The SAWs that never WAS: Part 3, XM248

Face of a Ford Aerospace handout promoting the XM248.

Obverse of a Ford Aerospace handout promoting the XM248. This is the second (final) version.

In the first part of this story, we looked at the least technically advanced of the 1979 contenders in the final round of US Army Squad Automatic Weapon tests: the XM106 Automatic rifle, a heavy-barrel M16A1 with a bipod, quick-change barrel, and ability to fire from the open bolt. In the second installment, we started telling the story of the most technically advanced contender, the XM248, but to do that we had to look at the history of the competition and its forerunner, the XM235.

As we left the competition, in approximately 1977, the XM235 certainly had the inside track. The Army reluctantly abandoned the idea of a 6.0 x 45 mm cartridge, and chose to stick with the 5.56 for logistical and Alliance-political reasons.

This is the 5.56mm version of the XM235. Note location of pistol grip.

This is the 5.56 mm version of the XM235. Note location of pistol grip.

One of the things that the innovative team at Rodman Labs did, before giving up the XM235 project, was to build a version of the gun for the 5.56 cartridge. (It’s not clear whether the 5.56 mm gun was made before, after, or at the same time as the 6.0 x 45 mm XM235). In everything except those detail changes forced by the caliber switch, the 5.56 XM235 was identical to the 6.0 mm gun: it had the two-tube receiver; the dual gas pistons; the rotating cam to drive the belt feed; the centerline, center-of-gravity mount for the ammunition-belt can; and a pistol grip offset to the right to clear the can, but directly on the weapon’s longitudinal CG.

Here's the reverse of that Ford Aerospace handout, showing the second version of the XM248.

Here’s the reverse of that Ford Aerospace handout, showing the second version of the XM248.

Ford Aerospace, which beat out Maremont for the XM 248 contract, was expected to do certain things to develop the weapon. The Army wanted it made ready for production, and produced in a short pilot run of 18 guns and accessories. They wanted all dimensions and measures to use the international metric system — Rodman had been working with inches and pounds, and in the mid-1970s, the Ford and then Carter administrations had committed the USA to metrication — something that would be dialed back to “voluntary” in the Reagan era (one of the few lasting effects of the government’s 1975-82 push for SI weights & measures was their use by the military for most measurements, which would continue). And the Army customers were willing to trade off some of the XM235’s remarkable controllability for a weapon that was suitable for ambidextrous operation: as a bullpup design, the XM235 favored the right shoulder, and the right-offset pistol grip compounded that.

Ford wound up making two distinct versions of the XM248, the first meeting the Army’s minimum requirements and incorporating a few Ford “Better Ideas” (to use one of the car company’s 1970s marketing slogans), and the second incorporating a wider range of improvements.

xm248_first_model

The first XM248 had the pistol grip moved back (from period images, about five or six inches) behind the feed mechanism and the “belt box” that was meant to hold link belts. The belt in a box was improved to offer “two-step load & go” capability; unlike other light machineguns, the a/gunner or gunner of the XM248 never needed to touch a belt. It was fully metricated, naturally. Further human engineering improvements included an ambidextrous charging handle under the forearm, an insulated forearm grip (the XM235 had only a sheet metal handguard, which tended to get uncomfortably warm in operation) and a larger (longer) buttstock. Ford touted the extended stock as a place to stow a spare bolt, but it was really extended to put the gunner’s trigger hand and firing shoulder back in the proper relationship, after moving the pistol grip!

The resulting gun was only a couple inches (or, in proper SI units, 5 cm) longer than the M16A1 (41.7″/1060mm), but it delivered 100 to 200 of the developmental XM777 rounds before reloading. It had a cyclic rate of 500 rounds per minute (on the slow, and therefore controllable, side) and weighed 11.7 lb. (5.3 kg) empty.

It also had the longest barrel (24″/609mm) of the contenders.

xm248_second_model

The changes in the second version of the XM248, which is the version produced in a quantity of 18 for development and operational testing, were many but generally subtle. The safety was redesigned to be more positive; the 100- and 200-round “Load and Go Ammunition Containers” were completely redesigned, the forearm and buttstock were also redesigned (the latter losing its bolt storage, and shortened by 0.3″/8mm). The sights, bipod, and disassembly of the bolt were all tweaked, and many changes were made with a view to production — after all, the XM248 had the inside track in the competition. Internally, these guns were functionally the same as the brilliant, world-beating XM235.

This is the XM235 stripped. We do not have any pictures of XM248 internals, but they were similar.

This is the XM235 stripped. We do not have any pictures of XM248 internals, but they were similar.

