Frame flex
Hello again, I was shooting a string over the chrony with my 12″ .22 barrel trying to set up the valve for my 18″ .22 barrel (Results below) and have now seen what the frame flex that WOK was on about.
I had the gun set up on a bipod on the front and the butt end of the tank resting on a piece of wood for a consistant shot though the chrony. Whilst holding the gun firm, I would have shots very low in fps. Which is I think the hammer not running well and the breech hitting the top hat at an angle. But with the gun sholdered, the results were consistant FPS
Here is a chrony string using 15.9 JSB’s a 12″ barrel with a starting pressure of 3300 psi to get the bell curve
784.2
777.3
839.5
456.9 *
851.6
850.8
860.2
847.6
872.3
842.8
856.4
873.0
858.6
861.4
851.4
865.6
877.8
869.1
866.9
870.1
868.7
851.6
547.7 *
853.0
641.6 *
803.8
542.8 *
858.8
864.5
865.7
862.1
847.5
448.0 *
853.6
850.8
858.5
850.0
853.1
848.8
572.1 *
850.8
532.6 *
842.6
696.8 *
763.2 *
829.7
834.1
739.0 *
832.0
* = Low shot due to frame flex and un-lubed breech o-rings
Seems like it should be PERFECT for when the 18″ barrel comes
Dave
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Some time ago I had simular results,
turned out the bottle collar was slightly loose and the flexing was just the grub in the collar not being tight enough,
JJ.. 🙂
yeah, the problem is we don’t know what to call it yet 😉
I think some guy sells a custom piece to help with frame flex on TAG 😆
If anybody wishes to observe how the frame can flex if held to firmly do this.
Mount a laser on the front rail on the gun over the barrel.
Look through your scope
Activate the laser
Put laser on target
Apply moderate side pressure with the grip hand while looking through the scope at the laser dot.
Watch the laser dot move as you increase or decrease pressure on the frame.
Once you know it is possible you will now have the knowledge “Why” it is important to not hold the gun to tight.
It is measurable and repeatable.
Frame flex what ??? No way … The hammer spring in the gun is not that serious—-You may need to just relax and shoot. The whole frame is tied together as one —-what frame flex?
It does seem a pretty substantial diffrence to me really.
Im getting my 18″ barrel tomorrow hopefully so will make sure that I lube the breech slide for better consistancy and will shoot a string with a starting pressure of about 3100 or 3200
Im sure that a 3000 psi tank could increase in pressure if left out in the warm sun. And that the tanks would be hydro tested way beyond the working pressures. I remember that an airgun cylinder from “Ripleys rifles” had a burst pressure of 14,000 psi
The makers would have a safety factor of at least 2 meaning that the tank would still not fail if it was pressurised twice as much as its working pressure.
Also, cronicash on this forum and on youtube has his gun set up for 240 BAR (3480 psi) with the standard AF tank. Im not sure about the rating of the burst disk I have only seen 1800, 3000, 4500, and 5000 psi burst disks
ANYWAY….. I dont feel that the slight over pressurisation of 100-200 psi would cause any danger to me
Dave
EDIT: Found out that tanks are hydro tested to 150% of their working pressure which means that a tank with a working pressure of 3000 psi would be tested to 4500 psi and expect to pass without any failure, thread stretching, bulging or size increase
I believe that frame flex does exist even though I have never had a problem with it, but a 3-400fps drop from frame flex seems like alot.
It also looks like the curve starts right at 3,300 psi. Isn’t that too high for an AF tank? 😯
It’s a highly accurate pellet gun, not an FN-FAL.
I know that it seems like a pussys excuse but it seemed consistant. When I put downwards pressure on the rifle when it is rested at the front of the frame and the rear of the tank, I would get a low shot but with the rifle shouldered, it would be a full power shot.
It seems to happen at the weakest point being the loading port where the frame is at its thinnest. This never happens to me when it is shouldered in a normal shooting position but I was just showing how a tight hold or something similar would produce inconsistant results.
Dave
I’m not a big believer in frame-flex issues/excuses. I’m sure it can happen, but if it does, then learn how to relax your posture, lighten up on your grip/hold and do what it takes to prevent flex from happening.
There’s no reason to tightly shoulder it or otherwise squeeze it like it’s going to recoil.
It’s a highly accurate pellet gun, not an FN-FAL.. it’s not designed to be shot like a Battle Rifle.
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yeah, the problem is we don’t know what to call it yet 😉
😆 😆