Measuring Barrels


Dear Technoid-

I did not start this to question the wisdom of the Technoid. Really.

I have some visiting shooters in town this week, and their shotguns are temporarily residing with mine. I saw a unique opportunity in these guns to do a little scientific comparison to see just what Browning is up to.

There are 4 vaguely similar Browning stackbarrels that I have access to for a bit. One is a ’69 FN Superposed “Lightning” with 30″ barrels. One is a late 80’s/early 90’s (I know it’s at least 4-5 years old) Citori Lightning Field model, 28″ barrels, standard Invector chokes. Gun 3 is a recent (last year) Citori Lightning Sporter, 30″ barrels, Invector Plus chokes. The last gun is a recent 425 Sporter, 30″ barrels and Invector Plus chokes.

Since I’m considering picking up a 425 of my own, I have been reading the Technoid archives where Browning’s “backboring” is reported as just increasing bore diameter while holding wall thickness the same. So if nominal bore diameter is .729 and Brownings Invector Plus bore is around a nominal .741, the OD of the barrels should be approximately .012 greater on the 425 and Lightning Sporter than on the older Lightning and the FN, right?

I measured the OD of all 8 barrels and took an average along their length. I also measured the exit diameter of the barrels. Here are the results:

So what does that tell us? I know that the Citori field has a bore diameter of .729 in both tubes. That makes the wall thickness about .043, pretty stout. Assuming that the 425 bores are .740 (I don’t have ready access to a bore gauge) that means Browning has reduced their wall thickness to about .038 in this particular example. I guess what I’m getting at is that Browning’s current “backbored” guns are just that – they seem to be just removing more metal from the barrel using their “old” barrel diameters.

The bottom line, though, is how they feel. Curse me for a heretic but I would take that 30″ 425 over the FN Superposed hands down any day of the week. The 425 seems to balance much better between the hands. So did another recent 32″ 425 that I handled at the range the other day. Is it possible that Browning is getting the message about barrel weight?

Respectfully submitted- Abe

Dear Abe,

Well done! Your are a true Junior Technoid when you start miking your guests’ guns! You are quite right in that it is a good chance to make a comparison. However, the problem with all comparisons are that they only compare what they compare.

I am unclear as to what you mean by an “Exit” measurement, but the OD measurement seems clear enough. Barrels are usually thinnest about 6-10″ back from the muzzle and that is where the OD measurements are usually taken.

Your measurements, especially that of a .823″ OD for a Belgian Lightning, made me curious so I went rooting through my gun safe. I didn’t have any of the Japanese guns to test, but here are the ODs I got 10″ back from the muzzle on some of my Belgian Superposeds:

1) FN 30″ Super trap #6 12 mm rib Over: .805″, Under: .804″
2) FN 30″ Super trap #6 16 mm rib Over : .809″, Under: . 807″
3) FN 30″ Super trap #6 12 mm rib Over: .808″, Under .810″
4) Browning B25 12 ga. Superlight Over: .800″, Under .804″

As you can see, none of my target guns came close to the .823″ you got on that ’69 Belgian Lightning field gun. My field gun was very much thinner as you would expect from a Superlight.

With .823″ ODs, that Superposed you miked would definitely be a log. Backboring a 30″ OU .015″ will pull out over 4 ounces. While this certainly isn’t an exact comparison to a gun that has .015″ more OD a certain distance from the muzzle because barrel exteriors have taper, it will give you an idea of what a little extra barrel thickness can do. 4 oz is an entire ton when it comes to additional barrel weight. Perhaps the gun you measured was a magnum mis-labeled as a Lightning. They can be pretty heavy in the barrels.

My barrel IDs are logged in separate notebooks and I don’t have the time to track them all down right now, but generally my Belgian Superposed guns run right around .723″ to.725″, seldom more. I can’t remember seeing a .729″. I am sure that I did, but it certainly isn’t common. Belgian barrel ODs are all over the place. Modern screw chokes actually encourage the makers to run their IDs more consistently, for obvious reasons. I have miked a whole bunch of Beretta auto barrels and seldom see one that isn’t .721″ to .723″. A couple of thou is pretty good tolerance for a production gun.

While I certainly can’t fault your opinion that the 425 had a better feel than the Superposed, and it certainly would with those huge Superposed barrels you measured, my Belgian guns measured differently. They definitely have the “feel” that I have yet to find in any factory screw-choke gun. I should point out why I generally prefer the balance of solid choke guns like the Superposed.

To me gun balance is, well, a balance of attributes. I want enough weight up front to swing well, but enough lightness to change direction as required. I want a field gun to be a bit quicker than a target gun because our feathered friends will do the strangest things when you are trying to put them in the pot. Once a clay target is launched, you know what you have.

The problem I have with some of the screw-choke guns is that “generally” the barrels are heavier than the solid choke guns AND that the additional weight is almost always added on right in the muzzle area, not spread out along the barrels. This is because the factory screw chokes are normally just added to a jugged and threaded barrel. The barrel gains the weight of those chokes all at the muzzle. It isn’t spread out. The guns can end up with all the life of a broomstick with a brick on the end. Gough Thomas, the famous English gun writer, called it “moment of inertia” or the barrels ability to change direction.

Now that screw chokes have been popular for over ten years, I am sure that the manufacturers are figuring ways to return a little life to their screw choke guns, but I still feel that they have a little ways to go in the OUs, especially when they go to the long screw chokes which weigh more. It is very interesting to compare the weight and balance of the English-market solid choke Miroku 38 or 3800 to the virtually identical American screw choke Browning 425. The only real difference is the screw chokes, but the feel and response of the guns are entirely different.

Your measurements would indicate that Browning is accepting thinner wall thickness in an attempt to bring more life to the gun. However, the problem still remains with the weight of those huge chokes right at the tip of the muzzle. I guess that it just depends on what you want. From the number of people shooting 425s with extended chokes, some shooters must want tip heavy barrels. Like a lot of things, perhaps people don’t miss what they don’t know about. FYI, the difference between a flush Briley .015″ Beretta choke and a 2X extended Briley .015″ choke is .41 oz. Two of them together add .82 ounces of weight right at the very tip of the gun.

Thanks for doing all that measuring. It will encourage me to wander down to the local gun store, micrometer in hand and check out this week’s crop of guns.

Best regards,

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

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