View Full Version : Ported shot gun barrels

February 2, 2008, 09:12 AM
If I ported the barrel on my mossber 500 smooth bore, would it make any significant difference in muzzle rise?

or are the ports on some shotgun barrels really a novelty and not of much use?

February 2, 2008, 04:14 PM
Only thing I see from the ported shotguns is a minute change and recoil and getting the guy next to ya peed at ya for the muzzle blast coming out the side..

February 2, 2008, 05:48 PM
In my experience, with heavy loads and ported barrels the shotgun tends to recoil straight back actually increasing felt recoil. To me, I like a little muzzle rise as you can ride it out and roll with it.

Again, just my preference.

February 2, 2008, 06:20 PM
The extra noise will probably outweigh any benefits you get. I'd stick with the standard barrel.

Frank Ettin
February 2, 2008, 08:14 PM
IME, porting has a very slight effect. However, you do see many competitive clay target game shooters with ported barrels. I shoot registered trap and had one for a while, but my current competition gun is not ported.

I think one reason that many competition shooters like ported guns is that we shoot a lot. A typical day of practice, most of us will shoot between 200 and 400 targets. In competition, we'll shoot 200 to 300+ targets in a day -- usually over several days. At our state championship, I'll shoot 1200 to 1400 targets over a 6-7 day period (I often sit out one or two events). Although we tend to use heavy guns and light loads, so recoil is pretty modest, the cumulative recoil associated with that much shooting can get very fatiguing and affect one's concentration.

February 2, 2008, 09:30 PM
Porting does only one thing effectively. It lightens your wallet, not recoil !!

February 2, 2008, 09:41 PM
My experiences with a Vang Comp ported 870 and buckshot differ. It's a combination of backboring and porting, and I don't know what percentage each does in reducing recoil & muzzle jump, but I can say without question it makes a difference on my gun.
I have another 870 of equal barrel length with a standard Remington barrel & the difference is enough to add the "without" barrel to the "To Do List". :)

February 2, 2008, 10:33 PM
The Vang and backboring probably is very different from what I experienced. Only ported barrels I've shot were Mossberg factory barrels. They annoy me so much that all of my current mossberg barrels are now unported.

Jeff Mulliken
February 4, 2008, 06:12 PM
The science is clear, recoil is mass times velocity. Backboring and ports on a shotgun don't change that. The laws of physics are not that flexible.

You can insulate yourself from recoil with a heavier gun or by diverting a little of the recoil energy to perform work in an autoloader.

You can reduce felt recoil by getting a gun that fits your body shape and learn how to hold it properly. That will change the way the recoil transfers to your body and makes things more comfortable...but the recoil does not go away.

But, increasing the diameter of the barrel a few thousandths or drilling a few upward facing holes at the muzzle dont actually make a difference in recoil. It's all a big fat placebo effect.


February 4, 2008, 07:02 PM
I strongly disagree.
You're putting it too simplistically.
Lengthening a forcing cone allows a fractionally longer constriction time in reducing the shot charge from its original column width as it comes out of the shell and enters the smaller diameter of the barrel. Elongating that process, even slightly, spreads the impact forces out slightly, which reduces recoil a bit as the energy/gasses acting on the rear of the shell are shoving the gun backward. Shotgun recoil is not entirely a matter of just the burning gasses shoving backward on the gun, it's a combination of that AND what happens as the shot column begins to strike the forcing cone. Lengthening the cone does have an effect on recoil.

Backboring increases the bore's diameter for most of its length. In conjunction with the lengthened forcing cone, it can reduce velocity, pressures, and resultant recoil. Again, you're spreading out the reactions inside the gun that produce recoil. Spreading out the individual steps that create the recoil along the way does soften it, without changing any of the laws of physics you refer to.

Both of those can & do have a very real affect on actual recoil.

Porting alone, aside from a very slight reduction in velocity (VERY), does not reduce recoil, as such. But, it does reduce muzzle climb, which can be a very unpleasant component of overall recoil. When you fire the shotgun, the rear hits your shoulder as it travels rearward, and the front pivots up to hit your face (at least to some degree). Porting, if correctly done, directs gasses upward just behind the exiting shot column to provide something of a rocket motor effect that pushes the muzzle downward before it reaches its normal high arc point.
No, you have not changed the energy levels inherent in the explosion and subsequent reaction to the shot, but you HAVE re-directed the energy of the reaction. Most people don't differentiate between the elements of recoil (shoulder thump & cheek smack), but if you port a shotgun that traditionally beats its owner's face & hand it back to him, after shooting it he'll probably comment on how much less recoil it has, solely based on how it no longer punches him in the cheek.

