Long post, but if you’re suffering with an unruly Airmaks Caiman, it might be worth a read:
I just picked up an open box Caiman 177 from UA for $800. It will be a gift for a relative who keeps borrowing my Leshiy Classic
I set it up with a simple but useful Vortex Spitfire 5X prism and an impulse air 1250 and cleaned the barrel. Immediately found a lot to like with the metal mags, nice trigger and overall feel - particularly nice off hand. However, right away there were some “issues”, first of which was that it shot 650fps at 280bar and increased to >1000fps down at 120-130bar. In other words, no regulator function. Given that it was at 240bar when I received it and it’s bag was somewhat dusty, I figured that the outer reg O-ring was kaput, due to prolonged stress, effectively bypassing the reg so that the gun was always operating at tube pressure (not my first such rodeo). The kind folks at UA gave me a set of Orings and I replaced them, which restored the regulator function.
However, upon tuning it to run around 890 with 10.3g JSBs, I discovered that it had another issue. I tuned it to shoot 890 on a full fill (280bar for me) but the speed then dropped in a gradual slope to 850 at 220bar and 810 at 150bar. This happened several times and couldn’t be tuned out, so I set about doing some internet sleuthing. Pretty quickly found this to be a common problem with Caimans, along with some other Airmaks models. Steve at AEAC documented it in a review and Shooter1721 reported it, along with numerous other owners on this forum. Steve described the gun as a 9/10 due to this issue. I think of it as more detrimental - at least a 3-pt deduction… Ya, I know, do the research beforehand!!! I did a bit, just not enough, apparently
. Sadly, after much more research, I couldn’t find a fix - aside from the obvious frequent refill scenario. Even with that, I was unhappy with the ES, which aside from the steady drop, showed a lot of fluctuation between concurrent shots. There is a Huma reg for the Katran which seems like it could be modded to fit (slightly different valve spring attachment). If anyone has done that, plz let me know….
Anyway, having been inside the reg to change the O-rings, I did notice a couple things that struck me as odd, from a design perspective:
The first is that the valve return spring attaches to the base (breech end) of the reg and traverses the plenum around 1.5 inches without any kind of support to keep the spring in a straight line! In other words, it can deform (bend/twist) rather than compress when the valve opens, placing a lateral stress on the poppet that could vary from shot to shot as the spring moves around. To address this issue, I fabricated a plastic guide tube to surround the spring and keep t straight without interfering with its ability to compress.
The second thing I noticed was that the reg piston had some kind of black plastic surface where it meets the reg screw nipple and the tube air enters the plenum (the most critical part of the reg assembly). It was pitted in the middle with a detent that was obviously caused by the nipple on the reg screw, suggesting that the plastic surface is rather soft. Many regs have metal to metal contact or use a hard delrin or peek disc to form a sandwich between the piston and screw. Since I was planning to order and mod a Huma Katran reg, I figured I had nothing to lose trying to “fix” the existing reg. So, I attempted to prize off the black plastic disc from the brass piston by running a razor through it perpendicular to the brass surround. It turns out that it isn’t simply a plastic cap but is instead protrudes right into the piston. Having cut it close to the surface of the brass exterior tube, I sanded and polished it so that the whole surface was flat and flush with the brass surround. I then drilled a tiny hole in the middle of the plastic and filled it to surface tension with some 15-minJB weld. Having a few spare delrin sandwich discs that come with FX Huma regs, I stuck one onto the surface of the middle of the piston and allowed it to cure 4hr in an inverted position. I then reassembled the reg and set it to 7/8 of a turn, same as it was before my audition of the delrin disc.
With the Huma Katran reg one click from being ordered (and the fact that it’s Sunday), I figured that I had nothing to lose by putting the gun back together and giving it one last shot with the my modded reg. I wasn’t optimistic, but I was pleasantly surprised. First and foremost, the descending speed issue is gone. It shoots 890fps from 280bar to 115bar, where it falls off the reg. ES is also much improved, similar now to my FX and Edguns, with none of the crazy shot-to-shot swings I was seeing before. So far, I’ve tested it over 4 refills, the first shooting pellets through the entire string and the others with punctuated groups of dry firing, so as not to waste hundreds of pellets. It also showed no sign of creep/POI shift after resting 4h at 200bar. Accuracy at 50y was “better than me” with both pellets and Zan 10 grain slugs (nice surprise!) the latter of which shoot at 875fps on the 890fps pellet tune, as expected with the higher friction from the slugs.
So, given that I made two changes at once, I can’t say if one or both was responsible for fixing the major issue of descending speed. My guess is that the reg fix is the most critical - suggesting that the stock black plastic piston cap is the culprit. I can’t imagine how a floppy valve return spring would produce a perfectly descending speed so I’d postulate that the spring fix (if it does anything) may simply improve ES/shot-to-shot consistency. Anyway, this is obviously just one gun that seems to have been improved. If you have a Caimen that you’ve sidelined due to these issues, please give it a try and let me know if you need any further info. Unfortunately, due to the haphazard nature of this work, I didn’t take any pics. There are a couple nice videos of a Katran reg refresh that can serve as a guide.
I will follow up with results of first shots after an overnight incubation at 280bar (creep stress test!). I then intend to put some foam in the stock to reduce its ability to act like the body of a string instrument, amplifying the hammer strike, which is markedly less noisy without the stock!
