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!