In article ,
jim rozen wrote:

[ ... ]

How does one decide on the proper spring, to replace the shorter
one? Say if one were going from a three shell tube, to a five
or six?

I would think that one would measure the diameter of the wire,
and the dimensions of the spring, then make one with twice the number of
turns in twice the length. (And you would also need to make the tube
enough longer to accept the difference in the fully-compressed length as
well.

To be sure -- measure the force needed to compress each at the
half-way point between the fully extended and fully compressed lengths,
and check that these are similar. Also -- check the force needed to
compress one shell's length from the normal empty length on each, and
make sure that they are close.

It may be that the springs used are some kind of progressive
spring, where as it gets shorter, there are more adjacent turns
touching, so it requires more force to compress the next increment, but
I doubt it. That would not make sense to me for its function. If there
were a way to do the inverse -- so it applied the same force throughout
its compression range, that would be better -- but I know of no way to
do that with a real spring -- though a gas spring might be set up to do
something close to that.

Enjoy,
DoN.
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