Porting may deliver a slight increase in shoulder recoil in re-directing the energy, or it may not, but I'll tell you beyond a shadow of a doubt that backboring and ports DO make a noticeable difference.

There are other areas on the gun you can address in "recoil reduction" such as a more efficient recoil pad, a better stock design, adding weight, and so on.
I have two 18-inch 870s and one 14-incher. The Vang Comp 18-incher has synthetic stocks and is probably the lightest of the three, the other 18-incher is a synthetic-stocked pistol-gripped (full length stock) PMAX with the added weight of a dedicated light fore-end. The 14-incher is an older Wilson Border Patrol model with full wood and a mercury recoil reducer in the stock.
The Vang Comp is by far the easiest on my cheek & shoulder with comparable 2 3/4-inch shells.

I'd say you don't understand what the cone, backboring, and ports do or how they work, but they do work. :)


February 4, 2008, 07:25 PM
Porting does not reduce recoil - but it significantly reduces muzzly jump. Porting is a big deal - keeping the muzzle down as you aquire another bird or target in the air.

Lengthening forcing cones does reduce recoil - look over the previous response - he laid it out well.

Would I port an 870 - not unless I was really in love with the gun and wanted to shoot it for everything .... Its also not something you should just do on your own - you should send it to a qualified shop like Briley in Texas and get it done right if you want it done / but it'll probably cost you about $ 100 plus shipping to have it done on a single barrel - but please don't just take a drill press to it and punch holes in it ...

Jeff Mulliken
February 4, 2008, 08:24 PM
Respectfully, this is all witch doctor stuff.

First expanding burning gasses do not push backward, the push equally in all directions.

The shot is through the forcing cone by the time pressure peaks so it does not reduce the peak at all.

The force expended going through the forcing cone does not generate a surge of recoil that can be perceived any more than you can percieve a difference in temperature of a hundredth of a degree in temperature.

If you could actually feel the difference in the shape of the forcing cone then you should also be able to feel the difference in recoil between your choke charge hitting a full choke vrs a modified choke but you cannot. And keep in mind that the shot goes through the forcing cone relatively slowly, no where near as fast as it is moving when it hits the restriction of the chokes when it is moving at near muzzle velocity

Lets assume you are right about over boring reducing velocity that can result in a reduction in recoil. If trus there are far better ways to reduce velocity, just go to a lighter load. However if you feel you need a specific velocity to do the job, say 1200 fps in a standard diameter bore then you just end up having to go to a hotter load in your overbored gun (to get back to the 1200 fps goal and gain nothing.

Most of this stuff is meaningless marketing, it's like getting a car with a speedometer that goes to 180 mph....it's cool but accomplishes nothing of value.

February 4, 2008, 09:48 PM
No Jeff, it's far from witchdoctory.

Your comment that expanding gasses push in all directions and do not push backwards is again simplistic and only partially true.

Those gasses only expand in all directions when the expansion occurs in a non-confined space. When the burn begins inside a cartridge the gases obviously will try to expand equally in all directions, but because the cartridge case creates an expansion chamber with limited space, the gases can only "push" so far in any direction before something has to give. In a modern cartridge, what gives is obviously the forward end when pressures reach a sufficient intensity to break the tension between case neck and bullet. At that point, the gases expand forward simply because there's no other place for them to go than following along behind (and pushing) the bullet or shot charge in a shotgun shell. And, here's where one of your "laws" comes into effect- equal & opposite reaction. The gases in the small combustion chamber push in both directions as they expand, moving the projectile forward by pushing against it, and moving the gun backward by pushing against the rear of the cartridge case/bolt/gun.
The bullet or shot column has less mass so the forces propel it farther, the rifle or shotgun has more mass (in addition to the multiplying factor of your own body mass resting against the buttstock) so the forces propel it a much shorter distance. The amount of actual energy involved in both directions should be equal (at least initially), but how that energy is used and directed is not.
The net result is that, as far as the shooter is concerned, those gases push the rifle backward.

