Tommy Gun

Question
QUESTION: was the most used version of the Tommy Gun used during WW2 the short barreled version.

ANSWER: Hello Robert.
  There were only 2 barrel lengths on the 'Tommy Gun' used during WW11. The M1928A1 .45acp, with the CUTTS COMPENSATOR was 12", which kicked off America's entry in the war after Pearl Harbor. In April 1942, the USSGM1 cal.45 had no compensator, thus the barrel was 10.5". There were other calibers experimented with, such as the M1923 in .45 Remington Cal. with a 14" barrel, and the .351 WSL Cal. with a 20" barrel.
  In 2006, Russia began exporting original 'Tommy Guns' into the US. These included all parts, including 10.5" barrels. However, they were not allowed to export the receivers. Any other barrel lengths today are modern copies. I hope this answered your question. Charles Gage

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QUESTION: So if I  purchased a semi auto version the closest to WW2 original would it be the Auto Ordnance model M1SB model.

ANSWER: Hello again, Robert
  I could not find any information on a M1SB, but I did find an M1SBR with the 10.5" barrel. Even though it is a semi-auto version, the short barrel(anything under 16") will require a tax permit to own. It can only be shipped to an NFA Class II manufacturer or NFA Class III dealer. Charles Gage

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QUESTION: I know a bout the tax and where to buy but what style Tommy gun was most used during ww2, that is the one I want to buy as the full automatics are way to expensive. You can go to tommygunner.com and see all the different versions made today. Thanks Will rate after this reply.

Answer
Hello Robert.
The USSGM1 was the most used during WWII by US troops. Although the M1928A1 began with WWII troops, the drum magazine with 50 rounds of .45 acp ammo was very heavy and unwieldy. It was hard to remove and replace the drum due to having a horizontal magazine insert. However, it would take a 'stick'(vertical) magazine as well, but it only held 20 rounds. GI's started taping two magazines back to back to increase the firepower, but the gun still jammed. The M1 replaced the M1928A1 soon after in April 1942. Holding a vertical 30 round stick, and closed  bolt (the M1928A1 had an open bolt) to stop entry of dirt and other debris, the M1 finished hostilities with a 'BANG'. It was replaced with the M1 Garand and M1 Carbine before the end of the war, but many soldiers continued to use them. They were even a favorite in Korea and Vietnam, until the M14 arrived.
So to answer your question, the only one that matches, on tommygunner.com, is the M1SB with the 10.5" barrel. The only other one there, is the TM1 with the 16.5" barrel. You do not need a tax stamp for this one. And thank you for calling my attention to that web page. Charles