EDM (electronic discharge machine) porting is available from:
Mag-Na-Port International, Inc.
41302 Executive Drive
Harrison Township, Michigan 48045-1306
See ad in June 1999 Skeet Shooting Review, p. 43.
EDM is also discussed in the Sep/Oct 1999 American Handgunner, p. 43 (coincidentally)where it is compared to a variation/revolution? in porting from Tom Novak at Leading Edge Tool (second article on Novak's product appears at p. 120 of same issue.
Leading Edge Tool
7135 Country Road 265
Palmyra, MO 63461
Apparently Novak's innovation is too "taper" the exit of the port in order to generate increased velocity (ergo increased dampening of recoil). This is described as being based upon the Bernoulli principle.
Since I was an English major I am not in a position to argue about that, but I thought Bernoulli's observations were themselves a function of the Ventura effect -- which I recall from sailing. As water flows from a wide path, like a river, into a narrow passage, it speeds up. This speeding up is the Ventura effect, I think.
The Bernoulli effect, at least as it is used in sailing and I guess aeronautics too, is the decrease in pressure on the surface of the sail or wing, as a consequence of the increased velocity of the wind passing over it, and as a result of which the sailboat goes forward and the airplane up.
In other words, I assumed that the tapering of the port to generate more velocity was a result of forcing the same amount of gas thru a smaller passage (a la Ventura) and not a result of decreasing pressure somewhere else(a la Bernoulli). But I'd be delighted if someone had a better explanation to share.
Rob is looking up the contact data for Ballistic Specialities.