Loads for an Auto Ordnance Thompson Carbine
Date: Jun 30 2016
Few firearms are more interesting than the Thompson submachine gun (SMG). While most of us will never own a true Thompson SMG, there are alternatives. In some cases the pride of ownership alone is worthwhile, but the Auto Ordnance carbines are useful for recreational shooting and competition.
The Thompson submachine gun was invented and developed by John T. Thompson, a well-known military man and fixture on the American firearms scene. Thompson is the other half of the famous “Thompson-LaGarde” cartridge tests that determined the proper caliber for a military handgun was .45. Early in his career, Thompson was impressed by the firepower of the Gatling gun and attempted to convince the military to adopt firearms with greater firepower. He ran into a brick wall with the staid conservative military of the day. Colonel Thompson retired from the military in 1914, just on the eve of the Great War. He made a name for himself again in the firearms industry, as his steady hand led Remington to produce thousands of rifles for the war effort, primarily for British and Russian use. Once the United States entered the war, production was turned toward producing arms for U.S. troops.
At his own expense, Thompson developed a fully automatic firearm suited to the needs of trench warfare in Europe. In Europe, stopgaps such as the snail drum Luger and the highly effective Winchester 97 shotgun were commonly used in trench warfare, but what was needed, Thompson reasoned, was a short firearm using the .45 ACP cartridge. Thompson’s Trench Broom hit several snags in development, as neither a gas-operated system nor a straight blowback proved suitable for what he envisioned. What he needed was a retarded blowback system.
The means of achieving a solution was provided by a patent by Naval Officer John B. Blish. The “Blish Lock” was a breech-locking mechanism that could be used with a blowback system. Originally intended for naval guns, the system worked well with the Thompson SMG. The bolt’s unlock in the simple blowback system was delayed until pressure abated and the bullet left the muzzle.
Thompson acquired financial backing, and soon the Thompson SMG was a reality, but it arrived too late for World War I, and the world’s armies were not likely to purchase the firearm in the near future. Just the same, a marketing team went to work in selling the Thompson SMG to the world.
The first and most famous public demonstration of the Thompson came in 1920 at the National Matches held in Camp Perry, Ohio. These were experimental firearms without stocks or sights. The first Thompson SMG had a firing rate of 1,500 rounds per minute and would empty a 100-round drum magazine in four seconds.
Soon Auto Ordnance contracted with Colt to produce the Thompson; about 15,000 were made. Lyman Gun Sight Corporation produced adjustable sights, and at a later date, the Cutts Compensator was added. Sales were disappointing with only 3,000 units sold by 1925.
The National Prohibition Act was a stimulus to Thompson sales. Gangsters purchased the Thompson primarily to guard their wares against other gangsters, and eventually the Thompson figured into quite a bit of gunplay, not only among gangsters but also against law officers. Anyone with a few hundred dollars could purchase a Thompson, at least initially. The industry policed itself, and once sales were tightened up voluntarily among dealers, the Thompson soared in price, with examples bringing several thousand dollars in the underworld.
The U.S. Coast Guard was given the task of chasing rum runners and became the first service to issue the Thompson. Soon after, the U.S. Marines purchased Thompsons, and the big .45s saw action in Nicaragua and Honduras. The firepower and combat efficiency of the design were proven in jungle fighting. Meanwhile, the U.S. Navy convinced Thompson to modify the submachine gun’s rate of fire, reducing it to a more controllable level and to make other modifications, including changing the vertical foregrip to a more conventional type. This became the 1928 Model. In 1932 the army began accepting its first Thompson submachine guns. The 1928A1 was procured in limited numbers.
Auto Ordnance struggled through the 1930s with limited sales, until 1939. An outbreak of hostilities in Europe brought an initial order of 3,000 units from France and practically open-ended contracts from Britain and the U.S. Colt was overloaded with other wartime production, and Auto Ordnance contracted with Savage to produce the Thompson SMG.
Wartime contracts demanded changes to allow faster and cheaper production. The Lyman adjustable sight was replaced with a simpler unit. Cooling fins on the barrel were deleted. The checkering once found on controls was deleted. Most important, the Blish Lock was eliminated. It was found that the Thompson functioned just fine as a straight blowback. The cocking handle was moved to the side of the receiver. The M1A1 SMG was not as pretty as the finely finished Colt Thompson SMG, but it did the business and served long and well.
After the war, the Thompson was found in the arsenal of many police departments and continued to see use in every conflict up to the Vietnam war and the various Middle Eastern conflicts. Today, a fully automatic Thompson is a true collector’s item, costing as much as a sports car or a new truck.
The Auto Ordnance Thompson is a faithful reproduction of the original. The modern version is in between the superior fit and finish of the Colt 1921 model and the later M1A1. It is well made of good material. The cooling fins and vertical foregrip are intact, and overall it gives the impression of a firearm that is carefully made.
The new Thompson does not use the Blish Lock. That’s fine, since it was incorporated into the action primarily because it was foreseen that the Thompson would one day be chambered for cartridges more powerful than the .45 ACP. This did not happen, although there were experiments with cartridges as large as the .30-06, a very few .38 Super and .30 Carbine examples and a single .351 WSL version. The modern .45 ACP Thompson is well served with the standard blowback action.
Don’t ask where the Thompson carbine fits in the scheme of things. I cannot imagine a role in which another firearm wouldn’t serve better. The longer barrel (16 inches versus the original’s 10 inches) dictated by federal law means the new Thompson handles a little differently than the original. With the lack of a full-auto option, any number of modern self-loading rifles will best the Thompson as a personal defense firearm, but nothing comes close for a pure fun factor.
