I was looking at the larger ar platform calibers a while ago.  I was wondering if anyone had experience with the 50 beo and the 458 socom. 
From what i gather the 458 is a little more expensive to shoot but had a wider range of head weights available.  Also it is a little harder to find.  The 50 is a little more wallet friendly but i think the ammo is a little less varied  but is easier to come by.  Ballistics seem to be pretty similar from what i had read with the 50 taking a slight advantage is energy delivered downrange.  The recoil was greater, not significantly, but enough to have a marked difference. 
Tromix seems to be the go to for the 458 and the 50 does not seem to have any one producer that would be better than another.  Not counting bargain/budget brands.

I assume your ar is going to be for pig hunting

A grendel may be able to do that and more

https://www.chuckhawks.com/modern_sporting_rifle.html

Or maybe a inertia driven 12 ga semi auto for a short range thumper.

I prefer the 450 bushmaster over 458.  Legal to hunt in more states.  Ammo is decent to find and buy.

OP,
What are you going to use it for?

https://www.arbuildjunkie.com/hog-hunting-the-best-ar-calibers-for-hog-hunting-via-todd-huey-of-lone-star-boars/

This is from 2018, so the big bore AR’s may not have been as common.

Huey liked the 6.8 and 7.62x39.  No love for the 6.5.   I think he shoots a lot at night and in open fields.  I would have thought the 6.5 would do fine based on its ballistics.

I had looked at getting a 450/458/50 or a semi 12 gauge after I brought along my bolt gun and was told at the private property “that we if ran into any poachers, we would be apprehending them”.  I was with 2 retired cops and one MP.   The MP had a 450, I don’t know what rifles the retired cops had…but one also had a G20 on him.   I wasn’t expecting that……

I ended up with parts to build a Grendel upper and a couple of semi 12ga shotguns.

450/458/50 are bigger thumpers than the grendel but I got the parts for the grendel since i considered it more versatile and more popular (easier to obtain parts/ammo). 

The 12 ga semi is really versatile - almost the same thump as 450/458/50, could be used for bird hunting and also for trap/skeet.  Ammo is readily available and relatively cheap

But yeah the 450/458/50 are thumpers and good for a stalker who may have to take multiple shots on a pig thru brush as it tries to run away

Like Omni mentioned, some states will only allow straight wall ammo….in case you plan to hunt up there

This is from 2018, so the big bore AR’s may not have been as common.
Huey liked the 6.8 and 7.62x39.  No love for the 6.5.

Todd Huey's favorite ammo in the interview is the .308. Since he is hired as an eradicator, it may boil down to the least expensive ammo per kill. This means that having to use half a dozen rounds to knock down a pig is not as effective as one .308 round. Now, the .458 Socom could be a prime round for a takedown, and for families of wild pigs. It may be helpful for hunter survival, for those not as experienced as Huey.

Q (from interviewer):  Wrapping up…I’ve always been curious just how dangerous these animals are.  What’s your opinion on that?
A (Huey):  I’ve killed…I’m right at 6,476 hogs right now.  I have had maybe 20 to 30 of them legitimately charge me out of all of them. Now, it can be dangerous, if you wound them, or you get a sow with its piglets, that can be dangerous.  I usually hit them before they get close enough.  But if you miss…yeah, you’re going to have a problem. They’re gonna cut up your legs, they’re going to knock you down.  It can be dangerous, but most of the time, they are trying to get away from you unless it is a sow protecting piglets, or a really aggressive boar.

As an inexperienced hunter, all I can recommend is getting a good cover.

Yes, saw the 308 at the top of the list but I assumed the OP was looking at an ar15 platform instead of an ar10 platform.

Hunting pigs on Oahu is a bit different from Texas. (Thermal scopes, using stand up tripods, large farms/ranches)

I assume Huey uses a 308 ar10 on a tripod.

I was thinking more for fun, maybe a little hunting.  Yes I was thinking the ar 15 platform not the 10. If that was the case i would just go 308.  Plus i like the oddball calibers for no other reason than not too many other people have them. 
The 458 also seems to out distance some of the other calibers when you start to stretch out past 200 yards, depending on your head weight.  Problem with that is around here over 100 yards is limited by range availability.  Mag wise, you can use the standard 30 rnd but the specialized ones are supposed to function better. 

ammo availability may also be an issue.  is there much 458 or 50beowulf ammo locally to buy?  I'm not sure bc I don't have those calibers and don't look for them at the shops.  do you reload?
probably if you can find them, they'll be expensive.  but I understand sometimes we just want something bc we just want it, and that's ok too.

I've thought about these calibers as well..........

For 50 Beowulf, I think Alexander Arms would be the “go to” since they developed it.  50 is proprietary and not SAAMI….I suspect that choices and availability of parts and ammo would be the worst of 50/458/450.

458 is also not SAAMI.  Only a few of the smaller companies make ammo

450 is SAAMI.  The bigger companies make ammo.  I think 450 will have the most support/availability/choices of parts, ammo, reloading equipment, reloading components and guns of the big 3 since it is SAAMI. 

If you just want something to shoot every once in a while at the range, all 3 will do.  But if you want the one with the most “support”, that would be the 450.

If you are just interested in the 458 and 50.  458 seems to have slightly better ammo availability.  458 was meant to use regular 556 mags.  556 mags need a slight mod to use them for 50

For me, I would lean towards 458 instead of the 50 because it has a little more support, it may not be proprietary and has a “military history”

For me, finding ammo is the most important thing since I’m too lazy to reload so I would start with the 450.  If later I still wanted a bigger thump, probably get a 458 assuming ammo is easier to find than 50.  I would get the 50 last even though it has the biggest range of bullet weights. 

If ammo availability isn’t important and shooting the heaviest bullets is, the 50 is it.

Miscellaneous
Is it me?  But isn’t Beowulf the most cheesiest name of the 3.  Thank god Alexander used Grendel instead of Beowulf for the 6.5.  I think using the name Beowulf is part of the reason it isn’t more popular…it sounds blingie/tacky….and this is coming from a Filipino….so you know it is tacky sounding. :-)
 

Holy cow.  Just saw someone selling 458 ammo, $100 for 20 rounds.   Glad I went the grendel route…picked up ammo for $25 for 20rds

if I were to go with a big bore AR, I would go .450 Bushmaster
seems like ammo isn't as expensive as the other big bore calibers and reloading bullets seem more available.  but I haven't been looking around too much

I've thought about these calibers as well..........

It would be great if Kentucky Ballistics ran some accuracy tests at 100 - 300 yds, for each of the rifles/calibers.

Best thing about this youtube creator (Kentucky Ballistics) is not just the fun he is having, but the list of his sponsors and recommended vendors.
https://www.kentuckyballistics.com/affiliates
I never heard of hiddenhybridholsters.com before, but anticipating we will get a ruling on CCW licenses by 2022, it never hurts to plan ahead. Safariland takes ages to respond to consumer requests.