What do you all think the effective range of a 300 grain Swift A-frame factory load in a 460 S&W is on an illinois whitetail? I know the shooter must do his part and at 100 yards I?m getting around 2 inch groups with my encore pistol and scope currently. I can do better and am considering a trigger job to help accuracy a little bit. I shot hornady sst, xtp, handgun hunter as well as Barnes and swift today. Swift was hands down the most accurate for me. Thoughts?

I would say 150 if you can hold it on him.
Be very aware of your drops

Revolver or single-shot?
MV with the 300 grain bullet?
What is the designed impact velocity range for that bullet?

It is a single shot, stainless, factory, 15 inch TC encore pistol barrel. I am not sure of the MV and I do not own a chronograph. Swift publishes 1907 in a 8.5 inch barrel. This is what Swift says about their a-frame bullet:
Heavy Revolver A-Frame? bullets expand at 950 feet per second, to 1.65x their original caliber, and maintain 97% of their weight. They are virtually indestructible at velocities in excess of 3000 feet per second.?

Understood.
How far are you capable with it when shooting from the field positions for hunting?
Which optic?
What is it zeroed at?

I know where you're going with this!!!

It is zeroed at 100 yards and it wears a Leupold variable pistol scope. I would not really use this in my treestands due to lack of a rest and being in the timber. I would use this more from blinds on field edges where a good rest is available.

The .460 should do 150-200 easily IF you have a good rest, good scope (2-6 or 2-8X), and have practiced at those ranges A LOT so you have the confidence in making the shot. The cartridge and gun are not the limiting factor...you are.
Sighting in 2" high at 100 makes longer range shots much easier.

x2

X3

If your shots are going to be 200 yards or under, it sounds like several people have answered your question already.
With that longer barrel, and increased MV's, maybe further.
The biggest determining factor is the ability of the shooter/hunter to keep shots in the vitals under pressure and on demand.
It would be important for you to actually group it at 150, 175, and 200 yards, to learn your drops, and how you can do group wise as things stretch out. Wind is another consideration past 100 yards too

Thanks for the information and I just ordered more of the Swift ammunition. I look forward to practicing at extended ranges and becoming more proficient.

A bit late to the conversation, but I'll throw in my 2 cents.

A 300 grain bullet that's within its expansion window is going to kill any whitetail in the country, even at the lower end of its velocity range. For the Swift A-Frame -advertised to still expand somewhat well down to 950 fps- and using the Federal factory load advertised at 1,750 fps -which was likely chronographed out of the 8 3/8" barreled Model 460 revolver- that gives us 950 fps out to 250 yards. MatchGradeMachine's velocity testing with a 300 grain handload out of a 15" barrel yielded 2,164 fps, which would retain 950 fps at about 325 yards.

The limiting factor in my opinion isn't power, or even accuracy. It's the bullet trajectory. At 250-300 yards, even out of a 460, the bullets are experiencing rapid bullet drop, to the extent that a 10 yard ranging error can mean a hit 3-5 inches high or low. That's not even getting into managing the wind, which will definitely come into play at those distances. Like Ernie said, as long as you've practiced and can keep your shots within the kill zone at the ranges you intend to encounter game, you'll be good to go.

We are looking forward to your range reports