Hi Bruce…

I spent an afternoon doing a little “backyard” patterning and thought you’d find the results interesting.

I shot 5 o/u guns with a variety of factory skeet loads…all #9’s (AA, Rem, Fed, Victory, Fiocchi) at about 20-25 yards. I shot 3 Remington 3200’s – 26″ skeet, 28″ skeet, 30″ field with Briley thinwall chokes, a Browning Citori Invector Plus, and a Beretta 686 Mobilbchoke.

My biggest surprise was that the solid choked Remington skeet guns threw a noticeably bigger, more even pattern than any of the guns with removable chokes (skeet chokes were used for all shooting)….

The solid choked guns should definitely better for skeet shooting. My “in vivo” patterning (skeet shooting) at Thunder Mt. with all these guns at one time or another would support this result. I didn’t think there would be such a noticeable difference, but there was. All of the choke tubed guns’ patterns were “center weighted” with a less even distribution of than the solid choked Remingtons. Also, there was virtually no difference between the 26″ and 28″ Remingtons. The Briley chokes produced a slightly bigger, more even pattern than either of the factory choked guns (Browning & Beretta), but still not nearly as good as the solid choked guns. Is this typical of comparisons between solid and removable chokes?

Another finding…at typical American skeet distances, there wasn’t much difference between the “el cheapo” Victory loads and the premium brands. Also, the Fiocchi and Victory shells threw slightly bigger patterns than the AA, Rem and Fed shells. Any rationale for he solid choked guns’ better performance?

Mike

Dear Mike,

Here is my guess as to why the choke tube guns had hotter centers than the factory choke guns: It is called the “jug effect” of screw chokes.

When screw chokes are installed in a gun, the installer makes sure that the rear of the choke tube skirt is well below the surface of the bore of the barrel. If the rear of the choke ever bulges up into the barrel, the next shot may well shoot the choke out. This was a problem with the original Perazzi MT-6 factory chokes.

To preclude this possibility, the mass production choke installers (like the Browning and Beretta factories) make sure that there is PLENTY of relief between the rear skirt of the choke tube and the bore of the barrel. Under normal usage, no amount of dirt and carbon build up will push the skirt up into the bore.

This big clearance is certainly safe, BUT the other side of the coin is that you now have a big “jug” and that influences pattern. Take, for example, a typical factory screw choked gun. The bore may measure around .725″, but the rear of the choke skirt will open up to a .740″ or .745″ before it starts to narrow down to what ever choke constriction it is using. Thus with an Skeet choke tube (nominally constricting about .005″) in place, the barrel might measure .725″ down the bore to a short expansion jug at the rear of the choke of .745″ and then back down to the choke constriction of .720″. Sure, the skeet choke would measure a normal .005″, but it would give tighter performance than that due to the jug effect.

Here is what happens. The shot wanders on down the bore until it gets to the jug relief at the back of the choke. It then tries to expand to that .745″ only to find that it then gets compressed back down to .720″. It has not gone from .725″ to .720″ like a normal skeet choke. It has gone from sort of .745″ down to .720″. This is a much bigger step and more choking than you bargained for. This was the whole principle behind the Cutts compensator and the Russian Tula jug chokes copied by Krieghoff, Perazzi and SKB.

These numbers are certainly not hard and fast. Some choke makers exercise better quality control and don’t jug their skirts as much (Briley for example has much less jug as your performance tests show). Others use a very short screw choke with a minimum jug, so the shot doesn’t really have the chance to expand into it as much and the jug effect is lessened.

To add to the confusion, most screw chokes are quite short when compared to a standard solid choke. The short chokes slam the shot around much more because their choke forcing cones are of a more acute angle, rather than longer screw chokes which let the shot ease into the constriction. Short screw chokes tend to distort the shot more, but have less jug effect. Take your pick, sir. The rope or the ax.

Longer chokes with distinct parallel conical sections are considered a bit easier to tune and develop. Most screw chokes do not offer enough length to do that. Also, chokes for different constrictions are actually different lengths. A properly developed full choke requires much more length than a properly developed skeet choke. This is easy to do with solid chokes, but all screw chokes have to be the same length.

Bottom line: screw chokes are convenient, but they rarely throw the very best patterns. It is all a trade off. You will find very few pigeon or handicap shooters using screw chokes if they can help it. Sporting clays, on the other hand, values the interchangeable feature of screw chokes quite highly. If just depends on the game.

On behalf of shooting science in general, I want to thank you for doing all that testing. You are hereby awarded the Junior Technoid Order of the Palm (third class)- the coveted JTOP(3)- along with all rights and privileges pertaining thereto. Wear it with pride. Your genuine hand printed Junior Technoid plastic pocket protector will shortly arrive via email.

Best regards,

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