I have an opportunity in 2017 to hunt elk in New Mexico. In a recent conversation with my FIL, who I will be going with, I mentioned wanting to use my pistol. He said that he didn't junk pistols were allowed. This will be a
S&W 460XVR.

I've looked online but can't find any definitive information

NM department of Game and Fish
2016 - 2017
Hunting

Page 62
Elk Licenses

Legal sporting arms;
Any Legal Sporting Arm: Centerfire rifle or handgun, .24 caliber or larger; shotgun, no smaller
than 28 gauge, firing a single slug; bow and arrow; crossbow and bolt; or muzzleloading rifle,
no smaller than .45 caliber.
Archery Only: Bow and arrow. Crossbow use by certified mobility-impaired hunters only.
Muzzleloader: Muzzleloading rifle no smaller than .45 caliber, scopes and sabots are legal for all elk
hunts. Bows and crossbows are legal sporting arms.

You can, I wouldn't advise it for sake of your success rates but you can sure try.

What unit are you hunting?

That I'm not sure of. It's a friend of my FIL and he has 28,000 acres he owns

It's not really any different than hunting with a bow is it? Keep my shots under 50 yards. I'll have my rifle with me in case I can't connect at a comfortable range

If it was archery season or ML no, but it will be post rut. Huge difference

Explain please. I've never even considered an elk hunt until I received an invite for the 2017 season. FIL went in late September or October, I can't recall, and connected with a nice 5x5 at 38 yards.

Central to northern NM Late sept is still rut. Rifle season they normally don't come to calls.
ML season is first of oct and it's very tail end of the rut.

By rifle season usually bulls are starting to move off cows and go to there safe places...usually. There is always the exception. If it's real hot still you can sit a water hole and most likely get one close.

First Rifle season is you best bet to be able to still call bulls in close.

Have you killed an elk would be the 1st question? If not I would def. Take a rifle if your serious about killing.If your hunting rifle season expect 200-500 yard shots, maybe you will get closer but that my experience as your usually hunting the next mountain side over glassing and if you try to get to close theirs a good chance you'll get busted. In the ruts a little different but that's bow or.muzz.

Sounds like an excellent opportunity.

What bobo said. Not only will they not come to calls, but they also don't call making it harder to locate. Also, bulls are stupid during the rut which is why it's easy to get close to them during archery season. They care about one thing and one thing only then. They quit caring about that after and don't let you get close. I'm not saying it can't happen, but the odds are much worse in November.

Have a good hunt

It may be legal to use a pistol, however, I'm guessing you'll be hunting elk during the rifle draw period. As stated in a prior post, you'll be hunting bulls post peak rut and most of them will be hooked up with cows and not coming into calls. I'd expect long range shots beyond 100yds.

In 2001 we hunted during the late muzzle loader season in Unit 15. Late season in that area, the bulls are scattered but you can find the bigger bulls then! I took this guy in the Apache NF in unit 15 and at 154 yards with my muzzy.

Here you go, a nice bull shopping at Walmart on highway 70 on the west side of the Downs.

Dogcather, it was like that when we did that job in Ruidoso, so bad, they have the middle of town golf course fenced off When we ate dinner, you had to wade through the game to get to your car, then on off days we golfed Dogcather has a nice herd running over town!

Check this out....
https://www.youtube.com/watch?v=FaHCMHE2Hmo

Going hunting with your father-in-law is important not to mess up.

He is giving you a great opportunity.

If you leave him unhappy, that unhappiness will be magnified ten fold with your wife.

Take a rifle, keep him happy, and have a great time.

Good luck.