|
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
|
|
|
|
|
|
|
3 members (MattH, weagle, 1 invisible),
1,036
guests, and
6
robots. |
|
Key:
Admin,
Global Mod,
Mod
|
|
|
Forums10
Topics39,905
Posts568,196
Members14,640
| |
Most Online9,918
Jul 28th, 2025
|
|
|
|
Joined: Apr 2011
Posts: 1,850
Sidelock
|
Sidelock
Joined: Apr 2011
Posts: 1,850 |
I'm new to shotshell reloading as I've only loaded rifle and pistol. So how does PeteM's chart relate to Lead Units of Pressure? LUP is what is listed in an old Lyman Shotshell loading manual I have. I'm used to CUP (copper units of pressure) for rifle and pistol. After reading and re-reading the shotshell manual I'm about ready to forget shotshells and stick to what I know and do best.
Practice safe eating. Always use a condiment.
|
|
|
|
|
Joined: Feb 2003
Posts: 4,120 Likes: 86
Sidelock
|
|
Sidelock
Joined: Feb 2003
Posts: 4,120 Likes: 86 |
Lead crushers and copper crushers are two different animals. The units do not convert well if at all, and neither is PSI.
Then we have dram eq., Tonnes, and all the various proof standards.
It can be disconcerting to wade through.
It's also pretty interesting, and part of the rich history of firearms development.
Keep at it.
"The price of good shotgunnery is constant practice" - Fred Kimble
|
|
|
|
|
Joined: Dec 2001
Posts: 12,743
Sidelock
|
|
Sidelock
Joined: Dec 2001
Posts: 12,743 |
It does depend on the type of powder, and the amount of it. It also depends on the payload being moved and the characteristics of the payload, ie crush section of the wad and weight of shot.
"The area under the curve" will determine final velocity, the slower powders peak later (thus they are called "slower") but not anywhere as much as you have described.
How far 'down the barrel' is down the barrel? The shot charge starts someplace between 2" and 3.5" down the barrel already.
Curves and traces from Winchester are presented in Butler "The American Shotgun". Corrected 'travel distance' of all loads in that book show less than one inch when the peak is over.
The average seems to be that the peak happens at about .5 millisecond, the shot charge has moved just less than an inch, and at that point it's going about 400fps.
You tell me how far 'down the barrel' that is. For a 3" shell it approximates 4" I suppose from the breech.
The salient lesson from all this is that the peak pressure happens in the chamber, thus "peak chamber pressure".
We need to add a little to this post. Remember the powder charge always lies "Behind" the shot charge. The pressure starts to rise immediately upon the powder being "Lit". Pressure stays behind the shot & wad. So look at the position of the shot charge inside the hull, then add that inch. The peak is not going to occur an inch out side the hull but rather inside it. The Gunmakers weren't barking up an empty tree when they put the thickest area of the walls over the chamber rather than 4-6 inches down the bbl. William Apperson; I'm not trying to be a Smart Alec either, but if your set-up is revealing maximum pressures @ 4-6 inches down the bbl you definitely need some more guidance. There has simply been too much verifiable data accumalated over the past 100 years or so for this to be the case.
Miller/TN
I Didn't Say Everything I Said, Yogi Berra
|
|
|
|
|
Joined: Jan 2002
Posts: 11,574 Likes: 168
Sidelock
|
|
Sidelock
Joined: Jan 2002
Posts: 11,574 Likes: 168 |
Sherman Bell compared the location of peak pressure between smokeless and black powder (4 different kinds of smokeless), and loads ranging from 1-1 1/4 oz, in "Finding Out for Myself, Part VI: Smokeless vs Black". Double Gun Journal, Nov 02. He used strain gauges at the 1 inch, 3 inch, and 6 inch marks with others farther down the barrel. They all showed the peak pressure at 1" from the breech, with drops of at least 1,000 psi by the time they reached 3". Smokeless powders used were SR 7625, Clays, Universal Clays, and Blue Dot. Even the FFFG black powder--which some "experts" suggested would peak farther down the barrel--showed a significant drop in pressure by the 3" mark.
JRB, as Jones pointed out, there is no direct conversion from LUP to psi. A rough "ballpark" formula is: LUP + 1,000 = psi. If you build in some cushion when applying that formula, it's close enough for government work.
|
|
|
|
|
Joined: Nov 2005
Posts: 4,598
Sidelock
|
|
Sidelock
Joined: Nov 2005
Posts: 4,598 |
|
|
|
|
|
Joined: Aug 2004
Posts: 411
Sidelock
|
|
Sidelock
Joined: Aug 2004
Posts: 411 |
2-piper, my mistake.After looking at the few traces that I have,the peaks occur 4to6 1/10's of a millisecond after detonation
|
|
|
|
|
Joined: Feb 2003
Posts: 4,120 Likes: 86
Sidelock
|
|
Sidelock
Joined: Feb 2003
Posts: 4,120 Likes: 86 |
Yes they do!
We figured it out.
Gotta love this board...
"The price of good shotgunnery is constant practice" - Fred Kimble
|
|
|
|
|
Joined: Apr 2011
Posts: 1,850
Sidelock
|
|
Sidelock
Joined: Apr 2011
Posts: 1,850 |
JRB, as Jones pointed out, there is no direct conversion from LUP to psi. A rough "ballpark" formula is: LUP + 1,000 = psi. If you build in some cushion when applying that formula, it's close enough for government work. Thanks L. Brown and Jones. This gives me something to start from. Maybe I'm trying to be too kind to my favorite doubles and should stick to RST. Yet I always did enjoy reloading for rifle and pistol.
Last edited by J.R.B.; 06/03/11 04:57 PM.
Practice safe eating. Always use a condiment.
|
|
|
|
|
Joined: Dec 2001
Posts: 12,743
Sidelock
|
|
Sidelock
Joined: Dec 2001
Posts: 12,743 |
WEA;
I'll buy that.
SG Jones;
Just wanted to make sure everyone understood that while the lead portion of the shot charge may be approaching the 4" mark as max pressure occurs the actual pressure point is behind the shot & wads. Thus as you said in last line, still, in the chamber.
Miller/TN
I Didn't Say Everything I Said, Yogi Berra
|
|
|
|
|
Joined: Feb 2003
Posts: 4,120 Likes: 86
Sidelock
|
|
Sidelock
Joined: Feb 2003
Posts: 4,120 Likes: 86 |
Understood Miller. Thanks.
Jim Legg would have loved this one.
"The price of good shotgunnery is constant practice" - Fred Kimble
|
|
|
|
|
