I've fixed three so far. There are several problems, but mostly, it's the barrel.
ORing change and some adjustments also gains a little.
Once done, they do yield about 400 FPS with GTO's and punch nice, clean holes at 10 meters in real targets. With lead pellets, they will yield 360 fps and punch clean holes in GOOD target paper (Kruger or National Target).
If interested, let me know in a PM.
HM
I can give you 400 fps with regular pellets.
There is now considerable information regarding the fault surrounding the breach seal on these which can easily be corrected as stated here. This should see the tragically low velocity of about 330 fps jump to 360 fps as mentioned. We then have some semblance of clean cutting cards at 10 metres, albeit not perfectly so.
I went further.
I really liked the look of the gun but numerous club members preferring its easier handling and zero reliance on bottle filling when compared to monster length PCPs..or the 46M Agricultural farm implement ...So i decided to have a play.
Correcting the breach was easy, using a quad seal, or a packing washer below the O ring, if wanting to keep the stock O ring. Some twirls of Floss can do this if you lack the engineering skill. It picked up 30fps. De-burring the barrel entry, with a countersink bit in the lathe gave me another 10 fps, barely anything but it improved consistency and ease of loading. It is then a simple case of tapping the barrel up against this seal from the muzzle end under slight clamp pressure and then fully tightening off the clamp.
Next up, I realised this gun is light on compression when compared with say a HW40 (390fps Finale) Going inside, I realised that the headspace is a bit too much, with the piston stopping a good 0.7mm shy of the TP bulkhead. I decided on an initial reduced head space of 0.2mm. I was concerned with closing the space fully on the bulkhead, preventing closure, possibly straining the cocking pivot pin. So went with 0.2mm. I was rewarded with 35 fps. I later reduced this space further to barely 0.1mm ...chasing the max risky but could not resist ..Only to lose all the gain ☹️ Cutting a long story short, the transfer port needs a tiny bit of headspace, or a slight suction occurs if the transfer port fully closed onto. Skimming back to 0.2mm restored the gained 30fps.
I found a particular liking for R10 pellets and Meisterkugeln in accuracy and velocity terms, hitting 400 fps and 407 fps respectively once tuned. Finally, and not really recommended for the unskilled, i picked up another 10 fps by reaming the transfer port to 4mm. Its tricky and you need to flush the transfer port before cocking the gun, or risk forcing fragments into the valve...I ended up blowing it out with an upturned aerosol spray...The 10fps probably not worth all that but i though i might get more...?
I can now flatten knockdowns at 15 metres and cards at 10 metres are punched clean.
As regard why the manufacturer could not do this ..I have no idea but before you dismiss the gun, its the only one potentially good enough at this price point for true competition, unless laying out at least double its cost.
Thats a great post buddy, something I will be trying with the one I have just received (340 fps)
I wrote to Chiappa Firearms about the 400 FPS but i have had no reply to that so far. How did you achieve the piston packing, Is it something that can be carried out in a basic tools, garage workshop.
Thanks for sharing it.
Thanks...Head space on a number i have done so far, averages 0.7mm (0.03) ...probably built in by the manufacturer to allow ease of assembly but too safe compared to the 0.3mm i have found in the HW40. You want to cut that in half by finding some 0.3 to 0.5mm shim. Trim to the shape of the piston ...not letting any stray the edge of the major diameter of the piston or you risk scoring the precious cylinder wall.....Then glue it on using a good engineering glue.
I went further, machining a new head for mine with a slightly thicker front, ahead of the O ring..
Taking up that dead space should give you 30 to 35 FPS but you need to ensure breach is sealing with the method above, or any increase in compression will not be realised....losing it through the poor breach seal...