To produce thousands of pounds force can be easily done with a screw. The problem is to secure the frame to maintain stationary while the force is being applied. Every pusher is trying to do just that. Only few do a good enough job. Rifle is hard for the pusher to straddle. Hammer and punch usually works better.
I like aluminum rod driven with big hammer. A serious wack to break it loose, followed by lighter taps to adjust. With this scheme, supporting the frame becomes critical. Again the frame needs to remain stationary. The best support I found is block of lead.
-TL
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