You only need two pennies to take the Sig apart and it is way easier to clean if you know what you are doing. It has far fewer parts and the ones it does have are very strong and well designed. The ONLY thing I do not like about the non SWAT Sig 556 is the heavy,"fish gill" hand guards but you can easily buy the lighter, far superior Swiss 551 hand guards on www.gunbroker.com
or on any Sigforum.com type site. It really is a MUST have change.
The Sig will run OK with the 55 grain bullet but its 1:7 twist is extremely accurate with the heavier bullets from 62 grn and up. If you want stopping power you should be using the 75 jhp anyway not the 55 grn.
Simply put the Sig has the reliability of the AK47 and the accuracy of the AR15. It is the best of both worlds.