XM261 45acp - ballistic characteristics study

Here is everything (and I mean everything) you ever wanted to know about the behavior of the projectile pattern(s) from the XM261 cartridge when fired through smoothbore and rifled barrels from the 1911 pistol. This was a thesis, circa 1973, from a Naval Academy student as far as I can tell, which I came across on a random internet search (PDF format):


Of interest; on page 6 (PDF pg 8), it makes mention of a different competing-design 45acp projectile which “breaks into 6 pieces” upon being fired. Would this be referring to the .45 auto “delayed-shot” cartridge with the fishing-line around the segmented projectile?

How does that XM261 look like?

Is this one??


Ray - I don’t think so. The projectile on your round should take a magnet. As far as I know, the XM261 Hi-Density Shot cartridge, loaded by AAI Corporation, should not. The round that came in my AAI box, lot number 45-3202, does not, and has an opague, tan color sabot. The lead shot in it can be seenhere and there through the sabot, but only the tiny portion of the circumference of each pellet that is bearing against the inside of the sabot. I believe the rounds like yours, which are found in WRA and W-W headstamp cases and have the same deep cannelure as that of the nickeled-case XM261, are loaded with Steel Mallory balls. The headstamp of my XM261 round is WESTERN.45 AUTO.

I have two of the ones like yours, but I have no official designation for them. I am sure there is one - I simply have not found it. While I love the .45 auto cartridge, my in-depth research over the past years has been centered on the non-Parabellum 9 mm cartridges, on some of which I have written articles, and on the 9 x 18 mm Makarov, and I have shamefully ignored the .45, not even scratching the surface on finding out what I should know about this round.

That report is very interesting by the way. Thanks, DK, for posting it for us.

John Moss


I’m pretty sure that we had a thread on this on the old forum. I seem to remember that there were several versions of the M261 and one of them was the tan colored capsule that you described.

The one I showed is headstamped WESTERN 45 AUTO and whatever is in the capsule is magnetic. I believe the designation on mine came from Dick Fraser.


Ray - I would fin it hard to believe that the XM261 designation was given to both rounds loaded with lead shot and those loaded with steel balls. Doesn’t make sense. However, consider what goes on with empty cases and empty boxes for the last decade or so, it would not surprise me to find that my box came with the wrong round it it.

I will pursue this issue farther.

It is interesting that your round has the WESTERN headstamp. My two, with dark gray sabot and steel shot, have W.R.A. and W-W headstamps respectively. One more I have to look for!

John Moss

This is the type of XM261 (not my photo) which I have always had, it does attract a magnet:

That’s the one that is in my XM261 box, I was actually on the phone when I wrote the first sentence. I am editing this. I think it is now established that the round in my XM261 box is correct for it. Now, since I cannot accept (I will if proven wrong, of course) that they would assign the same XM number to rounds so different as to have steel balls instead of lead shot, does anyone have the XM or M number of the round that Ray showed. Further, does anyone know the proper designations for the brass-cased round “W C C 7 3” with dark grey sabot, but with sabot split only in three segments, and for the steel-cased round “F A 53” that has a deep cannelure similar to the AAI round, but has a milky white sabot, split into four segments like most of the others, and taking a magnet only slight at the sabot?

The subject of magnetism of these rounds needs the clarification that one must use magnets carefully on them. They all have a very strong magnetic pull a little less than half-way down the case, indicating a steel obturator disc, most likely, is in most of them. Using a weaker magnet on the projectile, it is only the XM261 and the WCC 73 round that will take not take a magnet at the bullet tip or even the sides of the sabot above the case mouth. Of course, the FA round has a steel case, so one must ust a very weak magnet on the projectile. On that one, without knowing, which I don’t, or disassembly of the cartridge, which I am not going to do, one cannot tell if there is a steel obturator in the case or not, but it is deemed likely.

Interesting round. The cannelure on the neck of the FA round one lead me to believe it was loaded much later than the “53” case date would make one believe, although I don’t know that.
I am not sure exactly when the others were loaded. The WCC round would have to be 1973 or later, and the others would have to be just about the time that Winchester-Western did away with their separate headstamps of “WRA” and “WESTERN” and went to W-W, since they seem to be found with all three headstamps, probably indicating that brass with all three headstamps was still easy to find.

