Hammer bounce in a PCP

[Jay Butts]

I have yet to see a factory airgun that doesn't have hammer bounce. You can measure it with high speed microphone, even a well tuned gun has typically one extra valve opening and ones with poor tune - 8 valve openings per shot is the most I've measured. Bounce can be killed by smacking the hammer as it's bouncing back (BSA Blast tamer and Daystate Harper valve) or as Tricky-dicky suggested by using an SSG or short stiff spring (SSS) with negative preload. The hammer can also be caught on bounce and thus prevent it from hitting the valve again (Hatsan and BSA S10).

Wow, well that’s interesting. So you’re suggesting that every hammer bounces?

Good job I haven’t got high speed hearing.

So a spring holds the hammer slightly off the striking point and pulls it back once it’s struck?

 

[rkr]

Wow, well that’s interesting. So you’re suggesting that every hammer bounces?

Good job I haven’t got high speed hearing.

I only notice it periodically, sounding like a lose raspberry. This must be when it’s worse, worse as in more bounce?

You can't hear it on a well tuned gun, the extra valve openings are much smaller than the one that powers the pellet. On a bad tune they can be heard and they waste a lot of air.

Here's an example, muzzle blast recording from my 300 fpe .45 Evanix. Top two lines is with stock hammer spring with 6 valve openings, the bottom one is with SSS and has two valve openings. Air usage went down from 15 bar/ shot to 10 bar / shot. Time on X axis.

Stiff-spring_zps545c2d0a by abbababbaccc, on Flickr

 

[Jay Butts]

You can't hear it on a well tuned gun, the extra valve openings are much smaller than the one that powers the pellet. On a bad tune they can be heard and they waste a lot of air.

Here's an example, muzzle blast recording from my 300 fpe .45 Evanix. Top two lines is with stock hammer spring with 6 valve openings, the bottom one is with SSS and has two valve openings. Air usage went down from 15 bar/ shot to 10 bar / shot. Time on X axis.

Stiff-spring_zps545c2d0a by abbababbaccc, on Flickr

Wow, that’s fascinating…. So the bounce sound is actually wasting air?

That difference with the SSS is significant. Can there be any reason why manufacturers don’t fit these from new or is it something on the lines of a Delrin spring guide in a factory springer; is it down to production cost?

Oh, I’ll bet your 300ftlb is a beast!

 

[Tricky-Dicky]

I have yet to see a factory airgun that doesn't have hammer bounce. You can measure it with high speed microphone, even a well tuned gun has typically 1-2 extra valve openings and ones with poor tune - 8 valve openings per shot is the most I've measured. Bounce can be killed by smacking the hammer as it's bouncing back (BSA Blast tamer and Daystate Harper valve) or as Tricky-dicky suggested by using an SSG or short stiff spring (SSS) with negative preload. The hammer can also be caught on bounce and thus prevent it from hitting the valve again (Hatsan and BSA S10).

Yep! I agree, pretty much all the mechanical guns I Have seen have some form of bounce to some degree or other, very few manufactures address this issue which is pretty much unavoidable on a STD setup, even the expensive ones, and the result is wasted air.
A few more examples of SSG types.

 

[BallisticBill]

If you hear the fart, hammer bounce is extreme. Hammer bounce will occur before you can hear the fart. A bounce occurs in most guns (even SSG) but the fart is the result of multiple opening of the EV caused by energy transfer back and forth between EV spring and hammer spring. SSG isolates the hammer spring, disrupting the energy transfer. Blast tamers have a similar effect by dampening the hammer bounce.

Hammer weight, relative strength and preload of EV and hammer springs, and hammer stroke, and are all contributory factors. There's no universal solution by changing a single parameter and some PCP experts disagree on the approach. Essentially the solutions are directed at increasing resistance to EV opening (EV spring and dynamic plenum pressure) or reducing the residual energy of the hammer. Changing one or other parameter has consequential effects on EV and hammer balance which usually necessitates changes in other parameters.

 

[Jay Butts]

Yep! I agree, pretty much all the mechanical guns I Have seen have some form of bounce to some degree or other, very few manufactures address this issue which is pretty much unavoidable on a STD setup, even the expensive ones, and the result is wasted air.
A few more examples of SSG types.

