.50 Spotter-Tracer M48 12.7x76(77?)mm "LC 54"

I was told it was a 50cal based artillery spotting round. It measures about 13x76mm, but I can’t find it by these measurements. What is an official measurement designation?

OK, found it, it is 12.7x76

How come you know these details and don’t know the official designation? ;) ;)

It’s a Cal. .50 Ball Spotter-Tracer M48 (or M48A1 or M48A2).

it’s the 12.7 x 77 BAT, i don’t know where the 76mm designation came in…

What’s with the metric designation?? LC headstamp means it’s a US cartridge, the Cal .50 Ball Spotter-Tracer M48. Am I wrong?

Since the case is 76mm long I wonder where the 77 comes from.

Ray, when in service outside US forces mostly the metric designation is used. Hardly anybody uses the inch designations. And what was the year the US military adopted the metric system?

I realize that all “inch” US cartridges are known by a metric designation outside the US. But, if the cartridge is US manufactured, and is in a collection in NY, isn’t it appropriate to call it by its official US designation?

You guys know that I’m a stickler for calling things what they are, and this is another example.

Ray, that is perfectly fine. I just mentioned it since Vlad initially started with a metric designation and Duchamp kept on with it.

This may be getting a little confused, since I have noticed that some recent US .50 cal MG designs have been designated 12.7mm. Does that mean the cartridge will be too?

Incidentally, one oddity is the .338 Lapua (and the .338 Norma too). Not only are these new military calibres given inch designations but they don’t even comply with the normal military practice of using bore rather than bullet designations. They should be designated .330. Furthermore, this is usually translated into metric as 8.58mm or 8.6mm, whereas it should really be 8.38mm.


There’s no doubt that the governments and military of all countries make many decisions that most, even those of us with a military mind, cannot understand. The designations attached to both weapons and ammunition is the least of them. But, regardless, whether we agree with the decisions or not, disregarding the official nomenclature only adds to the confusion. We collectors who post on the IAA Forum should set the example.



my US army small caliber identification guide lists that cartridge as 12.7 x 77 as well as giving the other standard designations, i am aware this book has many inconsistancies but it usually gets the info on US materiel correct. i have noticed others refer to it as 12.7 x 76 as well, not sure how official this designator is but a quick search yields mostly 12.7x77 references.

Since I am not qualified to discuss 12.7x76 vs 12.7x77, I’ll ask a related question. BAT stands for Battallion Anti-Tank or Basic Artillery Trainer? Which one, or both?

Vlad, why trainer?
Wasn’t BAT a British designation?

Duchamp, military manuals outside the US usually say 76mm as they are also giving the case length as such in the drawings.

it’s battalion anti tank gun…

The M8C Spotting Rifle was mounted on the 106mm Recoiless Rifle. The ballistics of the M48 cartridges match those of the HEAT projectiles giving the gunners the range and elevation. Recoiless rifles are easy to spot after the first shot so being able to get a first shot hit was very important.

Posts are timing out - again. Aaaarrrggghh.

Regarding the various metric designations, are there published official listings of them? The US designations can be found in the TMs that are available with a little on-line searching, but what about other countries? For example, where do I find a drawing of the 12.7 x 76mm (or 77mm) and it’s official designation? Is it officially referred to as the “BAT” cartridge? Etc. Etc.