Some of you may remember I had picked up a badly converted 455 New Century with the intention of creating a replica of the New Century used in the 1906 Army Trials chambered for the 45 S&W Special. I have also acquired a 38 S&W Special, N frame cylinder to use for the conversion.

I posted about this on another forum and a poster there commented that the spacing of the chambers on the New Century was different from any other N frame. I find that very hard to believe. The bore is centered in the barrel which makes the distance frame from the extractor rod to the chamber the same.

Am I missing something?

Kevin

__________________
Unshared knowledge is wasted.

Know its apples and oranges but I have a 4.5 inch .38 spcl NS that a cas bud rebuilt from a martial .455 where he swapped the bbl and cylinder with new .38 parts. Nice revolver. I have a nice one in .38 with the longer bbl, it needed a little friend. Don’t know about the Smith though.

IIRC, the cylinder on a TL is slightly smaller than the later N frames.

__________________
John 3:16
WAR EAGLE!

I believe you are right. However I believe the chambers will still match the bore as the centerline of the axis is the same. People have put later cylinders in T-locks. As far as the specs on the 1907 guns the headspace is the same as the .455 Eley and a 455 chamber is more than long enough for a .45acp as they will drop in and end up about 1/8" less than flush with the rear face of the cylinder. The original round had the same rim as a .455 but was .923 in OAL. I think it would have fit and fired in a .455 cylinder.

__________________
dd884
JMHO-YMMV

There is a simple way to find out. Using a digital caliper, measure the size of one chamber with the ID jaws and rezero the caliper at that size. Then measure across 2 opposite chambers, outside of hole to outside of hole. The reading on the caliper will be the bolt circle, or diameter of hole centers.

Do the same for the other cylinder. If the final readings match, then they have the same bolt circle, and will line up with the barrel. If the readings are different, the cylinders have different bolt circles.

The reason this works is because you are subtracting one hole diameter from the final reading. That equates to half a hole on each side. This way allows you to quickly and easily find the center to center distance of 2 equal sized holes without doing any math.

Don't forget to clean the OD jaws and reset the zero with them closed when you're done, or your next measurement will be off by the diameter of the last hole.

__________________
protocalldesign.com

All N frame cyl center line axis to bore center line axis are the same including the TL, except one; the .357 N frame 8 shot. The barrel was raised which increased the distance between the two axis center lines for 8 chambers to fit in the cyl.

The key to using a non TL cyl in a TL frame is using the TL center pin/spring and extractor star assembly, which works in reverse of all later N frames. Hence why the TL recoil shield on the left side of frame does not have a divot to cam the ctr pin forward when closing the cyl.

__________________
Jim
S&WCA #819

I keep coming back to this thread to see if the work or the measuring has been completed.

Were the two cylinders in question ever measured?

I guess somebody better break out some calipers...
Measured a 29-10, 1917, and a TL, here's what I found:
TL
cylinder diameter 1.695"
length 1.568"
bolt-circle of chambers 1.076"
window height 1.722"
1917
cylinder diameter 1.705"
length 1.540"
bolt-circle of chambers 1.095"
window height 1.735"
29-10
cylinder diameter 1.715"
length 1.698"
bolt-circle of chambers 1.091"
frame window height 1.738"

The bore may or may not be the same distance from the crane, but the crane to chamber distance is surely NOT the same between the TL and a 1917/M-29.
So a 44 cylinder from a 29 will not work in a 44 TL regardless of diameter. You *might* be able to use a 44 cylinder and machine out to use with a .45 TL. The window is big enough for the cylinder, but depending on the top and bottom gap it may or may not clear once on the crane. I didn't measure the gaps, but they looked irregular enough that I'd bet money against a later cylinder fitting for diameter without lathe work or filing the frame window.

Those dimensions are informative but not really germane to the OP’s question. The cyl chamber ctr to cyl axis ctr radius measurement comparison is the issue.
As your figures show, they are “nominally” the same. Of course not exactly because all manufacturing is always within tolerance measurements, never exactly the same. That’s why barrels have forcing cones for the bullet to do the final alignment of chambers to bore.

By the way that’s the main benefit of smith’s MIM parts production; all parts are virtually identical and do not require expensive labor intensive fitting.

Also Mod 29 cyls are in a different size category than candidates for swapping into TLs. Not saying it can be done, but why, the chambers are bored too deep for any cartridge useful in a TL.

__________________
Jim
S&WCA #819

I disagree strongly, the bolt-circle is documented.
bolt-circle is what a machinist calls the diameter of the center of the holes in a circle, even if they aren't actually bolt-holes but rather charge holes. Divide by two to get the "The cyl chamber ctr to cyl axis ctr radius measurement" of which you speak.

Protocall designs method would be pretty accurate and if result was divided by 2 it would give cylinder axis to center of chamber (the key number). But, I hate measuring inside holes with calibers. So, here is how I would do it to get best numbers. At the forward end of cylinder place a pin from set of pin gauges in the center hole of a cylinder and another in chamber throat. Use largest pin that will fit these holes. Measure across outside to outside of the pins. This number, minus the radius of both pins, would be very accurate axis to center of chamber measurement.

