1117 barrel steel.

[jerrywh]

 This queston is primarily directed at Don Getz. But anybody wit hlots of black powder barrel making experience please chime in. Or a metalurgical engineer maybe.
   How is 1117 steel for muzzle loading shotgun barrels?? Thin barrels.

[davec2]

Hey Jerry,

I haven't used 1117, but I looked up the properties in one of my aerospace material reference books.  1117 is very close to 12L14 in all its important properties.  It just doesn't have any lead in it and not quite as much sulfur, but it is listed as a "free machining" grade.  Here are some of the properties:


Density:                                           12L14 = 0.284 lb/in^3         1117= 0.284 lb/in^3
Tensile (hot rolled)                            12L14 = 57,000 psi              1117= 62,000 psi
Tensile (cold drawn)                          12L14 = 78,000 psi              1117= 69,000 psi
Yield (hot rolled)                                12L14 = 34,000 psi              1117= 34,000 psi
Yield (cold drawn)                              12L14 = 60,000 psi              1117= 58,000 psi
Elongation (in 2 inches, hot rolled)    12L14 = 22%                        1117 = 23%
Elongation (in 2 inches, cold drawn)  12L14 = 10%                        1117 = 15%

It is not as machinable as 12L14 (i.e. the "machinability of 12L14 is listed as 160% as opposed to 1117 at 90%) but looks to be pretty much the same across the board in all the other categories.

Dave C

[jerrywh]

Dave2
   This is annealed. According to the figures I can find it has a yield point of 40000psi annealed.
 How do you figure out the psi. it should take to blow up a certain wall thickness of a barrel with a bore of .540    I think I know but I don't trust my formula.
  I plan on running some actual field tests soon on different barrel thicknesses

[davec2]

Jerry,

The hoop stress in a thin walled pressure vessel (i.e. the ratio of the inside diameter to the wall thickness is at least 10) is as follows"

S (stress) = P (pressure) x r (inside radius) / t (wall thickness)

In your example, if you wanted to calculate a safe wall thickness, you would rearrange the equation to:

t (min wall thickness) = P (pressure) x r (inside radius) / S (allowable stress)

For things in my work (that don't have to fly), I usually use the yield strength of the material divided by two (i.e. safety factor of 2) as the allowable working stress.  Using 40,000 psi for the annealed yield strength of 1117, I would use an allowable stress of 20,000 psi.  Assuming a shotgun max pressure of 12,000 psi, and using the ID radius of .540 / 2 = .270, the min wall thickness I would use would be:

(12,000 x .270) / 20,000 = 0.162 inches.  This would be at the breech only as the pressure drops off rapidly in the barrel.  If the breech thickness were doubled to .324, the barrel would have a safety factor of 4 instead of 2.  At a breech wall thickness of 0.243, the safety factor would be 3, and so on.  Now all of this assumes homogeneous properties of the steel and no flaws in the steel at the breech area (a safe bet with modern steels and never a safe bet with forge welded tubes - hence the practice of proof testing.)

To answer your question more directly, if the wall thickness were 0.162 and the ultimate strength of the material was 62,000 psi (here we would use the ultimate strength of the material with no safety factor) and the bore was .540, the wall should fail at:

t x Ultimate tensile / ID radius

[(0.162) x 62,000] / 0.270 = 37,200 psi

If the wall was 0.200 inches, it would fail at 45,926 psi  ..........and so on.

Also, as the material starts to fail, it obviously yields first.  As it yields, it work hardens and gets stronger (same effect you get by drilling too slowly through a material that work hardens badly).  So the material strength would probably be higher than the 62,000 psi and the actual failure would occur at an even higher pressure.

Just to confuse things a little, all of the above is for "thin" walled pressure vessels.  For a gun barrel, especially in the breech area, the ratio of the ID to the wall is more like 3, which puts it into the category of a thick walled pressure vessel.  The calculations for that are more complicated, but I have found that the thin wall analysis is adequate for these purposes.

Hope this helps.

Dave C

[JCKelly]

The other item of data that matters is its notched impact strength, specifically Charpy V-notch impact, measured in foot-pounds.
"Ntoched Impact Strength" roughly speaking, is a measure of the steel's ability to stretch a little, rather than snapping, at a notch. Say, the maker's name stamped in the barrel, nice sharp deep underlug notch, or a pre-existing flaw inside the steel.
Free machining carbon steels are not worth a bucket of warm refuse where notched impact strength = toughness is concerned.
Good luck.
An Aerospace quality 8620 or 4130 (NOT tubing) makes a nice tough barrel. Not a lot of fun to machine, of course.

[jerrywh]

Dave2 and Kelly.
   The info is just what I wanted. I have made a set of double 32" long 30 gauge barrels with silver soldered ribs. In the process of silver soldering the ribs the barrels were annealed twice because of the necessity of slow cooling to avoid any warping.  The breeches are .168 and the barrels taper down to a wall thickness of .043 at 11" from the breech. They are straight from there on to the muzzle. Belgian proof load is 139grs of ffg with and a rb of. 209 grs. The diameter of the rb is 6/10 mm less than bore size or about .520 the bore is .540.  I estimate the proof pressure at 10000psi at the breech. that could be high.
   Before I proof these barrels I am going to machine a 12" piece of 1117 with a breech wall thickness of about .155 tapered to a wall thickness of .043  2" from the muzzle. I'm going out and see what kind of load it takes to blow it up. I will work up in increments of 10 grs. using the same ball or 3/4oz of shot and a wad column .    
     I will breech it the same as the regular barrels. Any suggestions will be appreciated.
   PS-- the reason for the stress proof steel is it doesn't set up a vibration too bad when turning thin walled long tubes.  Also it is rumored tha ta lot of old shotgun barrels were made of it.

[Dphariss]

Dave2 and Kelly.
   The info is just what I wanted. I have made a set of double 32" long 30 gauge barrels with silver soldered ribs. In the process of silver soldering the ribs the barrels were annealed twice because of the necessity of slow cooling to avoid any warping.  The breeches are .168 and the barrels taper down to a wall thickness of .043 at 11" from the breech. They are straight from there on to the muzzle. Belgian proof load is 139grs of ffg with and a rb of. 209 grs. The diameter of the rb is 6/10 mm less than bore size or about .520 the bore is .540.  I estimate the proof pressure at 10000psi at the breech. that could be high.
   Before I proof these barrels I am going to machine a 12" piece of 1117 with a breech wall thickness of about .155 tapered to a wall thickness of .043  2" from the muzzle. I'm going out and see what kind of load it takes to blow it up. I will work up in increments of 10 grs. using the same ball or 3/4oz of shot and a wad column .    
     I will breech it the same as the regular barrels. Any suggestions will be appreciated.
   PS-- the reason for the stress proof steel is it doesn't set up a vibration too bad when turning thin walled long tubes.  Also it is rumored tha ta lot of old shotgun barrels were made of it.

1117 is not "Stressproof®" stress proof is a 1144 alloy and is specifically not recommended for firearms barrels by the steel maker than holds the trademark.

Dan

[jerrywh]

Dpharris
   Correct. 1117 is not stress proof.  But it machines well without inducing so much stress in the tubes.
 By the way. Riley at long Hammock barrel co. in Florida turned these tubes for me.  I have turned others  like these but my time is better spent engraving.