I have a new ROCK RIVER ARMS rra varmint with 20 inch barrel and the Wylde chamber. I need to know what to use for ammo? It dosnt like 55gr. Also can anyone tell me what the Wylde chamber is? I expect this to be a real tack driver when I find the right bullet weight. Anyone have any experience with this rifle? It has a wilson stainless bull barrel and a match trigger and a free float aluminum tube. It is nice. But the ultra max 55gr ammo I sighted the rifle in with wont group well. It did around 2 to 2 1/2 inches. I need to know about the chamber and what to feed this thing with that twist of 1:8
Thanks
Kelly223

Dont worry about the chamber.  It simply understated, is a hybrid of SAAMI and NATO.  

It's not the bullet weight that I have found that affects grouping at 100yds, as much as it is the quality and consistency of the components, and the cartridge as a whole.

FWIW, I have found three cartridges to be very successful in the RRA 1/8 Varmint upper:

Black Hills Blue box 68gr (50ct)
Black Hills Blue Box 52gr (50ct)
Wichester White box Varmint 45gr (40ct)

All of these group right at 1" all day long.  I have had trouble getting sub MOA reliably, but have had a few .75" groups and one .5" grouping.

I would like to try some Federal gold medal match.  I hear this barrel likes 69gr sierra's.  Dont know yet.

Best ammo of course is going to be a handload worked up for your particular rifle.

You might want to check out this thread in the competition forum:
www.ar15.com/forums/topic.html?b=1&f=10&t=152439

Should like 62grn and heavier bullets.

Quoted: Should like 62grn and heavier bullets.

And yet, I seem to get my best groups with 45gr.

I have a 1:9 barrel and have found BH 52 very good to 200 yds, and Sierra 69 handloads excellant @ 300 yds.  BH 75 (Hornady I think) also do well @ 300.  I would try the Federal GM 69 for sure.  Sierra 77 have a very good reputation but I don't know if they are available in a factory load.  Check GA Precesion for BH ammo.