Ported Effect on Velocity

Archer 9505 · October 18, 2010, 09:45 AM

Any data on the effect that porting a shotgun barrel may have on muzzle velocity, if any?

zippy13 · October 18, 2010, 11:32 AM

With modern (smokeless powder) shotguns, the powder is fully burned, and the charge at it maximum velocity well before any gas is vented by porting. Of course, this applies to shotguns with full length barrels. Obviously, if the barrel is shortened to a length where is powder burn is not complete, any porting will impact velocity. How much of an impact depends on the length of the barrel, the size/location of the ports, and the specific load used.

mete · October 18, 2010, 12:56 PM

"fully burned" ?? For a target load that is correct but for a full load the powder is burning after the shot leaves the barrel.
That means that porting has no use for target loads .We did tests to demonstrate this ! For full loads the porting does reduce recoil perhaps 10 - 20 %.
With either case velocity is not reduced !

BigJimP · October 18, 2010, 01:58 PM

What are you defining as a "full load" vs a "target load" ....

If you look at the reloading tables - for a 3" shell ...you might load 31 - 35 grains of Hodgdon Longshot into a 1 5/8oz or 1 7/8 oz of shot - into that 3" shell .... where if you want to ... for 1 1/8 oz of shot in a 2 3/4" shell you can load from 30 - 35 gr of Hodgdon longshot for velocities of 1420 - 1530 fps ...

and in a 28" barrel ....those hot loads of Longshot are still very clean with 1 1/8 oz of shot ....and loading them to 1 5/8 or 1 7/8 oz won't change the powder burn rate, so I doubt there is any powder burning beyond the first 18 or 20" inside the barrel ...whether it is a target or a field load.

In my opinion:
Porting has a lot of use for Target loads - by limiting muzzle jump between 1st and 2nd shots / but porting does nothing for recoil reduction in any gun ... How fast or slow the powder burns / is not part of the recoil formula ! ( only weight of shot and wad, velocity, and weight of the gun impact the recoil )...

zippy13 · October 18, 2010, 02:32 PM

I used the term "fully burned" generically -- sorry if I confused anyone. Many shooters couldn't care less about what's happening before the load clears the barrel. In an ideal situation, the powder would be fully consumed and the pressure hit its maximum just before the loads clears. This would produce the lowest "kick" possible, since the acceleration would be more uniform over a longer event time.

Most experienced shot-gunners have noticed, with two seemingly identically loaded shot shells, one may have a sharper kick than the other one. Chances are, the first shell contained a faster burning powder. Why use the faster powder if the slower one has less kick? It's simple economics:
If Red Dot and the slower Green Dot cost the same per pound, and for a given load the recipe calls for 18.0 gr of Red Dot or 19.5 gr of Green Dot most folks would go for the Red Dot. Typically shot shells are loaded with the faster power (within allowable pressures). As the shot charge increases, slower powders must be used to keep the pressure within limits. The shell makers understand this and don't want to spend more than is necessary on powder. Why do you think some of the "low recoil" loads cost more -- you're paying for a heavier charge of slower burning powder.

Mete is correct, with heavier loads, powder may still be burning after the shot leaves the barrel; but, it's no longer contributing to the pressure development. BigJimP is correct, too: Essentially the powder is "Fully burned (generically)" when maximum velocity is obtained (well before the muzzle), additional burning powder is wasted because it only contributes to the blast. Look at the internal ballistic diagrams of various shot shells, the pressure curves go flat (or linear) well before the muzzle -- some much sooner than others. In either case porting won't interfere with the velocity. Unless, as I indicated previously, it's done so far back in the barrel that the velocity hasn't reached its maximum.

Think of porting this way: physics dictates that anything that goes out the ports, doesn't go out the muzzle and will reduce recoil to some extent. If the pressures are high enough, porting may also have a "jet" effect that can be employed to reduce muzzle rise.

BigJimP · October 18, 2010, 03:43 PM

Ok, I'll agree -- that in theory, there might be a little reduction in recoil from porting

...( but not much ..) .../and I'll admit that I like my ported shotguns in 12ga and 20ga at least ...

but we seem to all agree there is no affect on velocity ...

/ which is what the OP asked ...

( powder burning as the wad exits the barrel ...would be more like a Roman Candle wouldn't it ....)

I can't say I've ever noticed any evidence of that happening ...but its possible, in theory at least ...

October 18, 2010, 09:45 AM	#1
Archer 9505 Senior Member Join Date: October 10, 2010 Location: Maine Posts: 213	Ported Effect on Velocity Any data on the effect that porting a shotgun barrel may have on muzzle velocity, if any?

