Bore Gauge questions

[Cold Spring]

Andy, I don't know anything about the bore mike you bought and perhaps it's atypically good, but generally those sold for a wide range of shotgun bores but with a single measuring head and one calibration ring will "drift" at the high and low end of its measurement limits. Thus readings will be most accurate within a narrow range +/- of the calibration ring diameter. Otherwise it could be several thou off true size. I well remember a popular bore mike I had at one time that was .015" off true size when calibrated at .700" diameter and measuring a 10 bore. After that I bought a Stan Baker bore mike set with three measuring rods and three calibration rings.

PS: I here use the machinist word "mike" rather than "mic" as seems to have been adopted into shotgun terminology nowadays.

[Pa SxS]

Parker bore diameters for 12 ga. guns up until about S/N 60,000 are over-bored. I'll let Dean display the chart from Austin. My 1882 12ga. hammer gun measures .756. I have yet to measure a Parker 12 ga. that reads the nominal for a 12 ga. at .729. They are all .732 or a few thousands higher. Don't know about other gauges. I have the Stan Baker micrometer set.

[Andy]

All new to me and thanks for feed back Frank and Chuck. His gauges seem to be very well received and reviewed and he's been helpful and this is the 10-12-16 gauge set. Chuck I do have a 12 g "live pigeon gun" that measure .730 on the nose. I agree the few thousandths don't matter I'm just trying to learn. And figure bore constriction.

Now, to complicate matters, I have a 16g Trojan that measures .660 R and .672 L or so. What the heck. Both measure F/F with a Galazan drop in gauge but constriction is more like LM/XF. So much to learn.... The gun is high condition and matches the "book"

[Dean Romig]

These pictures are from one of Austin Hogan’s several notebooks. They are all hand plotted by Austin and accuracy was his middle name. I wish I had been in on the conversations with him and Charlie Price and Bill Hoover and Bill Furnish, all very serious students of Parker guns.

For the porpose of this conversation, charts are simply to illustrate the fact that none of the changes in chamber to bore, as well as the chokes, didn’t begin or end with an abrupt angle but folllowed an ogee.


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[Cold Spring]

I have no doubt as to the accuracy of Austin's measurements and drawings for those specific guns but I often wonder when I see a "swell" (short enlargement) of the bore as it starts into the choke leade. Austin shows typical ogees but not swell profiles. Anyone who's measured enough shotgun bores with an accurate bore mike has seen that swell on various vintage makers and to include some earlier/modern fixed choke guns, for example Winchester 101's. Typically on heavier choked barrels and supposedly to act as kind of a short run overbore for bare shot.

[Dean Romig]

Frank, I wonder if the swells you describe are a result of jug-choking which is done from the muzzle end of the barrels in order to increase the bore dia. immediately before the constriction of choke taper had originally begun…?




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[Cold Spring]

Dean, I don't know if the swell was done from the breech or muzzle ends but it's long been described as a way to "normalize" the bare shot charge before starting into the choke. It's not as pronounced as jug choking. The earliest references to the swell I've seen were by Askins and Sweeley in the early 1920's as they experimented with borings and chokes for max long range pattern efficiencies, that was prior to the advent of the Super-Fox which was largely based on their work. What I wonder about now is what effect, if any, the swell has on performance with plastic shotcups. One of these days I'll do some comparative long range patterning with bare shot and shotcups to check for myself. Actually I had planned to do that in part for a DGJ article and that's why it slipped to the back burner when the editors pulled the plug. I've seen these swells on a few Foxes, Parkers, Winchester M12's, M21's and 101's.

[Double Lab]

Frank, I'd be willing to bet that those "swells" will have little if no effect when using plastic wads. As you well know that these plastic wads used in vintage guns designed to pattern loads with no shot protector have become a game changer in better patterns. JMO of course.

Andy, I've got a few instruments for measuring bore/choke dimensions and I've found very little concern over a few thousandths difference. I am concerned over bore diameters which are wildly over bored. Chokes, not so much. I'm always surprised on how they perform (the choke) even though they don't jive with the charts.

[Andy]

Thank you Daryl. Yeah, I'm in geek mode right now I guess. I have a 16g on 0 frame which the muzzle choke device says is F/F and it's been a great grouse gun and I think it shoots more like a LM/LM. I'm going to measure that one for sure this weekend. Perhaps I will at least look like I know what the hell I'm doing.

[Double Lab]

Originally Posted by Andrew Sacco

Thank you Daryl. Yeah, I'm in geek mode right now I guess. I have a 16g on 0 frame which the muzzle choke device says is F/F and it's been a great grouse gun and I think it shoots more like a LM/LM. I'm going to measure that one for sure this weekend. Perhaps I will at least look like I know what the hell I'm doing.

I've said this before and I'll say it again Andy...Just shoot the damn thing and forget about the chokes. Looks like you're doing that with that 16/ O frame