The SR556 is a great rifle for the money. The points to be aware of are as follows:
- Weight: The standard model is heavy when compared to DI and higher dollar piston guns. My advice is to go for the CLA model or the E model. The CLA is the lightest overall, but has a fixed flash hider. The E has a removable flash hider, and is only other model with the modular handguard (other than the Varmint gun).
- Trigger: The stock trigger on mine was the heaviest AR trigger I had ever felt. A Geissele is a fantastic replacement, but on a budget, it's hard to beat the $45 ALG QMS or the $60 ALG ACT. This is a must if you buy this rifle.
- Stock and grip: The rifle comes with the bog standard M4 stock and a rubber A2 grip with finger grooves. This is up to preference, but I would replace these two parts (and the triggerguard) with Magpul parts and be done.
- Sights - The CLA comes with Samson metal BUIS, the E model comes with plastic back up sights. Both fold, both will work fine.
- Reliability: Mine ate both steel case and brass ammo without any failures.
- Accuracy: Mine was about a 1.25" - 1.5" rifle with iron sights, but I never really tried too hard. Accuracy was plenty good for a battle rifle.