Member
Joined: 18 Nov 2005
Posts: 398
Location: S Fl
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PGG,
This is where a few diagrams would be worth 1000 words, but I'll give it a shot.
Ballisticians' bread and butter tool is the P/T curve. Pressure is plotted on the vertical axis, and Time on the horizontal.
Let's imagine 2 distinctly different curves.
In the 1st one, P shoots up to 11,000 very quickly, but falls to very low levels just as quickly.
In the 2nd, the P trace rises much more slowly and never gets above 9,000, then falls slowly back to near 0.
The 1st trace would look like the Matterhorn, while the 2nd would more resemble the Blue Ridge.
BUT, the amount of work done by the expanding gases is represented by the area under the curve, not by the height of the peak. So, although our 1st load produces 2,000 more Peak psi, it actually generates less useable "work" since it lasts for a much shorter time (talking milliseconds here).
The 1st load is typical in 1 oz game/target loads, while the 2nd is more typical in heavier 1 1/8 - 1 1/4 oz express type loads.
Don't confuse Peak pressure with marketing terms like magnum or express or hi-velocity. They don't necessarily have anything to do with each other, despite any hype from the ammo companies.
A high peak pressure is cause for concern in some older guns, might cause cracked frames, etc.
A heavy shot charge, conversely, produces more stress on old stocks.
So how do you choose ammo for an older gun? It's not easy, since the big 3 American ammo cos refuse to publish pressure data, though for their own liability reasons, it has to be within SAAMI specs.
That's one reason I like Fiocchi. Their catalog lists peak pressure for every shotgun load they make. Find a copy, it's interesting reading.
Hope this helps
Pete |
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" .......you have learned patience and stubbornness and concentration on what you really want at the expense of what is there to shoot. You have learned that man can as easily be debased as ennobled by a sport....." |
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