REPRO CHOKE BORE DATA

[Sam Ogle]

I was excited to trade a 26" single trigger pistol grip 28 gauge for "The Holy Grail;" a 28 ga 28" beaver tail straight grip double trigger. I couldn't hit a damn thing with it, so I measured the bores, and (from memory) "full" was almost 40/1000ths. I called it "silly full." So, I had a gunsmith open both bores to IC/IC. Suddenly, I could hit something with it. Do I now recommend doing that? Well, I guess I don't care what you do. My gun isn't going into a museum as long as I live. It shoots well at skeet, at doves, and I am pleased.
Sam Ogle

[MD*GSP]

Originally Posted by Bob Jurewicz

I have never measured the bores or choke constrictions in my Parker Reproduction barrels until recently. I found the results interesting, especially that for the 12 gauge guns with Ic/M markings.
Both 16 gauge barrels are original Krieghoffs!

12G 28" Ic/M Bores .732" R .006" L .010"
12G 26" Ic/M Bores .734" R .006" L .010"
12G 26" Ic/M Bores .734" R .006" L .010"

16G 28" Q1/Q2 Bores .661" R .004" L .006"
16G 28" M/F Bores .661" R .018" L .024"

20G 26" Ic/M Bores .618" R .011" L .015"
20G 26" Ic/M Bores .618" R .011" L .018"

28G 26" Q1/Q2 Bores .552" R .003" L.006"
28G 26" Ic/M Bores .552" R .006" L .016"

Bob Jurewicz

Very pleased to add to Bob's choke measurement chart:

16G 28" IC/MO Bore (R) .6632 (L) .6632 R .011 L .017
16G 28" Q1/Q2 Bore (R) .6631 (L) .6628 R .005 L .007

20G 28" Q1/Q2 Bore (R) .6225 (L) .6215 R .0065 L.009

[Dean Romig]

What I'm seeing in this thread are a LOT of inconsistencies, even on guns of the same gauge and same choke stampings on the flats.





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[Bob Jurewicz]

During the time of Parker Repro production Japan's production technology was very good but product variation was common. For example: barrels are not universally interchangeable in each gauge; forend wood dimensions vary within gauge; shooting dimensions vary widely, etc..
The choke variations I see do not strike me as unusually excessive.
Bob Jurewicz

[Heff]

I do not have it anymore, but if I remember correctly my 28" 28 ga. Mod/Full was .016 / .039
The full barrel was rediculously tight, and I considered opening both up to about .004 / .012 for the grouse and woodcock hunting I was using it for, but never got around to it. Spreader loads seemed to do the trick for me, and I eventually decided to sell it in get me a non-repro 20 ga. for grouse hunting. Oh um and a real light PH 26" 12 ga. and a 16 ga. Trojan and just recently a lovely zero frame GH 16 ga. The quest for the perfect grouse gun continues...

[MD*GSP]

I agree with Bob. I don't see excessive variation. Actually, in some cases, the consistency is quite impressive. My measurements, while precise, are not dead accurate only because I'm measuring point to point instead of taking a cylindrical measurement. Further, my point to point measurements do not reflect an average of dims measured across various points about the diameter. No shotgun barrel with a rib I've ever seen has been perfectly round.

[Bob Jurewicz]

We also must consider the variety of measuring tools.
Bob Jurewicz

[Dean Romig]

Or more to the point, the variety of people using the tools.... after all, .001" is .001" and .010" is .010" no matter which tool you happen to be using.





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[MD*GSP]

Dean, that's true (the variety of people using the tools) but the second half of your comment stating .001 is .001, not so much.

Yes, on it's face, you are correct - .001 is .001. The National Institute of Standards & Technology defines what .001 is. Fine. What most people don't understand as it relates to "size"; it sounds silly but "size" generally means nothing. Geometry is the key to measuring true functionality. Here's a photo showing several measuring tools that can obtain inside measurements.

I take my measurements using the green "Federal" bore gage. I position the gage & take my measurements north to south as the barrels are positioned proper. I can obtain a measurement out to 1/100,000th of an inch +/- with that gage. (splitting the graduations of 1/10,000th by eye). That's literally an inch broken into 100,000 equal segments for goodness sakes! Pretty precise? Not so fast! Drop the Comtor gage shown in the photo into that bore and compare that measurement to what the Federal gage says. It'll be smaller. Why? Because the Comtor gage is taking every variance of the bore such as an out of round condition, et al into consideration. The Comtor gage is telling you the largest size of a perfectly round shaft that will pass through the bore..THAT is true and bonafide accuracy! The Mahr bore gauge would be the second most accurate way to obtain a true measurement.

The Mitutoyo dial calipers, I suspect, are an example of what most people are using to obtain measurements. Trust me, that's not true precision but, it's close enough. The Federal gage I use, measures the bore in the same manner as the dial calipers however, it's much, much more accurate and has the additional advantage of detecting variances and geometric shapes in a manner the calipers simply cannot.

[Dean Romig]

Scot, Aw shucks Scot, you know what I meant...

Actually, I was referring to the tools most commonly used by most folks measuring our shotgun bores and chokes. But thank you very much for that excellent dissertation. Are you related to Spencer?





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