Springer muzzle blast

[evert]

I might have talked about this before.... but I've noticed that some springer setups give noticeably higher and sharper muzzle blast than others.
Its not directly related to energy output, and often lower energy can give a louder report than higher energy.

Can anyone explain what happens? What causes some setups to have a louder muzzle blast than others?

[piggy589]

Dieseling,combustion and barrel length?

[Shed tuner]

pressure". smaller bores, shorter strokes, etc all make then crack a bit.

[Tony.T]

pressure". smaller bores, shorter strokes, etc all make then crack a bit.

That suggests wasted energy to me? Or am I wrong- still learning about spring rifle tuning so all input is good!

[Shed tuner]

That suggests wasted energy to me? Or am I wrong- still learning about spring rifle tuning so all input is good!

wasting it from the muzzle is better than wasting more of it in the action...

[evert]

pressure". smaller bores, shorter strokes, etc all make then crack a bit.

No stroke change. Just a spring that gives lower muzzle energy.

[deejayuu]

Is it the wave effect? Guessing that any changes will alter the point on the pressure wave when air leaves the muzzle.

[evert]

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.

[Shed tuner]

No stroke change. Just a spring that gives lower muzzle energy.

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

[evert]

HTH - 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.

[dvd]

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.

[evert]

Dieseling,combustion and barrel length?

No. Well behave tuned guns with modern well fitting seals and very little lubrication.

Ive seen, or heard it several times now- a recent example is a full power (Norwegian full power, FAC to you) HW77k.
Little noise with the original spring, but a bit to lively, even with fitted guides. The gun makes somewhere around 13-14 fpe in the origginal format, I dont remember the exact figures.
I fit an after market spring on tight guides, and set preload with a delrin washer to give about 11fpe.

Suddenly the muzzle blast increases dramatically. what is happening? piston bounce?

I have had it happen with other guns too.