Parker 12ga bore diam.

Bruce Hering · 03-17-2022, 12:41 PM

Just checking my bore sizes. I have a GHE 12ga (1925) with Parker Special Steel barrels that shows bore sizes R .737, L .736. Do these sound-like original bores or have they been "honed".

Thanks

Randy Roberts · 03-17-2022, 01:08 PM

Bruce I believe that TPS will tell us .729 is the magical number. However I do not have any 12 gauge guns that actually measure that. The smallest bore that I can find in my group measures .731 in each bore. In looking at a half dozen or so others they all seem to range in the .733 to .736 range. Based upon my selection I would have no issues with the measurements you cited. Some of the guns I cited above are minty and undoubtedly never messed with so I feel comfortable using them as a guide.

Bruce Hering · 03-17-2022, 01:42 PM

Quote:

Originally Posted by Randy G Roberts

Bruce I believe that TPS will tell us .729 is the magical number. However I do not have any 12 gauge guns that actually measure that. The smallest bore that I can find in my group measures .731 in each bore. In looking at a half dozen or so others they all seem to range in the .733 to .736 range. Based upon my selection I would have no issues with the measurements you cited. Some of the guns I cited above are minty and undoubtedly never messed with so I feel comfortable using them as a guide.

Thanks Randy.

mobirdhunter · 03-17-2022, 04:11 PM

Bruce, I most certainly agree with Randy. It is seldom that my gauge measures exactly .729. I don't know just when Parker stopped overboring, but my older guns -- hammer guns and hammerless -- as I recall have larger than current nominal bores. Some may have been honed somewhere down the road, but I still think older guns are likely to have bores larger than .729.

Do you know the wall thickness at various points of the barrels? I like to know those more than the diameter. If you were closer...

Bill Murphy · 03-17-2022, 05:07 PM

Duplicate post

Bill Murphy · 03-17-2022, 05:08 PM

More likely than "been honed" would be "your micrometer isn't quite accurate" or "you didn't quite measure correctly". No big deal, that's just the way it is. What brand of micrometer are you using, or is it a micrometer at all? I'm guessing your bores are just fine.

Andy · 03-17-2022, 05:58 PM

If someone was to shop for a tool to measure this on the used market, what is the best tool?

Kevin McCormack · 03-17-2022, 06:53 PM

Quote:

Originally Posted by Andrew Sacco

If someone was to shop for a tool to measure this on the used market, what is the best tool?

For my money, Hosford's gauges hands down. They are expensive but they are incredibly accurate. His bore/choke gauge uses tiny collapsible fingers (3). I have run some comparison tests against a c. 1970s ball gauge which uses 3 small spheres on the brass head, which has proven to be very accurate. The range between the ball gauge and the Hosford gauge has never varied more than .003-.005 for the some 50 guns I have measured with them. No mystery using his instruments (he also makes an incredibly accurate barrel wall thickness (BWT) gauge.

Mike Poindexter · 03-17-2022, 08:28 PM

Austin H. put out an analysis of 12 ga. bore diameters on this forum years ago. He found that prior to S/n 70,000, there was a distinct "node" or cluster of guns bored .750-.755 , with a lesser node in the .730-.735 range. After 70,000, the large diameter node disappeared. I am attaching what I copied from his post back then.

Bruce Hering · 03-17-2022, 11:31 PM

Quote:

Originally Posted by Bill Murphy

More likely than "been honed" would be "your micrometer isn't quite accurate" or "you didn't quite measure correctly". No big deal, that's just the way it is. What brand of micrometer are you using, or is it a micrometer at all? I'm guessing your bores are just fine.

Bill: Yes, its a bore mic, Skeets. It seems pretty reliable checking against bore sizes measured with one of the "fancy" ones.