Pellet seating in my Mayhem gained 20fps!

[UlteriorModem]

Shooting the Benjamin Mayhem NP2 SBD in .22 calibre. Pellets - H&N FTT 14.66 grain.

I had been seating my pellets flush with the end of the breech. I was averaging right around 750 fps with an average of around 18fpe.

I got an air venturi pellet pen with an adjustable pellet seater with it. So I decided to try seating the pellets ever so slightly into the breech. Tried several seating depths and if you go to far the fps starts declining. But I ended up with the pellet set maybe 1.5mm or so into the breech. With that I was averaging around 770fps with an average of around a little over 19fpe!

The accuracy and consistancy of grouping seemed to get better with the seated pellets, but that is hard to quantify.

[Motorhead]

Makes sense ... hold the cork in the bottle until more pressure is available to launch it = more speed and lower ES

[UlteriorModem]

I'm also thinking since the skirt is already 'compressed' into the barrel you save a little energy there.

[bandg]

Could it be as simple as elimination of air loss (leakage) past the pellet after it is seated a bit?

[Motorhead]

If the seating has FULLY compressed the pellet skirt into rifling .... sealing issue perhaps
If seating simply has the pellet skirt now firmly up against the leade chamfer .... pellets no longer jumping ahead as pressure rises which actually will have it sit there until pressure rises enough to break it loose and send it down the barrel.

In a piston air gun pellets fully engaged into rifling break free easier and generally give wide ES figures over those that sit in place like a well fit cork.

[Mole2017]

I don't think of it as sealing anything differently so much as optimizing the piston stroke/pressure building/pellet motion cycle. Kind of like the arguments about pellets that are too heavy or too light--one causes the piston to bounce back off the column of air and the other lets the piston hit the end of the cylinder too hard.

Just the right amount of space behind the pellet is like finding the perfect weight pellet for your gun.

[Wolverineshooter]

Great to know. My Mayhem shoots around 760fps with CMHP. I will try your method to see if I can gain some fps.

[UlteriorModem]

Just as a point of reference, the 'probe' of the pellet setter is extended just a tick or two over 3mm.

That's what worked for me