goal: 250 shots per fill.

goal: 250 shots per fill.

Joined: November 17th, 2006, 3:51 am

February 24th, 2012, 1:47 am #1



What I want is a gun that runs on air (HPA plinker) that would give one pellet tin (250count) of shots per fill up. Knocking around plinking targets, the occasional back yard pest, some informal target practice....just fill it up, open a tin of pellets, and not worry about refilling until the pellets ran out.

Not quite there yet..but inside of something close to 10% of the goal.

HPA air powered .22 plinker (have a lot of .22 pellets on hand). 850PSI output, 13ci tank, shot from 3,000 to 1,000psi. 212 shots (and if I ran it until it went off reg, would be close to 225 shots). Low speed/low energy (557fps/14.6gr./10 foot pounds) but a very useful shot count.
[/IMG]

Yeah..its ugly...made form mostly spare parts.


Have become a bigger fan of adjusting striker weight when working with a constant pressure...co2 or regulated HPA air. NOT such a big fan when the gun has to deal with changes in air pressure...co2 over a temperature range or PCPs. With a constant pressure, the force holding the valve closed against the striker is constant, which favors adjusting the mass of the striker in order to get a short/fast valve cycle and save some air.

For low speeds, a weak striker spring and slow standard weight striker just promotes bounce...a slight brapp sound and a lot of wasted air for the speed.

So before playing with the striker weight, changed the transfer port to a smaller size. Adjusted the striker spring until it just had a tiny bit of tension on it when the striker was down (with no-tension, the rear pin tends to work its way out of its hole and occasionally jam up the bolt cycle).

Used EXACTLY the same gun, with only the striker changed:

#1.Standard weight: 55 grams.
RESULTS: 14.6gr./ 646fps/ 13.5 foot pounds / 105 shots per fill (3K-1K)..total energy out: 13.5X105 = 1417 foot pounds per fill

#2.Lightened: 46 grams. Lathed the back sides of the head and shirt, the central body of the striker. RESULTS: 14.6gr./ 596fps / 11.5 foot pounds / 155 shots per fill (3K to 1K)..total energy out: 11.5X155= 1782 foot pounds per fill
#1 (stardeard striker) at top, lightened striker at the bottom:
[/IMG]

#3'Lightened and shortened: 41grams. Lathed the body even thinner, and BOTH sides of the striker's head (which changed the stroke as well as the weight).
Here it is in the process of having its face set back a bit.
[/IMG]

(Be careful with the front, it is thin..too much and you expose the hollow for the front pin.) RESULTS: 14.6gr./557fps= 10foot pounds/ 212 shots per fill (3K to 1K)''total energy out: 9.9 X 212 = 2120 foot pounds per fill'.

NEXT STEP. Know it is a small amount, but the goal was 250shots per fill up. Rather than over fill the 13CI bottle, will flute the light/short striker and try to gain that 10% in shot count. If I can do that, and stay at 9 foot pounds will stop farting around with the damned thing,






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Joined: March 26th, 2008, 2:38 am

February 24th, 2012, 4:22 am #2

very good shot count already for 9-10 ftlbs.

I could shoot that thing for a month....and not run out.

Nice work, I may get in contact with you soon. Got a 2400karbine custom shop that I want to hop up a little, but keep shot count.

Have my cake and eat it too, ya know?


God bless,

Farmer
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Joined: November 17th, 2006, 3:51 am

February 25th, 2012, 1:42 am #3



What I want is a gun that runs on air (HPA plinker) that would give one pellet tin (250count) of shots per fill up. Knocking around plinking targets, the occasional back yard pest, some informal target practice....just fill it up, open a tin of pellets, and not worry about refilling until the pellets ran out.

Not quite there yet..but inside of something close to 10% of the goal.

HPA air powered .22 plinker (have a lot of .22 pellets on hand). 850PSI output, 13ci tank, shot from 3,000 to 1,000psi. 212 shots (and if I ran it until it went off reg, would be close to 225 shots). Low speed/low energy (557fps/14.6gr./10 foot pounds) but a very useful shot count.
[/IMG]

Yeah..its ugly...made form mostly spare parts.