The Thompson isn’t particularly accurate by reputation, and the magazines, either a 30-round stick or a 50- or 100-round drum, make benchrest shooting difficult, although the Thompson may be precise at moderate range once you have trigger time. The Thompson may be addictive, and there is a problem. It is expensive to fire any factory centerfire round, and firing a drum of 100 rounds of .45 ACP may make a dent in the wallet quickly. Handloading is the only way.
I have loaded more .45 ACP cartridges that all the rest put together. Just the same, I approached the Thompson with a fresh start and a new eye. There was no need to increase power; all that mattered was that the piece functioned. When dealing with a blowback design, increase power at your own risk. Battering is the result of a heavy hand with the powder measure.
Accuracy was problematic for the type of shooting intended, but I wished to obtain all the accuracy possible. Sight regulation at 50 yards was important. Beginning with the standard 230-grain bullet at 850 fps (pistol velocity), “hardball” loading seemed logical. I intended to substitute an affordable hard-cast, roundnose lead bullet for the military jacketed bullet. I had no idea as to feed reliability with SWC or JHP bullets, and they were not needed in this carbine. A supply of Rainier 185-grain bullets on hand had proven brilliantly accurate in several handguns, and it would be good if they could be used in the Thompson.
I learned some things about loading for a .45 ACP carbine, where most of the velocity is built up in the first 8.0 inches of the barrel. So, if a fast-burning powder was used, was I wasting the rest of the barrel? It was tempting to experiment with slower-burning powder, such as Accurate No. 7, but slower-burning powder results in heavy muzzle flash or even ejection port flash. The Thompson is unlocking before the powder is burned. This cannot be a good thing, and the results were erratic as far as velocity and accuracy.
Fast-burning powders are the best bet, as the Thompson was designed for military ball that used Bullseye powder. Loading for the locked breech 1911 is far different. A medium-burning powder in the locked-breech Colt may produce longer lock time and greater accuracy – at least that is the theory. With the carbine, faster-burning loads are definitely superior. Even with Titegroup, one of the cleanest-burning propellants ever, there was some blowback of unburned powder.
The hero for this work turned out to be Winchester 231 powder. After some experiments with 230-grain ball loads, my loads were cautiously worked up with Oregon Trail 230-grain Laser Cast bullets. A 230-grain hardball equates to 920 fps in the 16-inch barreled Thompson, and it seems that a load of at least 870 fps is required for reliable function.
There were no special considerations with crimp or powder selection, and the Thompson functioned fine with minimal barrel leading. As it turned out, traditional loads near the maximum listed in various manuals gave very good velocity and accuracy, with velocity in some cases nearing 1,100 fps. This puts the .45 ACP in a different powder category – like a .460 Rowland with little recoil but quite a weight penalty.
With comparable powder charges, lead bullets gave a velocity advantage over jacketed bullets, which is not surprising. For accuracy the Thompson preferred jacketed bullets. The Hornady 230-grain FMJ and 230-grain FP were used. Feed and function were good, and the FP was the single most accurate bullet used.
Surprisingly, the Thompson fed most JHP bullet styles. Several factory loads were also tested. Even the stubby Cor-Bon 165-grain JHP fed just fine. Velocity increase was more significant with this load. Firing factory rounds to confirm feeding reliability with JHP bullets led to experimentation with the Hornady XTP in 185, 200 and 230 grains. It is easy to perceive the difference in trajectory with the lighter bullets, and the 200-grain XTP in particular was the most accurate when addressing steel plates at 100 yards. I was also able to work up an acceptable load using the Rainier 185-grain bullet. This affordable jacketed/plated bullet gave good results.
In researching the Thompson carbine, period literature outlining accuracy testing from a Mann rest was intriguing. The Mann rest was a fixture often used to test intrinsic or absolute accuracy in firearms. (The Thompson was fired in semiautomatic mode.) According to a firing test undertaken with a Colt-produced Thompson on May 2, 1921, using Remington ammunition, the mean radius at 100 yards was 1.89 inches, 4.92 inches at 200 yards and 7.63 inches at 300 yards. At 500 yards the radius greatly expanded to some 20.45 inches. There were poor results in another test marked down to a bad lot of ammunition. Another test a year later showed less impressive results, including a 200-yard group that showed an average mean radius of 5.8 inches.
In a test of the shooter and the machine, cartridge designer Philip B. Sharpe assumed the prone firing position and carefully placed five shots into 2.5 inches at 100 yards with a commercial Thompson. Sharpe reported a 1.5-inch, 50-yard group as well. Could Sharpe’s 1933 results be equaled with the new Auto Ordnance carbine? I had the advantage of a longer barrel and a modern CNC-produced carbine and, most particularly, well-developed handloads, but the quality of the Colt SMG was the wild card.
A limiting factor was the trigger. While there is plenty of leverage because the Thompson is so heavy, trigger compression is heavy and seemed inconsistent. I engaged in over an hour’s dry-fire practice, split into 15-minute increments, to gain an advantage at the range. The occasional brilliant group followed by a flyer were simultaneously encouraging and challenging. In the end, firing from a solid braced position, several 3-inch, 100-yard groups were secured with complete concentration and proper trigger technique. The Thompson is more or less as accurate as the average unmodified .30 carbine or AK-47.
The shooting was most interesting, and in the end I gained a new respect for the Thompson. The piece is more accurate than my first impression and seems very reliable. I do not think I will be using the cumbersome 100-round drum, but it is an interesting option. The 30-round stick is plenty. The Thompson remains among the finest recreational firearms I have ever handled and an interesting piece of history.