The most significant changes were probably some external ones — to better adapt the weapon to standard Army accessories, like the M122 tripod and an unspecified night vision weapons sight (probably the AN/PVS-2).

This was the American contender, meant to go head to head with the Belgian and German guns — for H&K had gotten back into the competition after their disaster in DT/OT1. And their contender, the XM262, will be the subject of the next installment. We’ll finish with the evolution of the FN Minim/XM249, and then discuss how the actual competition shook out.

Thanks for joining us on this trip back to the 1970s!

(Note: most of this information comes from Smith & Ezell, Small Arms of the World, 11th Edition [1977] and 12th [1983]. Some came from DTIC docs and period trade magazines like Armies & Weapons. Having several editions of Smith & Ezell’s work is extremely helpful to the researcher; unfortunately it is no longer kept up to date, and the “yearbook” add-on, Small Arms Today, died with Dr. Ezell).

5 thoughts on “The SAWs that never WAS: Part 3, XM248

  1. neutrino_cannon

    Very interesting series. I have the patent for the original Rodman SAW design saved on my computer, and have puzzled over it from time to time.

    The picture of the internals is interesting. The bolt carrier looks like a Steyr AUG turned sideways. The design sounds impressive overall; it’s freakishly light for one thing.

    So, why was the Army unsatisfied with the idea of a SAW where the ammunition belt overhangs the side of the pistol grip? The then-standard M60 was the same way!

    The aim-disturbing rebounding of steel parts is also covered in Hatcher’s Notebook. He notes that many automatic pistols are better behaved if the slide is kept from reciprocating entirely.

    Indeed, if you have a high enough coefficient of restitution (steel on steel is about .7), a high enough ratio of moving parts group to total mass, and enough slide velocity at the end of the travel, a pistol’s frame will recoil with greater velocity than it would if it had no moving parts at all. So much for the autoloading mechanism “absorbing some of the recoil energy” or whatever cliched nonsense writers still employ.

    The actual explanation for what’s going on, with a solid grounding in Newtonian mechanics, is of course in Hatcher’s Notebook.

    I remember that the Bushmaster ACR prototype had an elastomer buffer at the end of the return spring to prevent just this sort of problem. I do not recall if the production version does also, but it seems like a good idea.

  2. Automatkas

    I want to thank you guys for making these kind of posts. It has been difficult to find a website with this kind of expertise and interest in weapons. Your post on the toggle lock mechanism was also appreciated with the examples in current much enjoyed. Since I read the machine gun by Chinn I have be looking for a modern version, Do you have any suggestions that are in the same vein?

    1. Hognose Post author

      Good question and we’ve been thinking about what a modern designer’s reference shelf would look like. Chinn and Hatcher’s Notebook are old, but irreplaceable. Rock Island once worked up a set of designer’s guidelines and best practices which is abvailable online… I’ll see if I can find the link again or if not, put my own .pdf up. Also, I recently found a website trying to address the very issues you’re interested in.

      One big problem with gun engineering books is that as their utility to engineers goes up (with the presence of sheet music — equations) their appeal to the public goes down.

  3. thebronze

    “The SAWs that never WAS”

    Really? Your title makes absolutely NO sense. It’s not “SAW’s”, it’s SAW. It stands for Squad Automatic Weapon. Please learn proper grammar. It should either be “The SAW that never was” or “The SAW’s that never were”. Your title makes you look like an ignorant buffoon. And IF you were an 18B, most likely you’re not (an ignorant buffoon).

    Other than that, great articles.

    1. Hognose Post author

      I was making a smart-ass riff off of SAW and WAS being mirror images. The crime on display here is deliberate rule-breaking, not hazy ignorance of the rule. FWIW.

      Also, if you’re going to be a Grammar Nazi, don’t go about it with half-measures. “The SAW’s that never were,” which you suggest as a grammatically-correct alternative, is not such. Apostrophe-s indicates possessive. Plural of SAW is SAWs.

      We are looking at plural SAWs that never was were. The XM235, XM248, XM262 and a smidgen on the XM233 and XM234, about which there is very little information to be had. We’ll also cover the XM249 because it, too, evolved a bit before it grabbed the brass ring of US military adoption.

      Tomorrow we’ll have an unexpected last installment on the XM235/248 answering some of the open questions about how the feed and bolt carrier work. Getting the XM262 stuff up this week depends on whether we have time to get some scans scanned before hitting the road. We’re not going to bring 50 pounds of books, old magazines, and H&K catalogs on a 3000 mile road trip; only an ignorant buffoon would do that.

      Thanks for reading and commenting.

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