of the twist. My Colt has a twist of 1:7 is that better than 1:9 ?

I don't know if I'd say it was better but it does have some advantages. Don't ask me why but the AR's I have with Colt 1x7 barrels are the most accurate bench rest shooting. That's with 52-62 gr bullets that I use for reloading and not just with heavy bullets either. See this is where the twist really matters. Faster twist, the heavier bullets you can use. A 1x9 barrel shoots 69 gr bullets very poorly in my experience, but a 1x7 can handle that and more. My Colt SP1 carbine has a 1x12 twist and shoots everything from .22 lr to 52 gr bullets just great.

Long story short is try a bunch of different bullet grains and see what works best.

buck, there is no better or worse just different.

The 1:7 barrel has an accuracy sweet-spot at a bullet weight of 69grn while a barrel with a 1:9 twist has an accuracy sweet-spot of 62 grn and just FYI a 1:12 twist barrel centers at 55grn.  Now this doesn't not mean you can't shoot bullet weights in a 1:7 up to 77grn or so but simply means - all other things being equal - you should achieve max accuracy with a 1:7 at 69grn.

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