106mm M40 Recoilless Rifle, History and Firing

The M40 was the final and largest iteration of the recoilless rifle in American military service. Designed to fix the shortcomings of the 105mm M27 that preceded it, the M40 was light and powerful, and added a .50 caliber spotting rifle to assist in being able to make first-round hits. The massive backlist of a recoilless rifle dictates that a crew generally only has one chance to make a hit before they must relocate to avoid retaliatory fire.

Thanks to Hamilton & Sons Firearms for permission to film their M40 and bring it to you!

45 Comments

  1. Improved Bulgarian log cannon someone once mentioned vs Turks in the 15th century etc; metal barrel, plugged end, vent holes, in a tree trunk thats bored out to fit with its back against a wall…

    BOOM! Trunk explodes, projectile hits Turks. Use a long fuse.

  2. A superb weapon still in use today. Having been vastly improved with enhanced gun mounts/carriages, and the replacement of the ,50 cal with a laser rangefinder. The Austrian and South African in particular are very good, there various clones of it that are also modernised. The fact that the bore is 105mm, but it is entitled as a 106mm weapon has always amused me, especially since the initial ammunition in use was that of its predecessor M27 105mm RR.

    • “(…)still in use today(…)”
      Generally speaking, it seems that recoilless rifles – if do not have inherent serious flaws – might linger in service for many years.
      SPG-9 developed in late 1950s: https://modernfirearms.net/en/grenade-launchers/spg-9-2/
      was relatively quickly replaced in Soviet Union by more potent anti-tank system, but as it was widely exported – still in use today and even in production (in Bulgaria).
      U.S. M18 recoilless rifle which debuted during WWII was still in service with U.S. forces during Second Indochina War.
      Finnish 95 S 58-61 adopted yet in 1958 year, apparently was still in use in Finland as late as 2011: https://en.wikipedia.org/wiki/95_S_58-61

    • The Australian War Memorial has a 106 mm recoilless rifle in the National Collection carried on a short wheel base Landrover. The alleged reason why it’s nomenclature is 106 instead of 105 is because of logistics so that it cannot be confused with 105 ammunition for the M101 105 mm howitzer, which apparently occurred in Korea where the wrong ammunition was at one time sent to a firebase.

  3. I was a Small Arms Repairman from 1966 through 1969 and worked on many of these. Most of the problems were with thr spotting gun feeding the white phosphorus rounds incorrectly and the .50 bullet exploding in the chamber with the action partly open. Needless to say the poor guy that was firing was instantly killed or severely burned. As I recall the magazine held ten rounds. Once in a while we had to replace a part in the firing mechanism. Thanks for the memories.

  4. Wow, great video. Both history and live fire. I was wondering, what does one have to do to own/posess something like this? Is it a class 3 situation like an automatic weapon, or is it even more restrictive? Also are civilians restricted in the type of ammunition they can own, only practice type shells?

    • Destructive Device (DD), Class 3 just like an SBR or SBS (and not prohibited from future manufacture like MGs).

      Practice ammunition is [Federally] unrestricted. If you can get explosive or incendiary shells, every one is a new DD – i.e. transfer tax, months to acquire, then gone in an instant if you so choose.

      • A slight bit of historical correction, but both the US Navy and Great Britain made some use of the Davis Gun (which use a counter-mass rather than a venturi) in WW I, but these were abandoned in the inter-war years.

