please help me on constructing a best AC

[Crimson]

replace the sniper rifle with the HP handgun, along with using the 73H FCS because that will make your lockbox bigger thusly making it easier to keep a lock on the faster opponent. Put a 69H handgun in your hangers because the Atlas can hold hangered weapons

Change your legs as well. The S3 legs are borderline heavyweight which will do nothing but slow you down. Dingo1, Dingo2, Cougar2 are all fast legs to help you out and you should be able to carry the load.

Downgrade your Radar to the standard one. Only use the Siren4 for missions with high ECMs, other than that the standard RA should get the job done.

Get rid of the GL for missiles because OBing with cannons is very difficult for even the most advanced pilots. Nypmhe+RM3 will fit on here.

A full parts list will help ultimately tho.

Good Luck