Local fellow has a 50 Browning MG (legal of course) and while visiting him and shooting the weapon he gave me a couple cases that are approx. 1/2 the length of the std. round and said that he thought they were used for "sight in rounds" for the 105 Recoiless Rifle used in Korea?? This was some couple years ago and was told also that the brass was available for something like ten cents each? Have no idea as to the performance or ballistics of the round, but for those really wanting a big bore, shoulder fired(???) this might be the ultimate kill any game anywhere. Case is LC and made in '68. Curious if anyone is familiar with the round and all input appreciated.

It's the 12.7x77mm, AKA the .50 cal spotter/tracer.

"50 Cal Spotter-Tracer, M48A1, which is fired from the M8C Spotting Rifle, that is mounted on top of the 106mm recoilless (BAT) for (Battalion Anti-Tank) Artillary Cannon. The Spotter-Tracer cartridge is smaller then the regular 50 caliber Browning Machine Gun (BMG) cartridge. It matches the trajectory of the 106mm cannon projectile to follow, to ensure the 106mm has a good target impact.The projectile has a primer at the tip to ignite a mixture that produces a smoke spotter on impact, and also a tracer cup in the rear of the projectile to produce a tracer out to 1500 yards."

The brass is available at Hi-Tech Ammo



50 Cal. Pulled Down - Spotter/Tracer - Virgin - Primed 100-$110 500-$525 1000-$1030


A friend of mine, Dennis C, develops lightweight .50 caliber rifles, builds the prototype, tests it, and sells the designs to various manufacturers. He has been working on a semi-auto rifle in this caliber. Dennis said the cartridge geometry is easier to work with than the .50 BMG for designing a semi-auto, and he can achieve near .50 BMG velocities with lighter bullets (650gr. and under) using a relatively fast powder.
I would love to have a semi-auto tactical .50 caliber rifle that weighs around 10#. This cartridge could be a good candidate for a bolt action rifle too, but I would wonder about it being practical as a rifle that one would want to carry around the woods, bush, brush, or whatever the local terrain may be, to hunt with. Not to mention, a muzzlebrake would be a must for this cartridge, hearing protection would not be an option, it would be required.

Hello goneballistic,
Thanks for the dope, good information. Yes, I can see all kinds of possibilities with this round in the form of a much more compact, lighter weight, single shot bolt gun?? Brass is not as cheap as I was told, but still not beyond reach would say. You are right about not being able to tote around, but thinking of long range shooting in fixed, prone, sitting position for either match shooting or long range varmint type application. How would you find out the load data for this round and known trajectory/ballistics for it?? I suppose someone from Aberdeen would know, but probably tough to source. I will do a search and see what I can come up with. As you mentioned sound and recoil issues are definitely there, but fairly easy to deal with via brake/hearing protection. Again, thanks for the information.

Now for the catch. Much of the .50 S/T brass out there has a flash tube that extends from the flash hole, up into the case. I don't remember exactly how far. It was intended to facilitate the tracer ignition. For our purposes, it needs to be removed and the primer pocket reworked with a small washer, to provide a new primer pocket floor and a new flash hole.
The best way is to buy only brass without the flash tube. When you buy .50 S/T, you should inquire if it has the flash tube, so you know what you are getting into.

OK, more good info. I would venture to say that the action for such a rifle, single shot, bolt type/falling block,etc. would have to be custom or original for I know of no commercial bolt action large enough to accomodate such a round. My thoughts would be to use a std. 50BMG barrel and shorten chamber area to match the round's case specs. I have access to fairly sophisticated machine shop w/ CAD/CAM, tracer arm, etc. and believe this winter will delve into the subject. I'll keep you posted on progress.

My understanding is that the spotting rifle round is a shortened version of the 50BMG, so it should be possible to make cases from the parent cartridge. Yes, NO?

I would venture to say that you are correct you could make S/T rounds from the std. 50BMG case, but not sure if that would be any economic savings after you secure the dies, etc. Is there a large difference in case prices between the two?? I was provided a source on the S/T cases and believe they were a buck a piece. 100 dollar bill would set you up w/ decent supply of cases. My plans are to build a somewhat minature "cannon," single shot, fired from bi pod, even a scale down model of a field artillary piece??? Have available farm with pretty much unlimited safe shooting distances and believe would be lots of fun seeing just what the round would do at extreme ranges. I'll have to do some checking as to the legality of building this item, but don't believe will be a huge problem?? Never know until you ask.