Dovetail/barrel thickness... Help!

[Daniels48]

Hi all,

I have been following, reading and learning from these forums a lot over the last few years and today I need to ask for some help. I have read numerous threads about the safe depths for dovetails vs barrel thickness and understand the rule of thumb is 0.100 minimum at the breach. I appreciate people cannot say 'yes or no' to this question, but here is my concern:

I got a Baker Rifle from The Rifle Shoppe and I'm at the last stage of building it, cutting the dovetails. The rear sight has gone in perfectly at 0.04 and is perfectly flush. The foresight is a different story... So the barrel is 0.880, the bore is 0.62 from groove to groove, land to land is 0.61. This means at the thinnest part I have 0.13 wall thickness. I have done a bubba and cut the front dovetail too deep to around 0.07. I don't have any batteries in my calipers at the moment, so that's the worst guess as these aren't easy to read and best guess is 0.063 (going by the mm and converting them, which are easier to read).

So this means I have at least 0.06 wall thickness between the base of the dovetail cut and the bore. My question is if this is 'safe'? It is at the muzzle end, so I am assuming the pressures are much lower but does anyone have any experience of whether there is a risk of this ringing the barrel or splitting it? If there is a definite risk, I might just cut my losses and order another barrel from Track or the Wolf, as I believe they and TRS get their barrels from the same supplier. Trouble is they're out of stock and it's backorder, but I'd rather be safe.

Any help or direction is appreciated.

James

 

[EC121]

I wouldn't worry about it at the muzzle. The thin spot is only at the tangent where the dovetail crosses the bore. Because pressure is measured in pounds per square inch, your thin spot is only a fraction of a square inch at the tangent. Might worry more about denting the bore. I once had a rifle that some yoyo had center punched the dovetail to tighten it up. He dented the bore inward at the dovetail.

 

[EC121]

If you want to see a botched sight, check this out. This is on a custom gun I bought. He said he wouldn't install the back sight where I wanted until I paid him. Then he did this. A .030" gap. There were still hacksaw marks in the dovetail I cleaned it up and patched it up with an insert under the sight to keep from having to replace the barrel.. It is 12in. from the breech. So far no problems.

 

[Daniels48]

Oh wow... Well, that's made me feel much better

Thanks guys, really appreciate the responses. I'm going to 'proof load' it just to make sure but I think it'll be fine. If it goes wrong, I'll post a picture in here just for the comedy value

 

[Col. Batguano]

Pressures drop from 50,000 psi at the breech to about 5000 psi at the gas tube vent on a Garand. That's about 22" down bore. On a ML'er starting at 15,000 psi at the breech, 40" down bore my guess is you'll be <5% of breech pressure, but probably more like 2%--300 psi. You'll get some strength / reinforcing from the sight base too--particularly if it's a tight fit on the bottom. It's a very small area. I wouldn't worry about it. Even if it does give way it's a long way away from your face. The metallurgists on the forum will need to weigh in on the yield pressure (with the sight installed over the dovetail) but a guess is that it's a LOT more than you'll ever come close to reaching, even if you try.

 

[Sidney Smith]

I hadn't even considered any of this when I cut the dovetails for my underlugs on my .32 caliber. I just bought a size that I thought would fit. I measured just now. My barrel is .820 across the flats. It's at .340 in the grooves of the bore. This gives me .480, divided by 2, or .240 between each flat and the bore. My dovetails measure right around .060 plus or minus. So that gives me .180 material between the bore and the dovetails.

I seem to be in good shape, but it has given me insight for when the time comes to cut the dovetails for the sights.

I can see where this would be an issue with a large bore and thinner wall thickness such as in the OP' s case. Good info to know.

 

[Treestalker]

I had a short rifle barrel donated to me because the rear dovetail and lug had been drilled for a pin; the hole missed the proper area on the lug and wound up cutting a I/2 circle under the lug and also the bottom of the barrel dovetail. It is a .50 cal. in 7/8ths FTF. I took it to a master welder who can tig/mig weld a fly's wing. Told him my sob story, and left it with him. I have left it there almost a year, got busy with other projects. Perhaps it would be better to simply close fit a new dovetail lug and test it ( he probably hasn't welded it yet; he usually waits until we can both be present, and I have not asked about it.) IIRC the dovetail is about 10" from the breech. It would be right above my supporting hand. The barrel is about 18" long for a blanket/canoe gun. Any Ideas? Or should I just cut it to pistol length? Thanks.

 

[Col. Batguano]

You still have about .14" of metal at the tangent (assuming half of a 1/16" pin hole) of the bore. That should be plenty, particularly if the hole is filled with a pin. Just don't go nuts with your load. It the pin seems overly tight when you go to drive it out, then you'll know some of the metal from the bore interior tried to deform its' way through the thin spot.

 

[Sidney Smith]

I wouldn't worry about it at the muzzle. The thin spot is only at the tangent where the dovetail crosses the bore. Because pressure is measured in pounds per square inch, your thin spot is only a fraction of a square inch at the tangent. Might worry more about denting the bore. I once had a rifle that some yoyo had center punched the dovetail to tighten it up. He dented the bore inward at the dovetail.

How did he dent the bore with a center punch? Did he punch the center of the dovetail or somethingI

I usually punch the dovetails to tighten up the underlugs just as a safety measure to keep them from loosening over time. But, I only lightly punch them on the corners of the flats.

 

[EC121]

He punched the bottom of the dovetail. It was a 13/16" .45 so there wasn't much metal left under the sight.

 

[Col. Batguano]

The pressure of a ball coming out under some pressure may help swage the barrel / bore back where it belongs. I've staked tenons before too, but generally find that a little (low temp) solder is a bit more positive.

 

[Vaino]

On the many MLers I've built, I've never "proofed" a bbl....just used a medium hunting load and function fired the gun…...Fred

 

[user 34300]

If you want to see a botched sight, check this out. This is on a custom gun I bought. He said he wouldn't install the back sight where I wanted until I paid him. Then he did this. A .030" gap. There were still hacksaw marks in the dovetail I cleaned it up and patched it up with an insert under the sight to keep from having to replace the barrel.. It is 12in. from the breech. So far no problems.
View attachment 34517

I would have refused the gun all together. If he can't install a sight the rest is a mess too.

 

[Col. Batguano]

Yeesh! Was the guy a former bridge builder or something?

 

[Pete G]

You guys should re-read the initial post. Seems to have wandered a little.