308 Wildcat?


Hello all,
I have come across this round in a large box from my uncle. It’s measurements are

6.17mm Bullet diameter
51.53mm Case length
6.90mm neck diameter
11.96mm rim Diameter

Headstamp of

(circle with + in the middle)
TW 66

The photo is next to a 30-06 Springfield.

Let me know if you need more information
Thank you


I know there might not be a large wildcat crowd here. Are there any sites or forums that may be able to help.


Possibly a .25 Souper, I believe the .308 case was just necked to .25 with no other changes.


I think “circle with + in the middle” is a NATO mark.


SKSVLAD–While the “circle with a + inside” is commonly called the “NATO” mark by most cartridge collectors, technically it is incorrect. The symbol is actually the STANAG (STANardization AGreement) mark. It is the symbol adopted by the Military Department for Standardization for NATO. The actual “NATO” mark is a stylized 4-leaf clover shape. The STANAG marking can only be used on ammunition of less than 20mm size that is made in conformity with the NATO standard and is interchangeable in any weapon chambered for that round, regardless of which NATO member county made it. The symbol itself is a simplefied depiction of the North Atlantic Treaty Organization symbol of a compass rose with 4 points.



It’s a 243 (6mm) wildcat made from a 7.62x51 case. If you can give more dimensions, especially the shoulder diameter, base to shoulder, and shoulder angle I can probably help more.

Scaling off your photo tells me it could be one of the 243 wildcats such as the 240 Page but that particular cartridge pretty much became obsolete in the late 1950s when the 243 Winchester was introduced. But, there has been a recent comeback of cartridges of that ilk. Basically, they are 243 Winchester with the shoulder pushed back and the angle increased to eliminate that the god-awful short neck of the 243W.



Thank you. The other dimensions are
Shoulder Diameter- 10.96mm
Base to Shoulder- 37.70mm (+/- a few tenths)

Unfortunately I don’t have anything to measure the shoulder angle. I hope that helps. Thanks



Unfortunately, those dimensions do not EXACTLY match any wildcats that I know of, but being wildcats, they seldom do. Every wildcat shooter who has a chamber reamer ground will use his own dimensions and even the reamer grinders themselves will often vary some of the dimensions as they see necessary.

Your cartridge is very close to the 6mm Walker International Long and since there were several variations of that cartridge I’d say that is what it is.

The 6mm Walker was developed by Mike Walker of Remington by necking down the 250 Savage and pushing the shoulder back to reduce case capacity slightly. The Long version is more recent and was made simply to get back a little of the case capacity. The original version was a short range cartridge and the Long version is, as you’d guess, a long range version.

The cartridge was very popular in it’s day but has been replaced by similar sized 6mm cases with more efficient shoulder angles such as the 6 HLS Hunter and in the last year by two cartridges from Scandinavia, the 6 x 47 Swiss Match and the 6.5 x 47 LAPUA. The brass for those two is of such high quality that wildcatting the 243W, 308W, and 250 Savage brass is a thing of the past.

That’s today’s lesson in wildcat cartridges. ;) ;



Thank you sensei!
Another mystery round off the list.



FWIW here’s a photo of the original Walker INTL and the INTL Long from my collection. By comparing the photos you can see that yours and mine are identical for all practical purposes.



Your not done yet, I’m about to relay better than 2 pounds of (inert and dummy) wildcats to you, that the gentleman in SC was kind enough to donate to your collection. At least one of them is mislabeled, so you will be having some more “wildcat ID” fun.

I’ve tossed in a few other things that you don’t have yet, also.


Careful Josh, collecting wildcats can be more frustrating than trying to read a woman’s mind. Nobody has made a good estimate of how many there are and, in fact, nobody can even come up with a good definition of a wildcat. At the same time, wildcats are both an attraction and a torment of cartridge collecting.

We’re all here to help so don’t hesitate to ask. And lots of pictures will help.



Thanks! “Wildcat ID fun” puts a spin on things more so than just ID and history. It’s probably a good thing to have some mystery rounds lying around just to remind me how how much is really out there. I have no misconceptions about ID’ing everything but I sure will try.

Thanks for the pictures. They look like a good way to organize. I’m currently stuck with a 640x480 webcam in a small vice to hold it steady but plan to get a real camera soon. I have yet to run into too many frustrations yet but even when I do I can sure imagine things worse. It’s like antique collecting but with items that are actually interesting themselves.