Fixed rear site base change when rebarrelled??

[Ed42]

I’m pretty new to the M1903 but I’m learning thanks to you folks and a couple of good books. I’ve been reading Poyer’s book and Canfield’s on the M1903 while trying to fill out the M1903 Data Sheets. My 03 is a 1918 Rock Island Armory rifle with a Springfield 8 42 barrel. Serial is 2940xx.

Question: How common was it when the rifle was rebarrelled in 1942 to also put on what I think of as a 1903 Modified rear fixed sight base WITHOUT the lightning cuts? It’s rounded on both sides .. no lightning cuts. Other than the rounded side rear fixed base, I don’t believe I have any other “1903 Modified “ features (maybe the slide screw.. windage knob)? From what I’ve been told by folks on the forums, this rifle went through at least two rebuilds in its life.. probably more. Any of your thoughts would be sincerely appreciated!!!! Cheers!

[Sapper740]

Lightening.

[Tom in N.J.]

GI M1903 barrels had the rear sight base installed at the point of manufacture. They always came complete with the the rear sight base. Change the barrel, you get a new base.

[Ed42]

Lightening.

You are correct!

---------- Post added at 07:22 AM ---------- Previous post was at 07:21 AM ----------

GI M1903 barrels had the rear sight base installed at the point of manufacture. They always came complete with the the rear sight base. Change the barrel, you get a new base.

Thank Tom in NJ!!!

[1903Collector]

I agree with all previous responses. The M1903 Modified Rear Sight Base, or Fixed sight base was introduced late 1st/ early 2nd quarter 1942. HOWEVER, since FIFO was not an industry practice back then the barrel assemblies made included a mix of the early and late (modified) versions. I have no data of when supply of all early version were exhausted. SA barrels as late as 8-42 were most likely made with late version fixed sight bases. Certainly all RA M1903 barrel assemblies after mid 1st quarter were made with the late bases. Oddly enough, USMC Sedgley barrels made thru EOP (1944?) were all made with early fixed sight bases (at least in my experience in observing scores of such barrels over the years).
I have seen some barrels (mostly interwar) found on arsenal rework rifles with late fixed sight bases. I have done so myself, but there are some issues to be aware of and addressed in order to assure proper alignment (Ill get to that in a moment).

The following may be not be as clear as Id like it to be, but I offer my best shot:

It is possible to replace just the fixed sight base on an existing barrel and I have seen evidence that it was probably done at a rework arsenal, but it is also possible that some were done by a private owner. You see, the hole for the pin that fixes proper radial alignment of the fixed sight to the barrel is match drilled with the fixed base assembled to the barrel and aligned by way of a production fixture). The book by Fred Colvin (1917) includes drawings and descriptive texts of most of the production fixtures for EACH operation that includes an attached fixture for the anti-rotation hole drill bit that assures repeatability of location and orientation from assembly to assembly for the match drilled pin hole. It appears to be to be approx 30deg (Im guessing here) right (clockwise) of the vertical center line. The center of the drilled hole is located exactly at the seem between the OD of the barrel shoulder and the ID of the fixed sight base at the 30deg position. Therefore, most, but not all fixed sight vases can be interchangeable with most, not all barrels. HOWEVER, there was more than one fixture and it appears that the fixtures were made with a different offset at a different angle than the more common 30 deg clockwise from TDC.

HOWEVER, it appears that some fixtures were made with the offset of the drill guide hole at an angle counter-clockwise from TDC. I have also observed some fixed rear sight bases with two alignment holes present (one right of center, and the other left of center). Finally, I have also observed some barrels with the alignment hole (that looks like a groove when seen with the rear sight base removed) that are located counter-clockwise from TDC (I am not sure of the angle left of TDC) . I do not recall observing any barrels with with two alignment holes (one on either side of TDC). I recall only observing barrels with holes on one side or another.

Having said all that, replacing a fixed sight base on an existing barrel will either require finding a used fixed sight base (that was removed from a barrel) and finding a barrel with the pin hole location of both had been previously matched drilled with the same fixture. A second, more reliable method would be to match drill a second pin hole with a fixture designed to drill a hole on the opposite side of TDC. Considering efforts required to reuse and reinstall a used fixed sight base on an existing or new barrel I would think this may not have been the primary practice at a rework arsenal, but it cant be ruled out. I can say, that creating a new anti-rotation pin hole with out a drill guide fixture is extremely difficult if possible at all.