I was wondering if someone could help me out with this. I have the S&W M&P Sport 15 II (5.56). I want to change calibers from 5.56 to .50 cal. I know theres .50 Beowulf, 50 BMG, and some other variations for 50 cal rifles. But I want to change caliber on my MP Sport 15 II to shoot .50 ammo. What do I need to do to accomplish this? (If its possible that is).

I know Safety Harbor Firearms sells complete 50 cal uppers. In their description they said "The SHTF 50 is designed to fit any MIL.SPEC AR15 pattern lower."

The problem is I can't tell if my AR is MIL.SPEC. Usually it says so in the engraving on the lower, or "Multi-Cal" like Anderson Arms lowers do.

Another person told me:

"The Bolt Carrier Group is the same, but the bolt is different. So you'll need the barrel, the bolt and the magazine all have to change to 50 cal. Everything else is standard AR."

With all that in mind, what would I need to do/get if I wanted to change calibers on my MP Sport 15 to shoot .50 ammo? Thanks for your help!

Mil spec is an overused term, really unless you get a way out of whack lower, they will work with pretty much any upper.

As to .50 caliber, there are a few different types of uppers.
A .50 BMG upper just uses the lower as a host for a single shot bolt type action.
.50 Beowulf is a 12.7x42, it uses your existing lower with an upper that will load from a magazine, you do need a 6.5 Grendel bolt.
The Beowulf is ballistically similar to a 45-70 round.

With the exception of the McCutchen upper, there is no way you can get a .50 BMG to work as a mag fed rifle in an AR, the magazine well is just not big enough.
The McCutchen works as it’s a side fed magazine, similar to the Stein.

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Thanks Gunslinger for the info. I'll need to research McCutchen as that's new to me.

As far as mag fed rifles, what about Safety Harbor?

SHTF 50 mag fed upper conversion – Safety Harbor Firearms

They say their uppers will work for any AR15 lowers. Altho it says Bolt Action Rifle in the description which is kinda confusing 🤔

Safety Harbor has been making them for a long while, never heard any bad about them, the top loader is new to me, hadn’t seen that one before, reminiscent of the British Boys anti tank rifle.

Yeah, since all your using is your lower, the .50 BMG uppers are bolt action as your buffer and springs would be beat to death by the recoil in just a round or two, it couldn’t handle semi auto.
All your lower does is provide a butt stock, safety, trigger, and hammer, the rest of it is useless.
There used to be a manufacturer that made a stripped down lower specifically for those uppers, it had no mag well, no buffer/spring, and a match type trigger.

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I got another newbie question. Is 50 caliber black power really 50 caliber? I've seen lots of old rifles that say .50 cal on the price tag, and the're cheap. Like $100 to $200. And I'm like "Wait, if I want to shoot 50 caliber, why am I looking at all these expensive BMGs and thousand dollar uppers when I can just get a cheap rifle? Or is that something totally different?

Caliber generally only refers to the diameter of the bullet.
Just like the 5.56, it’s basically a .22(4) caliber bullet, but it’s case length, powder charge and actual bullet length/weight are what define it.
A 5.56/223 are the same diameter as a .22 long rifle, and with a conversion, you can fire the .22LR out of your AR as both bullets are almost identical in caliber (diameter).

A black powder round may be nasty at close range, but it’s no where near the monster a .50 BMG is, even if both bullets have the same diameter.

A .50 BMG is a cartridge round that fires a 700 or so grain bullet at about 3000 fps, and can hit a target out past 1000 meters with ease.

A Black powder .50 runs about a 400 grain projectile at about 2000 fps and would be lucky to make it to 700 meters, and would take about a minute or so for a well trained BP shooter to reload.

On the left is one of my .50 BMG rounds for my Barrett, on the right is one of my loads (less percussion cap) for my black powder TC rifle, both are .50 caliber.



Navy SEAL, or Jed Clamppet.

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Dude if I could reach through the internet and slap you I would.

A little harsh but you get my point.

You bought a gun designed to shoot a overcharged 22. PERIOD.
The AR can be converted to larger calibers but at best they are half a&& conversions. In the long run there is really NO substitute for a 50 cal BMG rifle.

Notice I said 50 cal BMG. There is more then one 50 cal. If you say 50 cal 99% of people will assume you talking about 50 cal BMG, (Brown Machine Gun). This is the classic military 50 cal round. There are of course smaller rounds, like 50 Beowolf, 500 Smith & Wesson, 50 cal AE. etc.

list of .50 caliber cartridges - Google Search

SO if you really want to shoot 50 Cal BMG your going to need to get a 50 Cal BMG rifle. The various conversions, like SHTF, are just that, jerry rigs that use your existing lower and a new upper to shoot a monster round.

Most beat the snot out of the shooter and the gun. None have good reputations for either accuracy or long term durability.

And really, WHY do you feel the need for a .50 caliber?
There are other calibers out there that can reach as far, thump quite well, and don’t cost nearly as much to shoot.

Heck, my wife shoots a .243 for our 1000 yard matches and cleans house on a lot of the big bore shooters.

Unless anti material is on your agenda, it’s a waste of money and time.

Bigger is not always better.

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Just be glad I didn't ask if I could put 556 in a 223.

Thanks all for the good info!