AirGunTech: Re Engineering Spring Powered Air Rifles for smoothness, consistency, and to better suit UK power levels.

Autumn 2013, Little update what I have been upto

So…..the lathe blew up, typical Chinese lathe so my mates tell me, DC motors and carbon brushes that over heat…etc etc, so its all stripped out and will have a new 1HP 3ph motor installed with Inverter/remote start stop/speed control.

This means not much springer tinkering while i saved for the new motor etc…BUT that does not mean no tinkering πŸ˜‰

During the down time I rebuilt an old Mk1 Theoben Rapid ( yes a PCP) and it rekindled my love of the dark side…and i must admit it opened my eyes to just how good the old Mk1 Rapid is. Now I own 2 Rapids, this old Mk1 and a much newer Mk2 based MFR, the Mk1 is now shooting superbly however the regulator in the MFR is somewhat ill and has been sent to KevG here in the UK for s sprinkling of his pixie dust, I could have tackled the reg rebuild myself BUT Kev is a dab hand at Theoben regs, he knows exactly how they tick and what to do to them to improve them…he has forgotten more than I will ever know so why stress when he does such good work ;)…so back to the Mk1.

Early Mk1 Rapids are not regulated, this is ok but I wanted mine regulated, for a while I ran it with a paintball regulator and tank, this worked well but i always had a small leak that was very slow but very annoying…so I hatched a plan. KevG offers brand new built regs for the Rapids which he calls Micro core, what this basically means is he redesigned the regulator with a much smaller Belleville washer stack..and it just so happens its now small enough to fit in the bottom chamber on the old Mk1 Rapids with no modification to the chamber. Now, Kev is now offering a bespoke reg for the early Mk1’s, I opted to re drill the porting in the block of the Rapid to suit the regulator installation, I did this as I wanted the reg to cycle well on each shot. So new regulator to hand, a fresh ported Rapid valve to 6mm, a new .177 barrel with fresh porting set to 6mm taper to 3.9mm (0.177) and a rebuild was in order. I am not going to go into a ton of details on the build as many have rebuilt rapids and they are very easy to work on….however I must say im more than impressed with the efficiency of the gun, with a 235bar fill 400cc tank and 16inch barrel the gun will produce 370 shots before the pressure drops and it goes off regulator, a true fill it once a year gun if there was ever one created πŸ™‚

However….rebuilding the mk1 had me looking at the MFR (where i found the regulator was occasionally sticking) and….it had me looking if I could improve the efficiency of the Rapid action any.Β  The mk1 has 400CC, this will soon drop to 200CC as I plan on a stock change, the MFR is already set with a 200CC tank and again is a .177.

Two of the forums I frequent have some pleasantly technicalΒ  posters, the BSAOG forum has a lad called rkr and has a chap called Cloverleaf,Β now both of these guys have used a method of recording a shot cycle to either show hammer bounce, lock time, or both, I have no clue if one of these guys was the first to do so online but I will thank them for posting their results as it has shown recording the muzzle blast from a PCP is a great way of learning how efficient or inefficient the rifle is…so thanks lads ;)The program of choice is Audacity, its a free download, and would you believe you use buddy headphones but plugged into the mic socket on your computer to do the recording. Now I have used audio editors for a good while now so it was reasonably easy for me to navigate round and start recording and zooming in on the waveforms the sound recording made. It also makes it easy to see blast duration, if there is more than one POP (so hammer bounce).

So…lets see what a recording from the MFR looks like:




















I used both mics on the muzzle as I was just interested in air wastage thru double or triple tapping of the valve during a shot cycle, as you can see there are actually around 5 taps of the hammer with 3 releasing lots of air, which is not what is best for shot count, quietness and efficiency shot to shot. You can see the muzzle blast duration is just a nats over 0.1secons long…keep this in mid as we move onto something I developed over the summer.

During the summer months I decided to rebuild 3 of my BSA R10’s, they suffer from worse hammer bounce than the Rapid you see here, in fact much worse, unfortunately I do not have a before modification waveform to show you but i do have some after modification ones and they are quite something.
















