Ulysses wrote:
The first thing is inadequate amount of powder. The second thing is inadequate amount of shot. Those two things combined resulted in inadequate gas pressure at the gas ports.
The way to test this is to cut open a couple of Win Universal shells and take enough powder to weigh the same as your comparison reload of 17.3 grains. Then add enough shot to make it 1 1/8 ounce weight as in your comparison reload.
That is really not a good idea.
Look I added enough, 2 grains of powder, in my load.
I used 17.3 of clay dot.
I added 1/16 of shot.
My velocity was actually 2 fps less than the factory load.
I added 13% more powder, and my velocity dropped 2 fps.
My loads worked the action and threw the shells quite well.
Now imagine the factory loads are near maximum pressure,
which they should be, because they can make them cheaper
that way, and higher pressure loads burn cleaner. So we
got a shell running near maximum, and it is putting out
1160 fps. Now we increase the powder 13% and increase
the shot by 6%, what do you suppose is going to happen
to pressure? INCREASE. How much? who knows, that
is why it is not a good idea.
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My test proved beyond any doubt, in my mind, that
the main problem with Winchester Universal not cycling
many gas guns is the powder is just too fast burning.
This backs that up:
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Understanding max chamber pressure:
Max chamber pressure is the maximum that is achieved.
A load of fast burning powder obtains it's max pressure
when the shot charge has only moved very little. For
sake of understanding lets say it achieved the max
pressure when the shot charge has only moved 1/2 inch.
Lets say that pressure on a 20 ga target load may be
11,000 psi. Now look at what happens when the shot
charge has moved 1 inch. It now has twice as much
space to contain the gas. Since it has twice the
space, the pressure is dropped by half. So if max
pressure was 11,000 psi when the charge moved 1/2
inch then when it has moved to 1 inch the pressure
is dropped by half, and now the pressure in the
barrel is 5,500 psi.
As the shot charge moves on to 2 inches of travel the
space available for the gas has now doubled again,
and now the pressure has cut in half again, so once
the shot has moved 2 inches the pressure has now dropped
to 2,750 psi.
Likewise when the shot has moved 4 inches the pressure
is dropped by half again, now down to 1,375 psi.
At 8 inches of shot travel the pressure is now only
687 psi.
If your gas ports are 8 inches from the chamber, then
the gas ports see 687 psi.
Now take a slow burning powder. Lets say this powder
develops 10,000 chamber pressure, fully 1,000 less
than the fast burning one. Also lets say it burns
so slow that it does not get its max pressure until
shot has moved 1 inch. It takes twice as much time
or space to develop its MAX because it is burning
SLOWER. With this powder, when the shot moves 2
inches the pressure has dropped to 5,000 psi.
When the shot has moved 4 inches the pressure has
dropped to 2,500 psi.
When the shot has moved 8 inches the pressure has
dropped to 1,250 psi.
Now which one has the most pressure at the gas ports?
The slow burning does, in this example the pressure
is twice what the fast burning powder was even
though the slow burning had less MAX chamber pressure.
To get low power loads to work your gas action,
you are better off using the slower burning powders
and more of it, to get that pressure at the gas
ports. This does not apply to guns like the versa
max that have it's gas ports right up in the chamber
area.
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