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Thanks, Chuck. Haven't heard back from Orlen, yet.

SRH

Using a rudimentary choke gauge inserted into the muzzles, I determined that the right side is too-tight for Mod but less than full, so IM?. Left tube is clearly full choke. Not sure what the three stars are meant to designate but on my gun they are definitely not modified.

Do you have any idea what constriction they are in thousandths of an inch?

SRH

I wish I could, but I have no way to measure constriction as my equipment will not fit in a .410 bore.

.410 tubeset on the bottom, 28 on the top. No stars on the 28 gage set (choketubes). .410 forend is about 1/4-inch longer than the 28 forend. Proportioning is slightly different as well.

Interesting letter about the repair PISCO just did for me.



As I mentioned in another post, the triggers had devolved to approximately 6 1/2 lbs and 5 3/4 lbs of pull. I asked for 3 and 3 1/2. What I got back is pretty close to 3 3/4 lbs and 4 1/4. I can live with that.

The bores in my Dickinson are nowhere near .410. In fact, they measure .399" right and .398" left. So, just using a caliper to measure the muzzle I.D., then subtracting that from .410" won't tell you anything (unless your bores really are .410"). My other .410s are all over the place in bore diameters. The Yildiz is .400" and .399", and the Verona is .410" and .410". It seems the Turks aren't satisfied with building a "little gun", they want them to have undersized bores. If there was ever a gun that would be helped by overboring it would be the .410, IMO.

SRH

The Germans do the same thing, Stan.

Krieghoff = .4015 bore.

A call to them asking why resulted in no answer.

As for the chrome cutting... I once saw what Briley did to a perfectly good Ithaca/SKB extending the forcing cones. I'd skip that.

I can tell you one reason for the small bores.
When machining a bore, it is common practice to shoot for a dimension on the lower side of the tolerance. What that does is allows for maximum material to be left in case rework is necessary from a broken tool. AKA reduces scrap.

Say your machining a 20ga bore of .615 nominal with a tolerance of +/-.015. Most machinists would use the tolerance to their benefit, and shoot for .605. That leave .025 for any problems to be corrected yet still makes a good part.

Just the opposite on an OD. Leave it big yet still in tolerance.

By the way, you don't need a fancy dial bore gizmo to measure a 410.

A serviceable Chinese telescoping gauge set is about $20.

Mind you, this is not LS Starrett quality but it works just fine for this. Mine says $19.95 and I'm pretty sure it came outta Harbor Freight.

The trick is to measure the bore just behind the choke (or just before the recess if it's screw choked), torque it down and let it slide back down and out the breech (only necessary if there's choke, obviously). All the .410's I've measured (and admittedly it's only a handful) allowed the gauge to slide all the way back down and out the breech.

When evaluating the actual constriction of a screw choked barrel, don't forget the 'jug' effect of the necessary choke inlet. They all have this to some extent, and it's not a trivial factor. Thus, we find interchangeable chokes systems that shoot tighter than marked. A .020 12ga for instance after the jug effect is considered becomes a .025 or tighter. It's not just the modern wadding that makes new guns shoot tighter than the old timers.