I have had this rifle for a couple of years and never really tried to push it's limits beyond a few hundred yards but have recently stumbled across this site and saw some of the longer ranges achieved with other .223's. I am only looking to achieve efficiency to 500-600 yds with this rifle. The problem is the companies web site does not list very much information on the barrel specs other than what I have listed here. I've checked around online and have come up short as well. I was hoping maybe someone may have some additional resources or insight as to what my limit may be on how heavy a grain pill I can spit out of this thing with it's current barrel or what the twist ratio is. So far the heaviest I've felt compelled to shoot is 62g REM FMJ with success. I'm obviously not going to be able to throw 80 or 90g rounds but even a tad heavier than 62 would be nice. Once again I'm not sure what the limit for this barrel would be or what the limit for most stock .223 bbl's are for that matter so even that information would be useful. Thanks ahead of time for any information -This is my first post; hopefully this project will bring some interesting results. BRAND: Harrington & Richardson MODEL: Ultra Varmint Fluted Rifle SAFETY: Transfer Bar System TYPE: Rifle SIGHTS: NONE CALIBER: .223 BARREL LENGTH: 24" Fluted Bull Barrel FINISH: Blue OVERALL LENGTH: 40" ACTION: Single Shot WEIGHT: 7 lbs STOCK: Black Synthetic Skeletonized, Pistol Grip PACKAGING: Includes Scope Mount Rail & Hammer Extension CAPACITY: 1 FEATURES: Vertical Adjustment Knob on Stock, LOP 14 1/4" FEATURES: Adjustable Bipod Mount, Sling Swivel Studs BUTT PLATE: Black Vented Recoil Pad RECEIVER: Blue This is the stock image- Mine is currently outfitted with a solid bipod and a 3-12x50 optic and an improvised cheek pad. It shoots wonderfully with both 55g and 62g FMJ cartridges but I am anxious to get some heavier rounds through this if it's even possible.