Muzzle measurements
 

Before I sent my 1888 Top Lever Hammer gun to Breck Gorman, I measured each bore at the muzzle with an ordinary set of calipers. Curiosity I suppose, before I get the true multi point measurements from Breck. The PGCA letter revealed only that the bores were full & full. The muzzle measurements I got were .714 for each barrel. Without knowing what the tubes measurements are at the halfway point, does .714 reveal any relevant information aside from “that’s just what they measured.”? If the mid barrel bores were the nominal .729 could I speculate that the constriction was .015?
I understand that Parker bores were commonly over bored so my speculation is likely useless.

Parker’s in that timeframe were over bored, so your chokes could well be full.

The only way to know for certain is to measure the bore diameter through the entire bore forward of the chamber and cone, then do the math. I don’t think .015" is anybody’s full choke.






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Agree, though .714 seems restricted. The question becomes “restricted from what?”

I believe Breck will find the bore to be .750, I own a Parker from the era that has .750 bore s and chokes of .038/.038. It still has min walls of .038 in both barrels and it weights exactly per the letter. It's a 1 fame 12ga.

Craig, those measurements would please me.

Precisely...





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Barrel Measurements Received Today
 

Craig, you were spot on with your prediction. The measurements are a real blessing with MWT of .035/.034. Sort of interesting that the choke length in the left barrel is 4-1/2" and 5-1/4" in the right barrel. I'm extremely pleased with the findings, considering that purchasing an internet Parker with a "As is - No Return" policy can be very risky.
Would choke constriction of .027 be considered slightly tighter than "Improved Modified" by Parker standards? The PGCA letter indicated Full & Full.
Breck's findings:

True. Generally the tighter choke will have the longest taper but once again Parker Brothers show us to "Never Say Never."





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My compliments to Breck - that is the barrel evaluation our guns (eyes & fingers) deserve.

I believe however Breck's "end of chamber" wall thickness of .162" for a No. 1 frame 12g must be the BREECH end of chamber.
The muzzle end of chamber (immediately prior to forcing cone) is of more importance, with the MWT for usually > .105". Factory small bores may be as low at .090".
Because the angle of the cone exceeds the external taper of (most) barrels, the forcing cone MWT is usually the same or slightly greater than the end of chamber, and .110" would be typical.

Lots of numbers are here
http://parkerguns.org/forums/showthread.php?t=31791
and
http://www.doublegunshop.com/forums/...=379803&page=3