Air Gun Home :: View topic - Improving PCP Accuracy or Muzzle Velocity

mod90 · Veteran Member

Are there any modifications that can be made to PCP rifles to increase muzzle velocity? Maybe a valve adjustment or something? I ask because I'm going to get a PCP (Hatsan BT65SB) in the not too distant future, & I'm curious to know what performance mods might be available options.

rsterne · Moderator

Depends on if it's a detuned or full power model.... The detuned models can have the valve stem turned down to get back to full power specs.... Any of them can have the hammer spring preload changed with a screw adjustment inside the hammer.... More preload opens the valve more, releasing more air and increasing the power....

Anything you do to increase the power will reduce the shot count, pure and simple.... More of one, less of the other.... Eventually, extra air is simply wasted blasting out the end of the barrel after "Elvis has left the building".... so then you just use more air and get nothing in return....

Accuracy is mostly a matter of making sure the crown is a good one and finding the right pellets that the gun likes....

Bob

SMP · Silver Status Member

Everything Bob said above

and

Once you find a pellet that the gun seems favour then you can tweak the velocity up or down to tune the harmonic. My recent experience is that can improve a very good group into a "one hole wonder"

And if your ordering the Hatsan I have heard very good things about the airstripper you can get as an option

mod90 · Veteran Member

I'll be getting a full power version, no power restrictions where i am now thank god. I'm aware that an increase in the timing of the valve opening will add velocity & reduce the total number of useful shots. But how much of an increase in velocity could be gained? 100-150 fps? How about using a larger bore valve?

rsterne · Moderator

I have no experience with the BT65.... but on the AT44 I got a useful increase of about 20 fps with no loss of shots (24 within 4%), just a higher optimum fill pressure, using heavier (18 gr.) pellets.... Another 30 fps dropped the shot count to 15.... 10 more fps cut the shot count to 8.... Another 10 fps dropped it to 5.... further adjustment of the hammer spring dropped the shot count to 4 with NO gain in velocity....

The AT44 showed only margin gains decreasing the valve stem diameter below 0.100".... which is the size of the full power stem....

Bob

mod90 · Veteran Member

So I guess I better leave the thing as is when I get it. No sense trying to improve on perfection. Minimal fps gains on maximum shot count loss doesn't sound too appealing. Thanks for the advice & comparison Bob.