John Moss


When I said mine was magnetic I should have been more specific. It is, as you said, very lightly magnetic at the tip but more and more magnetic as you go down the “bullet”.

My notes from Dick Fraser do refer to it as an XM261.

I really don’t know anything more about this cartridge since it is not something that I would ordinarily collect. I only have it for reference purposes.

I would not consider it unusual to have an “XM” cartridge with variations in the bullet. That was common in the days of the “T” designations and the “XM” was really only a continuation of the “T” system. Perhaps the XM261 had cartridges with an “E” suffix to identify the different bullets?

Without even looking, I can think of one XM cartridge, the XM276, that has at least 6 bullet variations.

And, it was not uncommon for contractors to modify “T” numbers for their own use or to make up variations on their own. It may be that the commercial headstamped cartridges are not even official XM, but simply Winchester’s own version of the XM261.



I was not aware of the variations in XM products with the same number. You know much more about that than do I. There is not much of that stuff in auto pistol - some, but not the variety one finds in the rifle and machinegun cartridges. I bow to your greater knowledge on that and have changed my opinion, from what you have said, about the possiblity of duplication of the XM number.

I do not think, however, that Winchester (Olin) loaded the ones in question. My XM261 box shows AAI Corporation as the manufacturer, even though in Olin brass.

It is possible that the “odd man out,” the brass-cases W C C 7 3 with three part sabot was an Olin product though. I just don’t know. Boy, we do need Volume III, don’t we! I feel really stupid about knowing so little in the .45 department, since I have collected them for 45 years. I guess it was my love for it as a shooting cartridge that interferred with my interest in doing heavy research on each variation. Good excuse, anyway.

Thanks for your input and your help in making me understand some of this stuff about T numbers and XM numbers.

DK, thanks a lot for the image.

Here are images of sectioned rounds. The top one is the lead shot load with tan sabot (WESTERN headstamp). The lead shot is embedded within silicone. The bottom has the dark grey sabot (W-W headstamp) with the high density ‘Mallory’ alloy. Note the position in each of the steel base plates.

John, as for your 3-piece sabot, I suspect that it could be one of these variations:

To my eye, these have ‘AAI’ written all over them - the cyclindrical mid-sections and hemispherical ends are almost identical to the shot used in the .44 QSPR (although are larger that than the QSPR shot).

The steel cased ‘F A 53’ headstamped round is almost certainly the flechette load.

This is an example of the 7 x 7 flechette load. Apparently there is also a 8 x 8 variation. The rubber o-ring was used to keep the assembly together while the flechettes were hand placed in the sabot and rolled off when the assembly was loaded into the case. I was told by a former AAI employee that there wasn’t sufficient recoil to function the M3 Grease gun.


Paul - I was told that the F A 53 cases come in two loads, one with shot and one with flechettes, and that they are visually indistinguishable from each other. However, and I forget why and don’t want to search my roughly 18-inch deep .45 file right now, I was told by someone who knew this stuff that mine was not the flechette load. Perhaps it was from the overall weight, or something like that.

John Moss

I recieved the two rounds in my collection at the same from an auction. They were labeled:
W-W 45 AUTO - nickeled case, grey plastic sabot, high density shot "XM261"
WESTERN .45 AUTO. - nickeled case, whitish plastic sabot, visible shot “XM668”

I have not been able to locate any information on the XM668 disignation.

Hi John,

My flechette round is 31.2 mm in length (1.23") weighs 10.84 g.


Exactly what are “Steel Mallory balls”? Have not run into this designation before.

Ron - they are tungsten alloy pellets made of Mallory 3000 Metal. That’s about all I can tell you.

I have no information for this thread received from Frank Hackley, but I need to sort it out with my collection and try to get it straight which round is which. Ray, it seems, will be totally vindicated.

Maybe I’m just not clear on my XM designations - I had always assumed that the typical yellow-colored sabot with visible shot was the XM261, and that all others were variations thereof. But now it looks like the yellow-sabot version is the “XM668” and the black/gray sabot type with the larger mallory pellets is the “High density shot” type and is the XM261? Also, what is the designation (or slang title) of the flechette version? I see at this link the person who posted the photos has the yellow sabot type listed as XM668 and the black sabot type as the “XM26”, did he mean XM261?: http://www.pbase.com/tikkakoski/cartridges&page=4

I received an answer to my inquirty to Col. Frank Hackley, and will quote him here, paragraph by paragraph. After each paragraph will be my own comments trying to relate what he says to the specimens at hand.

