if its the plastic handguard forget it. They break pretty easily and Sig doesn't like to sell quad rails to customers (so I've heard).
Not even close!
The plastic will hold up, and has been for the Swiss military for quite sometime now...SIG will sell you the P-Rail front ends IF you have the coin for it, They are made by Troy Industries and Troy and several other manufactures offer the P-Rail forearm aftermarket.
As for that prickly forearm, I have both, and as many over at SIGforum.com have said, the P-Rail forearm makes for an even heavier and more unbalanced rifle... most folks have been selling the SWAT forearms and replacing them with the plastic ones, you may be able to get a good deal at the above mentioned website on a SWAT forearm.
The 3 P-Rails that can be purchased from several retailers and will allow you to mount all the swag a man could want on the classic, plastic forearm rifles. They simply bolt on with supplied bolts. The rail sets have two short and one, long tapered, unit for mounting whatever...the long tapered rail goes on the bottom and makes for a level plane in case you would like to mount a vertical grip.
The rifle is somewhat heavy but built fairly well. I still prefer an AR type rifle to the SIG 556 though. To each their own, the 556 has attributes which far surpass the AR and so vice versa. If I was on a breaching team, I would definitely want an AR, if a sandhog, either would do but the nod goes to the 556 being more robust and heavier.
Also I would bet the 556 exhibits less mechanical failures than an AR would...just my opinion. If the 556 had an non-reciprocating charging handle it would be nearly perfect, but....