i have the same problem no idea how to fix it though really annoying

What you are looking at is the reticle for the optics you attached to your swep. If you have your settings set so that you spawn with all attachments available, you could try disabling that and then manually spawning the attachments in the future. It's also always a good idea to disable all your addons except FA:S and then check to see if the bug/error/conflict remains. If that doesn't work then I reccomend reinstalling gmod itself and then starting over. Another suggestion is to uninstall FA:S and even unsubscribe from it. Then disable all your other addons, run a brief test on gm_construct or something to see if anything is lagging, if anything is reinstall gmod and see if you can find the addon that's causing the problem because it is possible that a separate addon is affecting FA:S and possibly other addons too. If your test comes back positive and there is no lag then re-subscribe to FA:S and see if the issue is resolved. If none of these work then you should probably verify the integrity of your game cache. IF THAT DOESN'T WORK then talk to someone who is actually a professional 'cause all my troubleshooting methods will have been exhausted. Hope this helps!

well i should probably try disabling all addons but FA:S ive tried re installing it but it has not worked

Well I hope you solve the problem!