10mm XM277 & SLICS

I was so excited to add this black cased factory dummy round to my collection. There are 3 case types in the series and this was the one I was missing. The round on the left is Type A, The middle 2 are Type C and the new addition is the Type B. All are headstamped ‘F A 6 1’.

The round was being developed for the USAF for a Gatling-type weapon.

Does anyone have a link available?

Nice, Paul! They seem to have been trying to push the muzzle velocity ever upwards, judging by the way the case capacity kept increasing.

The 6-barrel GAU-6 gun which was designed for this ammo is described in Chinn Vol.5 (pages 125-127). It was intended for aircraft use and designed for up to 8,000 rpm. However only one gun was built, and that was in .50 cal because 10mm ammo development was unsatisfactory (the 10mm does of course have the same case diameter and overall length as the .50 BMG). It was limited to 4,500 rpm by the strength of the links, so a linkless feed would have been needed to reach the designed rate.

The round was type designated the PGU-1. There were no seperate designations assigned to the various case types. The GAU-6 was the gun originally intended for the F-15, with a gun in each wing root I’ve been told. Early in development of the F-15 the decision was made that a single 25mm GAU-7 was a better alternative and the GAU-6 was dropped.

Tony, I have had the Type C and I believe it is a significantly longer case then the 50 Browning. In fact, Dale Davis had a prototype case on the shelf in his office (which is now either in the Museum at Eglin or in the Woodin Lab) that was made by cutting and joining two .50 cases.

Paul, congrats on the great find!!!


Yes indeed Lew - it’s the overall cartridge length that has to be the same, to be usable in the same basic gun design.

does anyone know the initial velocity of the projectile (I know it weights 33.5 grams)


links photographed in the late Herbie Woodend collection :

Unfortunately, I don’t know where they went :-(



This is the 10 mm prototype mentioned by Lew:

Thank you, all.

I’ve held the 2-piece case. It is at Woodin Lab.


Was the black color added to the case for any purpose or function?


If I recall it right it is a dummy.

Thanks so much.