Umarex Thompson M1A1 Part 4

Umarex Thompson M1A1 Part 4

Select Fire and Performance

By Dennis Adler

Select fire is a great option on an air rifle like the Thompson M1A1 submachine gun especially since the M1A1 seems capable of maintaining tight groups even on full auto, more about this later. The same can’t be said for the legendary .45 ACP models which are notorious for muzzle rise. Again, never having fired one I can’t speak to that with any personal experience, but those who have fired them say muzzle rise with the big .45 Auto Thompson has to be managed. I have fired other types of smaller caliber weapons on full auto and 9mms have increasing muzzle rise, so a .45 Auto goes without saying. Accuracy with any automatic weapon not only comes down to a proper grip to control recoil but trigger pull and learning to fire short, accurate bursts, which is hard to do. CO2 models like the Thompson allow a level of practice that simply is not available in the centerfire world without owning a real select fire Thompson and going through a lot of .45 ACP ammo. Of course, if you have gone that far the cost of ammo is probably not a big consideration.

Simply stated (without the technical explanation of all the parts involved), switching from semi-auto to auto, or SINGLE to FULL AUTO as stamped on the M1A1 receiver, moves the disconnector out of position allowing the trigger, which would otherwise be held by the disconnector until the next pull, to cycle continuously with the hammer striking the firing pin (or the release valve on the CO2 model), as long as the trigger is held back. This is where learning to fire in short bursts can help improve accuracy and conserve rounds. (While an internal hammer was used on all earlier Thompson models, the Savage Arms Co. redesign for the military’s M1A1 had the firing pin machined to the face of the bolt).
One obvious difference between the centerfire and CO2 models is that the charging handle on a centerfire M1A1 locks open on an empty magazine. Not so on the CO2 model. The gun simply stops firing. The charging handle only moves completely forward if the magazine is removed and the trigger pulled as shown in the center image. As soon as a magazine is inserted, far right, and the charging handle pulled, it remains in a rearward position, as shown in the first image, but not all the way back like a centerfire model. This also exposes the rear portion of the CO2 barrel in the ejection port.

With the Umarex, you can experience a small sense of what that is like, and to my surprise, firing the M1A1 for the first time on full auto, and keeping my same POA and shooting off the shoulder from 21 feet, the groups fired in five- to six-shot bursts were not bad at all . I had a dozen rounds left in the magazine after my velocity tests and flipped the selector over to full auto, squared up on the same target (after photography) used for the velocity tests, which already had 10 hits at 1.25 inches, and put the last 12 rounds into a spread of 2.5 inches, with some pretty tightly overlapping hits on the first 10 rounds. My first short burst was pretty close to POA. The second burst (shooting to empty) began to drift higher and left, so even the CO2 model has a little muzzle rise on full auto.

Using the same test target from the velocity test, I fired the remaining 12 rounds in the magazine on full auto with the same POA. I feathered the trigger to get two short bursts, the first closely overlapping the original 10 rounds and the second hitting a little left and high in the 8 ring.

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The trigger pull is heavy but smooth at an average of 7.5 to 8.0 pounds with a 0.5 inch take up to break the shot. The sensation of the bolt action recoil (which will not function with an empty magazine and thus there is no waste of CO2), is not as great as the sound of the Thompson blazing away on full auto, and I think that will be a feature every airgun enthusiast will be keen on. You can cock the action with the charging handle and dry fire to practice trigger pull, but the CO2-powered action will not operate with an empty magazine.

Velocity and accuracy with Daisy Match Grade Precision Ground Shot

Will more expensive steel BBs gain a little extra mileage with the M1A1? I ran 10 through the chronograph and average velocity was 430 fps (though this was after running 30 rounds through the gun, with a dozen of them on full auto). Velocity is going to decrease as the CO2 is expended but you can expect to see this gun getting over 400 fps pretty much until the CO2 is almost gone. 

Switching to the more expensive Daisy Match Grade Precision Ground Shot, I had a very tight 10-shot group from 21 feet firing from the shoulder.

The important difference with the Match Grade is whether accuracy is improved. Again shooting from the shoulder at 21 feet, 10 rounds hitting just a bit left of POA went into 0.93 inches with a best 5-shot group, all overlapping just below the bullseye at 8 o’clock measuring 0.25 inches. Again, the M1A1 is impressive fired semi-auto with its basic military fixed battle sights. My correction for POI vs. POA would be under and inch up and right at 21 feet, I was just a little off on this test and shots went slightly low and left but still a satisfactory 10-shot group.

For the next ammo and velocity test I switched to Hornady Black Diamond. These sometimes give a slightly higher velocity…
…but not this time, with an average downrange speed within 1 to 2 fps of the Umarex and Daisy BBs, but with yet another impressive 10-shot group from 21 feet fired semi-auto. The sights may be rudimentary but they are almost dead on with this air rifle at 21 feet. My POA corrections are less than an inch.

The only other steel BBs that I have found can make a slight difference in velocity and accuracy are Hornady Black Diamond black anodized BBs, which is usually my second go-to choice for velocity comparisons. Knowing that the test gun has already put about 50 rounds downrange in tests and has been in the magazine for three days, it will be interesting to see what kind of velocity I can get out of Black Diamond. Velocity was lower to start at 382 fps and the subsequent nine rounds dropped to 372 fps, 374, fps, 372 fps, 368 fps, 364 fps, 353 fps, 351 fps, 350 fps, ending with a low of 332 fps and I could definitely feel and hear the sound of the action changing with each shot, but accuracy did not suffer at all, and my 10-shot group with Black Diamond, shot through the chronograph off the shoulder at 21 feet, measured 0.93 inches with a best 5-round group all overlapping in a cut through the 10 and bottom of the bullseye at 0.43 inches. At least from this first full test, including 12 rounds on full auto, the average number of shots is going to be around 60.

I shot a second velocity test with fresh CO2 and Black Diamond and got a high of 441 fps but still ended up with an average of 430 fps for 10 shots, which grouped nicely on a 10-meter air pistol target from 21 feet. My aim was off a bit and I hit low, but my spread for 10 shots was 0.875 inches, with a best 5-shots (in an 8-shot group) at 0.375 inches. All eight rounds hit inside the width of a dime. The M1A1 continues to impress.

To be fair to the Hornady, I loaded new CO2 and re-shot the chronograph test with the Black Diamond, and got a velocity spread with a high of 441 fps and an average velocity of 430 fps with a standard deviation of 5 fps. I also shot another target and my spread for 10 shots was 0.875 inches with a best 5-shot group at 0.375 inches.

The period correct military peep sight, based on the Lyman “L” type fixed rear sight, and front blade sight align almost to POA at 21 feet, needing only slight windage and elevation POA corrections. The military sight on the M1A1 was also fitted with protective sight wings, which both protect the sight and block light coming from the side. Everything frames up nicely.

The new Umarex Legends M1A1 may be the most accurate CO2 blowback action rifle to date equipped with a basic, period correct military peep sight.

In Part 5 we move everything back to 10 yards.

1 thought on “Umarex Thompson M1A1 Part 4”

  1. You must be having too much fun testing this replica. Umarex doesn’t get these replicas out terribly fast, but they do them right , and this may be the leader of the pack. Close call because the MP 40 is so good

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