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I acquired a box full of miscellaneous components. In it was one of the old Remington red and green boxes marked 6.5mm Mannlicher-Schoenauer. The cases inside are head stamped simply 6.5 m/m. They appear to be similar in dimensions to what a 6.5mm M-S should be, except they have a short and very steep shoulder similar to what you would see for an "improved" cartridge. The shoulder angle appears to be somewhere around 40-50 degrees as best I can tell. I have never heard of an improved cartridge based on this case. Is that what this is, or is it something else?

There is a picture in the image gallery with the same name as this title. Thanks for any help.

Not sure what it is, but here is the pic from the image gallery.

It would help if you provided an overall photo of the case, instead of just a partial one, providing an idea of overall size. It would be even more helpful if you measured case dimensions, including length, head/rim diameter, etc.

Have owned rifles chambered for rimmed cartridges that had VERY generous shoulder areas. At one time had two .25-20 Winchesters, a Savage Model 23 and an 1892 Winchester. The difference between the chambers was so obvious with fired brass that I renamed the Winchester the ".25-20 Improved."

Maybe the 6.5x55 Improved Arch, see P.O. Ackley's Handbook, Vol. 1.

The pic posted from the Image Gallery is worthless for ID purposes.

Take a pic of the whole cartridge and use postimages.org to post directly to thread.

After you choose your image click on the hotlink for forums, that cpoies it then all you have to do is paste it in the reply box.

Sorry about that. The photo I took was the full view, but something happened between there and posting it. Thanks for the help in posting photos.

Here is some basic dimension info:

Overall length: 2.103" - 2.114" with at average of about 2.108"
Rim and head diameter are the same - 0.450" - 0.451"
Diameter at the shoulder - 0.421"
Approximate length to the shoulder - 1.73"

I don't think this is just an out of spec chamber since the brass appears to be resized. The neck inside diameter is 0.262" and the primers are out.

There is some handwritten load information on the box:
Bullet: 139 Gr. 6.5 mm no brand or style given
Powder: 36 Gr. HiVel #2 or 37 Gr. 4895. No indication as to which 4895.

https://postimg.cc/gallery/6B3R5bB

Per longbarrle's comment:

PO Ackley's book "Handbook for Shooters and Reloaders" Copyright 1962 has a 6.5x55 cartridge called 6.5x55 Improved Arch which has a very sharp shoulder similar to your picture. Ackley does not list sizes/dimensions in this book.

He does not list an improved 6.5x54. There are other improved 6.5 cartridges listed, but on '06 size cases and larger.

The 6.5x55 standard cartridge has a longer overall length and a larger rim diameter. It doesn't seem to fit. Interesting, though.

Haven’t found the cartridge but can clear up your load data. Hi-Vel 2 was discontinued in 65 and was replaced by RL7. Up until 73 IIRC H4895 was surplus IMR4895 and used the same data. They diverged when the surplus 4895 dried up and Hodgdon started having it made in Scotland.

Just to be clear, I don't know if the load data is for these cases or the original 6.5mm M-S that came in the box.

Those are just about the dimensions of the 6.5x52 Carcano military cartridge, which are very similar to the 6.5x54 Mannlicher-Schoenauer, but not exact. It was pretty popular back in the era when those two powders were still produced, due to many military rifles.. I also would not be surprised to see a little steeper fire-formed shoulder from one of those rifles--or be surprised if somebody "improved" one, which was also common in that day with LOTS of cartridges.

At this point, I am going to call it a 6.5 x 54 mm Improved! Not sure what good that does me since I don't know of any rifle chambered for it. I don't see the point in making one and getting custom dies. Fun stuff, though.

Thanks everyone for all your help. I am continually impressed by the amount of knowledge on this forum and the willingness to help. Thanks again.

wasnt the 6.5 Jap rimmed?

The 6.5x50 Arisaka is semi rimmed.

You're right. I made the mistake when looking at drawings of various 6.5 cartridges. Was also looking at the dimensions of the 6.5 Carcano--which is indeed very similar to the 6.5x54 MS--and a BUNCH of Carcanos also showed up here.

The 6.5x54 MS cartridge was produced in the USA by REM-UMC, Peters, Western, and Winchester before WWII. The cases heads from all four sources were stamped with the makers name and with "6.5 mm" only, without any more specific designation. In the Stoeger Shooter's Bible the last listing of this cartridge was in the 1949 edition. Only imported DWM 6.5x54 MS cartridges were listed after that year, so the cases shown by the OP are at least 72 years old.

SImmons' Wildcat Cartridges book from 1948 describes many improved cartridges, but none on the 6,5x54 MS case.
--Bob

That is great information. The cases in the box have both REM-UMC and Peters head stamps. It appears that these are indeed based on the 6.5x54 MS. I guess i will stick with calling it a 6.5x54 mm Improved.