|
S |
M |
T |
W |
T |
F |
S |
|
|
|
|
1
|
2
|
3
|
4
|
|
5
|
6
|
7
|
8
|
9
|
10
|
11
|
|
12
|
13
|
14
|
15
|
16
|
17
|
18
|
|
19
|
20
|
21
|
22
|
23
|
24
|
25
|
|
26
|
27
|
28
|
29
|
30
|
31
|
|
|
|
6 members (Drew Hause, Richard Hale, Hammergun, LGF, efl, 1 invisible),
1,742
guests, and
6
robots. |
|
Key:
Admin,
Global Mod,
Mod
|
|
|
Forums10
Topics40,271
Posts572,805
Members14,687
| |
Most Online32,084
Jun 14th, 2026
|
|
|
|
Joined: Jan 2006
Posts: 10,014 Likes: 620
Sidelock
|
Sidelock
Joined: Jan 2006
Posts: 10,014 Likes: 620 |
Thank you http://www.picturetrail.com/sfx/album/view/24488932Smokeless Powder data from Sporting Guns and Gunpowders: Comprising a Selection from Reports of Experiments, and Other Articles Published in the "Field" Newspaper, Relative to Firearms and Explosives, 1897  Using the estimated Lead Crusher Pressure (Cp) conversion to PSI (pound force per square inch) (Cp x 1.5) - .5 = TSI, TSI X 2240 = PSI 32 Gr Ballistite (1 1/8 oz at 1232 fps muzzle velocity = 3 Dram Equiv.) Breech - 2.9 Tons per Square Inch (UK, Long) = 8624 psi (2.9 x 1.5 = 4.35, 4.35 - .5 = 3.85 TSI, 3.85 x 2240 = 8624psi) 2 1/2" - 2.2 Tons = 6272 psi 6” - 1.2 Tons = 3718 psi 12” - .81 Tons = 1602 psi 18” - .33 Tons = 1120 psi 24” - .21 Tons = 694 psi Pressure data published by Neil Winston - www.claytargettesting.com. The shot leaves the (30") barrel at about 3.5 milliseconds after ignition. The pressure is down to about 500 psi by 2 milliseconds.  Red Dot and PB 
Last edited by Drew Hause; 02/03/14 01:42 PM. Reason: Pressures added
|
|
|
|
|
Joined: Feb 2006
Posts: 3,862 Likes: 124
Sidelock
|
Sidelock
Joined: Feb 2006
Posts: 3,862 Likes: 124 |
Thanks Drew. Nice to see a graph as words only tell a little.
David
|
|
|
|
|
Joined: Jan 2006
Posts: 10,014 Likes: 620
Sidelock
|
|
Sidelock
Joined: Jan 2006
Posts: 10,014 Likes: 620 |
David: Was Neil Winston the author of the SS article?
|
|
|
|
|
Joined: Feb 2006
Posts: 3,862 Likes: 124
Sidelock
|
|
Sidelock
Joined: Feb 2006
Posts: 3,862 Likes: 124 |
Drew, it was put on there by someone that was using this as a quote but never said whom it was from.
I will try and investigate it, hopefully I will remember what I typed in to get there.
David
|
|
|
|
|
Joined: Mar 2002
Posts: 7,898 Likes: 666
Sidelock
|
|
OP
Sidelock
Joined: Mar 2002
Posts: 7,898 Likes: 666 |
Spent five hours checking guns and gun barrels today. Found two more that did not pass. Neither was a gun which I have shot or planned to shoot any time soon. Both had thin barrels below .020. I know that some will shoot .020, I no longer will. Life is too good to risk it for a marginal gun. There are other guns to use and no reason to do another dumb thing in life. Ask yourself this question. Would you let your son use that gun? If you can not say yes then do not do it yourself. I also found three sets of extra barrels and two project guns that are not shootable but I knew they were marginal at best.
One Belgian single barrel gun has the thinnest chambers I have ever seen. They measured just under .060. This gun was a "gift" to me by an old black, colored man to older people, farm worker who lived on my family farm when I was a boy. He used this gun for many years and gave it to me near the end of his life. Its' value as a gun is zero but I was touched he wanted me to have it. The firing pin is now removed and I welded the firing pin hole solid so no one ever fires it in the future. I know he must have shot several hundred rabbits and more than that in squirrels and never had a problem with it.
Next week I will continue measuring and culling the herd. All is not lost since I am taking the time to clean and oil each gun. Also serial numbers are checked against my logbook and the estimate of value for each gun is being updated. I have a little log book to let my wife know what each gun is, and how much it is worth and suggested ways to sell them after I am gone.
We still need to shoot low pressure loads to be safe but having confirmed decent barrel wall thickness will let me be a little more at ease shooting these old guns.
|
|
|
|
|
Joined: Jan 2002
Posts: 11,575 Likes: 182
Sidelock
|
|
Sidelock
Joined: Jan 2002
Posts: 11,575 Likes: 182 |
This is the whole thing that I copied from the site.
The 3 inches is from the breech.
