.17-5.56 Experimentals

I have two .17-5.56 Experimental rounds. Both have the headstamp “F A 7 3”.

#1-Flat brass ringed in primer with red PA. Pointed magnetic FMJ bullet.

#2-Flat all black primer. NO primer crimp or PA color. Pointed magnetic FMJ bullet.

Anybody know what the difference is between the two and what is the proper designation for each one.


Good question.

The boxes are usually marked simply 17 CAL or 4.32MM CAL 17. I’ve seen them designated as 4.32x45mm (.17"Cal.) (XM16E1) and/or (FA T211). Not sure if any of these are technically correct.

Again, the SPIW book will probably have info. I don’t have time to look it up.

The ones I have with the black primer are dummies. I can’t say what yours is.


Ray–You might be right that the one with the black primer is a dummy. At least I can’t hear any powder inside. I can hear powder in the one with the normal primer. However, there is not much difference in weight. The black primer one weighs 147.9 gr. and the other one weighs 148.3 gr.
I would think the powder charge would weigh more than 0.4 gr. Perhaps there is a spacer in the “Dummy” round adding to the weight.

Do you know the designation for the dummy?