Would there be any advantage to fitting an SSG other than noise and air loss? Is there an improvement in performance?

Thanks for posting!

 

[rkr]

Wow, that’s fascinating…. So the bounce sound is actually wasting air?

That difference with the SSS is significant. Can there be any reason why manufacturers don’t fit these from new or is it something on the lines of a Delrin spring guide in a factory springer; is it down to production cost?

Oh, I’ll bet your 300ftlb is a beast!

By eliminating the hammer bounce the shot count is typically increased by 20-30%, that's what I've seen in my BSAs when adding a Blast tamer. Downside in SSS approach is much increased cocking effort and possibly trigger pull. SSG will help in that as the spring is under tension all the time thus allowing softer spring to be used. Many airgun manufacturers seem to be rather clueless about proper tunes, Korean guns being prime examples with notorious Korean cliff power curve where first shot is fastest and every shot after that slowing down. BSA and Daystate developed their hammer de-bounce devices but I don't think either of them uses those anymore. One of the reasons is probably UK power limit, those devices can be used to increase the power over legal limit and they of course cost extra to make, assemble and tune.

Yes, that .45 is indeed an interesting thing to shoot. Built for shooting in metal silhouette league, 20 kg steel rams need to be knocked down at 100M.

 

[Jay Butts]

If you hear the fart, hammer bounce is extreme. Hammer bounce will occur before you can hear the fart. A bounce occurs in most guns (even SSG) but the fart is the result of multiple opening of the EV caused by energy transfer back and forth between EV spring and hammer spring. SSG isolates the hammer spring, disrupting the energy transfer. Blast tamers have a similar effect by dampening the hammer bounce.

Hammer weight, relative strength and preload of EV and hammer springs, and hammer stroke, and are all contributory factors. There's no universal solution by changing a single parameter and some PCP experts disagree on the approach. Essentially the solutions are directed at increasing resistance to EV opening (EV spring and dynamic plenum pressure) or reducing the residual energy of the hammer. Changing one or other parameter has consequential effects on EV and hammer balance which usually necessitates changes in other parameters.

So is it a tripartite balancing act with hammer weight, hammer spring and hammer stroke all effecting each another? Very interesting..,

How accessible is the adjustment of these things to one with reasonable skills? I’ve known some that have just messed around with the hammer spring to adjust power. Pretty sure my mate can do this on his Steyr with nothing more than an Allen key.

 

[Tricky-Dicky]

Would there be any advantage to fitting an SSG other than noise and air loss? Is there an improvement in performance?

Thanks for posting!

On some guns an SSG will give better consistency, but this also depends on set up it's not a one-sided exercise, a bit like fitting a reg there are always other parameters to consider.

 

[Jay Butts]

On some guns an SSG will give better consistency, but this also depends on set up it's not a one-sided exercise, a bit like fitting a reg there are always other parameters to consider.

It’s an entire process I’ve never given much thought too. Every day’s a learning day.

Thank you for sharing your knowledge! It goes in one ear……… and stays!

 

[BallisticBill]

So is it a tripartite balancing act with hammer weight, hammer spring and hammer stroke all effecting each another? Very interesting..,

How accessible is the adjustment of these things to one with reasonable skills? I’ve known some that have just messed around with the hammer spring to adjust power. Pretty sure my mate can do this on his Steyr with nothing more than an Allen key.

All of the above, and plenum volume, pressure and transfer port determine the mass and timing of air exhausted. Secondary (and subsequent) EV opening caused by hammer bounce is going to reduce air efficiency but so too is excess air leaving the barrel after the pellet has departed.

Air efficiency on the primary opening of the EV depends on the duration and pressure of the air pulse, which is dependent on lift and dwell of the EV, plenum pressure & volume, and transfer port; it isn't directly related to hammer type (SSG or other) but is influenced by hammer energy and momentum. You may be able to change preload and port restriction on some guns easily but changing weights and dimensions of components (hammer weight, plenum volume, spring rates, etc.) isn't a simple.e matter of turning a screw. In addition to the engineering skills to disassemble, reassemble and modify parts, there's also the knowledge of what and by how much to adjust. Tinkering in the hope of getting everything in balance and optimised is unlikely to lead to a successful outcome.

