Had the SWFA 3-9x42 on my 16 inch barrell ar-10. Selling this rifle to buy a bolt gun and get into long range shooting. I'll be shooting 500 yards max for now. What's a good variable, higher power ffp mil/mil scope for around 800? I'm new to long range shooting and worried that I won't have a chance at accuracy with only 9 power at 500 yards. Thanks guys.