Pellets, friction and release pressure.

Pellets.

Most everyone uses JSB branded or re-branded pellets, HFT and FT competitors especially, new kid for domed and pointed pellet manufacturer QYS is gaining ground however, H&N while stopping the excellent Sniper range have brought out Baracuda FT…RWS, well most use them for plinking.

So why have I a started with pellets?

Pellets have a massive effect on the tune of the gun, they act a valve blocking the pressure from just releasing into the barrel. Springer’s rely on this valving effect to build pressure within the compression cylinder. Larger or harder lead tighter fitting pellets hold on and build pressure behind them higher than loser softer or smaller pellets. Each pellet has its own release pressure, this being the pressure that once hit the pellet starts to move down the barrel.
Larger or tighter pellets build a higher pressure BUT also have more friction, so normally produce less muzzle energy, lighter or smaller pellets build less pressure as they let go earlier. So tighter fitting pellets which many use are FTT 4.50/4.51 or Baracuda FT, H&N state 4.50 or 4.51 but when you actually measure them they are usually larger than this, FTT 4.51 its not uncommon to measure a 4.55 head size, FTs are around 4.53, this adds to the friction within the barrel and they usually fly a little slower so create less muzzle energy, however its not the head size that is the most influential here its the skirt size. The skirt on a diabolo is larger than the head and for good reason as this is the part of the pellet that acts as the valve.
Barrels on well made springer’s have what is called a lead in, this is a chamfer that is machined into the breech end of the barrel that excepts the pellet. It allows easier feed of the pellet into the breech/barrel but also it allows the skirt of the pellet to sit against the chamfer and form the seal without compressing the skirt. This is why it is important to not push the pellets into the bore of the barrel, you lose that valve seal and it effects the peak pressure within the compression cylinder.
Understanding pellet release pressure, you then start to understand how different barrels can have an effect on pellet performance. Tighter match grade barrels suit smaller pellets, the barrels are usually quite long, if a tight/larger pellet is used the friction is just to high and the pellets start to lose speed before they exit the barrel. You can get over this with more input energy but that can add to recoil and surge so barrel matching to pellets is critical.

With regard to most springer’s they use essentially sporting barrels, these suit pellets 4.50 to 4.53 usually so we shall focus on pellets within this range and how we can effect how those pellets fly with how the tune has been implemented.
The long standing rule of springer’s make more power with lighter pellets and less with heavier pellets is actually not quite true, as I work thru what I have learn’t it will become clear that you can actually make springer’s push heavies with more power than lights or you can get a reasonable balance across the weight range. Its actually not uncommon for me to see 11.5fpe with JSB 16gr Exacts and the same 11.5FPE with RWS 11.9gr Hobby, on the same .22 rifle, its all in the release pressure and peak pressure generated behind it.

Check back soon for further ramblings about pellets.