I have a .243 Ruger #1A setup for whitetail with 85 gr Sierra HPBT Gamekings. It shoots like a house on fire and I plan to leave it alone.

I also have a Remington 600 6mm that I would like to setup as a varmint rifle. I tried the 55 gr Nosler BT's when they first came out but results were not that great.

What other loads are worth considering?

I use mollied 58 V-Max's over 46 gr of Varget in a 1-8" long barrel for 3900+ and half-minute accuracy.

Seat deep! You'll never reach the leade anyway.

Redial

There are so many good combinations out there for a 6mm Remington that you should not have trouble finding one that works. I will list for you a few of my favorites below. These are loaded in Winchester cases and use a Federal 210M primer.

I will list for you the velocities I get, even though your Model 600 probably has a pretty short barrel. My rifle is a custom job built on a Model 700 that has a 26 inch Shilen barrel.

47.5 gr IMR 4831/ Sierra 80 Blitz / 3431 fps
49.0 gr H 4350 / Nosler 70 BT / 3653 fps
46.5 gr H 4350 / Nosler 80 BT / 3470 fps
48.0 gr H 4350 / Sierra 70 HPBT / 3556 fps

All of these load will shoot under a half inch in my gun when I do my part. The favorite is the 80 grain Sierra Blitz. I have killed varmints a heck of a long ways out there with that one.

The Sierra 70 grain match bullet load is just listed because it is so darned accurate. This bullet is sort of erratic on varmints. It opens up well one time then fails to expand the next.
But it shoots those wonderfully small groups.

Good Luck

My most accurate load in a M700 Bdl sporter 22" bbl isNosler 70gr BT, 40 gr- IMR 4895,WW brass, Fed 210M primer.I have not chrono'd it but it shoots 3 shot clover leafs at 100 and 3/4" at 200.I like Varget also 39.5 gr.

I know this is a heavier bullet than you mentioned but I sure do like 46 grains of H-4831 with the 100 grain Nosler Partition.

I also have a Remington 600 6mm. I inherited it, so had no idea how many times it had been shot. I loaded up some Nosler BT's, 55 gr., and pushed them with Varget powder. My first 20 rounds covered a nickel at 100 yards, but I found that the more I shot, the less accuracy I got. So I cleaned it. No improvement. So, I backed off on the velocity ( I was getting 3600 fps) and accuracy improved. My conclusion was that this rifle really does not like the really hot loads, so consider that when you are working.

My 6mm(Rem M700) was a bad copper fouler until I firelapped it. Lapping made the gun usable, didn't hurt the groups any, but did drop the velocity around 50fps. These loads are with mollyed bullets so with uncoated buulets you might back off a bit.

60gr. Sierra-44grs. of IMR 4895---3475fps.
70gr. Speer TNT-43grs. of IMR 4895---3360fps.
85gr. Speer BT-48grs. of IMR4831---3190fps.
Win. brass & #200CCI primers.
I use my 6mm mostly for coyote calling and it thumps them noticeable harder then my 22/250s or my Swift.