Got back to the metal lathe yesterday. Took an hour just to find where they had the tooling this time and set up the lathe and dial caliper correctly. There's a lot of little steps even starting from a pre-made grenade body and it wiped out two days of shop time.
Here's the situation: in the James Cameron SF movie Aliens there appears an iconic weapon which is described on-screen as firing "10mm caseless armor-piercing" and "30mm grenades."
The latter is for all appearances used by Ellen Ripley near the climax, by Lieutenant Gorman in manual mode earlier, and is worn in bandoliers by many of the Colonial Marines. And it is a popular replica prop -- more specifically, it is a necessary prop for Colonial Marine cosplay. And I am one of very few people who have made a machined all-metal version available for sale.
James Cameron admits to Aliens being "his Vietnam movie." There are references in prop and costume design to the American equipment of that war. The grenade attachment itself has similarity to the army M203. Because of both this historical connection, assumed doctrinal/tactical considerations, and some scant evidence from the film, various third parties have assumed there are alternate loads to the red-capped round Ripley is seen loading in the elevator scene (and using against the Alien Queen).
These sources do not quite agree.
To harmonize, I've put the movie first. The only dialog mentions are "30mm grenade launcher" and "M40 grenades." The main leeway I have in the movie references is that the scenes are usually in dim, often colored, light (the Lieutenant Gorman/Private Vasquez scene is monotone red light), and the grenades are rarely in focus.
Of course, it must be pointed out that there were a very small number of "hero" grenades carved from actual aluminium snap-caps by the movie's armorer, Simon Atherton. The majority of what appear in bandoliers on uniforms are likely to be wooden mock-ups painted silver. I have seen images of one such, but insufficient provenience to know if it is screen-used. In several screen-shots the grenades show visible wearing or flaking of the red paint.
In any case, the aggregate data from the film is that at least three cap colors appear, those grenades are otherwise identical, and no other shapes are seen. With the exception of Wierzbowski (I'll get to that).
Next comes organized third-party listings, such as graphics found from various sources (one is tentatively sourced as from the Aliens Legacy Forum. As an example of these secondary sources, The Aliens Technical Manual has sufficient errors right off the bat to remove it from any primacy against other aggregates of alternate designs. It also, perhaps fortunately, has few images and relies on verbal descriptions. There are, fortunately, no real disagreements in nomenclature between these, although no two sources give identical selections. It is in the shape and coloration that the major disagreements lie.
Below this are individual fan-made creations, as most of these lack identification labels and many are guided primarily by technological limitations, not by artistic considerations. They do, however, take primacy in clarifying the kinds of details that a physical prop shows off better than does a stylized graphic.
Lastly, there is reference to real-world analogs and presumptions about mechanism and doctrine. I would love, for instance, to argue from real-world human-machine interface that different loads should be different tactually; the soldier shouldn't have to guess in the dark, or in dim red light, which of several otherwise identically shaped loads she is reaching for. But there is a ready-made answer within the film itself; the film is about the hubris of technological fixes and the real-world failure of all that fancy gear when facing a less technologically sophisticated enemy who is smart, tough, and on their home ground.
So here's the harmonization:
M40: HEDP (high explosive dual purpose), this is an armor-piercing shaped charge with sufficient blast radius to be used in antipersonnel mode. It is dual-triggered, on firing, and manually by removing the safety cap and pressing on the button. It has a specific groove pattern, a "parting zone" that appears to be a crimp, an a red plastic safety cap with one white stripe. There is some argument that "HEDP" is meant to refer to the dual-role as a hand grenade and may have no specific armor-piercing qualities.
M38: HEAP. Presumed optimized towards armor penetration, this might actually be a sabot instead of a shaped charge. It is identical in body pattern; it may be a poor choice for load selection in the dark, but might be justified as interacting with the Pulse Rifle's internal mechanisms. Going by the Newt close-up, this has the same plastic safety cap in green.
Here's where things get interesting. The graphic I found at Aliens Legacy gives all the rounds as having tapered caps. This clearly disagrees with the film. The Aliens Technical Manual only shows the M40 cap, and gives it as tapered. The tendency in other secondary sources is that the M40 cap has straight sides, the M38 tapered, and the M51A has a rounded top to the cap. The tendency is also in secondary sources to show all rounds as having double stripes. Most of this is clearly contradicted by the film. However; almost all secondary sources agree that the first three of the grenade family have an identical groove pattern.
M51A: Bounding anti-personnel. This is a clear analogue of the real-world "Bounding Betty" mine. It seems odd to put in a grenade, but this is consistent enough across third-party sources and fits so well within the milieu of the film we just have to assume some kind of auto-righting mechanism. Same groove pattern, straight-sided blue cap with dome; of the third-party sources that give each of the top three a different safety cap shape, the consistency is that M40 is square, M38 is tapered, and M51A is straight-sided with a rounded top. It isn't required that under every safety cap is an identical button, but given the auto-righting justification above only a sabot round makes absolutely no sense in that kind of dual role. (There are other button inconsistencies later, so even this isn't beyond possibility; perhaps they simply used the same shell with different loads.)
