I posted this on another forum. I have 45ACP? cartridges that are headstamped 45auto, 45ar, and 45ac. What do I have?

ACP= Automatic Colt Pistol
AUTO= Automatic
AR= Automatic RIMMED, made for a specific revolver, so that moon clips wouldn't be needed to load it.
AC= Automatic Colt
Except for the AR ones, they are all "plane Jane" 45acp.

Thanks very much for the reply.

Yep - TG nailed it .

We know the 45 Auto Rim is different because of the rim. The first 45 developed for the Colt pistol was called 45 AC but it was much different then the 45 ACP we know today. Read here:

.45 Auto Cartridge History

By Stefano Mattioli

Spring of 1904, nearly 100 years ago, the Frankford Arsenal as well as the civilian Industry were asked by the U.S. Government to develop an .45 caliber pistol round to improve the existing pistol rounds and to compete with the ready available .45 caliber revolver rounds of good fame.

The Arsenal however put it on “wait and see”. Not so for the folks at Winchester Repeating Arms Co., that in conjunction with COLT Mfg. Co. came up, just after a few months, with a new .45 caliber round housed in a modified .38 Colt pistol model 1900, the .45 Automatic Colt.

Cartridge length was .900″ (22,86mm), case was brass and of .470″ (11,938mm) diameter, bullet a 200 grains cylindro-spheric gilding jacketed, extraction area had .085″ (2,159mm) in length and markings were “W.R.A.Co. .45 AC” on the base and a “W” on the primer.

Now, after the official introduction in 1905 by Winchester Repeating Arms Co. & Colt Mfg. Co. of the .45 AC together with the Colt model 1905, the folks at Frankford Arsenal began to activate matters, starting and trying to better up the existing round. They ended up with a slightly modified .45 cartridge with a longer case and heavier copper-nickel jacket bullet of 230 grains, named “Cal. .45 Automatic Pistol Ball Cartridge Model of 1906” (FA M1906) to be on time for the upcoming tests planned by the Government for June 1906. The Government however couldn’t set on both of them and in the spring of 1907 contracted the Union Metal Cartridge Co. to design another .45 cartridge based on the existing one but with a shorter case. After 5 more months, the cartridge named “.45 Automatic Colt Government” (UMC M1907) was ready. Again, other modifications, a larger extraction area, were needed and the Government reordered the Union Metallic Cartridge Co. and Winchester Repeating Arms Co. to redesign it as needed. At the end of 1908, two close to identical cartridges emerged from this request (UMC M1908 & WRA M1908). At the same time, in 1908, the folks at Frankford Arsenal worked on another .45 cartridge (FA M1908), hoping to get the contract for delivering test ammunition to the troops. This contract, however, was issued to UMC, that started delivery of the test ammunition in the year 1909. This round was basically the same as the UMC M1908, but had a cannelure on the bullet just over the case mouth. Markings were ” U.M.C. .45 A.C.P.” (UMC M1909). After the tests, this round was finally and officially adopted, after some slight modifications (drop of the cannelure), by the Government as the ” Cal. .45 Automatic Pistol Ball Cartridge, Model of 1911“. This was August of 1911. The ammunition makers could start their production. The first cartridges, Model of 1911, known to be issued came from the Frankford Arsenal (FA M1911) and had the markings “F A 8 11“( the 8 stands for the production month).

If a cartridge is marked 45 AC it may very well be one of the old originals.

http://www.sightm1911.com/lib/...artridge_History.htm

The 45AC that I have are Peters. It has a silver[nickle] brass with no cannelure. It has a roundnose copper bullet. I have some others with a few different headstamps.

Butch, Measure a case on a 45 ACP that you know is the more modern 45ACP for sure and then measure the case length on those Peters that your have and let me know what they are. It would be rare, but you may very well have some samples of the very first 45's mentioned in that article I posted here. They would be of value to a collector.

As near as I can measure, it is .898 on the Peters, I looked and found a box of Western 45 Automatic with 230 grain Lubaloy bullets. They are headstamped E C S 43 and have a real shallow and narrow extractor groove. I also found a box of Remington Kleenbore 45 Auto Rim with 230 grain lead bullets.

You'll notice in that article extractor groove is mentioned along with they came out with the case cannelure. Like I said the original cartridges which were for the modified 38 Automatic pistol would be very rare.