On Thursday, September 19, 2013 at 10:07:56 AM UTC-7, Ed Huntress wrote:
On Thu, 19 Sep 2013 08:49:21 -0700 (PDT), PCS
wrote:

I would think your push bar problem is less about compression and more about bowing.

It's so constrained by the bore that there would be no significant
bowing.

I'd think that it's important for the mating faces to match well and
to be most of the bore diameter.

So, does this mean your pushrod can be a stack of dowel pins, all ground flat on the
ends? The case-hardening of a dowel pin makes good burst (compressive) strength,
and a dozen two-inch pins doesn't break the piggy bank.

I've heard of using hydraulic force to push a button through a (threaded) barrel.
I wonder if some type of a grease gun would have enough pressure?

Hydraulics might work, but that just makes this BIG project. Easily available
hand pumps will do 10kpsi, fluids will go to 50-100 kpsi (with custom pumps).
If the pushrod is a piston, 0.3" diameter, it only gets 900 lbs force with
10kpsi.