(A different problem with real-world analogs has to do with the specific blue. They appear to be a light blue, far too similar to the distinct "training round" blue standardized in the US Army. I guess we must assume that semiotic standard has changed by the period of the film).
There's a last interesting possibility; the clearly, tactilely distinct caps could be a late innovation. Given the murk of the film I don't think there is any scene showing blue-caps that can't be justified as having domed tops that just aren't properly visible in that shot. The same justification could be used to assume tapered green caps; this would make the "Newt" grenade an aberration explained as old stock from before the change-over (since they were pulling every bit of salvage and hidden-in-pockets ammo for their defense). It is also plausible they were all tapered at some point and the manuals are using outdated images.
For Aliens cosplay, however, straight-side caps is consistent. They are also easy to make. So this is why I say my props above are almost correct; the only change I would make it to add a slight dome to the blue cap.
M108: Canister. Presumably the Sulaco crowd didn't pack any, because they'd certainly have come in handy. The third-party sources are remarkably consistent in showing an identical groove pattern to the "big three," no safety cap, and a broad flat nose with some sort of black plastic disk. This is clearly explainable as some sort of disintegrating cover over the payload. A manual fire button also does not seem to make sense. There is some argument that what gets ejected would be different; does the body of the round fly downrange then a secondary charge kicks out the shot? In any case, this is a straight-forward build. (But also superfluous for straight-up Sulaco marines cosplay).
M60: WP/incendiary. The sources are a little unclear as to the exact weapons action here but white phosphorus is very, very Vietnam. The manual states white markings, all other sources give yellow. The sources (all sources are third-party, with one possible exception to be discussed) seem to converge on it having no safety cap, and a domed top with a wide, flat button. This is quite consistent with secondary employment as a hand grenade. The major disagreement in the sources is whether it shares a groove pattern with the "big three," or whether it has a unique groove pattern and a yellow paint band on the lower third.
And here's the Wierzbowski problem. In some scenes this one character appears to have a grenade with a yellow cap. And it appears to be the same square safety cap as the M40. So here's my explanation; Wierzbowski made a field modification. As issued, the M60 has a yellow plastic ring around a metal button (similar to that of the M40 but wider and less tall). Either Wierzbowski didn't trust this, or the ring functions as a safety and is considered difficult to wrestle with in the field; either way, he has replaced it with a discarded M40 safety cap and dipped it in the same yellow paint other marines have been using to paint slogans on their armor and helmets.
The other issue with the M60 is harder to reconcile. I'd argue against having paint on the sides as that could foul the weapon, but the only third-party depictions of the smoke grenade also show color bands on the grenade body. The tie-breaker has to be the movie; a yellow band should probably have been as visible as the yellow cap, thus, we have to assume this has the same standard body as the M40.
M61A: Smoke. This is the only smoke listed in any of the secondary sources, and in that source is shares a groove and banding pattern with the CS grenade. Doctrinal similarities seem to call for a variety of colors, and those would you would think have different nomenclatures as well, but none of that is provided. It has no safety cap, and a similar rounded top and broad flat button as the M60, lacking the color ring on the top (what I am assuming is a plastic ring that may function as a safety clip). The groove pattern is definitely different from the M40 standard, consisting of two wider grooves creating a defined band which is colored with (one presumes) the color of the smoke. The button may also share the same color.
M67A: CS. This is an odd one; it either shares a banding pattern with the M61A or has the same basic groove pattern as the M40, however, the majority of sources are consistent in giving it two narrow red stripes which may or may not be in shallow grooves. It has a gently domed top, no safety cap, and also lacks a button. For this, I simply have to wave hands in the direction of assumed Colonial Marines doctrine. Since they aren't visibly carrying protective masks, perhaps it was determined that this payload was unsafe to deploy at throwing-arm range.
M72A1: Starshell. The depictions are consistent; this lacks most of the standard groove pattern but has longitudinal grooves running down the length of the body. It like many of the alternate rounds has a domed top and no safety cap. It also has a button. The conservative answer here is that this is a self-righting shell, like the M51A, and thus can be hand activated as well as fired horizontally (instead of requiring the operator to point their weapon at the sky). Other possible answers are that the button is non-functional, or only looks like a button. Lastly, the technical manual claims it is marked with an embossed "S." This is not entirely inconsistent with the nature of the graphic depictions.
M230: Baton round. I didn't notice any depictions on my earlier searches. This has certain practical difficulties, depending on exactly what parts of the round can be and are extracted from the shotgun-like action of the weapon (hurling a metal case down-range would rather contradict the intent of a baton round).
Oddly enough, the general answer to the question of making alternate loads available for cosplay is a simple one; paint the caps different colors. This even applies to the Wierzbowski; cosplayers are more likely to want to mimic his documented field modification than the hypothesized standard-issue version.
The majority of the alternates lack safety caps, which is mostly to the good, but they also tend towards gently domed tops -- which are hard to machine. They also tend to buttons, which are a known labor issue (as a reminder, my last machining trip took over four hours just to set three buttons). About half of them also involve body colors, which could be an issue (especially if chambering is intended).
Lastly, they just aren't that interesting. Only the star shell is significantly different-looking and requires enough new machining tricks to be really tempting.