how thin is thick enough

F

fourspear

Plastic

Joined

May 1, 2008

Location

Dayton, Wyo

• Feb 27, 2014

• #1

I am needing advice on a dovetail cut for a front sight on a barrel that is .710 muzzle dia. and .412 bore. The sight that I am planning to install requires .080 depth for the dovetail which leaves .069 wall thickness under the dovetail. Is this enough wall thickness for safety?
This barrel is chrome/moly and chambered for 405 Win. Thanks, Red

 

A

abarnsley

Titanium

Joined

Mar 24, 2005

Location

Palmer, Alaska

• Feb 27, 2014

• #2

You can cheat, and take some off of bottom of dovetail on the front sight... Old Savage over unders used a shallow dovetail..

I have seen plenty of thin lever gun barrels at front sight area.. Even in .454 Casull.. Pressure is down quite a bit at muzzle though. You could figure out hoop strength at dovetail cut if worried about it.. You have known barrel steel properties..

I like at least .060. from bore. Have seen front sight screw holes (factory Marlin centerfires) that were .025 from bottom of hole to bore..

Many Euro double rifles and drillings get thin at muzzle, but they prefer silver/braze soldered on sights..

Going on a Win 95 Big Stick I hope ??

 

G

Gazz

Stainless

Joined

Sep 7, 2004

Location

NH

• Feb 27, 2014

• #3

I can't remember where or in who's book I read it, (P.O. Ackley maybe?) but somebody did a test on barrel wall thickness on a '03 Springfield type rifle in 30-06. The barrel diameter was turned down in small steps and fired each time with a standard load and then a proof load. It wasn't until he reached .063" wall thickness that the barrel failed with the proof load but was fine with the standard load. That is about all I remember though.

 

GGaskill

Titanium

Joined

Feb 14, 2001

Location

Central AZ

• Feb 27, 2014

• #4

I think it was Hatcher who did that experiment. I would take .010"-.020" off the bottom of the sight and go for it. .405 Win is not a high intensity cartridge and with that big bore, the pressure should be pretty low at the muzzle.

 

MilGunsmith

Stainless

Joined

Mar 6, 2006

Location

Sandyston, NJ

• Feb 28, 2014

• #5

The barrel experiment is in Hatchers Notebook. Remember that that thin section is only in one small spot as the dovetail is at right angle to the bore and only tangent to one location.

 

A

Artv

Aluminum

Joined

Aug 26, 2013

Location

Indian Head, MD

• Feb 28, 2014

• #6

GGaskill said:

I think it was Hatcher who did that experiment. I would take .010"-.020" off the bottom of the sight and go for it. .405 Win is not a high intensity cartridge and with that big bore, the pressure should be pretty low at the muzzle.

Click to expand...

I think IMHO that this recommendation is sound. Gazz also notes experiment with the .30-06, which usually is 60,000 psi while the .405 WCF is around 44,000.

Art

 

GGaskill

Titanium

Joined

Feb 14, 2001

Location

Central AZ

• Feb 28, 2014

• #7

Presumably Hatcher used government .30-06 which is not loaded particularly hot; in copper crusher pressures, perhaps 48000 to 50000 CUP. Then again, .405 Win probably goes less than 40000 CUP.

But his test was really not exhaustive. I would expect that the barrel would have burst eventually from fatigue failure even at a larger diameter. One shot is not 100 or 1000 and a M1903/03A3 barrel would be expected not to fail before it was shot out.

 

MilGunsmith

Stainless

Joined

Mar 6, 2006

Location

Sandyston, NJ

• Mar 2, 2014

• #8

I routinly drill and tap barrels for piezo-electric pressure gages. These are at many locations on a test barrel, but chamber (case mouth) is leaving a wall thickness of 0.098" with a 0.060" hole thru it on 5.56mm (.223) and is seeing 60,000psi. The hole usally erodes before cracking and we can get 3-4000 rounds out of test barrel. At the weapon port location on a 20" barrel, the pressures have dropped to 10-12,000psi. So at the muzzle you shouldnt need to worry too much. I have seen the barrels that Hatcher worked with, they are still in storage.

 

F

fourspear

Plastic

Joined

May 1, 2008

Location

Dayton, Wyo

• Mar 5, 2014

• #9

Thanks to all for the information, this helps to get an idea of what is actually taking place as far as pressure is concerned. I modeled it in cad and as MilGunsmith pointed out with the cut tangent to the bore, the surface area affected is really quite small.