  5. I had a platoon of 8 guns mounted on M825 Quarter Tons when I was assigned to 3-60 Infantry back in 75-76. Annual Service Practice was always fun, but in 76 we were scheduled to transition to the M220 TOW missile and were told by the ammo supply point at Yakima to fire everything they had. Over two days, everyone qualified many times over. Ordnance must not have believed the numbers in the log books when we turned ’em in. Some points – 1. Ammo, High Explosive Anti-Tank (HEAT), Anti-Personnel (APERS or Beehive),firing a huge number of flechettes, High Explosive Plastic (HEP) “Squash Head” 2. It couldn’t be fired inside a building or bunker because of back blast and you had to make sure there wasn’t a wall that would reflect the blast when you otherwise clear. 3 http://www.warwheels.net/M825RRmutthaugh.html (no one ever called a M151 or M825 a “MUTT”, a term invented by Ford but never used by the Army. Only poseurs in the collector or modeling community use it today) 4. https://media.moddb.com/images/mods/1/19/18132/m40rcl2.jpg 5. British Equivalent 120mm Battalion Antitank (BAT) and lightened Weapon Of Magnesium Battalion Antitank (WOMBAT) https://en.wikipedia.org/wiki/120_mm_BAT_recoilless_rifle

    • A friend of mine who had to deal with the M151 during the TOW era never calls it a Mutt, or anything that printable. Mainly due to the cheap-ass rear swing axle (like a VW or a Corvair) that makes it likely to roll over if somebody tries to take a corner too fast, a fault that was never rectified in any variant.

      People buy refurbished M151s on the surplus/collector market today, and it amazes me that states actually license them for highway use. Every one is an accident waiting to happen.

      Of course, some people still drive Ford Pintos, too.

      cheers

      eon

  6. When the Canadian military retired these, some were sold (to Mexico i think?), and a bunch given to the provincial government Ministry of Transport in here in British Columbia for avalanche control along the highway going through the coast mountain range.

    They were retired, whether because parts and ammo were getting scarce, or because of too many duds, or because the security required for their custody was too much of a pain in the ass I don’t know. They were replaced by dropping sacks of ANFO from helicopters instead.

    If you drive the highway and know what you are looking for, you can still see the permanent emplacements off the side of the highway. A round concrete stand with permanent mounts embedded, and a small road sign with a cross-hair pattern for use as a permanent aiming stake. The problem slopes were pre-surveyed, so you set up, aimed at the stake, then adjusted from a table to aim on the location the avalanche control technician had chosen, and BOOM!

    Most of the highway through the Rockies lies in National Parks, so there they use a combination of helicopter drops and a detachment of Canadian Army 105mm artillery. They also have pre-surveyed permanent gun mounts on various places along the highway. One of the guys I did Officer Basic with went arty and did a stint as the OC AVCONDET and says it was the best assignment of his career.

  7. The trigger explanation (pull to fire the spotter .50, push to fire the 105) implies you can’t fire multiple spotting shots, but you have to fire one. Wouldn’t that spotter shot alert the enemy, especially if it’s a distinctive phosphorous exploder?

    • Ref 50 cal 1. You don’t have to fire the spotting rifle to then fire the 106 2. You can fire multiple shots from the 50 cal as the mechanism reverts to neutral after you fire a round (of either type). The ranges shown in the picture I posted earlier on ammunition are too conservative. The manual says 1100 is max effective range, in practice, trained gunners can hit tank sized targets out to 2000 meters (or at least my guys could). What’s with this “Fire in the Hole” BS…The proper announcement is “Fifty On the Way” followed by “One Oh Six On the Way”. Same as in tank gunnery. Last, the breech with the four vents is screwed in to the barrel during manufacture. During use, each round erodes the vents to the stream of high pressure and temperature gas. When the vents have reached their limit, the gun starts to recoil forwards. You turn it in, draw a new one and the old one goes back to arsenal where the vent piece is unscrewed and discarded and a new one installed (provided the rifling isn’t worn out also). In practice as all rounds fired are recorded in a log book, when a gun reaches a certain number of rounds it is sent in for breech replacement and after another it is scrapped due to being worn out.

      • I was a small arms repairman (45B) in ’67-70 although I never actually worked on a 106, but I have a faint recollection of the venturi/vent piece being screwed in some specific amount every 400(?)rds to adjust for the erosion, and that if you screwed it in too far you got the forward thrust rather than balance or the regular recoil that came with the wear. It was not considered worn out until you ran out of adjustment. In the Youtube video where they trash a Land Rover (Range Rover) with the back blast, the the vent piece in the worn-out M27 can be seen screwed in apparently all the way.

