HW97K, Gammo GX-40 and a Combro CB 625 Test

[microdave]

Hi All

Looking for some advice, guidance or experiences of testing HW97, Gammo GX-40, or any other Air Rifle using the CB 625. I’ve been shooting for many years but only recently looked into chrono testing.



I’ve had the 97K for approx 15 years and recently bought first PCP which was the Gammo (affordable starter).



On field tests the GX-40 seemed significantly more powerful than the 97; chrono tests confirmed this.



I tested both using the CB 625 and took several shot average: results were as follows:



HW97k (.22) – 490 fps using 16 gm pellet and 505 fps using 14.5 gm pellet; both roughly equate to 8.25 to 8.5 ft lbs



GX-40 (.22) – 543 fps using 16 gm pellet roughly equating to 10.5 ft lbs



My thoughts are as follows:



How accurate are CB 625s

Would you expect a brand new PCP such as GX-40 (which I believe has BSA workings) to be closer to 12 ft lbs

What could be going on with 97K and whats best way to tackle issues.



Appreciate any ideas

 

[Eddie_E]

I would check the size of the transfer port is around 1/8" (3.2) and adjust the hammer spring to 3 or 4 turns in from full out. In the US we shoot that gun at around 20 FPE.

 

[Bluecup]

Microdave,

I have the Combro cb-625 and F1 chrony in the green box and they read exactly the same, I modded my combro with the external 6v battery so I do not have to push the reset after every shot and now that is the only one I am using. I always had problems with the light and the alignment on the F1. As for your other questions about the HW97 and Gammo I do not have any experience with them.

Good luck,

Jim

 

[Eddie_E]

The GX40, Urban, Coyote and Buccaneer are all using the same action in a different stock. The only difference is there are 105cc and 165cc air tubes. UK versions are limited by transfer port size.

 

[microdave]

Thanks to all those who read post and offered advice – much appreciated.

The GX-40 was tested at RFD with an array of pellets and shot between 10.7 and 11.1 ft lbs. He seemed confident that this was within expected range; (he also shot the display model which gave similar results). I suppose I was expecting a more consistent 11.25 to 11.75 from my first PCP but considering the budget price and all the variables I am more accepting of its performance.

As for the 97, I stripped it down and found it caked in grease. I cleaned it up, lightly greased it and reassembled. It sounded much better but was still hovering around 8 ft lbs.

My main observations from the strip were as follows:
Piston seal had brown marks in areas (burns from dieseling?)
Breach seal also looked brownish
Main spring was intact but seemed very ‘weak’. It took literally no force to reassemble back block to the barrel/cylinder assembly (seem to remember by old HW77 requiring a fair bit?)
Nylon spring guide and washer seemed ok

I think I may opt for kit such as V mach, TbT, etc (even come across an Australian company offering top class kits?). Hopefully this will restore it somewhat.

Feel free to add any input on tuning a 97….

Thanks again