I sold my 10FP after shooting a friends PS90. I loved the round but wanted an AR styled rifle to change barrels when needed. Am I able to swap the bolt face on a .223 set up to fire the 7.62X39 or do I have to swap the bolt carrier, buffer and spring as well? Has anyone had any issues with the 5.7 upper swap? What optics do you use with the 5.7 upper?