interesting observation on pumpers....
Select Gate
READ GTA FORUM RULES BEFORE POSTING
GTA Forum Help Desk
GTA Announcement Gate
Dealer Area
GRIP
AirgunWeb Airgun Videos
Airgun Repository of Knowledge
Vendors and Vendor Videos
AirGun Expo 2021
Airgun Expo 2022
Contests and Giveaways!!!
Welcome New Members
In Memoriam
GTA Contributing Members
Shot Show Videos
Hajimoto Productions
Airgun Detectives
Air Gun Gate
BB Guns and Such
"Bob and Lloyds Workshop"
American/U.S. Air Gun Gates
European/Asian Air Gun Gates
PCP/CO2/HPA Air Gun Gates "The Darkside"
Air Archery
Vintage Air Gun Gate
Air Guns And Related Accessories Review Gates
Hunting Gate
Machine Shop Talk & AG Parts Machining
3D printing and files
Buyer's, Seller's & Trader's Comments
Bargain Gate
Back Room
Target Shooting Discussion Gate
Target Match Rules
Shooting Match Gates
Field Target Gates
The Long Range Club
100 Yard Match
Discussions By States
Welcome,
Guest
. Please
login
or
register
.
Did you miss your
activation email
?
1 Hour
1 Day
1 Week
1 Month
Forever
Login with username, password and session length
Home
About
Help
Old GTA
Gallery
Search
Stats
Login
Register
Advertise Here
GTA
»
All Springer/NP/PCP Air Gun Discussion General
»
American/U.S. Air Gun Gates
»
Crosman-Benjamin Air Gun Gate
»
interesting observation on pumpers....
« previous
next »
Print
Pages: [
1
]
Go Down
Share This!
Author
Topic: interesting observation on pumpers.... (Read 1226 times))
plinker99
Shooter
Posts: 81
yes
interesting observation on pumpers....
«
on:
August 15, 2013, 01:55:55 AM »
i was wondering about all the advantages for a flat top valve & piston for power mods. on my crosman 760, i trimmed the valve nose & shimmed the pump cup. i also put a 3/16"d x 3/8"l magnet inside the valve spring to reduce the valve volume a little. i didn't stuff the piston yet. here's some chrony shots at 5 pumps with crosman copper bb's with the pump arm closed & open...
1st group
1) pump closed 452.1
2) pump closed 447.6
3) pump open 438.5
4) pump open 431.7
5) pump closed 443.2
2nd group
1) pump open 432.?
2) pump open 429.7
3) pump closed 439.8
4) pump closed 441.2
5) pump closed 451.?
6) pump closed 460.?
7) pump open 435.?
3rd group with 6 pumps
1) pump open 462.2
2) pump closed 477.4
it seems that the air left in the head space on the last pump gets added to the shot when the pump arm is closed.
i was wondering if anyone with a flattop valve & piston setup can try & see if they get similar chrony results.
any comments & observations are welcomed.
thanks,
plinker99
Logged
honolulu, hi
rsterne
Member 2000+fps Club
Bob and Lloyd
GTA Senior Contributor
Posts: 26958
GTA Forums Person of the Year 2017
Real Name: Bob
Re: interesting observation on pumpers....
«
Reply #1 on:
August 15, 2013, 01:21:13 PM »
Makes sense that the air left in the headspace in the pump cup flows through the check valve and adds to the shot.... With a flat topped piston, that air would already be in the valve, along with the cup headspace air from all the previous pumps.... That's precisely how reducing the headspace with a F-T-P works.... The air that would normally be left in the cup headspace ends up in the valve on each pump instead of expanding back up the pump tube when you open the pump handle....
Bob
Logged
Coalmont, BC, Canada
🇺🇦
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
plinker99
Shooter
Posts: 81
yes
Re: interesting observation on pumpers....
«
Reply #2 on:
August 15, 2013, 06:10:47 PM »
hi bob,
thanks for the reply. after i posted this, i was thinking that since i gained 10+ fps with the pump arm closed with 7 pumps, i should get 70+ fps more with a flat top setup. as you mentioned, more of the air in the headspace gets into the valve on each pump.
i'm still hoping someone with a flat top setup can post some chrony numbers with the pump arm open & closed to see how much better it can be.
thanks,
plinker99
Logged
honolulu, hi
Print
Pages: [
1
]
Go Up
« previous
next »
GTA
»
All Springer/NP/PCP Air Gun Discussion General
»
American/U.S. Air Gun Gates
»
Crosman-Benjamin Air Gun Gate
»
interesting observation on pumpers....