S510 ultimate sporter R

[shw]

Hi all ... I’ve read a similar post about this and I’m unsure of what the outcome was ... . I have the above rifle in 177 ( the factory regulated one . I’m not sure which make reg the factory uses )
which is a bit low on power in my opinion.. it’s currently at 10.7 ft lbs. and I’m looking for about 11.5 ft lbs .. so I’ve adjusted the power grub screw (is this called the Venturi screw?) and it’s made no difference..
any advice as to where to go from here..

[tonyc]

I heard AA make their own reg. They were going to use Huma but decided to make their own. A few issues have been reported where the reg wasn't working properly so the guns would run at low power when the cylinder pressure was high. I'd suggest you chrono a full string to check the reg is working and check the reg chamber pressure. If these are ok then you may need to reduce valve spring pre-load. Before making pre-load adjustments it's worth checking/cleaning the hammer rail to make sure the striker is sliding freely.

10.7 ft lb with what pellets? Could just be your pellet choice. 11.5 is probably too high with JSB/AA 8.44gr - it will run over 12 with JSB 10.34gr.

[shw]

I’m using jsb 452... 844 grain .. which I use in my regulated hft 500 and I’ve set that to 11.7 and works very well.. I assumed that the s510 would be the same in adjustability..
seems strange that the Venturi adjustments hardly make any difference... if anything the power is decreased !

[tonyc]

If you unscrew the venturi screw past the point where the transfer port is unrestricted you are creating dead space below the screw, adding to the transfer port volume, which theoretically should cause a slight power reduction. I've never tried measuring how much, just found the point at which the screw starts to reduce power then backed off half a turn and set maximum power on the valve pre-load. It seems like your power may be limited on the firing valve pre-load. It's how I have mine set, adjusted to 11.2-11.3ft lb with 8.44gr. With 10.34gr the same setting gives me 10.6-10.7ft lb.