Lets go back to the early 70's when Diana started manufacturing 6 series pistols ( Winchester 363's ) etc ... the ERA of the GISS 2 piston recoiless spring piston air pistols.
For years there was much info ( Diana Collective ) where one could glean technical info from the old timers of the era posted onto the web by folks who followed there journey.
Here now 50 years later much of that info is no where to be found leaving some questions on some of the finer tuning tricks or ideal set up specifications ?
So today I found myself rebuilding a Winchester 363 that mechanically in 98% shape, tho piston seals were long ago rotten & crumbling.
Having a set of ARH poly seals went about cleaning it all up, Minor tube hone and polish up the sliding parts and pieces.
With the ARH replacement SEAL and rear Buffer/guide fitted and gears all timed correctly it came time to INSTALL THREADED END CAP and screw it on so the original staking screw threads and hole lined up. No problem but it took just shy of 2 full turns of cap compressing against the counter piston to do this.
*POWER was sub par only shooting a 7g pellet @ 310 fps and pistol had an odd BUMP / SHAKE upon discharging ?
Now this had me think a tad more on the mechanics of these twin pistons being geared together .. Huh, if I'm preloading the counter piston the gears are moving the primary piston away from roof of compression chamber ... While at the time of firing has the primary piston being mechanically stopped via gear bind & This CAN'T BE GOOD ?
Not only may we break a gear post but it just seemed wrong in that BOTH pistons in my mind should come to rest being bottomed out at each end simultaneously ? Thus the primary piston can make max compression stopping itself via air cushion ( Like all spring piston air guns ) and counter piston coming to a stop against its buffer.
The gears that sync the pistons motion should in my reasoning go slack on load when pistons come to rest, or very close to that.
** So I backed off the rear cap to the point rear piston buffer contacted cap. With a gear cap finger tight started adding rear cap preload on buffer until gear cap was easy to turn indicating there was no loading on the gears. This happened at @ 3/4 turn of preload on rear cap. ( tightened the gear cap )
Over the chrony once again ... same weight pellet & @ 440 fps and absolutely zero vibration or felt recoil ... Thump noise, no motion.
While I've read about shim thickness's after a measurement of how far buffer stuck out rear of tube ... just never a WHY a given thickness was recommended ?
The explanation of the physics of the system and clearances to get correct operation I've never seen documented & thus a 50 year old mystery perhaps comes to light once more.
IF ANYONE HERE IS OF AN AGE WHERE THESE GUNS ARE KNOWN TO YOU AND CAN ELABORATE ON THIS ABOVE THREAD .. PLEASE DO .. I'm all ears.
Scott S
For years there was much info ( Diana Collective ) where one could glean technical info from the old timers of the era posted onto the web by folks who followed there journey.
Here now 50 years later much of that info is no where to be found leaving some questions on some of the finer tuning tricks or ideal set up specifications ?
So today I found myself rebuilding a Winchester 363 that mechanically in 98% shape, tho piston seals were long ago rotten & crumbling.
Having a set of ARH poly seals went about cleaning it all up, Minor tube hone and polish up the sliding parts and pieces.
With the ARH replacement SEAL and rear Buffer/guide fitted and gears all timed correctly it came time to INSTALL THREADED END CAP and screw it on so the original staking screw threads and hole lined up. No problem but it took just shy of 2 full turns of cap compressing against the counter piston to do this.
*POWER was sub par only shooting a 7g pellet @ 310 fps and pistol had an odd BUMP / SHAKE upon discharging ?
Now this had me think a tad more on the mechanics of these twin pistons being geared together .. Huh, if I'm preloading the counter piston the gears are moving the primary piston away from roof of compression chamber ... While at the time of firing has the primary piston being mechanically stopped via gear bind & This CAN'T BE GOOD ?
Not only may we break a gear post but it just seemed wrong in that BOTH pistons in my mind should come to rest being bottomed out at each end simultaneously ? Thus the primary piston can make max compression stopping itself via air cushion ( Like all spring piston air guns ) and counter piston coming to a stop against its buffer.
The gears that sync the pistons motion should in my reasoning go slack on load when pistons come to rest, or very close to that.
** So I backed off the rear cap to the point rear piston buffer contacted cap. With a gear cap finger tight started adding rear cap preload on buffer until gear cap was easy to turn indicating there was no loading on the gears. This happened at @ 3/4 turn of preload on rear cap. ( tightened the gear cap )
Over the chrony once again ... same weight pellet & @ 440 fps and absolutely zero vibration or felt recoil ... Thump noise, no motion.
While I've read about shim thickness's after a measurement of how far buffer stuck out rear of tube ... just never a WHY a given thickness was recommended ?
The explanation of the physics of the system and clearances to get correct operation I've never seen documented & thus a 50 year old mystery perhaps comes to light once more.
IF ANYONE HERE IS OF AN AGE WHERE THESE GUNS ARE KNOWN TO YOU AND CAN ELABORATE ON THIS ABOVE THREAD .. PLEASE DO .. I'm all ears.
Scott S
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