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Pellet Seating

pellet toolDo you own one of those gorgeous little Beeman pellet seating tools? I do. It was one of the first accessories I bought after buying my first quality air rifle, a Beeman R7. The pellet seating tool is well made, it’s attractive, and it’s pretty cheap. Years ago a lot of “experts” recommended using it to push a pellet into a barrel until it engaged the rifling for best accuracy. Let’s see why that might not be the best advice.

Imagine a loaded spring air gun at the moment of firing. The piston, propelled by the mainspring, is compressing the air in the compression chamber, transfer port and barrel into a smaller and smaller volume. The pressure is building up behind the pellet, until there’s a high enough pressure to overcome the friction and inertia of a stationary pellet. As the piston reaches the end of its travel, the buildup of pressure slows it down a bit, until, ideally, the pellet begins moving just as the piston comes to a stop.

Now suppose instead of placing the pellet right at the breech, you slid it all the way up to the muzzle. As the piston forces air into the barrel, there’s a large volume of air to be compressed, so pressure doesn’t build up as high, and the piston isn’t slowed down as it reaches the end of its travel. The piston slams into the end of the compression chamber, and the pellet has just enough pressure to pop out of the end of the barrel with very little energy.

Now suppose you load the gun again, and this time you only slide the pellet halfway down the barrel. Lower air volume, higher pressure, and more energy extracted form the spring. Now load it again, and push the pellet just a quarter way down the barrel. And again, pushing it just an eighth of the way…

You see where this is going, The closer the pellet is to the breech, the higher the pressure, and the more energy is extracted from the spring. Pellets should be loaded just far enough so that the skirt is flush with the breech.

Ah, you say, but what about the other end of the pellet seating tool, the ball shaped one? Beeman tells us in their instructions that it’s used for “smoothing out the skirt”. Truthfully, any pellet whose skirt needs smoothing after loading is probably of too low a quality to be used in a precision airgun, and a soft tool like your thumb won’t damage the skirt of a pellet the way a hard metal tool will.

But don’t throw away your pellet seating tool. I think they make great good luck charms for important matches.

3 Comments

  1. Louise wrote:

    Where can i purchase a pellet seating tool?? I live in Dorset…

    Wednesday, March 3, 2010 at 8:27 am | Permalink
  2. Mike wrote:

    So have you proved that the 1/32″ that the seating tool might push the pellet against the rifling, ( thats what it is with my BSA Super Star MK II) chronographs any slower then flush with chamber mouth?

    Monday, April 4, 2011 at 12:05 pm | Permalink
  3. mje wrote:

    Proved? Well, I demonstrated it to my own satisfaction, as have others- at least in spring guns. With PCP guns it may be a different matter, as a much larger volume of air is released on firing. Thing is, there’s no good reason to seat a pellet in contact with the rifling in air guns. This idea of seating a bullet so that it just touches the rifling from firearms, where the pressures and velocities are much higher- like 50,000psi and 3,500 fps.

    Monday, April 4, 2011 at 12:29 pm | Permalink

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