I'm leaning toward these 2 now for a groundhog gun. I'd want something that I can get in a good over the counter fat barrel factory gun Rem , Savage, Tikka etc.
Is one more accurate than the other or has more potential? More range? Better in one way or other?
I would be reloading.

Had both, assuming you have brass availability, the 6mm will offer more speed if wanted, and the longer neck may improve potential for accuracy, and mine was 5 shot, one hole accurate, a Ruger 77V chopped to 21" before it became mine, though loud.

I think any heavy barrel will serve you well, 243 gives you more options in guns and ammo-factory if you need/want some day. May have to get an older Rem to get a factory 6mm or Ruger for that matter. Many more guns in 243, it will also do very well with accuracy and performance, though given choice, for a reloader, a 6mm is nice. Ask anyone who has had/has one.

wanna be a wildcatter? Want blazing speed?
Suggestion: buy a Savage 12BVSS in 223. Comes with a 1:9" twist. Will stabilize 80gr bullets like the Nosler and Sierra. Buy a $20 bolt head in 308 size. Rechamber the 223 to something really fast...22-250 or 220 Swift or Improved, or a 22-284 like I did. 80gr VLD's over 3500fps and low.3"s at 100yds. The 80gr VLS-type 22 caliber bullets hold a flat trajectory far beyond 600yds; one that no 6mm can match. Plus you go one up on all of your buddies in the Big Johnson Match!!

Rich
DRSS

All that gunsmithing seems a little intimidating for me. Also, with 6mm or .243 I can run to the hardware store if I'm stuck for shells.
The Remington 700 VLS seems like a nice option in 6mm Remington. What about the .243 WSSM? I don't know what guns are sold in that, besides Winchester and Browning. I'm not much of a fan of either.

As to factory ammo options, the standard 22-250 in fast twist would give you the options to use factory, or load your own, so that leaves you options that may not be with 22/284, and it will reach out there. Guys using 22 BR's with fast twist get close to 22/250 fast twist speeds and the accuracy is incredible, top with say 75 amax that expands and you would have something.

That said, a 243 or 6mm with 75 or 87 vmax or similar is no slouch.

How far do you plan for typical shots, and your furthest shots?

.243 WSSM is the ticket

I wore out a VLS 6MM with 70 gr NBT`s over enough 4064 to get 3700 and it was an awesome rig.

I would like a wind-bucking bullet that I would have a high likelyhood of popping a groundhog or crow at 500 yards. I reckon a .243 - .264 caliber bullet makes the odds for that best. .243 and 6mm are chambered in rifles that are commonly made in factory varmint rifles.
Does this logic sound reasonable to you all?
Maybe a .22-250 is more up my alley for this. I've owned one before, but the .24 calibers seem to my thinking a little more 'wind resistant' at the longer ranges. Help a brother out here...

Oh yeah, typical shots would most likely be crows and ghogs at 250ish. I have to go road tripping for groundhogs, but that would be the target species. The .223 would be the around the house gun where crows and coyotes are the main game around home.

My observations in the field are that shooting 70 Nosler BT's or 75 Hornady V-Max's out of 6 Rem's will be good to well beyond the distances you would normally require. The Rem 700 would be a great choice, go for it!

If you want something to buck wind good and shoot at something 500 yards away, get a 25-06. I got a winchester 700 sporter last fall and I expect it to out range and be less wind sensitive than my 243. I don't know it's full potential yet but right before I bought mine I shot a friends post 64 winchester 25-06 at metal targets at 500 yards at our local range and hit it every time. I plan on shooting at stuff this year as far as I can see it.

I think the 6mm Rem. is somewhat superior to the .243 Winchester. But, unfortunately, the 6mm Rem. is becoming obscure while the .243 is thriving. Accuracy will depend on the individual rifle, but the 6mm Rem. will give you a small velocity edge with any bullet weight.

My 6mm Rem. -- a Remington 700 Varmint Special (the one with the heavy barrel) -- really likes the 70 gr. Sierra Matchking over about 41 grains of IMR 4064. There isn't a varmint in the world under 80 pounds live weight that could stand up to that.

Knowing what a 70gr does at 3400, at 3700 it must hum! My 6BR loves the TNT's. Now, that said, I agree with poster, save for a fast twist hot 22, that a 6mm bore is a great way to think range, energy, drift in wind, etc.

To the point about a 25-06, if you are shooting random targets, not volume like prairie dogs, a 25-06 in a good gun can do some amazing long range work, perhaps somewhat bettering a 6mm or 243. You will find more 25-06 I believe in current production guns vs 6mm, though more 243 than any in heavy barrels.

It seems you want performance, to 500 yds at max, and factory ammo options, a 243 has likely more options on ammo, but if you load, a 25-06 has plenty of options to keep you going. Don't rule out consideration of the 25 bore, any of the 3 will do you well, brass components and cartridge availability might be in order like this in my mind, 243, then 25-06, then 6mm. If you find a great 6mm with low barrel mileage, it might be a great balance. If in no hurry, you should find a good heavy barrel in that chambering. Let us know what you do, no bad choices there.

My personal preference is the 6mm Rem, hands down... in a long action...

However, I would recommend the 243 instead to most people...

It has much more readily available ammo ANYWHERE ya go... and will do most of anything that the 6mm Rem will do...

It is just more practical for the non handloader... and even if you are a handloader.. I bet their are a thousand 243s in service for every 6mm Rem in existance...

But that is another reason I like the 6mm Rem.. I like to walk the path less traveled...but I also have owned a lot more 243s than 6mm Remingtons...

I'll tell you, after that Ruger 6mm, it would be hard to convince me a 243 would outshoot one! That thing shot like crazy! FC brass, match primer, H450 powder, now disc., and a 97gr Hammett bullet, ONE hole 5 shots! Yes, 100yds.

My buddy BEGGED to have it, sold it to him, only complaint, at 21", it was LOUD. But, could never knock the accuracy it had at all.

I imagine a 243 or 25WSSM would do very well, but that is getting TOO much off the beaten path for how available I like components, ammo, etc.

I shoot a 6mm BR, 2 25-06, and 2 243's.

The most accurate rifle I own is a black metaled Sendaro in 25-06. It's been bedded in Bisonite and the trigger is adjusted.

I would eiither buy the 6mm or the 25-06. Though 243 is cheaper to buy and load for.

I've had both. I prefer the 6mm because I like the longer tapered shell as it works in my Mauser actions. If you don't reload I would go with the 243. It is easier to fine ammo.

Currently I have the option fo a 243 or 22-250 only because after several years I've shot the barrel out of my 6mm and it is waiting for a replacement.

the VLS I had was super fast,with the 87 V-Max and RL-19 it would push 3450 and the 95 gr NBT with RL-22 would go 3250 if you loaded it out long and in single shot mode,loaded to mag length it would knock about 75-100 fps off.

it actually shot the heavy bullets a little tighter but I liked the trajectory and splatter factor of the 70 gr bullets.

the most accurate load in that rifle was the 85 Sierra GKBTHP and IMR-4831.

As has been stated, the 6mm will outperform the .243 everytime velocity wise. However, as has also been stated, it's getting harder and harder to find rifle and ammo for the 6mm remington.

One option open for you to get 6mm performance and available ammo, is the .243 AI. You can fire standard .243 ammo in a pinch, and the gunsmith work is minimal(setting back barrel, and rechambering).

As to the 25-06 having superior wind bucking abilities, at the ranges you're planning on shooting, the added recoil would overweigh the slight benefits you will see imo. Not to mention the wider availability of high quality 6mm bullets as opposed to the .25 cal offerings.