Some fps result from Crosman 760 / M4-177 tethered HPA experiment

[AirCats]

starting a thread to share some data from my 760/M4-177 tethered HPA experiments.

HPA conversion:
-- the valve nose was drilled and tapped to 1/8" NPT; a Ninja micro-bore remote was connected directly to the valve. Only the valve and the Ninja remote line are pressurized.   
-- valve body was drilled and tapped to 4mm-0.7mm, and bolted to the tube. (so the valve body does not move when the striker hits the valve stem.

Three configurations are tested:
A) factory striker with factory striker-spring guide/spacer;
B) reduced weight striker and reduced thickness spring guide (to reduce the spring preload)
C) same as config-B, but with a striker block to limit the max valve lift to ~0.1". This striker block is drilled and tapped to 4mm-0.7mm and bolted to the tube.



 

[AirCats]

Configuration-A, using factory striker and striker-spring guide/spacer

*pellets used were Daisy HP (since it is in-expensive), pellet weight about 7.5gr*

*** fps @ psi test ***
--the ninja line was connected to a Hill pump MK3 (the total volume of croman valve and HPA lines, is about 8cc).
pressurizing the system using the Hill pump, then shoot and record the fps and end pressure. fps #'s were from a pro-chrono. line pressure was read from the gauge on the Hill pump.
 
(2000psi start) --> 843fps --> (1800psi) --> 818fps --> (1620psi) --> 793fps --> (1480psi) --> 742fps -->(1280 psi) --> 732fps --> (1120psi) --> 698fps --> (980psi)

(1500psi start) --> 766fps --> (1320psi) --> 731fps --> (1100psi) --> 691fps --> (950psi) --> 645fps --> (780psi) --> 607fps --> (650psi) --> 556fps --> (520psi) --> 500fps --> 0psi (all air dumped).


*** efficiency test
--- ninja remote line was connected to a 13CI Ninja bottle. The output pressure of bottle is around 1100psi.  The bottle was pumped to 1600psi then shot to 1200psi (internal pressure. The output pressure should remain around 1100psi the whole time), and record the # of shots and fps. Bottle pressure was read from a 2" gauge, gauge accuracy is supposedly +/-2% mid-scale.
--Took 38 shot to drop bottle pressure from 1600 -> 1200 psi; 674~697 fps, ave=686, sd=4

[AirCats]

Configuration-B, using reduced-weight striker and reduced-thickness striker-spring guide (reduce the spring tension and pre-load)

*striker nose is grind down, weight reduction ~ 10%; spring-guide base thickness is reduced, to reduce spring tension. The striker is close to "free flying" (no spring tension) when it reaches the valve stem.

*pellets used were Daisy HP, pellet weight ~ about 7.5gr*

*** fps @ psi test ***
-the ninja line was connected to a Hill pump MK3 (the total volume of croman valve and HPA lines, is about 8cc).
pressurizing the system using the Hill pump, then shoot and record the fps and end pressure. fps #'s were from a pro-chrono. line pressure was read from the gauge on the Hill pump.

(1500psi start) --> 752fps --> (1320psi) --> 731fps --> (1200psi) --> 710fps --> (1100psi) --> 682fps --> (980psi) --> 656fps --> (900psi) --> 635fps --> (800psi) --> 601fps --> (720psi) --> 570fps --> (620psi) --> 540fps --> (520psi) --> 509fps --> (500psi)


*** efficiency test
- the ninja remote line was connected to a 13CI Ninja bottle. The output pressure of bottle is around 1100psi.  The bottle was pumped to 1600psi then shot to 1200psi (internal pressure. The output pressure should remain around 1100psi the whole time), and record the # of shots and fps. Bottle pressure was read from a 2" gauge, gauge accuracy is supposedly +/-2% mid-scale.
--- 42 shots, 672~702fps, ave=693fps, sd=4

==> this configuration is more efficient than config-A

[AirCats]

Configuration-C ( same as config-B, but with a striker block to limit the max valve lift to ~0.1" )

*pellets used were Daisy HP, pellet weight ~ about 7.5gr*

*** fps @ psi test ***
-the ninja line was connected to a Hill pump MK3 (the total volume of croman valve and HPA lines, is about 8cc).
pressurizing the system using the Hill pump, then shoot and record the fps and end pressure. fps #'s were from a pro-chrono. line pressure was read from the gauge on the Hill pump.

