• Mossberg Owners is in the process of upgrading the software. Please bear with us while we transition to the new look and new upgraded software.

Barrel porting

John A.

John A.

Unconstitutional laws are not laws.
Staff member
Administrator
Global Moderator
While I have ported my 22lr barrel in my suppressed AR upper barrel, this was my first attempt of porting a shotgun barrel.

I'm not entirely certain what diameter hole to use for the port itself or what center to center factory port spacing are (and if anyone wants to measure some for me would be appreciated), but from everything I have read, on longer barrels, the porting should start at approximately 22 inches from the chamber to allow ample time for the powder to burn.

So, I started the porting on this one at 23 inches and stopped at 25 inches, and that took into consideration for the mouth of the screw in choke so the porting wouldn't interfere with it because on a Winchester gun, the choke tubes are rather long and go pretty far back into the barrel.

I think the next barrel(s) that I do, I will probably space the ports a little closer to each other and at perhaps 3/8 of an inch apart instead of 1/2 inch apart next time. I know that staggered porting pattern looks nice and fancy, but I can't really see them being any "more effective" than porting that is all placed in-line. After all, the objective is to port gas, not to be "all pretty and junk" LOL

The drill angle of my port holes does not come straight out the barrel where the center is (relative to the straight line to the bore--see the first two pictures below) and is pointed up and somewhat at about the 11 o'clock position to vent some of the gasses up to help control muzzle flip some, and not directed back towards the shooter. I mainly didn't want to increase noise when it's being fired, but I did want to possibly decrease follow up shot times on fast movers.

winchester barrel porting 008.JPG

winchester barrel porting 009.JPG

So, I'm looking to you guys for suggestions on port placement on future barrels. What would you do?
 
Yes.

I have a little manual X/Y mill vise that I use with my drill press.

And I will note that flat face 4 flute endmill bits work better and wander less than a drill bit. ;)
 
Looks great, and I applaud that you're willing to take on a project like this! I know you have a good deal of experience with firearms and fab processes but I look at this and it would scare me to begin that first hole! Lol

The only thing I've been told about the location of the porting vs benefits of porting is that it seems to be most effective about 6" behind the muzzle.
 
Rossignol, it would be a LOT more difficult on a standard barrel and I doubt I would attempt one of them without a jig, but on one that has a vent rib, you simply rotate the barrel so the edge of the rib is against the top edge of the milling vise, measure to ensure the ports are where you want them and use a square to make certain that everything is true to each other and that makes sure it's centered by default relative to the rib/bead/top of the barrel.

To make it easier, I wrapped the barrel with 2 inch masking tape prior to work and made my marks on it with a pen so that ensures that the angles and placement are where I want them and makes drilling everything much easier.

Maybe these pics will explain it better.

milling 002.JPG

milling 003.JPG
 
I have some.

Magnetic with rubber contact pads.

(the vise wasn't tight, I was just holding the barrel in place for the pics)
 
John A. said:
While I have ported my 22lr barrel in my suppressed AR upper barrel, this was my first attempt of porting a shotgun barrel.

I'm not entirely certain what diameter hole to use for the port itself or what center to center factory port spacing are (and if anyone wants to measure some for me would be appreciated), but from everything I have read, on longer barrels, the porting should start at approximately 22 inches from the chamber to allow ample time for the powder to burn.

So, I started the porting on this one at 23 inches and stopped at 25 inches, and that took into consideration for the mouth of the screw in choke so the porting wouldn't interfere with it because on a Winchester gun, the choke tubes are rather long and go pretty far back into the barrel.

I think the next barrel(s) that I do, I will probably space the ports a little closer to each other and at perhaps 3/8 of an inch apart instead of 1/2 inch apart next time. I know that staggered porting pattern looks nice and fancy, but I can't really see them being any "more effective" than porting that is all placed in-line. After all, the objective is to port gas, not to be "all pretty and junk" LOL

The drill angle of my port holes does not come straight out the barrel where the center is (relative to the straight line to the bore--see the first two pictures below) and is pointed up and somewhat at about the 11 o'clock position to vent some of the gasses up to help control muzzle flip some, and not directed back towards the shooter. I mainly didn't want to increase noise when it's being fired, but I did want to possibly decrease follow up shot times on fast movers.

