To add to BCRider's comment: Remember, these pistols are not finely finished Colt Gold Cups. So, some attention to detail might be lacking. I would definitely check the chamber first. Is it smoothly polished? Are there any obvious machining marks or rough spots inside? Some attention should also be paid to the barrel's feed ramp. Could be that a bit of polishing of the ramp is in order, too. It is possible the cartridges are catching on some unseen rough spot on it, on their way into the chamber. Enough to cause the firearm to fail to go fully into battery. Likewise, in and around the chamber mouth. Also, check the barrel to slide lockup. Does anything look abnormal on the contact surfaces? While you're at it, check the link. Cracked? Installed properly? I'd definitely try the "plunk" test first though, if for no other reason than to eliminate one variable.
If changing out the spring still remains an issue, you might Google: "Wolff Springs". Before replacing the spring, try to find out the "weight" of the spring the SAM pistols use. Then make your choice. One last thing.....it may also be possible that, during sustained fire enough powder residue or gunk builds up in the chamber to cause a momentary hangup while chambering a round. How much smoke are you seeing exiting the barrel, when it is fired? Are you getting more hangups before or after, 50 to 100 fired rounds? Before or after, switching from factory loads to reloads...or vice-versa? Sometimes you have to do some Sherlock Holmes sleuthing to get to the bottom of these things, but the answer will usually reveal itself once you eliminate all the possibilities.