Following is the best explanation of pressure and velocity versus
length in a shotgun barrel that has ever been posted here.
Almost all shotgun powder burns within the first 2 inches
of the chamber. A typical fast burning powder will burn
in the first 3/4 inch of the chamber. This is where
maximum chamber pressure is attained. A typical fast
burning powder like Red Dot might give a chamber pressure
with a certain load of about 10,000 psi at that point.
This is why a chamber is very thick on a shotgun barrel
back at the chamber and gradually becomes thinner as
it gets further from the chamber.
After that first 3/4 inch, the pressure and tempurature
starts reducing. When the shot has travelled twice as far,
then the already burned powder which is now gas has
twice as much space available and the pressure therefore
drops to 1/2 what it was at 3/4 inch travel.
So when the shot has traveled 1 1/2 inches the pressure
drops to 5,000 psi if it was at 10,000 when the shot
had traveled 3/4 inch and was at max chamber pressure.
Likewise when the shot travels twice as far again, to
3 inches the pressure drops to half again. So when the
shot has traveled 3 inches the pressure is about 2500 psi.
This can be carried out on down the barrel and the
pressure keep reducing by half as the shot travel
doubles onward down the barrel. Here is a table giving
shot travel vs pressure.
inches:pressure
3/4 : 10,000
1 1/2 : 5,000
3 : 2,500
6 : 1,250
12 : 675
24 : 338
So as you can see as the shot travels further down the
barrel the pressure reduces. Since the pressure is
very high early on, the shot accelerates rapidly early
on. With 10,000 psi back initially it is accelerating
very fast. Once it gets out to 24 inches though the
pressure is only 338 psi, so the shot is accelerating
very little after that point.
Adding barrel length does give extra velocity, but its
not a lot once you have a barrel length approaching 30
inches. If you had a 2 inch barrel and increased it
to 4 inches though your velocity increase would be
very large. Increasing from 28 inches to 30 though
might only give you about 10 feet per second.
If you make the barrel very long, say something like
8 feet the pressure has dropped so much that the
gun hardly makes any noise. This barrel length thing
is why an 18 inch riot barrel is so much louder than
your 30 inch trap gun. The pressure wave let loose
upon the air at 18 inches would be substantially
higher than the pressure wave let loose from a
30 inch barrel.
The above explanation is not entirely accurate,
because barrel pressure also drops with temperature
as well as with getting more space available, and
the powder is also cooling as pressure drops, but
the above explanation is accurate enough to think
of it that way as a close approximation.
Nice mathematical formula, easy to remember. Also inaccurate. Pressure tests by Dupont in the 30's, with 3 smokeless and 1 black powder, show that pressure is right around 4,000 LUP at 8" from the breech; still between 3-4,000 at 10" from the breech. Which is as far as the graph goes. Sherman Bell's pressure tests, reported in DGJ, summer 2002, show pressures on either side of 2,000 psi, depending on the powder (he tested both smokeless and black) at 12" from the breech. So while pressures do drop quite rapidly, they don't drop as rapidly as the quoted formula would lead you to believe.
|
|
|
|
|
Joined: Dec 2001
Posts: 12,743
Sidelock
|
|
Sidelock
Joined: Dec 2001
Posts: 12,743 |
Note that when two different charges of different powders push a given load of shot to the same speed the same amount of work has been done. The burning rates of the powders will determine which has its pressure peak the quickest & highest. If you calculate out the total pressure beneath the curves in each case they will be very nearly identical, they're just proportioned differently. This proportioning can of course be important. A powder that peaks too high can be Undesirable, obviously. Also a powder that peaks too low can be equally undesirable under many climatic conditions.
Miller/TN
I Didn't Say Everything I Said, Yogi Berra
|
|
|
|
|
Joined: Jan 2006
Posts: 10,014 Likes: 620
Sidelock
|
|
Sidelock
Joined: Jan 2006
Posts: 10,014 Likes: 620 |
I added the Ballistite pressures to the graft above, using the estimated Lead Crusher Pressure (Cp) conversion to PSI (pound force per square inch)
(Cp x 1.5) - .5 = TSI, TSI X 2240 = PSI
32 Gr Ballistite (1 1/8 oz at 1232 fps muzzle velocity = 3 Dram Equiv.)
Breech - 2.9 Tons per Square Inch (UK, Long) = 8624 psi
(2.9 x 1.5 = 4.35, 4.35 - .5 = 3.85 TSI, 3.85 x 2240 = 8624psi)
2 1/2" - 2.2 Tons = 6272 psi
6” - 1.2 Tons = 3718 psi
12” - .81 Tons = 1602 psi
18” - .33 Tons = 1120 psi
24” - .21 Tons = 694 psi
|
|
|
|
|
Joined: Jan 2002
Posts: 11,575 Likes: 182
Sidelock
|
|
Sidelock
Joined: Jan 2002
Posts: 11,575 Likes: 182 |
Drew, that 12" number would be close to the lowest readings Bell got at 12". His highest were a bit over 2,000 psi.
|
|
|
|
|
