/32" thick.  The corresponding dovetail in the barrel is cut 1/32" deep so that the barrel and tenon material can be filed and polished at the same plain.  There is considerably more than .032" of barrel steel between the bore and the tenon.  It is always a good plan to make a full scale drawing of your barrel and tenon with whatever dovetail you intend to cut, just to satisfy yourself that you have ample steel remaining.