October 18, 2010, 12:56 PM	#3
mete Senior Member Join Date: June 14, 2004 Location: NY State Posts: 6,575	"fully burned" ?? For a target load that is correct but for a full load the powder is burning after the shot leaves the barrel. That means that porting has no use for target loads .We did tests to demonstrate this ! For full loads the porting does reduce recoil perhaps 10 - 20 %. With either case velocity is not reduced ! __________________ And Watson , bring your revolver !

October 18, 2010, 11:32 AM	#2
zippy13 Senior Member Join Date: August 23, 2008 Location: SoCal Posts: 6,442	With modern (smokeless powder) shotguns, the powder is fully burned, and the charge at it maximum velocity well before any gas is vented by porting. Of course, this applies to shotguns with full length barrels. Obviously, if the barrel is shortened to a length where is powder burn is not complete, any porting will impact velocity. How much of an impact depends on the length of the barrel, the size/location of the ports, and the specific load used.

October 18, 2010, 01:58 PM	#4
BigJimP Senior Member Join Date: February 23, 2005 Posts: 13,195	What are you defining as a "full load" vs a "target load" .... If you look at the reloading tables - for a 3" shell ...you might load 31 - 35 grains of Hodgdon Longshot into a 1 5/8oz or 1 7/8 oz of shot - into that 3" shell .... where if you want to ... for 1 1/8 oz of shot in a 2 3/4" shell you can load from 30 - 35 gr of Hodgdon longshot for velocities of 1420 - 1530 fps ... and in a 28" barrel ....those hot loads of Longshot are still very clean with 1 1/8 oz of shot ....and loading them to 1 5/8 or 1 7/8 oz won't change the powder burn rate, so I doubt there is any powder burning beyond the first 18 or 20" inside the barrel ...whether it is a target or a field load. In my opinion: Porting has a lot of use for Target loads - by limiting muzzle jump between 1st and 2nd shots / but porting does nothing for recoil reduction in any gun ... How fast or slow the powder burns / is not part of the recoil formula ! ( only weight of shot and wad, velocity, and weight of the gun impact the recoil )...

October 18, 2010, 02:32 PM	#5
zippy13 Senior Member Join Date: August 23, 2008 Location: SoCal Posts: 6,442	I used the term "fully burned" generically -- sorry if I confused anyone. Many shooters couldn't care less about what's happening before the load clears the barrel. In an ideal situation, the powder would be fully consumed and the pressure hit its maximum just before the loads clears. This would produce the lowest "kick" possible, since the acceleration would be more uniform over a longer event time. Most experienced shot-gunners have noticed, with two seemingly identically loaded shot shells, one may have a sharper kick than the other one. Chances are, the first shell contained a faster burning powder. Why use the faster powder if the slower one has less kick? It's simple economics: If Red Dot and the slower Green Dot cost the same per pound, and for a given load the recipe calls for 18.0 gr of Red Dot or 19.5 gr of Green Dot most folks would go for the Red Dot. Typically shot shells are loaded with the faster power (within allowable pressures). As the shot charge increases, slower powders must be used to keep the pressure within limits. The shell makers understand this and don't want to spend more than is necessary on powder. Why do you think some of the "low recoil" loads cost more -- you're paying for a heavier charge of slower burning powder. Mete is correct, with heavier loads, powder may still be burning after the shot leaves the barrel; but, it's no longer contributing to the pressure development. BigJimP is correct, too: Essentially the powder is "Fully burned (generically)" when maximum velocity is obtained (well before the muzzle), additional burning powder is wasted because it only contributes to the blast. Look at the internal ballistic diagrams of various shot shells, the pressure curves go flat (or linear) well before the muzzle -- some much sooner than others. In either case porting won't interfere with the velocity. Unless, as I indicated previously, it's done so far back in the barrel that the velocity hasn't reached its maximum. Think of porting this way: physics dictates that anything that goes out the ports, doesn't go out the muzzle and will reduce recoil to some extent. If the pressures are high enough, porting may also have a "jet" effect that can be employed to reduce muzzle rise.

October 18, 2010, 03:43 PM	#6
BigJimP Senior Member Join Date: February 23, 2005 Posts: 13,195	Ok, I'll agree -- that in theory, there might be a little reduction in recoil from porting ...( but not much ..) .../and I'll admit that I like my ported shotguns in 12ga and 20ga at least ... but we seem to all agree there is no affect on velocity ... / which is what the OP asked ... ( powder burning as the wad exits the barrel ...would be more like a Roman Candle wouldn't it ....) I can't say I've ever noticed any evidence of that happening ...but its possible, in theory at least ...