can anyone tell me how to port my barrel?
how to calculate the porting holes diameter to the bore caliber?

Here are the steps to take.
(1) Take the barreled action out of the stock and remove the scope.
(2) Check the address for Magna-port.
(3) Carefully package the barreled action and send it to them to be ported.
(4) Patiently wait for it to get back.
(5) When it gets back re-install the barreled action in the stock.
(6) Carefully measure the holes cut by Magna-port..they will be the correct size and in the correct location.

Simple wasn't it? This is one of those things that if you must ask how to do it, you're probably not qualified to do it.

I don't think this is a job you would want to tackle with a drill press, Dremel tool, or a Craftsman variable speed drill! Sure, you can make holes in the barrel, but you will be leaving burs on the edges of the holes and probably damage the rifling.

Porcupine,

May I suggest that you contact Mag-na-port at the following:

Mag-na-port International
41302 Executive Drive
Harrison Township, Michigan 48045
(810) 469-6727

Good Hunting !

I heartily disagree with spending a lot of money to have your barrel professionally ported. If your going to ruin a perfectly good gun anyway by porting or installing a muzzle brake, then why not just bore the holes in it yourself? That way, you'll have more money left to go out and buy yourself a replacement barrel that doesn't have the offensive and useless porting.

Now think about it. What are you going to accomplish by porting?

1. Lowered bullet velocity.
2. Muzzle blast damaging to the shooter.
3. Muzzle blast DESTRUCTIVE to bystanders.
4. Possible deteriation of accuracy.
5. But it won't seem like it kicks as much because the noise takes your mind off of the recoil.

If recoil reduction is your goal, I would suggest that the recoil that's bothering you is not that which you experience shooting under field conditions, but rather shooting from the bench in sighting and load development. That being the case, buy or build yourself a recoil absorbing bench rest and leave your barrel unmolested.