[TheRockofSweden]

Hi!

New to pumps and been lurking around different forums, but i cant find the answer to this.

Holding pumphandle forward on my empire sniper gets me a lower fps reading och and farty sound, let the handle do its own stuff and kicking back gives a higher fps almost 20 or so and a much quieter shot without the farting sound.

input around 250psi from a sidewinder, hammerspring a few turns in maybe shot 1 case with it.

Is it how it works and i have to live with it?

[Nahib_Stilgar]

That doesn't make sense? You should get a higher FPS by holding the pump handle forward. You may get the fart but at least the bolt cant blow backwards...

not holding the pump handle may stop the fart, but you should LOSE velocity due to the laws of physics. Equal and oposite reaction...

The fart is caused by hammer bounce. it can be fixed with a mixture of springs and air pressure...

[gospeedgo1]

There are a lot of theories as to why this may occur. One that I am starting to think more about is holding the pump handle forward, the ball may get hit with air harder which can result in some higher initial drag which lowers FPS since most pumpers match or underbore. Not holding the pump handle maybe decreases how hard the paint is hit with air or how it is hit with air, decreases the initial drag, and results in higher FPS. It depends on many factors though. On my snipers with Venturi and open face bolts, the FPS stayed about the same between holding vs no holding. I have tested it on different occasions.

[EvilAuthorityX]

I've had a few snipers that were like that. can't explain it

[drgonzo]

Could be bolt-to-transfer hole misalignment. Port alignment improves while the bolt blows backward. A gun with good alignment should not exhibit this behavior.

Try holding the bolt slightly back and firing, see if you can induce the FPS increase.

[TheRockofSweden]

will buy the clock and check it out, maybe som vids of it, but it wont happen the nearest week.

And try different positions

[Castro #66]

I've had a few do it as well, though usually not 20 fps different. Try using a different barrel bore to see if it evens out.

[TheRockofSweden]

bought a virtue clock yesterday might try it tonight, was using the .685 with summerpaint in minus 2 degrees celcius ,did not want to underbore that much

[ridebmx211]

Ive had guns go both ways, the only wierd thing is that, and i know this is an OPINION and do not want to start an arguement on it) but not holding the handle forward seems to make my shots more accurate. IDK if its due to the lower pressre or what. It also doesnt affect all guns the same, BUT its notieable on my T2.

[Castro #66]

I've seen that sort of thing as well, but it's tricky. I also used to snapshoot much better by switching my forward hand to the reg... so it might require some testing.

[russc]

Originally Posted by ridebmx211

Ive had guns go both ways, the only wierd thing is that, and i know this is an OPINION and do not want to start an arguement on it) but not holding the handle forward seems to make my shots more accurate. IDK if its due to the lower pressre or what. It also doesnt affect all guns the same, BUT its notieable on my T2.

I also find that letting the pump handle blow back makes my shots more accurate.

+1 to attack for reg holding.

The only thing I can think of is that it acts as a regulator - the bolt is the piston and it recoils with the air, and once it reaches velocity the transfer port is cut off.

Transfer port misalignment is 100% what causes quiet shots when you don't hold the pump.

[PureInsanity]

i was playing around with this today and also found that NOT holding the pump handle increased ball-to-ball accuracy.

*i repeated these groups of 5 shots a few times and got just about the same results every time.
*fresh paint matched to a 16" .684 UL

NOT HELD:
5/5 hit directly on top of the first shot at 20 yards

HELD FORWARD:
3/5 hit directly on top of the first shot at 20 yards

possible reason my test might be invalid:
the 2-pieces of my stock orracle bolt aren't perfectly alined. the air hole on the bottom of the front delrin piece is rotated ~5 degrees off axis from the back (alum) section.

good excuse for a new bolt, though.

[ridebmx211]

Originally Posted by PureInsanity

i was playing around with this today and also found that NOT holding the pump handle increased ball-to-ball accuracy.

*i repeated these groups of 5 shots a few times and got just about the same results every time.
*fresh paint matched to a 16" .684 UL

NOT HELD:
5/5 hit directly on top of the first shot at 20 yards

HELD FORWARD:
3/5 hit directly on top of the first shot at 20 yards

possible reason my test might be invalid:
the 2-pieces of my stock orracle bolt aren't perfectly alined. the air hole on the bottom of the front delrin piece is rotated ~5 degrees off axis from the back (alum) section.

good excuse for a new bolt, though.

NICE, can you do that same test over a chrono?

[PureInsanity]

i can do a real test when the weather permits a trip to the field.

but until then -

a local pawn shop happens to have one of those small yellow chronos for sale. if i can talk them down to around 45 i'll pick it up..assuming it works.

i'll secure my gun in all axis' and hand inspect ~30 balls (for now) for a test of half HOLDING and half NOT holding. i was thinking 20 yards is just about right; they're velocity should outweigh other conditions that are trying to skew the results, but it's not so close that a spyder would be ball-on-ball. hope that reasoning makes sense.

if i can use a better chrono (hopefully 2), i may even map each shot on a grid.

[ridebmx211]

I have one of the small yellow chronos, it works well enough. I may try the same test, but it sounds good

[EvilAuthorityX]

I think i figured it out.....

long story short left and right play in the back block/pump arm/pump kit causes rotation of the bolt being held forward. misaligning the the bolt to the left/right causing lower velocity and inconsistent shots (inaccuracy)

this is less likely on guns that are completely tightened down or stabilized (dual rods, stabilizer rings, etc) thus most people get the expected increase in velocity when holding the pump handle forward

when using such bolts as ANS quick pull, or twist lock, the bolt is always aligned thus the shot will alway be the same. (which many people have noted)

the size of the bolt inlet hole is also a factor in whether or not you gun has the chance of misalignment, even with side to side play.

[Castro #66]

Maybe I don't understand what you're saying... you think rotational misalignment is to blame? I believe that my Ultralite (twistlock) does the same thing.

[EvilAuthorityX]

other factors are probably to blame as well, but from what i can see right now playing with a few different snipers. rotational misalignment certainly is present in guns that have play in the pump stroke.

[drgonzo]

Originally Posted by PureInsanity

i was playing around with this today and also found that NOT holding the pump handle increased ball-to-ball accuracy.

*i repeated these groups of 5 shots a few times and got just about the same results every time.
*fresh paint matched to a 16" .684 UL

NOT HELD:
5/5 hit directly on top of the first shot at 20 yards

HELD FORWARD:
3/5 hit directly on top of the first shot at 20 yards

possible reason my test might be invalid:
the 2-pieces of my stock orracle bolt aren't perfectly alined. the air hole on the bottom of the front delrin piece is rotated ~5 degrees off axis from the back (alum) section.

good excuse for a new bolt, though.

This sounds like a classic operator issue, the front hand introducing instability/inaccuracy. There is also the possibility of subconscious influence on the results, you just don't aim quite as well when holding because you automatically assume it's not going to be as accurate.

[PureInsanity]

i went into it completely non-biased or trying to influence it in any way. i just wanted to know which, if any, would help a ball fly straighter.

also, there wasn't much room for user error. i was sitting on a chair with my tank between my thighs. i wasn't even sighting down the gun, just crotch-shooting at a large rock wall and seeing where they hit.

[drgonzo]

Yeah not a valid test, period.