 

[Jay Butts]

All of the above, and plenum volume, pressure and transfer port determine the mass and timing of air exhausted. Secondary (and subsequent) EV opening caused by hammer bounce is going to reduce air efficiency but so too is excess air leaving the barrel after the pellet has departed.

Air efficiency on the primary opening of the EV depends on the duration and pressure of the air pulse, which is dependent on lift and dwell of the EV, plenum pressure & volume, and transfer port; it isn't directly related to hammer type (SSG or other) but is influenced by hammer energy and momentum. You may be able to change preload and port restriction on some guns easily but changing weights and dimensions of components (hammer weight, plenum volume, spring rates, etc.) isn't a simple.e matter of turning a screw. In addition to the engineering skills to disassemble, reassemble and modify parts, there's also the knowledge of what and by how much to adjust. Tinkering in the hope of getting everything in balance and optimised is unlikely to lead to a successful outcome.

Many thanks for the explanation, I’ll have to read it a few more times to get a proper grasp.

BTW, I’m not considering any tinkering. My limits are with springers and whilst I’ve worked with high pressure vessels in the past, I’m aware of the dangers when unqualified.

 

[TimD81]

All of the above, and plenum volume, pressure and transfer port determine the mass and timing of air exhausted. Secondary (and subsequent) EV opening caused by hammer bounce is going to reduce air efficiency but so too is excess air leaving the barrel after the pellet has departed.

Air efficiency on the primary opening of the EV depends on the duration and pressure of the air pulse, which is dependent on lift and dwell of the EV, plenum pressure & volume, and transfer port; it isn't directly related to hammer type (SSG or other) but is influenced by hammer energy and momentum. You may be able to change preload and port restriction on some guns easily but changing weights and dimensions of components (hammer weight, plenum volume, spring rates, etc.) isn't a simple.e matter of turning a screw. In addition to the engineering skills to disassemble, reassemble and modify parts, there's also the knowledge of what and by how much to adjust. Tinkering in the hope of getting everything in balance and optimised is unlikely to lead to a successful outcome.

its basically trial and error and a sprinkling of experience thrown in then its in the hands of the gods lol

 

[Tricky-Dicky]

Tinkering is how we all learn nothing ventured and all that, I know I wouldn't have the knowledge I have now if I had been too scared to take a risk.

 

[Bill.B]

Unfortunately it's a standard feature on Brocock PcPs with a floating hammer which is why I traded in my Sniper HR. I just couldn't live with the noise.

 

[Agnutty]

Cheers Mike… I might just take a look. Although none of mine do it, it’ll still be interesting to see what engineering has been carried out… I’m nosy like that.

Thanks for posting.

No problem. I wish he was still participating in the airgun world. Rsterne was an absolute pioneer who offered everything he did to advance the airgun industry for free. Many of his concepts are used still in commercial production. I followed his step by step directions on doing the porting and valve body mods. It certainly made my gun more spicy. Anyway I'm rambling on. Good luck

 

[Jay Butts]

No problem. I wish he was still participating in the airgun world. Rsterne was an absolute pioneer who offered everything he did to advance the airgun industry for free. Many of his concepts are used still in commercial production. I followed his step by step directions on doing the porting and valve body mods. It certainly made my gun more spicy. Anyway I'm rambling on. Good luck

I’ll have to look him up, sounds like it could be some interesting stuff to read up on.

Ramble away my friend, it’s all good.

Cheers.

 

[PestWeForget]

its when hammer spring is too strong or cylinder pressure/reg too low or combination of both so either reduce hammer spring or up reg slightly or fit a slingshot lightweight hammer if possible

Makes sense what your saying. After having my ghost for a while which I bought new, I was wondering why it was a bit down on power when I chrono'd it and had developed a slight hammer bounce over time. I noticed that the reg pressure gauge had dropped to around 85 bar from what it was originally set at 100bar. So I've adjusted it back and the bounce has gone away now. Power now reading around 11.3ftlb with sovereign hunters but stopped there as the fx chrono probably has at least a manufacturers tolerance of 0.2ftlb, so don't want to tweek too much without a more accurate chrono.

I was wondering if the belleville washers had lost a bit of tension after running in, that it causes the reg to equalise at a lower output pressure. Like gas valves do over time as the springs loose tension, so a slight tweek brings them back up again.