"Modified artillery bores" Topic

No, this isn't intended to include me. It may, but that was not the intention.
I've been reading about artillery pieces that were produced in two different bores. The Schneider-Danglis 75 mm was designed by Greek Colonel Danglis and produced by Schneider in France. Once they'd finished the Greek production run, Schneider went looking around for somebody else to buy the gun. The Russians said, "Sure, but can you make it in 76.2 mm?" So, the Russians bought the rights and produced these in 76.2 mm for their infantry gun. Skoda produced a 100 mm howitzer, and people showed interest and bought some, but others really wanted it in 105 mm. So, Skoda complied and countries like Turkey had 105 mm Skoda howitzers.

So, the question is would the different bores have looked much different? I can already see that for 15 mm or even 28 mm guns, a 1.2- or 5-mm difference in bore width would not be visible. Would relatively small changes like this have driven other changes, though? More muscular recoil systems? Thicker barrels? To what degree can I happily use my Russian 76.2 as a Greek 75? Is this a whole new redesign or just a partial redesign?

Grelber

The bore is merely the opening, so no that would be discernable on a table.

However, if each customer wanted a different carlber, that might change the length of the barrel, the calibre in order to better suit the ammunition desired.

Possibly even a change by putting a muzzle device on barrels if the customer wanted too. Being the late 1930s when that started to gain vogue.

Some of those minor differences were simply a product of legacy measuring systems versus metric. Schneider made a 4.2" howitzer (107mm) for the Imperial Russian Army that was adopted in 1913 by the French, rebored to 105mm. The difference in weight of shell would be minor, and for all practical purposes undetectable. In the legacy system, 76.2mm equals 3 inches.

For the purchasing army, compatibility with existing ammunition stocks may also have been a factor.

The critical measurement is the propellent. If everything on the carriage is capable of handling the pressure exerted by the propellent discharge (breach, recoil system etc) you can modify the bore diameter to your heart's content. IIRC in the US army they used the same carriage for a gun of lesser bore size and a howitzer of larger bore size. The gun barrel would be longer than the howitzer barrel, the gun longer range but the howitzer would have a larger shell.
Minor changes in bore size were easy wins. IIRC the Germans took Soviet 76.2 guns and converted them to use their own 75mm ammunition.

Thanks very much for the input! I couldn't see any differences in the photos I found, and the sources I went to talked like any differences were minor, and probably not noticeable when scaled down. After 35 years dealing with military configuration control, one does learn to at least ask the question, though.

Grelber

Even the QF 75mm gun fitted to British tanks in WW2 was just a rebored 6pdr. As long as the barrel walls are thick enough, minor reboring is fine.

I wouldn't try and convert a 75mm to 150mm though….