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Air Gun Home Forum Index » Rifles » Improving PCP Accuracy or Muzzle Velocity
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Improving PCP Accuracy or Muzzle Velocity 
PostPosted: Fri Dec 02, 2011 11:13 am Reply with quote
mod90
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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.
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PostPosted: Fri Dec 02, 2011 11:42 am Reply with quote
rsterne
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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

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Fri Dec 02, 2011 12:58 pm Reply with quote
SMP
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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

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Sean
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PostPosted: Fri Dec 02, 2011 1:48 pm Reply with quote
mod90
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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?
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PostPosted: Fri Dec 02, 2011 1:55 pm Reply with quote
rsterne
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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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Fri Dec 02, 2011 2:55 pm Reply with quote
mod90
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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.
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Improving PCP Accuracy or Muzzle Velocity 
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