Backboring A B-25


My question is regarding Belgian F.N. Browning Superposed shotguns. I am presently shooting a 28″ Browning GTI as well as a 30″ Browning Ultra for sporting clays and trap. After reading through the Technoid archives I discovered your concept of taking a 30″ F.N. Superposed with fixed chokes and having it fitted with thin walled screw chokes for versatility without added muzzle weight. I am assuming that your trap F.N. guns have 2 3/4″ chambers.

I would like to try it with a 1961 3″ chambered magnum F.N. superposed. I understand that overall it would weigh more than your F.N. trap. My question is are the barrels similar in wall thickness and weight or would mine be overweight in order to handle the 3″ magnum loads? It weighs 8 lbs. 2 oz.

Compared to the trap guns at 7 lbs. 12 oz. My barrel is 30″. The field stock fits me well.

Thank you,


Dear Karl,

Generally FN made their B-25 3″ field guns heavier. Most standard field style B-25s that I have fooled with have been somewhere in the 7 1/2# area. My FN Super Traps are right around 7 3/4#. The B-25 trap guns for the American market are sometimes a touch heavier than that. I can’t tell without seeing the gun, but my guess is that your 8lb. 2oz 3″ gun has especially heavy barrels. If you pull off the forend, you will find the barrel weight stamped near the breech ends. It will read 1kg560 (1.560 kg) or something like that.

If the gun has more weight up front than you would like, you can simply have it backbored before having it screw choked. Check with Briley on what they charge for this service at this time.

The nice thing about backboring is that you can make the barrels weigh just about anything that you want within reason. Those 3″ bbls will have plenty of extra steel. and still have enough room for thin wall screw choke threads. Briley will be quick to tell you if you are trying to back bore out too much to also accept screw chokes.

How much you want to back bore out is up to you. If your bores are .723″ and you wipe them both out to .733″ you will lose 2.75 oz from 30″ bbls factoring in the chambers and forcing cones. You are the best judge of how much you would want to take out, but a 3 oz weight reduction from the barrels will be quite noticeable.

Best regards,

Bruce Buck
Shotgun Report’s Technoid
(Often in error, never in doubt.)

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