Umarex Thompson M1A1 Part 3

Umarex Thompson M1A1 Part 3

Built to perform

By Dennis Adler

The idea behind the M1A1 was to take the then current M1928A1 and modify the design to make it faster and less expensive to manufacture, in order to meet the needs of the U.S. Army, U.S. Army Air Forces (consisting of both Army and Marine Corps pilots), United States Marine Corp, U.S. Navy, and Coast Guard during WWII. The Thompson M1A1 design was adopted in April 1942, so this latest Umarex Legends model is based on a design that is now 78 years old. Compared to the rest of the Umarex Legends, the M1A1 is a youngster, historically. As the most refined (as in easiest to manufacture) of Brigadier General John T. Thompson’s designs, (Thompson passed away at age 79 in 1940, more than a year before the U.S. was drawn into WWII), the various Thompson designs leading up to the M1A1 had all been proven in combat (M1928A1), both by the military and federal agents (FBI and Treasury) during the Prohibition Era, U.S. Postal Inspectors, various state and local law enforcement agencies, and in foreign conflicts. The Savage Arms improvements to the M1A1 made the Thompson more efficient for combat use by simplifying the firing system, and building improved stick magazines that held 30 rounds, that were easy to load, attach and most importantly, remove to clear the action in the event of a jam. (The same design had already been developed for the 20 round stick magazines).

During WWII, approximately 1,700,000 Thompson Submachine Guns were produced and used in every major battle fought from 1942 to the end of the war in 1945. The guns were heavy at an average of 10 pounds, but slung over the shoulder small enough for easy carry. This WWII soldier armed with an M1A1 is also carrying a Model 1911A1 in an M1916 JT&L 1942 leather holster. (Library of Congress)
Matching the new Umarex copy of the WWII Thompson M1A1 is a CO2 powered Model 1911A1 in a World War Supply copy of the JT&L 1942 M1916 U.S. marked holster.

M1A1 and CO2 magazine comparison   

Build a Custom Airgun

The simple combination of the CO2 within the BB magazine (first used with the Legends series in the M1932 Broomhandle Mauser Model 712 with a single CO2 cartridge) was expanded upon with the MP40 using two CO2 cartridges to power the gun. The design for the M1A1 is taken directly (internally) from the Umarex Legends MP40 submachine gun. The exterior design follows the look of the M1A1’s 30-round box magazine, which was approved as standard in December 1941 to replace the earlier 20-round XX and L-type drum magazines (which could not be used with the M1A1 design). The 20-round and 30-round magazines were lighter and easier to carry in quantity in the field.

The WWII era Thompson M1A1 was designed to only use stick magazines, the most common of which held 30 rounds of .45 ACP ammunition. (Photo courtesy Rock Island Auction Co.)

If you look at the left side of an M1A1 magazine and the CO2 magazine, the profile is almost identical with the six witness holes and magazine guide channel. The BBs loaded into a forward chamber loading port and the magazine has a fairly easy to manage follower and spring. This is only seen from the front or ¾ views of the CO2 magazine, and holds the correct number of rounds for an M1A1.

The Umarex Thompson CO2 BB magazine closely duplicates the size and design (excepting for the CO2 mechanism) of the M1A1 30-round magazine. The Umarex M1A1 magazines load the correct 30 rounds of .177 caliber BBs to match the .45 ACP’s capacity.

Loading CO2 and BBs

This is the same as loading the MP40 magazines, with two 12 gr. CO2 cartridges loaded back to back in the CO2 chamber. With the seating cap turned down, both are pierced (one by a pin at the top of the magazine, the other by a pin in the seating cap) and the chamber fills with CO2. Loading BBs is a simple process, especially with a speed loader. Hold the follower and spring down below the loading port, pour in up to 30 BBs, carefully release the follower and you are ready to insert the magazine into the receiver. Pull the charging handle and the gun is ready to fire. (Be sure to keep the safety selector on SAFE when inserting the magazine).

The Umarex magazines are expected to be available at the same time as the M1A1, so there shouldn’t be an extended wait for spare magazines, as is sometimes the case with new models.
Like the magazines for the German MP40 CO2 model, the Thompson M1A1 uses two 12 gram CO2 cartridges loaded into the CO2 chamber back to back. The rear CO2 cartridge is pierced by the pin in the seating cap (center of the cap in photo) which also has an O-ring to seal the polished internal air chamber when it is turned down.

Velocity checks

For today’s test I am using Umarex Precision steel BBs and firing 10 rounds on semi-auto through the ProChrono chronograph. The gun is rated at 435 fps. My first run with fresh CO2 clocked 438 fps, 431 fps, 430 fps, 430 fps, 431 fps, 431 fps, 432 fps, 433 fps, 431 fps, 430 fps for an average velocity of 431 fps and a standard deviation of 2 fps for 10 shots fired at 15 second intervals.

The follower tab is large enough to get a solid grip on with a thumb nail and hold down while loading BBs through the loading port. This is one of the least frustrating magazines to load CO2 and BBs into.