Let us say center pin is .344 and chamber pin is .455 on TL and .344 and .358 on a model 28-2 cylinder. I am just guessing on center hole as I do not currently have a dissembled N frame cylinder at my desk. But if I divide all the pins in half and then subtract those radius from the OD to OD measurement made earlier, I will have an accurate cylinder axis to center of chamber radius. .344/2=.172, .358/2=.179, .455/2=.2275.

BTW using Protocall Designs method, an old complete rust bucket 44 TL, my carry 325 and a set off digital calibers that all happen to be in my desk drawers.
325 chamber diameter .476 and outside to outside of 2 opposite chambers was 1.605. 1.605-.476=1.129/2=.5645

TL chamber diameter .458 and outside to outside of 2 opposites was 1.585. 1.585-.458=1.127/2=.5635

So even by that method they are with in .001

Maybe after wife and I play our morning cribbage match I will go out in shop and use pin gauge set and better calibers.

OK. First the center hole on a N frame is .384 and radius of that is .192

On an Model 28 cylinder that has been reamed to 44 special and took a .430 pin in throat. Radius of .214. I got ..9575. .215+.192=.407 .9575-.407=.5505 for a axis center line to chamber center

On the triple lock a .431 (Ø of .2155) fit the chamber and the same .384-.192 center and a measurement of .9585 which gives a axis center to chamber center of .2155+.192=.4075 .9585-.4075=.551

So by that method a triple lock cylinder came within .0005 of a N frame cylinder and I suspect that is within tolerances.

BTW that is a circle diameter of 1.102 on TL and 1.101 on the 28-2
cylinder

I tried it again using the tightest pin in one chamber and the next size smaller pin in opposite chamber and came up with same final numbers. The TL being .001 bigger OD to OD than the 28 cylinder.

This is interesting. I re-checked my TL cylinder with pin gauges and got bolt circle values from 1.077" to 1.0785" depending on the chamber. This means that either there is something hinky about your TL cylinder or mine. My gun is a mid 3-digit. I'd be very interested to know where in production the cylinder you measured falls.

mine is higher than that. Left it out in shop. I also have a nice 455 TL I will check.

OK rust bucket 44 TL has serial number 114xx

455 TL has serial no. 12493 and gave me 1.098

I also checked some other N frame cylinder I have in parts drawer. A recessed 44 mag gave 1.098 and another 1.102, also A 45 acp gave 1.100

A variations from 1.098 to 1.102 if .004 and from center line to center of chambers .002. I don't find that especially odd or huge. I should measure each chamber of a few cylinders sometime just to find out how much they do vary. But then I wouldn't be surprised to find some variation in a bunch of frames if you were to measure from center of bore to center of yoke either. In fact I would not be surprised to find that bore C/L to outside of barrel threads had a .001 or so variation.

I do however find your measurement 1.078 interesting. That is ..02 smaller than any of mine. Can you drop a bore size pin down the muzzle and have it pass into the cylinder??? Of course the bore is about .010-.012 smaller than groove so might not tell much. Be interesting to see what number was from center of bore to C/L of yoke barrel is. With cylinder off yoke and yoke in place a measurement from a bore sized pin sticking out of forcing cone to top of yoke barrel would tell that story if you added 1/2 the pin diameter and 1/2 the yoke barrel diameter.

Well I don't see any disagreement, we're on the same page.

Except of course about "charge holes"; when they have a shoulder in them like the TL and subsequent revolvers, they're chambers.

__________________
Jim
S&WCA #819

Okay, this is a very busy month for me but next week, I get some time off. Then, I will measure the TL cylinder, a couple of ACP cylinders and the 38/44 cylinder and post what I find.

I will also ship the 38/44 cylinder off to have it recorded and chambered.

AND, if anyone is interested, all these calculations have given me a head ache and some heartburn! Time to get my cylinder done and installed on the 455 First Model.

Kevin

__________________
Unshared knowledge is wasted.

Hi Kevin,

Yeah once you measure your TL cyl length and compare to the 38/44 cyl, you'll know what slight adjustment might be needed in length to drop into your 455 frame. I would check this before re-chambering it if you haven't already. Check for cyl fore and aft movement ("cyl end play"). You might need a shim dropped into the cyl center hole for the yoke shaft to take up end play.

Worse case scenario if the barrel to cyl gap is excessive, you may want to look for another cyl. If too tight or won't close, you could have the front of the cyl "faced off" to match your TL cyl length by whoever re-chambers it for you.

I don't anticipate any issues with the cyl diameter or the timing. Although every cyl swap can be slightly different, mine have always been simple.

__________________
Jim
S&WCA #819

Jim,

I converted a Model 28-2 to a 4”, tapered barrel 45 ACP. Everything came together, eventually!

Thank you for reminding me to check the cylinder length. I would have probably skipped that important step.

Kevin

__________________
Unshared knowledge is wasted.