Quoting Frank: “The XM261 was a High Density Shot loading made under the Viet Nam era ENSURE program for field evaluation under combat conditions in VN. The sabot contains 16 tunsten alloy pellets (Mallory 3000 Metal) and was similar to the earlier XM668 but used a reinforced sabot to withstand the heavier shot load. The XM261 sabot had a slightly longer body and blunter nose as compared to the XM668. AAI delivered a 2000 round lot during Oct. 1967 for shipment to VN, These rounds were loaded into commercial nickel-plated cases H/S: W R A 45 AUTO and WESTERN .45 AUTO with a 4-segment light gray plastic shot sabot. A heavy smooth cannelure near the case mouth retained the sabot and the primer was sealed with red waterproofing.”

John’s comment: this is pretty good ID of itself, indicating that the gray-sabot round with
nickeled case and WRA 45 AUTO headstamp is the XM261. The bullet is magnetic, so that squares with the Mallary-steel alloy pellets. The only possible confusion is that as you see, there are two headstamps for this type, one of which duplicates an XM668 load. The latter load has the tan sabot though, so there should be no confusion. The overall weight of my round with WRA headstamp is 248.3 grains.

Quoting Frank: “The earlier XM668 was similar except was loaded with No. 2 lead shot into a tan or milky-white plastic sabot. The cases used in the initial loading were commercial nickel-plated H/S: WESTERN 45 AUTO. A second lot used a different sabot made from gray Nylong plastic loded into nickel-plated case H/S: W-W 45 AUTO.”

John’s comment: The first lot FRank describes here is clearly the round pictured earlier and the one I first and erroneously described as the XM261 Hi-Density Shot cartridge. Ray was probably correct in the identifcation of his round as the XM261 - since it had the duplicated WESTERN headstamp, he would need to weigh it to be sure, but it is pretty positive he was correct. Certainly, I was wrong. My specimen with WESTERN headstamp weighs 238.8 grains, squaring with Frank’s indication that the first XM668s were a lighter charge than the XM261.
Frank indicates that the second lot of the XM688 was loaded in W-W cases and had a gray sabot, like the XM261. He mentions that the sabot of the 2nd lot XM688 is shorter and more rounded. My round in W-W headstamp has an overall length longer than the XM261 with WRA headstamp, 1.228" for the XM668 as opposed to 1.214" for the XM261, which does have a sabot with a blunter tip as Frank described. We are well aware that the longer sabot of the XM261 could simply be seated deeper in the case, making a shorter OA cartridge length than the XM668 2nd Lot. That is not troubling to us. The only question is that what should be our 2nd lot XM668, with W-W headstamp, has a magnetic projectile. It take a very weak magnet at the front end of the sabot (meplat). This should not be a result of any draw from the steel obturator deep in the case, which draws the same weak magnet much more heavily when the magnet is placed on the case side. However, since there is a steel obturator, the question about what the shot is made of in these 2nd lot XM668 is uncertain. Frank did not address the material of the shot load in them.

Quoting Frank: “Your plain brass case with military H/S (W C C 7 3) with a 3-segment light gray plastic sabot w/o deep case cannelure is probably the XM261E1 which was loaded later in 1973 at FA using either a 9 or a 12 tungsten alloy shot loading. FA called this loading the “improved shot” but testing was a complete failure.”

John’s comment: Very little comment required. Our round squares completely with this description. It indicates again that Ray was perfectly correct about very different rounds having the same basic XM number, although in this case with the “E1” modifier.

Quoting Frank: “If this does not fit your boxes, then someone probably mixed the rounds?”

John’s comment: Well, it is possible it came to me with the wrong roujd in it. I would love to say that it is simply impossible that I mixed them at any time while reviewing this question of identity, something I am sure I have done before. However, we all know that would be pure balloney. I might well have mixed them up myself. Sorry Ray - it is that mixup that caused me to challenge your identification of the XM number of the tan Sabot round. I shan’t do that again!

I hope this has made this slightly less confusing, although perhaps it is still only as clear as mud!

John Moss