Gas Venting And Recoil Reduction


Dear Bruce,

Does all this gas porting on shotgun barrels really work to reduce recoil?

Charlie

Dear Charlie,

I’ve done this one before, but not for a while, so here goes. I’ll vent on venting.

There’s no question that the gas from a firearm can be used to reduce gun movement. That’s why tanks and field canon had those shields on the muzzle for so many years. The gas, jetting forward from the muzzle, would hit the shield and push the shield forward. Since the shield was attached to the barrel, it acted to reduce recoil. The downside was that the muzzle blast to the side, due to the redirected gases, was horrendous.

Rifles and pistols have used gas deflection in the form of “compensators” for years. Rifles tend to use gas deflectors the same way canons did- to lower general recoil by having the gas push all around the deflector. KDF and Browning market two of the more popular ones. They do work too.

Pistols generally do not use compensators to reduce rearward recoil as much as they use it to reduce muzzle jump. This is done by venting some muzzle gas straight up at the muzzle tip.This keeps the muzzle down a bit when the gun is fired. Compensators on pistols work well in certain calibers.

Shotgun have been used with both devices. The Cutts Compensator, adapted from Colonel Cutts canon muzzle break and used on the tommy gun, is meant to reduce rearward recoil by providing a cage with thick slots for the gas to push against. The Cutts Compensator was also employed to alter pattern and to provide extra muzzle weight (whether you wanted it or not).

Shotguns currently often employ “porting” to reduce muzzle jump. This basically involves holes drilled in the top of the barrel towards the muzzle to vent gases upwards and thus push the muzzle downwards.

Here’s the issue: gas redirection works well in canons, rifles and some pistols because the gas pressures involved are VERY high. The more gas pressure, the better the system works. Shotguns are more problematic. The gas generated at the muzzle of a shotgun pales in comparison to that generated by a modern high power rifle or pistol. For example, a 30-06 rifle operates at just under 60,000 PSI. A 12 gauge shotshell is under 11,000 PSI.

And that’s not all of it either. Those pressures are just in front of the chamber. By the time the gases get to the muzzle, the very much larger bore of the typical 12 gauge shotgun has permitted the gasses to expand and lower pressure to a much greater extent than the shorter, much narrower rifle or pistol bore. I don’t have muzzle pressure numbers and I’m not going to spend the time to calculate them now, but the difference is very great.

The bottom line is that shotguns obey the same laws of physics as rifles and pistols. Gas redirection, whether used to reduce recoil or reduce muzzle jump, does work. However, I maintain that due to the very much reduced gas pressure at the shotgun muzzle that it doesn’t work very well. There just isn’t enough gas to make much difference. Yes, there may be some difference, but not much. It all depends on how sensitive you are.

But one thing’s for sure. There is enough gas to make a big difference in the noise. Standing next to a shotgun with a Cutts Compensator or the current Japanese Brownings with ported barrels is not a thrill. The noise is greatly increased. Other forms of porting with better design to not seem to increase noise as much.

It’s all a question of balance. Some people feel that porting helps shotgun muzzle jump enough to detect and feel that the increased noise for their shooting pals is worth it. Others don’t agree. I won’t even get into the aesthetic considerations.

Does barrel porting reduce recoil? I don’t think so. Standard shotgun barrel porting vents the gas at right angles to the barrel and upwards. The goal is to push the muzzle down to reduce muzzle jump. To reduce recoil, it would have to push the muzzle forward (in the opposite direction of the recoil). To do that, you would have to direct the gas rearward, not at right angles, or push it into a shield like the muzzle brakes on the old tank canons. Some porting is cut at a rearward facing angle to attempt to do that, but I’ve never noticed any difference. Perhaps someone more sensitive than I am would.

Obviously, gas venting will reduce recoil to the extent that it reduces muzzle velocity. But that’s hardly the tradeoff you want to make. Generally porting doesn’t affect muzzle velocity enough to be a consideration.

Bottom line: I don’t think that gas porting in shotguns is very effective because the gas pressures involved are so low. I didn’t say it didn’t work at all. I said it didn’t work very well. It does work, but the big question is whether it makes enough difference to justify the increased noise and barrel cleaning required. Browning Japan has gambled that porting is a good selling point. Beretta has taken the opposite view and ports few guns.

One thing’s for sure, if a gun is ported, you can’t unport it.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)
<http://www.ShotgunReport.com&gt;

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2 Responses to Gas Venting And Recoil Reduction

  1. Nick Capitumino (@NCapitumino) says:

    Bruce–This is in regards to does porting reduce recoil. I have a 20ga browning A5 and had purchased one of the Japanese screw choke barrels for it. I use the gun for sporting and generally set the friction rings for heavy loads with oil on the mag tube so the gun absorbs almost all the recoil but still functions. The gun was set up that way prior to sending the barrel of to Magnaport for their Proporting. Being kind of a technical guy myself I took a box of my reloads and fired about half to insure the gun functioned 100% and put the rest aside to see if the porting made any difference upon the return of the barrel. As you well know the A5 is recoil operated. Upon return of the barrel a couple weeks later the barrel was installed and the test commenced. Temperature was the same but now the remainder of the box of shells would not eject. There was evidently enough recoil reduction to require me to switch the friction rings to the light load setting for the gun to operate properly. That said I believe recoil reduction is minimal and would not pay to have it done on any other gun. There is my $.02 on the subject.

    • Bruce Buck says:

      Nick,

      Your comments are very helpful. Thanks so much for doing that work and then sharing it with us. I talk a lot and do a little. You did the real work in experimenting with the before and after of porting affecting recoil.

      You demonstrated that the long recoil action of the Auto-5 Browning is sensitive to porting. I’ve not tested an Auto-5 for before and after mechanical function, but I have shot O/Us before and after porting. If there was a rearward recoil difference in those, I couldn’t sense it. Maybe I’m just one of those insensitive guys. That Auto-5 of yours is obviously more sensitive than I am. Ever thus. Thanks for the input.

      Bruce

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