What's opinions of the chambering in a AR15, 20", 1x9 twist?

Great little round. I have had 3 with 1/10 and have a bolt gun with a 1/14 twist.
Does fine up to 80 gr bullets and is easy to load for. Probaly at its best with 60-75g bullet weight range and most powders that work for 223 also good with 6x45.

I have a 6X45 chambered in one of my ARs. It shoots the old Sierra 80 grain SSP (single shot pistol) bullets great. These bullets were designed for the 6mmTCU and perform wonderfully at the velocities produced by the 6X45. They are a bit hard to find now days due to being discontinued by Sierra, but the 90 grain Nosler ballistic tips also work very well with that round.

Mine is extremely accurate and when I run the can on it, it is pretty quiet too.

The 6x45 is often underestimated as a hunting round. A 243 is considered great out to fairly long range on deer and antelope. With an 80 grain bullet the 243 is about 3400 FPS and the 6x45 2900. Sounds like a big difference, however at 150 yards the 243 is the same velocity as the 6x45 at the muzzle. If you think the 243 is enough at 500 yards the 6x45 is equal at 350.

Be sure to get the right twist for the bullet you plan to use.

M

I don't know about great, minimal might be a better answer when it comes to the 243 and deer size game. Since the 6x45 runs an average of 500-550 fps slower and almost half the ft-lbs with any given bullet that seem to put it in the DQ category.

like Andrew says "if you like it, well you know"

You consider the .243 "minimal" for deer? I will be sure to tell all the thousands of deer and antelope that have been killed by a .243 that. While there is no good way to definitively prove it, I would say that the only rounds that have killed more deer than the .243 are the .30-30 and the 30-06. Deer are not armor plated and they are really not that tough.

I have killed multiple deer with both the 6X45 and the 6mmTCU. All of them have gone down relatively quickly. With today's modern bullets, as long as you put the bullet where it belongs the deer will go down.

Mine has killed DOZENS of deer, pigs, and coyotes. It is a 22" bolt with 1:10 twist. I shoots the 85gr Sierra GK at 2705 FPS with a moderate dose of H335. Easy to load for, and far more effective on game than the 223. It is my go-to truck gun. Very underrated chambering, in my opinion...