.30 unknown to me-7.62x36 Grendel

Here is a subsonic round I picked up in the early 90’s either at Grendel or Knights Armement.
If I remember well it was designed to be shot in a modified M16.
It was given to me as a 300 Whisper and I put it in my drawers and forgot it.

Right now, sorting my rounds, I check it again and I realize it doen’t fit with a 300 Whisper.

I had a loose bullet but I don’t know where it is.
The bullet was heavy and very long.

What is it ?

It is undoubtely slightly longer than both standard 300 Whisper and 300 Blackout, but a large number of wildcats with similar dimensions were made. I have a similar round with a 37,5 mm case, for example. Anyway, your round will fit into a standard 300 Whisper chamber, since it is 35,67 mm long (CIP - L3).

Almost any reloader uses 223 rem brass instead 221 Fireball cases, since the 223 is far more common and cheap.

Can you provide rim to shoulder lenght?

I teach History, but I think the missing rim-to-shoulder measurement is 27.68mm.


Although this is very similar to the .300 Whisper, this cartridge is designated 7.62x36 Grendel and was made in the early 1990’s by Grendel, Inc. of Rockledge, Florida for their S-16 suppressed rifle.

For comparison, the measurements of a contemporary (c. 1994) .300 Whisper made by Cor-Bon from a .221 Rem. Fireball case has a case length of 34.25-34.60 mm, a body length of 27.05-27.30 mm, and a neck lenght of 6.16-6.41 mm.

Derived from the 1960s USAF IMP experimental, Type 3 cartridge.

No info about a 37,5 mm variation? I have always looked for an “official” name

Thank you very much

In fact when it was given to me by Grendel I haven’t the name, except it was 30 caliber.
It is a few years later in France when the drawing was made and I asked what it was, the people said 300 Whisper (surely because at this time this last cartridge was new in France and people didn’t know exactly what it looks like)