The barrel blueprint in the tech section is from the Rock Island Arsenal, the blueprint in the book from Nicolaus and Associates shows the Springfield Armory blueprint and they appear to be Identical. This older blueprint (the same one as on The Sight's) from the Springfield Armory shows different dimensions for the radius and angle dimension at the top of the barrel feet, .500 and 28deg 30', while the Tech Section Blueprints show a .0438 and a 24deg referenced from the center of the slide stop pin hole; also this one shows a .750 +/- .005 dimension at the bottom, from, it looks like the front of the slide stop pin hole to the end of the barrel hood, while that particular measurement doesn't appear in the Tech Section print. If it is from the front of the pin hole to the end of the hood, I can't get the math to work, at least my math doesn't work.
Are these different or a revised barrel?
Is the .750 dimension a reference to the length of the barrel hood from the front of the slide stop pin/hole, or is the .500 radius dimension just referenced from the barrel hood for the centerline of that radius?
Odd to give a dimension from the edge of a hole vs. the centerline. High school drafting teacher said that was a no-no. That can't be the detail for locating the link hole. Wish I had a .45 barrel to measure against. The .750 measurement is considerable longer on a 10mm. Clearly out of my league. But I hope somebody replies with the scoop.
The 28deg 30' is the angle of the sloped, front portion of the lower lugs and is the same on all 3 blueprints.
The 24deg establishes a reference line from the pin hole center to locate the center of the radius of the link clearance cut in the 2 later blueprints.
The earlier Springfield Armory blueprint (got mine from TheSight) locates the cleance cut center differently. Instead of the 24deg angle, it locates the center point of the radius .750 +/- .005 forward of the hood and vertically by the "0.080 minimum..." caveat. The .750 is just for locating the clearance cut and is not related to the slide stop hole.
Don't know for sure whether the earlier print describes a different barrel because there's no barrel part number on the print. All three prints may describe the same barrel, but with different layout methods.
Thank you Niemi, I didn't think I quite had it right. After you replied, I looked again and DUH... the 28deg 30' is everywhere, didn't see it before because it's in a different view. I saw the one radius was different and the other dimension appeared different. I guess being for a different measurement altogether is a good enough reason.
I didn't think the .750 could/should be to the front of the hole, but it sure "looked" like it.
I do like that older print though, it makes the chamber area easier to understand (at least for me).
Quote:
I saw the one radius was different...
The radius of the clearance cut is actually the same on the three prints: "0.500 - 0.062" and "0.438 + 0.062" have the same range of values (0.438 to 0.500), just different nominal values.
Curious. The "nominal" value I have always understood to be the optimum/ design value. Tolerances are then applied only to allow for the realities involved in trying to make the thingie. It is still preferred to make the part as close as possible to the nominal dimension.
This change in dimensioning suggests that the original design ("nominal") value wasn't all that important. Makes you wonder why the revised dimension then wasn't expressed as 0.469" +/- 0.031" -- which is yet another way to annotate the same range of allowable dimensions.
Yes, curious indeed. Unless maybe later on they decided that a smaller "preferred" radius would make for a slightly stronger chamber bottom? Or maybe... uh... er... who knows?