(2000psi start) --> 712fps --> (1920psi) --> 736fps --> (1820psi) --> 786fps --> (1720psi) --> 777fps --> (1620psi) --> 800fps --> (1500psi) --> 791fps --> (1380psi) --> 770fps --> (1280psi) --> 744fps --> (1100psi) --> 714fps --> (1000psi) --> 680fps --> (900psi) --> 655fps --> (820psi) --> 625fps --> (750psi) --> 593fps --> (680psi) --> 558fps --> (600psi) --> 530fps --> (520psi) --> 504fps --> (500psi) --> 475fps --> (450psi) --> 408fps --> (350psi) --> 374fps --> (300psi)

---- took 11 pumps (Hill MK3) to bring the system pressure from 300psi back to 2000psi----

(2000psi start) --> 670fps --> (1920psi) --> 692fps --> (1820psi) --> 775fps --> (1750psi) --> 796fps --> (1620psi) --> 806fps --> (1520psi) --> 801fps --> (1420psi) --> 772fps --> (1280psi) --> 745fps --> (1150psi) --> 710fps --> (1000psi) --> 680fps --> (920psi) --> 656fps --> (820psi) --> 629fps --> (750psi) --> 598fps --> (680psi) --> 565fps --> (620psi) --> 533fps --> (550psi) --> 504fps --> (500psi) --> 470fps --> (450psi) --> 437fps --> (400psi) --> 410fps --> (370psi) --> 369fps --> (300psi)


*** efficiency test
- the ninja remote line was connected to a 13CI Ninja bottle. The output pressure of bottle is around 1100psi.  The bottle was pumped to 1600psi then shot to 1200psi (internal pressure. The output pressure should remain around 1100psi the whole time), and record the # of shots and fps. Bottle pressure was read from a 2" gauge, gauge accuracy is supposedly +/-2% mid-scale.
--- 40 shots, 695~714fps, ave=705fps, sd=3

==> this config seems to self-regulate between 1800psi and 1400 psi
==> efficiency is about the same as config-B.

[BigTinBoat]

You've got way too much hammer strike. That 760 was designed as a dump valve, with stock hammer and spring. Try a lighter spring. (maybe one from a 2240) At those power levels you should see a 50 to 75 % increase in the number of shots. Right now you are in the .83 -.93 fpe/cuin range. At 8FPE you should be seeing 1.5 easily.

The only time you were not wasting air (as I see it) was at 2K pis with the limiter on the strike (config c). But once the pressure got to 1920 your velocity started down hill. Once you see a "curve" (velocity raise and the lower) as the pressure drops you are getting close.

With the spring you have now you could run the gun at a regulated 2K (in config c) and see much better efficiency.

[Matt15]

Very interesting!! I thought about doing the same thing to my 2100 a couple years ago.

[AirCats]

You've got way too much hammer strike. That 760 was designed as a dump valve, with stock hammer and spring. Try a lighter spring. (maybe one from a 2240) At those power levels you should see a 50 to 75 % increase in the number of shots. Right now you are in the .83 -.93 fpe/cuin range. At 8FPE you should be seeing 1.5 easily.

The only time you were not wasting air (as I see it) was at 2K pis with the limiter on the strike (config c). But once the pressure got to 1920 your velocity started down hill. Once you see a "curve" (velocity raise and the lower) as the pressure drops you are getting close.

With the spring you have now you could run the gun at a regulated 2K (in config c) and see much better efficiency.

yeah, it is not very efficient, even the MK-177 tethered HPA (which doesn't self-regulate at all), is 20% more efficient than this M4 tethered. But I don't want to use pressure higher than Co2, so 1100psi will be the max.

I will probably need a lighter striker if I want to install a lighter spring, so the lock-time doesn't get too slow...

[Rob M]

nice work , i converted my 417, no numbers

Crosman+417+pumper+converted+to+CO2

just paste that you will see it.. my guess is 700 on a fresh co2 fill, tops.