As far as the forcing cone goes, look at a bottlenecked rifle case. We are reducing the gas's expansion outlet to far less than it would be in a comparably volumed straightwalled case. Why do you think we use an angled shoulder? Why not use just a square 90-degree step down to bullet diameter?
Take two cases with equal internal volume, one straightwalled with the "escape hatch" opening having the same diameter as the case body, the other with an angled shoulder that eventually reduces the escape hatch opening to half of the case body's diameter. Insert equal volumes of powder, and seal off the case mouths. Ignite the powder.
The straightwalled case mouth offers a much larger opening for the burning gases to use in expanding forward out of the case. The bottlenecked case has a constricted mouth with a much smaller opening for those gases to escape through. Expansion rates should be essentially identical between the gases in both case BODIES, but the internal pressures of the bottlenecked round will push those gases out through the case mouth at a much higher speed and pressure simply because it's venting the same volume of gas as the straightwalled case, but with a much smaller opening to do it in.
The angled shoulder serves to slightly retard a very sharp pressure spike that would be caused if the shoulder step was an abrupt 90 degrees.

Look at it another way. In a closed system, such as your garden hose, you can see essentially the same effect in watering your lawn if you do it by hand.
You turn the tap on and you are moving X volume of water through that hose between tap and end. You decide you need to reach farther beyond the end of the hose than the normal flow will carry. You twist a spray nozzle on the hose end. Now, in getting that water stream to travel farther, you're moving the same volume of water, but by constricting the opening where the water comes out, you've increased both pressure behind the nozzle and the velocity of the water coming out.

In applying that to the shotgun barrel, and bearing in mind that this is all happening in a tiny fraction of a second on ignition, the forcing cone is your case shoulder and your hose nozzle. Your burning gases are pushing forward and moving the shot charge out of the larger shell diameter into the forcing cone to be "sized down" to a smaller bore diameter at the forward end of the cone. In a typical factory-length cone, the column slams into the rear of it with X amount of force and X amount of energy (can't give you exact figures). At the same time (equal & opposite) the gases are also pushing the gun backward. Part of your recoil at this point is determined by how hard & fast the shot column hits the cone & the resultant amount of energy and pressure required to reduce its diameter. Very simply, lengthening the cone gives the column a longer travel (fractional, but it does exist), a less abrupt slam into its initial constriction, a longer time frame (again, fractional but real) to spread out the forces propelling it into and through the funnel, and reduced pressures in the opposite direction (backward) to move the gun into the shooter's shoulder.
This is not a placebo, nor is it imaginary. The fact that you can't "feel" it happening doesn't make it fiction. It all happens too fast for the human nervous system to separate out the various aspects of the recoil-producing steps and reactions that occur as the shot travels down the bore.

Backboring, in slightly increasing bore diameter, both works with the lengthened forcing cone to provide a more gradual shot column constriction after going through the cone, and reduces pressures slightly, which also helps in recoil reduction.
Again, the column's travel time and your own nervous system combine to make it impossible for you to separate out any individual stage of this process, such as the column's final constriction into whatever choke (cyl bore to full) you may have on your gun.

Porting works as described previously.
Bottom line is that all of the above work together to spread out the effects of the energy involved in firing a shotgun shell, and in modifying certain stages from shell to muzzle that create recoil.

This all works most effectively as a package, although porting alone can & does reduce the cheek smack referred to earlier.

As mentioned, there are several other things you can do to affect recoil.
I personally dislike dropping down to lighter or reduced-recoil loads in my defensive 870s. I prefer to use the standard stuff and just set up my guns to deal with that more efficiently.
The velocity losses involved in backboring and porting are far less than I'd end up with in using reduced velocity/recoil loads, and patterns are often tightened, too, in the process.
Adding weight has other inherent problems.

My PMAX barrel will go to Vang one of these days when I can catch up to it, and the 14-incher would too were it not for the fact that the original Scattergun Tech people that built it installed a permanent choke sleeve that I don't think I want to risk with the porting process. :)

Everybody has to make their own decisions, but there are reasons why all of the new Winchester & Browning shotguns are factory backbored, and why Vang sells a hell of a lot of his guns to professional users.

The reasons are not "meaningless marketing" and it has nothing to do with "cool". It's real, and it accomplishes quite a bit of value.


February 5, 2008, 10:03 PM
Porting?...Just a PIA to clean.

February 5, 2008, 11:48 PM
As in Hocus Pocus ( Creedance Clearwater Revival),, "I put a spell on you,,,,, now,,, your mine"

February 6, 2008, 01:10 AM
Couple pokes in each hole with a wet pipe cleaner followed by a couple with a dry one does it for me. Adds maybe three minutes at most to the cleaning session. :)