Choke Marks


Dear Technoid,

I use a improved modified choke in my bt-99 for trap. It is a Browning Midas choke and is marked .715 for constriction. I recently bought a Remington 870 wingmaster and realized their choke tube with a similar constriction was called a light modified. The improved modified Rem choke is much tighter than I use. My question is will these two chokes both with .715 constriction pattern similar even though they are refered to differently.

James O.

James,

Both chokes could be quite correctly named. The whole idea of a choke is constricting the bore of the shotgun. A certain amount of constriction is supposed to produce a pattern with a certain percentage of shot in a 30″ circle at 40 yards.

The benchmark bore diameter of a 12 gauge shotgun barrel is .729″. That’s because one pound of lead, dived into 12 different parts and each part made into a ball would produce a ball of .729″ diameter. 20 gauge is one pound of lead into 20 parts. Each one being a ball of .615″ diameter. And so on.

BUT… very few makers adhere strictly to a .729″ bore diameter for a 12 gauge barrel. Some are less, many are more. It all depends on what they want to advertise. “Overbored!” “Backbored!” etc. Typically 12 ga barrels can vary from more or less .723″ up to .740″, with some even more open.

In the choke industry, it is generally accepted that a .020″ constriction will yield a 60% pattern in a 30″ circle at 40 yards. That 60% pattern is considered a Modified choke. Not all Modified chokes measure .020″ constriction by any means, but you get the idea.

Of course, the shell has as much to do with it as the choke does, but the gun makers don’t like to get into shells because it takes attention away from their gun.

If Modified is generally .020″ constriction in a 12 gauge, a Light Modified choke might be around .015″ constriction. An Improved Modified choke might be around .025″ constriction.

So, how can one choke constriction marked .715″ be both? I’ll bet you know already. It’s because the barrel interior diameters of the two guns are different.

If the barrel bore on your Browning Midas were an overbore of .740″, then a .715″ choke would give it a .025″ constriction and that would be your Improved Modified constriction dead on.

If the barrel bore on your Wingmaster were .730″, then a .715″ choke would add up to a .015″ constriction, right on Light Modified.

And it just so happens that Remington does bore it’s barrels right around .730″ sort of, and the Japanese Brownings are around .740″ bores. If you are referring to a current Midas Browning choke tube fit to the Japanese Brownings, then it makes sense. The original Belgian Browning Midas grade guns had bores right around .725″ and didn’t use choke tubes.

So, bottom line, the same choke constriction used in barrels with different bore diameters will produce different chokes. Has to. Got to. Your chokes are correctly marked.

Best regards,
Bruce Buck
Shotgun Report’s Technoid

Advertisements
This entry was posted in Shotgun related and tagged . Bookmark the permalink.

Leave a Comment

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s