It does increase power but I have never pushed the length of the barrels of these type pistols to find at what point it cannot increase power any further, or begin reducing it as you rightly suggest,
The 3 mods I have done are all in keeping with the look of the guns rather than spoiling there appearance.
My HW75 had extra length of barrel to the true muzzle instead of stopping 28mm short as design.
This gave me approx. 22 fps.
The 40 has a shorter void/compensator design which adds almost 20mm of extra length for 17fps and the FAS 604 sight extension allows 34mm of increase. It was difficult for me to work out exactly what the increase was here as I had also had a small gain from having no choke built into the Walther barrel blank in Mikes mod.
I.E 34 mm barrel increase but also un-choked Walther barrel gaining about 15fps or so with some pellets for a total of almost 40 fps
As a note for mods before zorching this post......MAX increase never exceeded 3.4ftbs in any of the work under taken here!
Phil, you got the family name right, BSA, but this rifle is a precharge pneumatic, the good old Firebird with a couple of bling parts. Also have its stumpy little brother the Spitfire.
Regards, Baz
Just for additional info Baz (or anyone else interested) I have proved fairly conclusive that the FAS barrel crown IS beneficial, even versus that of Walther barrel blank I tested against.
I used a variety of ammo Monday evening over the club range rested at 10 Mtr with both barrels.
Mike asked me to trim the Walther barrel down to design spec, as he disliked the extension on but wanted to see if the Walther barrel gave any improvement over the Italian rifling instead of just wasting it.....it didn't, despite great care with the crowning.
Although the un-choked Walther barrel gave approx. 15 fps extra across all the pellets used, the FAS barrel cut group sizes by up to 3mm. The RWS R10 and excellent Geko (recommended) both better through the choked bore of the FAS.
We closely inspected the rifling but couldn't see the choke but after pushing the Geko through with a un-felted cleaning rod, clearly felt the slight restriction at the last 20mm and deeper cut rifling was present under a small magnifier when the pellets popped out.
Conclusion....stick with the FAS barrel but go for the valve mod...20fps available with that but be careful.