View attachment 9801

View attachment 9802

So, I'm looking to you guys for suggestions on port placement on future barrels. What would you do?
Click to expand...

the only thing I can offer is for ports to really work on a shotgun the ideal configuration it more small holes instead of less large holes.
It is real hard to get ports to be effective on a shotgun because of the low pressure at the muzzle

Less big ports work better on things like magnum metallic cartridges

Idea is that the big ports bleed off too much pressure before it can act as a force to "push down" on the muzzle...just not enough gas pressure, it can mess with some semi auto shotguns reliability

I like your angle , steeper the better I would think for keeping the muzzle down
 
I could certainly make the ports smaller next time. And closer together.

Just leaning back in my chair thinking about it a little, I know in order to retain the most pressure in a hydraulic bulldozer or backhoe or bucket truck system is using smaller diameter lever valves.

The smaller the hole, the higher the pressure that builds up in the hose.

I suppose the same could be said for small barrel ports would make a stream of expanding gas, compared to large holes that would have a quick forceful puff.
 
Not to derail the topic, but in hydraulics, pressure is controlled by resistance to flow. The control valves themselves have no bearing on how much pressure the system works at, only the speed the system works. I understand your train of thought though. Your flow of gas through a smaller diameter hole results in higher velocity, producing more opposing force. In this instance the pressure is already present, within the barrel. Kind of a backwards hydraulic system i guess.
 
Yes, the pressure is there, but in pneumatics, it's the same principle.

The pressure of the expanding gasses coming through a smaller hole will have more pressure outside the barrel than if it had a larger hole.

back on hydraulics for a moment, a garden hose without a nozzle compared to how the water acts through a smaller nozzle.
 
Because you have multiple ports, it seems it would port less pressure through each successive hole. For them to be equally effective, maybe they should get smaller as you approach the muzzle.
assuming equally effective is what you want.

Maybe you want the pressure to ramp up as the shot approaches the muzzle?

You want the recoil peak and the port reaction peak to occur at the same time right?
 
Do you need pics of the ports on a 28" 500 barrel, John? I'll dig it out and measure it for you if you do...
 
Best advice i can give is whats already on my ported barrell can definitely feel the difference in muzzle rise. I can get better images and measurements if you need.

uploadfromtaptalk1447664685721.jpg

Voodoo
 
Looks good John.

Word of advice if hunting from a enclosed blind (pop up tents included) make damn sure those ports are outside with the muzzle when you shoot else your ears will be ringing for a while. Ask me how I know.
 
MikeD said:
Looks good John.

Word of advice if hunting from a enclosed blind (pop up tents included) make damn sure those ports are outside with the muzzle when you shoot else your ears will be ringing for a while. Ask me how I know.
Click to expand...
Very sound advice Mike i feel your pain
 
Thanks guys. Lots of good discussion.

If anyone could measure the diameter of the holes, that would be helpful.

Caddman, you bring up a very good point, one I hadn't really considered, but I believe is correct.

Smaller ports nearest the muzzle would equalize the pressure as a whole, but after thinking about it, the port farthest from the muzzle would also have the longest duration.

I'm far from being an engineer and being able to calculate such things. I'm sure speed and pressure and port diameter and probably even the inside barrel diameter would all have to be taken into consideration to properly calculate such a feat.
 
John A. said:
Thanks guys. Lots of good discussion.

If anyone could measure the diameter of the holes, that would be helpful.

Caddman, you bring up a very good point, one I hadn't really considered, but I believe is correct.

Smaller ports nearest the muzzle would equalize the pressure as a whole, but after thinking about it, the port farthest from the muzzle would also have the longest duration.

I'm far from being an engineer and being able to calculate such things. I'm sure speed and pressure and port diameter and probably even the inside barrel diameter would all have to be taken into consideration to properly calculate such a feat.
Click to expand...
Ill take my verniers home and measure up after work
 
You must log in or register to reply here.
Back
Top