Ballistics for .405 spotter cartridge

Does anyone have inforamtion about the external ballistic characteristics of the .405 XM-75 10x43 Spotter cartridge? Would it make a good cartridge for a semi-automatic rifle? Thanks

There is some information (but not external ballistic) given on page 100 of the 1968 Frankford Arsenal ammunition pamphlet I recently posted here. But what would be the advantage over using a caliber already available (as both ammunition and AR-15 style rifles) such as the .450 Bushmaster if one wishes a large diameter, heavy bullet? I understand it’s great for use on Texas feral hogs. I’ve fired it some (and have a box of the first production run of the Hornady ammunition from about 2007) but not at anything living. See for .450 ballistic information.

I didn’t notice, but the .405 Spotter cartridge is stated to use the high pressure-low pressure design, I guess sort of like the rounds used the M79/M205 grenade launcher.

Probably no advantage to .405 Spotter over .450 Bushmaster at all. But, I wouldn’t really know until I found out what were the.405 Spotter’s ballistics. Mainly just speculation. Thanks

I don’t know the ballistics, but the belted case would require rather steeply-curved magazines.

Muzzle velocity with the spotter pistol was 950 fps / 289.56 m/s (new cartridge: 820 fps / 249.936 m/s) with a 9.5" / 24.1 cm barrel lenght.

Commonly found .405 Spotter cartridges do not have the high-low pressure system of later models (mid to late 1960).

What was this spotter cartridge used with? I assume as an auxiliary to some (or several) larger-caliber weapon(s).

Dennis, it was originally designed for the Super-PAT spotting pistol for the 90mm T234 recoilless rifle but it was finally tested with the XM14 spotting pistol for use on the M67 90mm recoilless Rifle. The “pistol” designation was probably chosen beacuse the “rifle” term was already applied to the recoiless gun.

Correct me if I am wrong - The ballistics of the original spotter load would have been developed to suit the trajectory of the larger weapon it was attached to. So this may have actually been well below the potential ballistics of the spotter cartridge.

The first thing that came to mind was a recoil-less rifle, but I know little about those. The idea was to get on target with the spotter rounds, and when a hit was made, then immediately fire the larger weapon. The trajectory match would have to be close out to the maximum range of the larger caliber weapon, therefore the spotting cartridge must be loaded with a suitable projectile and powder charge to achieve that, rather than to achieve maximum velocity. Would be nice to see a sectioned spotter cartridge case with the high-low design feature.

950 fps from a 9.5 inch barrel. What bullet weight for the .405 Spotter?

alpinehunter: exactly

Use of a Hi-Low pressure system, as mentioned, also shows it is a low power cartridge, because this system is used to make sure that a tiny propellant load (in relation to case volume) burns in a consistent way.