i use core locks with my .270 and also have good groups. haven't missed an animal yet with them. i'm sure i will soon though.lol

You could just have a bad one. These single shots can be tuned to shoot well, and sounds like you've touched on most of the basics.

Did you try shooting without the forearm stock? Take it off completey and shoot it, and if the group tightens up that is the problem. Some solve that by placing an "O" ring on the take down screw, between the stock and barrel lug.

Also check that there is no play at all when the action is closed. Any play or clunking sound when you twist or shake the actin is a sign it's not locking up tight, and that will ruin accuracy for sure.

Barrel heat on those light barrels is another factor, and letting the barrel completely cool is critical.

If it were mine and I had done all the above and still bad results, I would take a small dremmel tool and a cone shaped stone and place the point of the stone into the muzzle and lightly hit the crown with it.

At this point it's just a last ditch effort to salvage the gun, and I would have nothing to lose. But that would be me if it were mine, and I'm in no way telling you to do that!

Check on line for Rossi's customer service number. Don't know what the factory return policy is for Rossi, but I know H & R will have you send it back and they will fix it, and in most cases replace the barrel if they also can't get it to shoot.

rossi's suck...i would trade it off as soon as I could

Give the barrel a good cleaning

Yes, I was just thinking the same things. Your barrel could also have some rough spots and need to be lapped.

JB Bore Paste or Flitz to polish the barrel, lands and grooves.

Front rest should be on receiver, not barrel or forend

I had the same problem! Try shooting ammo under 90 grains and see how that works for you. If not, get rid of it!
Lance

...and some rifles can take a hundred rounds before they group worth a darn. Some shoot better clean than dirty and others like it somewhere in between. It's a little early to chuck it imo.

This may be off topic, but has anyone ever returned a firearm due to problems with accuracy? Seems like there are so many potential causes of accuracy problems (as seen above), it could be difficult to make this happen.

Remington are 1:9 1/8 twist. I believe I have read in my reloading manual over the years that the twist was change to stablize 100 grain bullets. Some even tried 105 grain reloads. I reloand 95 grain Nosler B-Tips and mine is literally a tack driver. You might try going down to an 80-90 grain bullet.

I was having the same problem with my h&r youth.
ended up with winchester superx in 80 grain it will shoot 3in group now. go figure a 10in group with hornady 95grain and then turn around and shoot a 3in with a lesser ammo????