Have become a bigger fan of adjusting striker weight when working with a constant pressure...co2 or regulated HPA air. NOT such a big fan when the gun has to deal with changes in air pressure...co2 over a temperature range or PCPs. With a constant pressure, the force holding the valve closed against the striker is constant, which favors adjusting the mass of the striker in order to get a short/fast valve cycle and save some air.

For low speeds, a weak striker spring and slow standard weight striker just promotes bounce...a slight brapp sound and a lot of wasted air for the speed.

So before playing with the striker weight, changed the transfer port to a smaller size. Adjusted the striker spring until it just had a tiny bit of tension on it when the striker was down (with no-tension, the rear pin tends to work its way out of its hole and occasionally jam up the bolt cycle).

Used EXACTLY the same gun, with only the striker changed:

#1.Standard weight: 55 grams.
RESULTS: 14.6gr./ 646fps/ 13.5 foot pounds / 105 shots per fill (3K-1K)..total energy out: 13.5X105 = 1417 foot pounds per fill

#2.Lightened: 46 grams. Lathed the back sides of the head and shirt, the central body of the striker. RESULTS: 14.6gr./ 596fps / 11.5 foot pounds / 155 shots per fill (3K to 1K)..total energy out: 11.5X155= 1782 foot pounds per fill
#1 (stardeard striker) at top, lightened striker at the bottom:
[/IMG]

#3'Lightened and shortened: 41grams. Lathed the body even thinner, and BOTH sides of the striker's head (which changed the stroke as well as the weight).
Here it is in the process of having its face set back a bit.
[/IMG]

(Be careful with the front, it is thin..too much and you expose the hollow for the front pin.) RESULTS: 14.6gr./557fps= 10foot pounds/ 212 shots per fill (3K to 1K)''total energy out: 9.9 X 212 = 2120 foot pounds per fill'.

NEXT STEP. Know it is a small amount, but the goal was 250shots per fill up. Rather than over fill the 13CI bottle, will flute the light/short striker and try to gain that 10% in shot count. If I can do that, and stay at 9 foot pounds will stop farting around with the damned thing,





TESTING PELLET WEIGHT:

So, even down tuned so far, and running on tiny puffs of 950psi air, it still shows an energy gain as pellet weight increases. Kind of expected that, but was wondering if I finally got one running on so little air that the heavy weights would DECREASE energy (evidently: NO).
[/IMG]

Still seeing something near 200-220 shots per fill. Does seem that the heavy weight pellets BOTH give more energy and more shots per fill, but its not a drastic amount.

Neat thing abut regulated HPA bottles is that the shot count stays proportional to tank pressure. With an 850PSI output, if you get 100 shots from 3K to 2K, will get another 100 shots from 2K to 1K.

Top two pellets, 25 shots each. RWS SuperDomes on top, JSB 13.5gr. on bottom:
[/IMG]


YES...I do wish I had that flier back on the last JSB target...if not for that....but as I shot it, it has to count.

Like all unchoked barrels, seems to be quite picky about what it will shoot and what it will scatter. With the better pellets, will work out fine for back yard practice, plinking, and the occasional pest bird.

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Joined: March 16th, 2009, 1:43 am

March 3rd, 2012, 3:46 am #4

let me congratulate you, your gun is amazing!!! when you get tired of it let me know... I have played with a qb78 which i run on HPA also but i use the original tube running on 1500 psi. So far it shoots 16 shots at 720 fps average with 14.3 crosman prems. I was wondering if you replaced the spring inside the valve with a stiffer spring, you might just increase your shot count to reach your goal. That will save you making the hammer too light (it does look like it needs more meat...lol) and reuse the original air port diameter... my .02...

gabe
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Joined: November 17th, 2006, 3:51 am

March 11th, 2012, 2:46 am #5

..other things kind of took over for a bit, but sooner or later will be back at that gun trying to eek out a few more shots per fill.

Changing the return spring does change the valve cycle, esp. when running at low pressures (850 out put)...will give that and a slightly different valve stem a try.
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