Question on an IMI 5.56 headstamp

I received the following question and decided to pass it along to people who would know what they were talking about.

You are listed as a reference by International Ammunition Association, Inc. for their information regarding IMI ammunition. I have some IMI ammunition I have a question on.

The box says the ammunition is this


It has a headstamp of


It looks to me like IMI on top, a 1 and 6 on the sides, and 20 on the bottom. There is no circled + sign.

If I were to pick this spent casing up off the ground, how would I know it was 5.56 vs. .223 or anything else?

Thank you for your time,


RAJ - if you were unfamiliar with the 5.56 x 45 mm cartridge, and did not have the box for the ammunition, you would not know it is a 5.56/.223. Although the box for this ammo, if the correct one is shown, is a mixture of commercial and military style boxes, and therefore hard to know exactly where this ammunition was destined to go once manufactured, the headstamp is a military style.

Military headstamps very often do not have the caliber designation of the cartridge on the headstamp. When the ammunition is produced for a military, or in some cases for civilian use, military headstamping regulations of the country that ordered it, or if a member of a group like NATO, the parent group’s regulations. In the case of civilian-contracts, the headstamps can be the result of designs submitted by the end-user of the ammunition, or if not specified, by the factory that makes it.

It is assumed that the country that is issuing the ammunition to its troops knows what caliber it as, as do the soldiers to whom it is issued.

In civilian ammunition, if the countries producing it follow CIP or SAAMI (CIP - European governing body for commercial ammunition specifications; SAAMI - American governing body for the specifications), than it is those two organizations that set the general guideline for what information the cartridge headstamp must contain. However, many countries and manufacturers do not comply with CIP and/or SAAMI specifications.

Obviously, never attempt to use any ammunition until you have verified the caliber (case type), its suitability for the gun you wish to use it in, or the type of loading (some loading types, such as armor piercing, tracer, incendiary, explosive, etc. are illegal for civilian possession and/or sale in some countries, or in some States within countries. Other combinations can simply be dangerous to the user.

In this instance, the box label clearly indicates that the 5.56 mm ammunition original to the box is ordinary Ball M193, and suitable for military weapons of that caliber. There are some differences between the normal military 5.56 x 45 mm NATO cartridge and commercial .223 of most commercial ammunition, although frankly, I have found them to be generally interchangeable. As always though, caution must be used.

John Moss

The circled + sign is intended for cartridges that conform to a NATO Standardization Agreement. In 5.56 mm it is STANAG 4172. The U.S. M855 or the Belgian SS109 designs are examples.
The M193 cartridge is the original U.S. military version of 5.56 mm, does not conform to the (later adopted) STANAG and therefore would not have a circled + sign in the headstamp.


Agreed that the M193 doesn’t fulfil StanAg 4172, but markings sometimes don’t follow the correct convention and have to be taken with a pinch of salt! These recent RG M193 rounds have the StanAg ‘cross in circle’ on the box (but at least it’s not on the headstamp.)

RAJ, who is not a Forum member and cannot post himself has asked me to thank you all for your inputs.

His box and cartridge are interesting with a strange combination of box and headstamp with an interesting mix if military and commercial characteristics.

I’d be interested if anyone has any other ideas on these rounds or if someone has seen something similar in another caliber.

Does anyone have anything else to add???


Lew, it seems IMI has a tradition in such “hybrid” military-commercial boxes.

RAJ was kind enough to send me a number of these boxes, each with 20 (I think) fired cases.

If you want one, let me know—Not a sell or trade-a gift!


A strange thing is that the numbers across from each other(the side of the headstamp) have many variations.
I have seen anywhere from 03 to 17 for sure, there are probably more than that.

IIRC, these numbers represent the case forming stations on the rotary machines at the ammunition factory. Similar to the octal numbering system dots used by Lake City on their SCAMP machinery. I’ve seen nearly identical headstamps on 5.56 made by IMI for Federal, where the IMI was replaced by FC in the 12 o’clock position.

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