doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Ithaca 20ga Flues

I have a Ithaca Flues in 20 ga serial number 368797 i believe mfg in 1923. I need an education on some of the measurements and markings on the barrel.

I measured bore diameter and right was .615 and left .610. Would it be common to have different bore diameters on the same gun? I have an Ithaca chart that indicates bore diameter for 20ga should be .615.

There are markings and numbers on the barrel I don't understand. Stamped on both barrels is (for what I can make out) 'SB8C9TB' . Right barrel table marked 2 and left marked 4 Rear lug marked 8 and front lug marked '1' with ' ��.er Proved'. I don't understand any of this. If someone can interpret that would be great. Thank you.

They�ve been polished
Flues� have a �Nitro powder proved� stamp commonly in an oval
4 & 2. Full n mod

Nice simple light 20�s

He he he
I grabbed my 20 gauge Flues out of the rack.
She felt heavier than usual.
I opened that action as normal when I touch a gun.
It was then I spotted the two Savage 410er inserts
What fun, what fun
Mike

All that and "all" 20 ga Flues models left the factory with 2-1/2" chambers.

Polishing would not explain a .610 bore diameter if standard is supposed to be .615. .610 is tighter than that, not more open. That's maybe a little more difference from one bore to the other than you would expect, but it's not unusual to find a few thousandths difference in bore diameter.

It sounds like one barrel was finish reamed and polished a bit under nominal bore size. But .005" under or over isn't real unusual or at all alarming in vintage guns. These things weren't built on CNC equipment with cookie-cutter uniformity. I was kind of concerned about a 16 ga. straight grip G Lefever I had bought that had both bores about .007- .008" over nominal 16 ga. bore size. I thought I made a big mistake when I neglected to take my Stan Baker bore gauge when I inspected the gun. The gun was in great original condition, and I had no reason to suspect it had been honed or polished. I later learned that it wasn't uncommon to find an unhoned Lefever that much overbored.

Thankfully, Larry explained to us that .610" is smaller diameter than .615". Who knew... until our ex-intelligence analyst pointed out the obvious? (Deep sigh... eyes rolling....) Too bad he didn't comprehend what the grey man Clapper Zapper said had been obliterated by polishing. I'd explain it to him but I don't think he'd accept it. Besides, some sensitive guys might get offended if I corrected him, and rat me out... again.

And what tool was used to measure the diameter. I have a Skeets gauge, it works well but won�t give the readings consistent like a internal micrometer will. Lot of mechanism and distance between the feelers and dial. 3 thousandth slop is about what I expect.

Of course my internal mike that reads half a thou consistently will only measure a inch deep. My take away is something like a Skeets gauge gives a good indication of bore size and choke constrictions, don�t be too concerned about accuracy. Precision deep internal micrometer cost way more than most of us want to spend.

Apology�s In advance if the measurement is precise.

Boats

Hey, I just meant the Nitro Powder Proved stamp was polished out

I have a Starrett telescoping gage with about a 12" handle. For as far as it will reach into a barrel I can easily read the diameter to within � .001" with no problem.

As I recall (Don't own one) the Skeets gage is a dial bore gage. Used them many times in my years as a machinist. Could certainly get a reading within � .0005" with one of those. You have to set them with a ring gage but the bore contacts are diametrically opposed in a dial bore gage. A solid bar connects to the dial indicator. If it won't read closer than .003" then its total junk, best to throw it away & don't depend on any reading you take with it.

An internal micrometer works on essentially the same principal, except you're reading a micrometer thimble rather than a dial. The still have a solid bar going down the length of the shank many of these have three contact points which allows for better checking of out of roundness, but not greater accuracy.

Skeets not a Starrett by a long shot.

Boats