I’ve seen a double rifle with Mag-na porting but it just had two small ports near the top instead of the usual 4. Most double rifle users are purists and they would have a coronary and go into convulsions if that were done to their double. I personally wouldn’t do it to a double because it would destroy any resale value.
Mag-na-porting isn’t too popular anymore. Became popular in the 70’s through 90’s for both rifles and large bore revolvers. It became less popular because number one, its doesn’t reduce recoil as much (only up to 15% reduction) as the super loud KDF/Accubrake style muzzle brakes that reduce recoil significantly more but are very loud.
No, Mag-na-porting is NOT significantly louder than a non ported rifle. I owner several and currently own two rifles, one with just 2 trapezoidal slots angled to the top which only reduces muzzle rise, no recoil reduction, so it allows one to return on target much quicker. I doubt it would affect accuracy on a double.
From a practical viewpoint, if one had it done to a double rifle, it likely had little to do with recoil reduction and much more to do with significant reduction in muzzle rise, an excellent feature for a professional stopping a charging buffalo or elephant, getting a quicker second shot.
