Outpost75
03-23-2019, 08:53 PM
I examined today a 1918 date of manufacture Colt New Service in .45 ACP. Its bore slugs .443", groove is .451", cylinder throats are .456” Cylinder gap pass 0.007”, hold 0.008”
A 1914 date of manufacture .455 Eley has bore .444", groove .454" with cylinder throats also .456"
A 1923 date of manufacture .45 Colt has similar bore, groove and cylinder throat dimensions to the .455
238505
The chambers of the .45 ACP Colt New Service have EXACTLY the same dimensions as my 1914 date of manufacture Colt New Service .455 Eley, except for the difference in chamber length which resulted from the .45 ACP cylinder being faced off at its rear to clear the moon clips. It is quite apparent that Colt used leftover .455 cylinders from its British revolver contract and simply machined additional head clearance on them for the moon clip and changed the dimension of the frame lug to correctly position the cylinder.
238506238507
When .45 ACP Ball ammo is inserted without clips it drops goes all the way into the chambers, stopping with the case heads flush with rear of the cylinder, the case mouths coming to rest against the chamber cone.
Contrary to common Internet lore, the .45 ACP New Service chambers were NOT bored “straight through”, as they have a normal angled transition from the case mouth in to the .456 cylinder throats, which is evident in the photo.
Colt M1917 revolvers which were reworked for WW2 issue have the square stop surface to permit headspacing .45 ACP rounds without using the half-moon clips. Later WW1 guns will also have the purpose-built .45 ACP cylinders with the square stop surface, as the supply of leftover .455 cylinders from the British and Canadian contracts, which could be faced off, was exhausted.
A 1914 date of manufacture .455 Eley has bore .444", groove .454" with cylinder throats also .456"
A 1923 date of manufacture .45 Colt has similar bore, groove and cylinder throat dimensions to the .455
238505
The chambers of the .45 ACP Colt New Service have EXACTLY the same dimensions as my 1914 date of manufacture Colt New Service .455 Eley, except for the difference in chamber length which resulted from the .45 ACP cylinder being faced off at its rear to clear the moon clips. It is quite apparent that Colt used leftover .455 cylinders from its British revolver contract and simply machined additional head clearance on them for the moon clip and changed the dimension of the frame lug to correctly position the cylinder.
238506238507
When .45 ACP Ball ammo is inserted without clips it drops goes all the way into the chambers, stopping with the case heads flush with rear of the cylinder, the case mouths coming to rest against the chamber cone.
Contrary to common Internet lore, the .45 ACP New Service chambers were NOT bored “straight through”, as they have a normal angled transition from the case mouth in to the .456 cylinder throats, which is evident in the photo.
Colt M1917 revolvers which were reworked for WW2 issue have the square stop surface to permit headspacing .45 ACP rounds without using the half-moon clips. Later WW1 guns will also have the purpose-built .45 ACP cylinders with the square stop surface, as the supply of leftover .455 cylinders from the British and Canadian contracts, which could be faced off, was exhausted.