Custom Syn-Rod build

[BRAAP]

Finally put my goodies together with a handful of shots over the Chrony, time to share.

Goal is to achieve to between 900-1000 FPS with a .25 Syn rod shooting JSB Kings and PolyMags, be very quiet, refined, convert to Bull-Pup, enjoy.
Purchased new .25 Synrod. early last year. Cocking the gun was almost impossible, (the ultra stiff, dragging cocking action that many new Synrods seem to be plagued with), with under 400 shots had more than a handful of double loaded pellets as result. Max velocity I could get out the rig with JSB Kings was in the 850's.
Ordered MDRL stock kit.
Ordered extra gauge block and .25" valve body to mod.
Ordered 10 lb and 12.5 lb hammer springs.
Ordered WAR NBH hammer.
Dad has a .25" Synrod so mods I performed were also done to his at same time.
Being a custom engine builder specializing in customer cylinder head building/porting/machining, applied some of the air flow improvement strategies to the Syn-rod using the Mill and lathe and hand tools, (mind you, many of the strategies for engine performance dont "port" directly over to air gun valves/ports, pressure, dynamics, flows, etc are different). Dimensioned the factory valve body and poppet rendering it in A-CAD 2D to get a better idea how close some of the port relationships are, where material can be removed, and not be removed etc.

In short, the valve body work was a success meeting my goals thus far, though I admit with the WAR valve, all this effort and work is not something I will be doing again, WAR valve is the way to go.

Mods performed;
Gauge block bored out.
Factory Transfer port opened up to .154" ID.
.166" barrel port, slightly radiused in the pellet seat, (pellet depth insertion for the pellets to be used verified deeper than port)
Factory valve body bored out to .500", region surrounding the poppet head opened up to 9/16" up to the valve seat for less valve-head shrouding. Bore behind the poppet opened up a skosch. Velocity port sealed with 2 part epoxy to fully eliminate the port and set screw installed, (Epoxy locked it in), Valve body exhaust port opened up to .160", "carefully" radiused to throat to the valve seat port. Undercut the poppet valve stem behind the head and slightly radiused poppet head edges. Back side of valve body bored to accept small O-ring to help reduce pressure bleed that leaks pas the valve stem itself. Poppet spring replaced with soft spring just strong enough to hold the poppet close for filling from zero psi.
Main tube cleaned, chambered the gauge port in main tube to allow O-rings of gauge block and valve body to pass with less tendency to cut/shave the O-rings removing/installing from the filler end. Polished/buffed region of the hammer slide area, deburred the hammer bolt slot and sear slot. Heavy dose of DuPont Chainsaver w/Teflon on the hammer.
Cocking blot polished as well and breech bore for the cocking bolt, Slick50 ONE lube on the cocking bolt.
Divers Siilcone grease on all O-rings and air related components.
WAR No Bounce Hammer
Air Stripper holes opened up and angled forward.
2 holes drilled in 2 of the baffles flanks, those two baffles are first in line.
3 small holes drilled in base of shroud to allow venting of shroud pressure, Mr Clean Magic Eraser wrapped/crammed between barrel and shroud at base to damp the flow of pressure venting to the shroud relief holes.
Lawyer spring straighten out.

Valve body;













Valve stem seal;





Gauge block;

[BRAAP]

Initial assembly was with 12.5 lb hammer spring, pressurized to 2500 PSI, left over night to verify no leaks.
Next morning all good, time for some Chrony testing, all shots made with .25" JSB Kings
HS 0 (full CCW)
HT 0 (full CCW)
JSB Kings

1009 fps 3100 PSI
999
991
985
978
964
956
943 2250 PSI
AIR HOG
Tried HS +4 for giggles, 1013fps, (pretty sure my transfer port/barrel port/valve body exhaust port is the bottle neck)

Next string;
HS 0
HT +5cw
970fps 3100 psi
1007
1000
1000
993
983
982
972 2600psi
Better on the air consumption, still on the back side of the curve.


Next string;
HS 0
HT +8cw (from 0)
946fps 3100psi
951
969
977
978
965
979
980 2750psi
974
965
960
957
948
942
931
921 2100psi

Much better, down in the velocity/energy range I want and now some semblance of a velocity curve.


Next string
10lb spring this time
HS 0
HT +4 (from 0)
978fps 3100psi
979
976
987
982
977
973 2600psi
A bit hot still.


Next string, factory hammer spring;
HS 2cw
HT 2cw
958fps 3000psi
967
940
978
974
971
965
973 2750psi
969
977
961
956
952
947
938
927 2200psi

Not bad, diving sharply around shot 14-16, left at this tune/settings for now.
Now ready to install the MDRL stock.

[screwwork]

Nice drawings, build, tune and photos
You have some good skills, you should checkout some of pakprotector's valve posts on how to increase the efficiency of air flow thou the valve outlet port. Douglas added a 0.2 thick x valve body Dia alum puck and epoxied it in to the valve and redid the poppet seat, valve throat and angled the valve outlet to increasing the flow to the transfer port.
I noticed you enlarged the end of the spring and bored out the valve inlet body with a step in it for the spring to be secured and not go through the bored out valve body.
In an other photo the valve inlet body was completely opened up and you inserted a rod to hold the spring in place.
I have been dreaming about using a rod as a spring holder for the valve poppet, but I would have thought it would still need tube connected to the rod to act as a guide so the spring wouldn't slip past the rod and I would lose my tune?
Did or have you seen any changes in your tune over time due to the spring slipping on the rod?

Thanks for sharing you build, Randy

[BRAAP]

Nice drawings, build, tune and photos
You have some good skills, you should checkout some of pakprotector's valve posts on how to increase the efficiency of air flow thou the valve outlet port. Douglas added a 0.2 thick x valve body Dia alum puck and epoxied it in to the valve and redid the poppet seat, valve throat and angled the valve outlet to increasing the flow to the transfer port.
I noticed you enlarged the end of the spring and bored out the valve inlet body with a step in it for the spring to be secured and not go through the bored out valve body.
In an other photo the valve inlet body was completely opened up and you inserted a rod to hold the spring in place.
I have been dreaming about using a rod as a spring holder for the valve poppet, but I would have thought it would still need tube connected to the rod to act as a guide so the spring wouldn't slip past the rod and I would lose my tune?
Did or have you seen any changes in your tune over time due to the spring slipping on the rod?

Thanks for sharing you build, Randy

Thank you Randy.
The threaded poppet spring retainer was bored straight through, drilled across it to accept a roll pin that the spring now rests against. The roll pin occupies a fair amount of the free area so not as much gained free area as it would appear, some, but not a lot.
The spring is very light, only a few grams is required to compress it, softer than ball point pen return spring. Its there only to hold the poppet on the seat when filing from empty.

[BRAAP]

Installed the MDRL stock today, put the Hawke Varmint 4-16x44 Side AO.
Its a little heavy, being non traditional design has non traditional feel when packing, doesn't fit the standing gun rack either, amongst the other guns it's a misfit pig...