I have a Thompson M1A1 made by Kahr Arms and is used for plinking/ target shooting, just a fun gun. The question is, after two to three shots, the spent casings stovepipe. I was wondering if it is the magazines or the gun itself. How can I fix it.
Can I stretch the magazine springs to help it feed better or is there something else anyone can help me with. Thanks.

I would try using different ammo first.  I wouldn't think that stovepiping would be caused by the magazine.

As above, try different ammo.  
Shoot standard 230 grain, round nose, full metal jacket.  
Cheap ammo often doesn't work right.

Also:
Clean and lube the gun, clean and lightly lube the magazine.
Try a different magazine.  Bad mags can do weird things.

DO NOT stretch the springs.  Stretching springs RUINS the spring.  
If the springs are suspect buy new FACTORY strength springs.

Has the gun been fired enough to break it in?  Many guns give problems for the first several hundred rounds.

If after the abouve it still jams, DON'T screw with it.  This almost always makes things worse.  
Send it back to Auto Ordnance to be repaired.

And check the extractor for damage.

Thank You for the suggestions.

Is it every 2-3 rounds throughout the entire mag?

If so, check the extractor but also check the chamber as well. These tend to have a tighter chamber than it should.

Make sure quality ammo is being used.

Would it function better with +p?