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!

[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.

[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.

[TonyL]

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?

[TonyL]

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"?

[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...

[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.

[NickG]

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 )

[Geoff555]

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.