Porting a Shotgun??

[sarge1572]

OK. I'm NOT a machinist, or a gunsmith...per se. But I do have a great deal of mechanical experience and have worked on MANY gunz (and they didn't blow UP when I wuz done) I'm a factory trained armorer in several pistols, and long guns so I'm not asking this question lightly...

I have a "couple" of O/U shotguns I use to shoot trap. I want to port one of them. I'm willing to THROW IT AWAY if I screw it up, but I don't think I will...with your help.

In order to port an O/U 12 GA shotgun 2 3/4" chamber, fixed chokes (Modified - top barrel, Full - Bottom Barrel) is there a formula? If the shotshell is a significant issue, this is used EXCLUSIVELY for trap. No hunting, no skeet, no ground squirrels, no drive-bys, no gophers, or anything else you can think of.

Is there a fixed number of "ports"? Fixed distance between port locations? Fixed angle to open the port in the different "choked" barrels?

How do I determine the size of the port and the number.....and WHERE they are located as well as the distance apart? How far from the muzzle do I start? How do I determine that distance?

Phew. I've worn myself out.

Any reference material is welcome. I have my trusty Makita standing by and my Home Depot drill pack. (OK. you purists go to another question. You have NO sense of humor. I KNOW drilling holes in my shotgun barrel is serious business so no bloviating, or worse... droning on and on about the potential hazards - I'm looking for the INSTRUCTORS in the group. I'm GOING to do this even if I do it wrong. I'd just like to do it right...the first time, and not blow up because I'm DAMNED pretty and don't want to ruin my shamefully good looks!!!! COME ON!!!! LIGHTEN UP!!!!)

The shotgun is a Daly/Miroku O/U 12 ga in VERY GOOD/excellent mechanical condition. 26" bbls, top barrel modified choke (fixed) bottom barrel full choke (fixed)

What size ports, how many, what distance apart, what angle into the barrel, how far do I start from the muzzle, what angle from vertical (looking down from the top of the barrel)...

and I need to know the information for each barrel. Is it different for the full choke VS the modified choke barrel?

Why do the shotguns I see show the top barrel with ports at the bottom, and the bottom barrel with ports at the top?

If there is a mathematical formula because of the pressure, angle, distance from the muzzle, full choke, modified choke, etc?

Can you direct me to that source?

OK. I REALLY need a nap.

No preaching about the potential danger. I KNOW the potential. But somebody has already figured all this out. If you're willing to share it thank you. If not, look for my "experiment" on the 6 o'clock news and an O/U on sale in CalGuns with MINOR COSMETIC DAMAGE.

(no, really, lighten up....really)

Thanks for ANY help. I'm doin' this... (OMG! I sound like a teenager)

Jeff

[Pyrodyne]

This might help.. have a look at one of these in person.

Citori 525 Golden Clays

[ar15barrels]

I start about 3" to 4" back from the muzzle.
Angle the barrel muzzle down by about 15 degrees when you clamp the barrel in the vise.
Use a center drill as a regular drill bit will not drill a hole at an angle on the side of a circle.
Drill a precise row of 5/32" holes on 1/4" centers on the top of the barrel.
A 3" long row of ports is a good start.
When you index the barrel left and right for the other two rows on the top barrel, move back 1/8" from the first hole and index the barrel enough to visually set the first hole and then move back 1/4" for each of the next holes.
I like to put one less hole to the left and right of the center row to form a nice diamond.
3 rows is enough on top.

On the bottom barrel, you will want two rows on each side as they will have more sideways angle than the top barrel.

[sarge1572]

WOW!! You make is sound so simple!!!! I bet you've done this before.

Thanks for the pic, and for the great description of how to proceed. This is going to the top of the "project" list.

Jeff

[ar15barrels]

I bet you've done this before.

Yes.
The hard part is the indexing, especially on an over-under.

[Manic Mechanic]

Thanks a lot! The info is much appreciated. I did some porting last night on the mill and it turned out pretty good.