Again for this waveform both mikes were at the muzzle, what you need to focus on here is the blast duration, 0.0160secs, the MFR (although .177) has a blast duration of around 1/10th sec, this R10 has just a nats over 1/100th of a sec. I have a feeling some of you will question/may say I just chopped the waveforms…trust me I just edited them to the first silence, what you see here is the total sound both rifles make and its duration in full. Also note on the R10 is just 1 pop, not 5 pops, this means the R10 is seriously more air efficient now, even more than the Rapid MFR.

Next up an older test on a custom BSA Scorpion SE /R10 hybrid in .25calibre i built for pest (rat) control, like the .22 R10 this one has a custom hammer but the action is unregulated.














For this recording I set Audacity to record at the breech and the muzzle, the top waveform is the breech, the bottom waveform is the muzzle, the gain was also higher so I made some notes on the capture to try and explain what I feel is happening on the waveform, the action muzzle blast lasts for 0.015 seconds, the bottom waveform as what we shall call a pre peak which is the hammer ping as its striking the valve, then the muzzle blast hits the mics and lasts for just over 1/100th of a second…just like the .22 R10 above. Now the top waveform is a little more complicated, the first peak i feel is trigger sear noise as i release the hammer, the green area is hammer to valve strike, then i get the black area which I can only put down to the hammer being dragged away from the clearly does not open the valve again IMO although if it does its for a seriously short duration.

The .22 R10 now runs without a regulator BUT with the anti hammer bounce hammer system in place, I just replaced the 200CC tank with a 280CC one and gained my lost shot count back easily, in fact the rifle produces a higher shot count unregulated than the rifle achieved with its problematic regulator it had originally using the 200CC tank. The 0.25 Scorpion SE/R10 hybrid is basically a buddy bottled .25SE in an R10 stock, again it features a 280CC tank and from this one I have seen over 300 shots, in fact I gave up counting πŸ˜‰

If you are into PCP tuning, consider giving Audacity a try, use some cheap ear bud style headphones as mics and play around with mic gain etc so you can record a shot and stretch the waveforms out and look for hammer bounce and multi valve opening…you don’t now need a high speed camera to watch the valve you can listen to it and see the waveforms it creates.

To finish, the plan is to recreate a similar set up with the hammer in the MFR and the Mk1 Rapid as I have done with the R10’s, I will then report back and try to show a before and after comparison, im hoping I drop down from a pop lasting 1/10s to one lasting 1/100s like the R10’s are doing. Also…people always ask which silencer is best on a PCP, or what mods make them better, consider if the rifle has multiple hammer/valve strikes the silencer is working really very hard to mute the long duration sound..often the shot will sound like a short fart rather than a single pop. If you instead work on reducing the hammer strikes the silencer you use on the rifle will suddenly become way more efficient, the .25 here is now so quiet with a standard HW silencer its like i doubled the length of that silencer…

Now I just need to get the lathe rebuilt πŸ˜‰


Happy tinkering πŸ™‚













  • Hi Tony. How about an article on the HW99s .177 when the lathe is back up and running?
    ATB Dave

  • when i have the 99s exactly how I want it I will re strip it and get an article together, I want to machine up some grub screws into new transfer ports for some fine tuning and need the lathe for this. The lathe is just waiting for a new belt and machine a keyway into the motor pulley, the motor is turning now etc….ohh and i need to mount the remote start stop etc…so this week πŸ˜‰

  • Hi Tony,

    An excellent read as always and thanks for crediting me for the work on the audio recording of the shot cycle – I’m glad you found the technique useful πŸ™‚

    I developed this process myself and to the best of my knowledge I was the first to post about it on the ‘net; however this doesn’t mean I was the first, of course.

    Anyway here’s a link to my original post on the AAOC if anyone’s interested πŸ™‚



  • Really solid read! Thanks

  • Hi Tony. Unfortunately Cloverleafs item on AAOC no longer seems to be available. However, my question to you is regarding “Audacity” for checking hammer bounce etc.
    I would have thought that it would be necessary to ensure that a pellet was being discharged when doing these tests in order to ensure that the valve “open” duration takes into account any differences which may be caused by, for example, a really tight pellet vs. a really loose one potentially affecting the “back pressure” on the valve.
    Of course, this may be negligible…… I don’t know…….
    You don’t mention whether the rifle is loaded when you do your tests with “Audacity”. Is it, or does it vent straight to atmosphere unhindered by a pellet?
    Look forward to your response.

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