It was probably longer than that .......

My 1st was a 45 Colts RBH. I shot it some but spontaneously about a year after I got it ammo went from about $18/50 to $40 something. Suitable bullets were 25-40/100 with factory cast coming in around 50/250 ...... I loaded some factory cast at what was about a 200 gr 950 fps MV advertised load . Well 4 hit in about half of the bottom of a 5 gallon bucket at 25 yd and the recoil of the 5th made me question my skills .

At home I found that the Blackhawk had what amounted to 3 pairs of chambers that were basically a .453, 4 ><.454, and a .455 throats . The .455 tossed about 2.5" out of whatever was grouping at 25 yd and the .453 was where the substantial increase in recoil came from probably. Very shortly after this I started casting my own .
I lapped the throats to a fairly uniform match of the largest at .4546 . The .455 still tosses but sized .454 it's 6 inside 5.5" at 50 yd standing unsupported . A 250-260 gr SWC or SWC HP at 1050 fps isn't exactly a plinker either .

Years later I picked up an ACP cylinder for it and to my delight even the +P loads shot remarkably well. No kidding they did the throats are .4542-.4543.

A few more years go by and I get a S&W 1917 made in 1918 I slugged it and it won't chamber over a .453 it throws the 250 and 260 gr SWC all over and I'm seriously bummed out . I load some 200 gr SWC and they're not great but definitely better . Well I guess they were left overs from a BP adventure and almost dead soft. Which means that when I moved the loads up to 75% of the window it was grouping 4 together and and although very consistently tossing 1 ea at 8-2:00 . I slugged and measured again. Looked for out of round etc . Eventually I bought a Bubba sister . It was reamed to 45 S&W throats apparently matched and it shoots all of the bullets the Ruger does even when they're stoked up to +P+ ..... Which is still under ACP start loads but 18-19 kpsi is hot in a 14kpsi cartridge.

What I really wanted was to be able to run 1 sizer and I had resigned myself to and a bought a 230 SWC for the OM 1917 . Which also worked out nicely for running the S&W in the Colts carbine.

I bought a.454 reamer thinking I would ream 3 cylinders at least clean up and fix an out of round. Much to my both delight and disappointment the reamer was a slip fit in the Ruger ACP cylinder that just moved . It did cut a burr off the Colts cylinder, I suspect it was the chamber that was originally.453 .
The 45 S&W was finger turned through in full contact but I doubt that it actually cut anything but carbon.
The OM 1917 however delivered ony intention . One chamber only scuffed the back half of the throat but cut clean on the front half . 4 cut the full length of the throat but left hints of blue in almost ripples . The last hole was cut full length of the throat no blue remains. Now one must understand I only have tools to measure absolute to .001 and the .0002 is eyeball between the .001 marks . It's looks like the difference between a kiss and cutting the blueing off is someplace in the neighborhood of.0012 .

I wish I had bought the .4545 reamer on the other hand I'm happy at this point that 18 of the 24 chambers are under .001 different and that a possibly invisible defect has been removed and might just close up the groups a little more in the hunter .