pressure". smaller bores, shorter strokes, etc all make then crack a bit.
pressure". smaller bores, shorter strokes, etc all make then crack a bit.
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.
video transferred to DVD, USB etc. Old negs and photos scanned to digital media
www.digitalconversions.co.uk
Is it the wave effect? Guessing that any changes will alter the point on the pressure wave when air leaves the muzzle.
For a while I was thinking it may be that my setups with tight vibrations reducing guides makes the muzzle blast more noticeable for the shooter.
But the OEM springs in the HW95 and HW77k dont give the same muzzle blast, even when they are on tight guides.
Sorry, can't help, but looking forward to seeing some explanations on this.
I have tried a few guns over time with lowered swept volume that seemed louder and assumed this phenomenon may be down to having to work that lower volume harder. Could be wrong, though, and certainly not the case here.
Maybe the wave theory mentioned above?
Or I wonder if it has more to do with spring force at the time of pellet release / piston bounce? Maybe even material composition of the spring itself and differing harmonics?
Can't remember now.......would gas rams do this?
THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
NEXT EVENT :- August 3/4, 2024.........BOING!!
Another (maybe daft?) thought to lob in there.....as well as causing other undesirable issues, I wonder if guns running too low preload may also exhibit similar symptoms, when the spring is unseated from its rear guide bearing, causing "spring to guide slap"?
THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
NEXT EVENT :- August 3/4, 2024.........BOING!!
i didn;t say the stroke was changed
let's say all things are equall and you simply change the spring for one that gives lower ME...
what could have happened to give lower ME ?
Less spring energy - no clear affect on muzzle pressure
Slower spring acceleration, but more preload (softer spring) - this will reduce piston bounce, increasing air pressure in the barrel
heavier (weight) spring - will also reduce piston bounce, increasing air pressure in the barrel
slowing spring - reduces peak pressure, and muzzle energy, but also reduces piston bounce, so potentially more pressure at the muzzle on pellet exit (althouth lower peak pressure at pellet start)
There are so many variable, but the above are all possible explanations based on the limited knowledge I have.
Another way to look at it... ME is largely (but not only) correlated to peak pressure behind the pellet.
Muzzle crack is (almost totally ?) related to barrel pressure at the time of exit.
So how can you get lower pressure behind the pellet at start, but higher at muzzle exit ? Answer: piston bounce, which at it's most extreme sucks air back from the barrel, or at leastprevents the flow from the chamber. So any spring change that decreses piston bounce, can increase muzzle crack. FOr that same spring to also decrease ME, it only needs to have less energy. The two are not mutually exclusive.
HTH - JB
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.
Thanks!
Your words "barrel pressure at the time of exit" has to be the correct place to start investigating.
I'm not confident that its easy to pinpoint the exact effect, but your ideas helps to organize my thinking a bit better!
In the 77k theres less preload with the spring giving 11fpe than the FAC spring, and the recoil is quick, but not sharp.
With the OEM/FAC spring, the recoil feels a bit more "restricted", indicating to me that there may be a bit more bounce.
I don't have an answer to this, but when setting up 21 mm tunes I have experimented a lot with set ups that make more fpe with light pellets than heavy or bouncing, and indeed the opposite, at the same stroke and not noticed any change in muzzle report. All on the same spring just altering piston weight and pre load ( just for information sake )
Hello, I had a small thought ( those knowing me at this point will groan, loudly.) if there is a small extension on the barrel, say of 4" , same bore, with a port in the side leading to a pressure transducer would a difference be noted with loud or soft reports?
Cheers all.
Geoff.
Master of creating amazing ideas, all carp mostly.
Another way to look at it... ME is largely (but not only) correlated to peak pressure behind the pellet.
Muzzle crack is (almost totally ?) related to barrel pressure at the time of exit.
So how can you get lower pressure behind the pellet at start, but higher at muzzle exit ? Answer: piston bounce, which at it's most extreme sucks air back from the barrel, or at leastprevents the flow from the chamber. So any spring change that decreses piston bounce, can increase muzzle crack. FOr that same spring to also decrease ME, it only needs to have less energy. The two are not mutually exclusive.
HTH - JB[/QUOTE]
We'll put and agree 100%.
I have a Diana mod 6 pistol which is not exactly a powerhouse, but it cracks quite a bit and there is no dieseling. I thought maybe the recoil absorbing dummy piston eliminates the bounce and eliminates any negative pressure just before the pellet's exit which produces the crack, but then again I have other Giss type Diana rifles with obviously longer barrels that shoot faster than the pistol but don't crack.
So on this basis, I presume barrel length is part of the equation when it comes to determine which crack and which don't. I would think that at roughly 600fps, the pellet is still in the approx 15inch barrel when the compression piston has stopped moving, meaning rapidly falling pressure behind it, hence no crack.
But then again most things including cracking in airguns are the result of a combination of many variables.