I'm actually writing this post to give away a secret porting method which I came up with over 25 years ago. I spent 6 months developing it, kept it under wraps thinking I might some day set up to do it and patent it then, but I never will.
First I'll discuss the several porting methods I've looked at through the years and why they aren't good for cast bullets. - All I've seen use large ports, and the manufactures say the porting works by venting off powder gasses to prevent the jet action of squirting it out the front. First off, they are all wrong about venting off the gasses causing significant recoil reduction. If the porting method does indeed reduce recoil it is because the forward edge of the port hole gets slapped with the powder gas as it turns it upwards, while the back edge of the port hole gets almost no pressure. Large ports are required to make it work at all, and the muzzle blast becomes horrific and bombastic. If the ports are larger than the distance from base of bullet to first lube groove, the gasses blasting around in the port wipes the lube out of the groove and the barrel will lead for the rest of the barrels length. Gas checks will keep it from building up, but it doesn't help accuracy to have the bullets hinder parts striped of lube. So the problems with all the porting I've seen , in a nutshell, are, here is almost always significant velocity loss, muzzle blast if far worse, and recoil reduction is hard to measure or feel.
The concept I came up with uses a simple 60 degree included angle hole drilled into the barrel. Go deep enough to leave a .1 inch hold into the bore. Put your first hole no closer than 2 inches from the muzzle and go back from there. I put three or four on each side of the barrel at about 45 deg from perpendicular. If porting a rifle, start the first holes 4 inches from the muzzle, or even more, then a half inch to one inch apart. Whatever looks best to you.
Here's how and why it works. The tiny .1 inch diameter hole lets off very little steam, and doesn't change chrono readings at all. As the rapidly forward moving gas squirts out the tiny port it slides up the 30 degree angle expending it's energy rapidly as it slides/impacts this relatively wide surface, compared to a straight port hole. After extensive shooting the forward half of the port will be blackened by powder gas and the rear half will remain clean white steel. Because the gases are spread out and energy is absorbed on the ports front edge, they leave the barrel at a far lower velocity than from a large straight port, which in itself lessens the blast from the ported gas, but it is also directed forward, away from the shooter. The result is dramatically reduced recoil AND MUZZLE BLAST IS REDUCED! Because of the small amount of gas vented off, muzzle velocity isn't reduced at all, on revolver or rifle. When measured at the shooters ear with a sound meter, the report is reduced, but though not dramatically. But recoil reduction is dramatic, and controlable by the number of ports installed. For example. A 357 Ruger blackhawk I had shot all bullet weights from 125 to 240 grains into the same group without changing the sights. Before porting, a Charger Arms buldog, 44 special, with 3 inch barrel, shooting a 280 gr WFN at 1100 fps, drew blood from my hand in three places after firing one cylinder full. After porting there was no pain at all with the same load and it shot to the sights, whereas it went way high before porting.
The ports can be drilled, the best drills being single flute. Try all the brands available to find the sharpest. I drilled through with a .090 drill first then opened the port up with the 60 deg included angle champher bit.
All drills push up metal as they break through, and this must be minimized. A very shorp bit is mandatory, with light feed pressure as you get close to breaking through. Also, fill the barrel where the porting will be with cerro safe and wait till it has time to expand to the max. While drilling, use water with soluable cutting oil applied liberally so the metal temperature at the break through point doesn't get warm enough to soften the Cerro safe. Melt the cerro out after drilling and the job is done. A few lap shots is good but not required.
Any of you interested in porting with this method, are welcome to have at it, on a personal basis for make a business of it. I should have has since enough to give it away at least 15 years ago.
Please post any questions or problems you have and I'll answer the best I can.
