Swedish Screw Chokes

Dear Technoid,

I’ve just found your site. I really like it. But there is no doubt you’re sometimes in error.

You claim chokes should have a forcing cone and a parallel section. How do you intend to prove that? In fact, some guns – high quality stuff, like the swedish stainless Flodman – uses screw chokes with just a forcing cone. No trace of a parallel section. And I can guarantee that they produce patterns just as good as any “parallel-section-choke”. Like you pointed out, it’s a Gaussian thing.

The question of “better” chokes only apply to the Full end of the scale, you say. Well, it might be as bad at the Cylinder end. Certain shells don’t produce a cylinder choke pattern when shot from a straight cylinder bore, while the same shell can produce the desired pattern from a screw choke barrel. This is often achieved with a parallel section that has a diameter in excess of the bore, so I guess skirt drop-off isn’t always bad.

Why bother, you might think, choose another shell. It’s not that simple. Over here (Sweden) we have several sporting competitions sponsored by ammo manufacturers, and only there stuff is allowed. So you can see the problem, right?

best regards
Ralf R.

Dear Ralf,

I don’t believe that I ever said that a choke HAD to have both a forcing cone and a parallel section. I believe that I said that MOST do. I am well aware that many chokes have only the tapered area. All swaged chokes are this way. If I lead you to believe otherwise, I apologize.

The theory behind the parallel section is to “stabilize” the shot momentarily. Whether it works or not is, well, Gaussian. The fact is that most of the better choke specialists use a parallel section, especially where the choke is of tighter constriction.

As to the skirt drop off altering the pattern of a cylinder bore screw choke, it should tighten it if anything. Some screw choke skirt drop offs are so long and deep that they act as a “jug” choke. Jug choking is a common way of introducing some choke to a cylinder bore barrel by grinding a recess just behind the muzzle. How much of a recess you can grind depends on the thickness of the barrel steel.

I haven’t fooled with a Flodman or Caprinus for over a decade, but the ones that I shot were early screw choke guns and their chokes were of an early design. I really liked the gas operated ejectors on those guns. Too bad that they never caught on here in the US. They were pretty pricey here.

Best regards,

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

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