doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Chokes/Bores/Patterns don't match?

I do extensive pattern testing with all my shotguns and "generally" factory choke designations, bore measurement at the muzzle and patterns are consistent except for two 20 ga's. One a Red Label purchased from the factory, designated Skt/Skt; measures at the muzzle Skt II/Modified (don't know true bore dia.)shoots with multiple "standard" 7/8oz loads true Cyl. and Full. With extensive testing I have been able to come up with barrel specific loads to give me Imp./Mod. patterns. The second gun, an SKB, came with factory designated Mod./Full chokes. Without pattern testing the barrels were sent off to a "noted" barrel smith to be opened to Imp./Mod. Chokes were honed to desired constriction based upon bore dia. Chokes at the muzzle still measure exactly Mod./Full, which means the bores are both appx. .010" undersize. Pattern testing again with multiple standard loads resulted in Cyl./Full patterns. Coincidentally or not, the same barrel specific loads developed for the Red Label worked in the SKB to give me Imp./Mod. patterns. But why don't the choke measurements and patterns (extreme both ways) match?

Are you measuring the chokes and bores with a bore gauge?

I understand that Kreighoff has a FIR of .003 and have seen .010 in Remington bores from gun to gun. That can have a major effect on chokes, now add in varation in machineing chokes. A plus .003 bore and a minus .003 choke adds up to a full change of one constriction size in a 20 gauge.

bill

Measuring with micrometer. I understand the relationship of bore-choke size. But if the chokes are constricted to the proper dimension relative to bore size why the wide discrepancies in pattern, one loose, one tight, relative to what they should produce with pretty much all "standard" loads?

Appears you are only measuring the chokes at the muzzle.

Don't assume anything about the bore size.

Measure it. Mystery likely solved.

I agree with Shotgun.

Best,

mike

We had a lot of trouble getting Briley and Kolar skeet tubes to throw good patterns. Turns out they both have trouble with good forceing cone polish. Putting the 410 tubes in a lathe and polishing the forceing cones with 600, 1200, 2000 grit and then buffing with crome rouge. With .003 chokes my 410 added 24 bb's to a 30 inch circle at 20 yards. Similar improvements were found on 28 and 20. The SS or ti chambers are very hard to polish.
You may want to check your forceing cones.

bill

How many patterns per set of parameters are you shooting? What method of analysis are you using? Do you have a copy of Dr. Andrew Jones' recent book on patterning? I suspect you are shooting too few patterns and that your analysis is insufficient. Shotgun patterns are way variable.

If you're just counting holes in a 30" circle at 40 yards, they should not vary a whole lot from shot to shot with the same ammo--assuming you're drawing the circle AFTER the shot, just in case you're a bit off target.

Something I always do is cut open a shell or two and do a pellet count rather than assuming, for example, that a shell which is supposed to contain an ounce of 7 1/2's has a pellet count pretty close to 350, which is what it should have. In extreme cases, I've found that pellet count can be off from standard by as much as 10% plus or minus, which of course will impact your % when you count holes in paper, if you don't first count pellets in the load.