doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Barrel thickness ?

What is considered safe for barrel thickness , does the type of metal matter ? Where would you take the measurement at ? ie muzzle , half way down the barrel or in front of the chamber? Should thickness be consistent for the entire length?

Depends. Yes. Customary measurements at 9" from muzzle and breech but I like to know what's happening at the front of the chamber before the cone. Not if you want a gun you can get moving.

jack

This from the Griffin & Howe site:
http://www.griffinhowe.com/abbreviations.cfm
A rule of thumb states that the minimum barrel wall thickness should be .020" in a 12 gauge gun.

From the PGCA site:
http://www.parkergun.org/forums/forum1/595.html
We who shoot Damascus barrelled guns look for a minimum of .025 wall thickness...

A real smith will no doubt set us right (but I thought it was more like .030")

I shoot guns with far less wall thickness (if it is thin in the 'right' spot) than many will.

I also know that I will own those guns forever as I will not try to pass them off as anything different than they are.

I won't admit how thin they are on this forum since I don't want to be flamed.

80 thou at the end of the chambers; and 20 at the thinnest point, provided that's more than half way down the bbls (there is almost no pressure after the shot passes the half way point, although there is some longitudinal stretching at the choke if the constriction is heavy). The issue with thin bbls toward the muzzle is if you dent them, the dent cannot be invisibly repaired. Guns don't blow up past the midpoint unless there is an obstruction in the bore, in which case all bbls will bulge.

The Birmingham proof house regularly proofs guns at .018. They will dent easily but barrels will proof that thin.

Mike, Don't you think you should clarify at what point on the barrel this .018" wall thickness is? I don't think Birmingham will proof a barrel with .018" thickness, 3" or 4" ahead of the chamber. When people ask about barrel wall thickness, they really need to be told at what point on the barrel these measurements are safe. I have my own guidelines, but they may not be correct. They do however work for me.

Dave, the proofhouse does not say where the .018 thickness is located. Measurments are usually taken 9" from the breech. But, the letters that I have seen usually only say minumum thickness is .0XX. My personal line in the sand is .020 no closer than 6" to the breech.

The BORE is measured 9" from the breech. The barrel walls are measured over every inch of the barrel.

There is no legal minimum thickness for barrel walls. If a gun with 12 thou barrels is submitted for proof and it survives the proof load, it will be stamped with the requisite proof marks.

Usually, the barrels are at their thinnest 4-8 inches from the muzzles.

A number of factors affect the viability of a gun with thin barrels:
Is it in proof? - For this, you need to measure the bore.

Is it pitted or bulged or dented or otherwise defective?

What is the profile of the whole barrel? I recently worked on an old Purdey with 20 thou plus everywhere except a gradually tapered 3" section, 6" from the muzzles, where it went down to 17 thou.

The gradual taper imparts less stress than a steep change of profile. The gun had otherwise clean 30" barrels with True Cylinder and Half Choke.

The gun was in proof and in otherwise good condition and very reasonably priced. It constituted a viable shooter if used with 65mm cases and 1oz loads and used with care. As aprevius poster said - the key thing is to avoid getting any dents in it.

Greener once carri3d out experiments where he reduced the last third of the barrel walls until he could cut them off wuith a penknife. With each reduction in thickness, he fired the gun. At no point did the walls fail upon firing.

I have posted this on several occasions but has been some time now. This comes from a large book entitled "The New Hunter's Encylopedia" I acquired many years ago. It is stated as being derived at, by the "Brussels Convention" of 1914;
For bbls of 12, 16 or 20 ga the minimum wall at forward end of chamber (regardless of length) for bbls made of "Ordinary Good Steel" shall be 2.3mm (.090"), for 24 & 28 ga 2.4mm (.095"). For "Special Steel" these may be reduced by .2mm (.008"). They do not give the actual taper of the bbls but indicate the "Minimum" thickness should not come till within the forward third of the bbl with it being set @ .6mm (.024").
W W Greener reported on testing some bbls which held normal loads with the "Forward" portion of the bbls so thin that after the firing he simply ripped them open with a pen knife.
Personally I would not want that .020" to come back as far as where I grip the gun, but would not be overly concerned if were out ahead.the pressure curve is beginning to level out after about 10" from breech, exact point depending upon load.