I installed an MF19-125 nitrogen die spring in my custom
Daisy P1000 on Sunday 6 DEC 2009. This is a large unit,
.747" OD, so it can only be used in large diameter pistons.
The ID of my Daisy/Hatsan piston is .780"
Photos here:
http://www.gatewaytoairguns.com/airguns/photos/photo-thumbnails.asp?albumid=142Paul at N-Forcer built this custom high speed unit for me with a
maximum stroke length of 113mm. I centered the motion of the unit
in the airgun by trimming the spring block so that the normal
overtravel during cocking is maintained and the piston in the ram
doesn't contact its internal seal at the end of the power stroke.
To mount the unit, I made a centering bushing for each end. Because the
difference between the ID of the piston and OD of the MF19 is only
.033", I drilled (3) 3/16" vent holes in the piston to allow air to enter
during the firing cycle.
This made it necessary to clean and relube the airgun. The airgun will
diesel for a while until the misplaced lube burns off, so my
velocity numbers are worthless as yet. (They went from an average
of 951 fps with an SD of 7 to one measured shot of 1150 fps.)
I can't shoot indoors because of the sonic boom (it sounds like a bull
whip), and the smell of burning Honda moly 60. The odor of moly 60 is
not nearly so pleasing as that of standard non-detergent motor oil-lol
The perceived recoil is much quicker and lighter than before, with no
torque around the axis of the tube, and no vibration after the shot.
Cocking force increased as expected. My only disappointment has
been that the cocking and firing are so much quieter that the sound
of the piston dragging on the compression tube while cocking and
its "ring" when it slaps the end of the tube during the shot are
too easily heard and are now quite objectionable.
I think the fix will be a .005" thick self-adhesive teflon
or UHMWPE tape stuck to the inside of the tube along the friction
path of the rear of the piston. I thought about buttoning the
piston, but it's free to rotate, so buttons would get sloughed off.
Sunday the 13th, I got to the farm to plink for about an hour.
The dieseling quieted down after about 50 shots. The groups with
CPHP's opened up from approx 2" to 8"+ (!!) at 30 yards.
I think they are still transonic even without dieseling.
With 8.3 grain Superdomes, I was able to hit the fruit of
the passion flower vines at 35 yards and then hit the
fractional pieces which were broken off by the earlier shots.
If the weather is good next weekend, I'll run some chrony numbers
and shoot some groups.
