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Old 9th July 2015, 04:56 AM
hmangphilly hmangphilly is offline
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Join Date: Nov 2013
Location: wimborne
Posts: 576

Originally Posted by Nick G View Post
I don't think a bouncing piston will drag the comp tube rearwards as the cushion of air its bouncing on will drive the comp tube forward. Interesting problem, and frustrating I should imagine.
thats true nick and completely clutching at 'what ifs ' ...and 'may be's ' but to refine the idea down ....

if the firing pressure diminishes to to the point that it's no longer trying to part the tube and piston , but the piston still has rearward inertia, there's a split second before the mainspring can halt and reverse that movement.
i wonder if there's a point where conditions have caused the seal or piston bearings to grab the comp tube enough to move it.
robs rifle will hold its poi for a while , then go dow for a bit , then back up a bit and then kind of hover around.

this might be relevant...
On robs 97 action there is contact at all times between comp tube and linkage.....theres no slack at all .the unerlever pulling the comp tube up against the breech seal

On his tx , the under lever definitely stops closing the comp tube some way before it latches in the rest position......there is slack ....the comp tube sealing againt the breech seal ,as you say ,by it's forward movement due to stiction and compression

sure, its all happening in less than the blink of an eye, and any movement will be tiny , but on this particular rifle , as rob said to me in conversation, could impart movement or a shock wave all along the cocking linkage and lever to the point of maximum leverage, at the muzzle end of the barrel.

at the very least, there has to be an alteration in the downward pressure permanently exerted on the muzzle end of the barrel when the underlever is latched in its rest position.

as i said it's all a theory that i'm desperately clinging on to .
but i've got it into my head now and need to prove or disprove it ,

perhaps something as simple as grinding a little meat off the closing surface of the link arm would suffice , this would give a similar set up as the tx seems to be ...not that keen on that either to be honest , but at least it 's not shifting as far as we know.....i'll have a think

oooh eureka moment
eccentric pivot pin......hmmmmmm

Just an after thought
We're there any pukka target rifles that had an under lever attached to the barrel ?

Last edited by hmangphilly; 9th July 2015 at 06:22 AM.
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