  8. I remember that the M40 recoilless rifle was used to arm a few tank destroyers, but the big problem for those vehicles was the reloading cycle, which required a crewman to get out of the vehicle, eject the spent casing, and load a new shell (this took at least a minute). If you failed to incapacitate the enemy tank upon first sighting, you were dead. I could be wrong.

    • Cherdog your talking about the ONTOS (“The THing”) which was a quite ingenious way for the USMC to provide tank-attack vehicles, armed with six M40A1 with 18 rounds. Developed for the USMC new aerial envelopment tactics in the early 1950’s,it a vehicle of its time, but when considered obsolescent in the 1960’s it found its niche. Being totally superb in all it did in South Viet Nam. Normally fired single rounds, but, when it fired all six incredibly impressive. A long time friend (sadly gone to his maker) one Warrant Officer Class One, Aussie Ostara commanded a SVN Province Reconnaissance unit in 1968 in the recapture of Hue. One of his dining out stories was how a Marine ONTOS came up to support him when pinned down by North Vietnamese in a 7 storey concrete building, fired all six barrels simultaneously. The vehicle jumped up in the air, and the building collapsed. The US Army wanting it for its Airborne Divisions dropped it because it did not look like a tank and adopted the M56 Scorpion with a short 90mm gun that looked like a tank. The USMC purchased 297 ONTOS, and in their last years struggled to keep spare parts up for these superb vehicles. The https://www.defensemedianetwork.com/stories/m50-ontos-the-forgotten-tank-killer/ is a good article on the vehicle.

  9. Cherdog your talking about the ONTOS (“The THing”) which was a quite ingenious way for the USMC to provide tank-attack vehicles, armed with six M40A1 with 18 rounds. Developed for the USMC new aerial envelopment tactics in the early 1950’s,it a vehicle of its time, but when considered obsolescent in the 1960’s it found its niche. Being totally superb in all it did in South Viet Nam. Normally fired single rounds, but, when it fired all six incredibly impressive. A long time friend (sadly gone to his maker) one Warrant Officer Class One, Aussie Ostara commanded a SVN Province Reconnaissance unit in 1968 in the recapture of Hue. One of his dining out stories was how a Marine ONTOS came up to support him when pinned down by North Vietnamese in a 7 storey concrete building, fired all six barrels simultaneously. The vehicle jumped up in the air, and the building collapsed. The US Army wanting it for its Airborne Divisions dropped it because it did not look like a tank and adopted the M56 Scorpion with a short 90mm gun that looked like a tank. The USMC purchased 297 ONTOS, and in their last years struggled to keep spare parts up for these superb vehicles. The https://www.defensemedianetwork.com/stories/m50-ontos-the-forgotten-tank-killer/ is a good article on the vehicle.

  10. Lightweight, accurate, cheap…
    And requiring one spare operator for each shot cartridge.
    The perfect choice for a shahid. LOL

  11. Various comments state that the 106 was the last recoilless rifle in US Military Service, but it is not. The M67 90mm served in the Army until the 1990’s, then the disposable AT-4 came into service. The Swedish 84mm Carl Gustav in its M3 and M4 variants remain in use, the M3 was adopted by the 75th Rangers to replace the M67 (the USSF and the SEAL Teams used the M3 also, the SEAL community had used the M2 variant in limited quantity from the 1960’s). 1,000 plus of the superb M4 were purchased in 2017, and further numbers purchased reported since. With it further reported that the Army wishes to make it a standard infantry weapon? Al Jazeera news last night reporting on the complete withdrawal from AFGHAN had a item showing AFGHAN Army commandos in action with a M40 on a two wheeled carriage, in direct support of a infantry attack.

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