SCAR 17S will not fire

Clean the firing pin, bolt, bolt carrier and firing pin of shipping grease.

Did you run a pipe cleaner through the firing pin channel in the bolt??

With the bolt pushed to the rear the pin should protrude a bit out of the bolt face when the pin is pushed forward.

Improperly sized brass on handloads can cause light strikes in any gun.

Take outbtge firing pin retaining pin and recheck it may have been assembled improperly. The firing pin should be installed with the bolt full forward and the bolt cam pin in and the hole in the cam pin aligned with the rear of the carrier and face of the bolt to allow the firing pin to go full forward. Once the bolt is extended with the firing pin in place insert tge firing pin retaining pin in the rear portion of the carrier. It should not be flush but just slightly raised. If it goes in full flush easily its misding the retaining oring or the ringbis damaged. Do not use anything but finger pressure to insert the retaining pin as it can possibly bind the firing pin if excess force is used.

The bolt and firing pin should move freely by tilting the carrier. If it does not it needs to be properly lubed. Stay away from frog lube it clogs firearms especially in cold weather.