More impressive was my 21 foot target shot through the chronograph with all 10 shots (fired single action from the shoulder) inside the 10 and bullseye at 1.25 inches center to center with seven out of 10 in overlapping groups of no more than 0.25 inches. POA correction at 21 feet was 1-inch up and 1-inch right of the bullseye.

The count is from the front of the CO2 BB magazine and it is easy to see how many rounds are left up until the last five rounds which are above the edge of the magazine well.

This is an impressive beginning for the shooting tests with the Thompson M1A1. Right out of the box (well, this is a sample gun and there was no box) this is one of the best handling and most authentic WWII era copies I have seen thus far from Umarex or any other manufacturer in terms of attention to detail, operation, and first test accuracy. I have handled several original Thompson models over the years, including one that was issued to the FBI in the 1930s, and though I have never had the opportunity to fire one, this gun feels right from past experiences. And there is another plus to the authenticity of the design, with all of the correct dimensions, the CO2 model will work with a number of actual WWII era M1A1 accessories that we will look at in the coming weeks.

While I tend to take less effort on accuracy when chronographing shots, after the first two rounds on target I was able to adjust POA by an inch and put all 10 shots through the chronograph on target at 1.25 inches with all but three into groups measuring 0.25 inches. This is an auspicious beginning for the Umarex M1A1 shooting evaluations.

In Part 4 we will have additional velocity tests with different BBs and more semi-auto tests for accuracy at 21 feet and beyond.

7 thoughts on “Umarex Thompson M1A1 Part 3”

  1. Denis
    From what I’ve seen so far in your reviews of the Legends M1A1 Umarex has gone and done it again. Looks to be high quality fit n’ finish and may end up (for the time being) the “pièce de résistance” of the Legends line!
    I have quite a few of the Legends airguns and apart from a few of the earlier replicas which were flubs (the C96 Broom Handle Mauser was more toy than anything) most of the Legends guns are pretty high quality. Even my original NBB Luger with the cocked barrel fireing mechanism after thousands of shots is still going strong. It’s a great 25 yard high velocity plinker. Mine still shoots at 440+fps! The only problem I’ve ever had with that gun was one of the mags wore out and stopped working!
    I see on one of your M1A1 photos that there is what looks to be a small “v” notch on top of the rear sight blade. Being directly above the peep aperture I’m just wondering if it can be used for distance shooting. Also can the rear sight be loosened off and maybe repositioned a little for windage or can windage be corrected by drifting the rear sight blade?
    Looking forward to your next installment.

    • Red

      I haven’t tried the V notch yet, will let you know. As for removing the rear sight, the housing is screwed down, but windage adjustments are not possible from what I can see. Being a sample gun I am not going to start screwing (or unscrewing) around with it as it has to go back for others to use. As far as I have been able to determine in my tests, the sights as is are excellent and very little POA correction is needed at 21 feet.


      • Red

        I did a quick test using the V notch, which is very hard to see against the target, but it will put shots about 3-inches higher. However, I also went and shot a short test from 10 yards with the peep sight and put shots inside the 10 and X, so I don’t see any practical reason to use the V notch over the peep hole, even at 10 yards. I think the M1A1 is going to be a surprise for longer range accuracy with BBs averaging over 400 fps.


  2. Denis
    Back again and off topic.
    Well, yesterday afternoon I got my brand spanking new Barra 1866 Cowboy in the mail. Sure is a pretty looking gun.
    After a good cleaning and lube and about 10 shots I consider the gun broken in, mostly. No BB’s so far! Apart from the maintenance and fileing some sharp points off the end of the trigger the gun is now shooting extremely well.
    The Barra Cowboy has a lot in common with the Umarex NXG/APX and the Crosman Bushmaster ACR in that the pump heads are very similar or possibly the same.
    The NGX/APX was disappointing in that it didn’t shoot very tight groups due to the wiggle and twist in the frame while shooting.
    The Bushmaster was super accurate with the El Cheapo Daisy wadcutter and hollow point pellets. It’s main problem was the silly little pellet clips with manual indexing and the fact that the gun made more noise while pumping than when being fired!
    Shooting the same El Cheapo (locally about $4 per 500 count) Daisy pellets the Cowboy was sighted in with about 5 shots at 10 metres. The resulting groups were about ½ inch +/-, shooting off hand standing at 10 metres. No noticeable difference between the wadcutters or the hollowpoints.
    Loading at first was a major problem. With the bolt open the loading area was just too small for big kids fingers! After about 15 shots I discovered the trick to loading.
    Place a pellet faceing BACKWARDS on the shelf in front of the breech.- gently push the pellet back towards the loading trough. As it falls into the loading trough it will topple over into the correct orientation. Close the bolt. After 60 shots loading is now effortless!
    Next week I’ll submit the Chrony results For the Daisy pellets.

    • I think for the money, if you want an inexpensive, multi-pump pneumatic that looks like an Old West rifle and can shoot BBs or pellets with decent accuracy, the Barra 1866 is going to stand tall. I didn’t encounter the loading problem with pellets that you did (smaller fingers I guess) but it is harder to load than most. Your trick sounds as good as any for making the process quicker. The trigger is the one thing Barra needs to change so users don’t have to file down the rough edges.


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