8 replies to this topic

[noobert]

Length of barrel = Diameter of plunger squared times length of plunger

Is the Diameter of the plunger with the o-ring or without the o-ring?

[CaptainSlug]

With. Formula is only loosely applicable.
I don't follow it and generally only decide on the barrel length after testing the blaster without a barrel to see what kind of volume of air it's moving.
I can use this method to gauge the output of both spring and pneumatic blasters. I've never tried using a barrel longer than 14 inches.
Most spring pistols won't need more than a 3-inch barrel, but the most powerful springers will need up to 12 inches of barrel.

Edited by CaptainSlug, 07 April 2008 - 08:21 PM.

[noobert]

I only have limited supplies to work with so I can't really test different sized barrels.

[keef]

Well, Go to Home Depot with the plunger tube and ask for a pair of Calipers. It can tell you the diameter of the plunger, from one side of the ID, to the other.

[noobert]

keef, on Apr 7 2008, 08:29 PM, said:

Well, Go to Home Depot with the plunger tube and ask for a pair of Calipers. It can tell you the diameter of the plunger, from one side of the ID, to the other.

Then do I measure the plunger with or without the o-ring?

[CaptainSlug]

noobert, on Apr 7 2008, 08:21 PM, said:

I only have limited supplies to work with so I can't really test different sized barrels.

I don't test different lengths unless my initial guess produce unexpected results. The blasters that NEED a longer barrel usually can output enough air to rustle curtains from a few feet away.

noobert, on Apr 7 2008, 08:33 PM, said:

Then do I measure the plunger with or without the o-ring?

With.

[donz2323]

hey CS how does this formula work? Isn't there other varible here that include how tight the barrel is around the dart, and how fast the spring expands (springers) or how fast air is released (air tankers)?
Isn't the target barrel length basically the point where the force of the expanding air can nolonger exert a force on the dart? any longer would result in slowing down velocity. I just don't know how this formula can work?

[Carbon]

donz2323, on Apr 28 2008, 01:34 AM, said:

hey CS how does this formula work? Isn't there other varible here that include how tight the barrel is around the dart, and how fast the spring expands (springers) or how fast air is released (air tankers)?

No. The boltsniper formula is only a basic "rule of thumb" ratio for barrel length to plunger volume. It doesn't take into account coefficient of friction of darts, and isn't applicable to air guns.

Quote

Isn't the target barrel length basically the point where the force of the expanding air can nolonger exert a force on the dart? any longer would result in slowing down velocity. I just don't know how this formula can work?

Right. You want to use as much pressure as possible to expel the dart from the barrel, in order to eliminate the "puff" of power which causes a dart to fishtail. The 1:4 ratio is only a starting point.

Edited by Carbon, 28 April 2008 - 06:34 AM.

[PC III]

If you only have acses to a small barrel, drilling holes in a ring around the barrel about 1-.5'' from the end will eliminate that "puff" by letting air out the sides.