I just picked up an open box Caiman 177 from UA for $800. It will be a gift for a relative who keeps borrowing my Leshiy Classic
I set it up with a simple but useful Vortex Spitfire 5X prism and an impulse air 1250 and cleaned the barrel. Immediately found a lot to like with the metal mags, nice trigger and overall feel - particularly nice off hand. However, right away there were some “issues”, first of which was that it shot 650fps at 280bar and increased to >1000fps down at 120-130bar. In other words, no regulator function. Given that it was at 240bar when I received it and it’s bag was somewhat dusty, I figured that the outer reg O-ring was kaput, due to prolonged stress, effectively bypassing the reg so that the gun was always operating at tube pressure (not my first such rodeo). The kind folks at UA gave me a set of Orings and I replaced them, which restored the regulator function.
However, upon tuning it to run around 890 with 10.3g JSBs, I discovered that it had another issue. I tuned it to shoot 890 on a full fill (280bar for me) but the speed then dropped in a gradual slope to 850 at 220bar and 810 at 150bar. This happened several times and couldn’t be tuned out, so I set about doing some internet sleuthing. Pretty quickly found this to be a common problem with Caimans, along with some other Airmaks models. Steve at AEAC documented it in a review and Shooter1721 reported it, along with numerous other owners on this forum. Steve described the gun as a 9/10 due to this issue. I think of it as more detrimental - at least a 3-pt deduction… Ya, I know, do the research beforehand!!! I did a bit, just not enough, apparently
. Sadly, after much more research, I couldn’t find a fix - aside from the obvious frequent refill scenario. Even with that, I was unhappy with the ES, which aside from the steady drop, showed a lot of fluctuation between concurrent shots. There is a Huma reg for the Katran which seems like it could be modded to fit (slightly different valve spring attachment). If anyone has done that, plz let me know….Anyway, having been inside the reg to change the O-rings, I did notice a couple things that struck me as odd, from a design perspective:
The first is that the valve return spring attaches to the base (breech end) of the reg and traverses the plenum around 1.5 inches without any kind of support to keep the spring in a straight line! In other words, it can deform (bend/twist) rather than compress when the valve opens, placing a lateral stress on the poppet that could vary from shot to shot as the spring moves around. To address this issue, I fabricated a plastic guide tube to surround the spring and keep t straight without interfering with its ability to compress.
The second thing I noticed was that the reg piston had some kind of black plastic surface where it meets the reg screw nipple and the tube air enters the plenum (the most critical part of the reg assembly). It was pitted in the middle with a detent that was obviously caused by the nipple on the reg screw, suggesting that the plastic surface is rather soft. Many regs have metal to metal contact or use a hard delrin or peek disc to form a sandwich between the piston and screw. Since I was planning to order and mod a Huma Katran reg, I figured I had nothing to lose trying to “fix” the existing reg. So, I attempted to prize off the black plastic disc from the brass piston by running a razor through it perpendicular to the brass surround. It turns out that it isn’t simply a plastic cap but is instead protrudes right into the piston. Having cut it close to the surface of the brass exterior tube, I sanded and polished it so that the whole surface was flat and flush with the brass surround. I then drilled a tiny hole in the middle of the plastic and filled it to surface tension with some 15-minJB weld. Having a few spare delrin sandwich discs that come with FX Huma regs, I stuck one onto the surface of the middle of the piston and allowed it to cure 4hr in an inverted position. I then reassembled the reg and set it to 7/8 of a turn, same as it was before my audition of the delrin disc.
With the Huma Katran reg one click from being ordered (and the fact that it’s Sunday), I figured that I had nothing to lose by putting the gun back together and giving it one last shot with the my modded reg. I wasn’t optimistic, but I was pleasantly surprised. First and foremost, the descending speed issue is gone. It shoots 890fps from 280bar to 115bar, where it falls off the reg. ES is also much improved, similar now to my FX and Edguns, with none of the crazy shot-to-shot swings I was seeing before. So far, I’ve tested it over 4 refills, the first shooting pellets through the entire string and the others with punctuated groups of dry firing, so as not to waste hundreds of pellets. It also showed no sign of creep/POI shift after resting 4h at 200bar. Accuracy at 50y was “better than me” with both pellets and Zan 10 grain slugs (nice surprise!) the latter of which shoot at 875fps on the 890fps pellet tune, as expected with the higher friction from the slugs.
So, given that I made two changes at once, I can’t say if one or both was responsible for fixing the major issue of descending speed. My guess is that the reg fix is the most critical - suggesting that the stock black plastic piston cap is the culprit. I can’t imagine how a floppy valve return spring would produce a perfectly descending speed so I’d postulate that the spring fix (if it does anything) may simply improve ES/shot-to-shot consistency. Anyway, this is obviously just one gun that seems to have been improved. If you have a Caimen that you’ve sidelined due to these issues, please give it a try and let me know if you need any further info. Unfortunately, due to the haphazard nature of this work, I didn’t take any pics. There are a couple nice videos of a Katran reg refresh that can serve as a guide.
I will follow up with results of first shots after an overnight incubation at 280bar (creep stress test!). I then intend to put some foam in the stock to reduce its ability to act like the body of a string instrument, amplifying the hammer strike, which is markedly less noisy without the stock!
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. I have been known to stick a grain of corn or a Hawthorne berry into the center of my putty target.