I have a safe full of race guns and practical SHTF arms and am now looking to build something purely for fun.  One of my SBR'd lowers already has a 7.5" upper chambered in 6.8 SPC as well as an 11" upper chambered in 5.7x28.  Instead of a whole new gun I was thinking of just building another upper but this time something that would vaporize cinder blocks, bricks and the like.  I would also like to keep this upper short, say 10.5" to 12".

The two obvious choices would be a 50 Beowulf or a 458 SOCOM.  I know nothing about either.  As far as ammo goes I would be reloading my own rounds so availability of brass would be a consideration.  Does either round use AR mags with standard 5.56 followers or am I going to have to stock completely different mags?

Any recommendations and help would be greatly appreciated,
MadDog

Finding brass for either one will be a challenge, and not cheap.
Even finding loaded ammo is a chore.

The beo uses regular mags with differet follower, the 458 uses unmodified gi mags.
I heard pmags are too narrow in front to use.

458 has a ton of bullet choices because it is same as 45-70.

both hit hard. Both are pricey. Both are alot of fun.

458 is the answer

Why?  Can you be more specific?

Both?

More common projectiles, more projectile variety, standard AR mags with standard followers.

Everything from ~100gr aluminum projectiles to the nasty TTSX, to 400+gr banded solids.

This.

OP, have you shopped for either one?  I would wait a while.  People want thousands for uppers right now.  

http://www.gunbroker.com/Auction/ViewItem.aspx?Item=379209082

I would go with a 450 Bushmaster right now.  Have had ammo on the shelf for it for the last 12 months at our local Academy.  Even through the drought.  I don't reload, however.  Need to terribly.  

I am a Beowulf guy, but haven't seen any ammo for it in a long time.  Speaks with authority, hits like a brick.  Just fun.  

Doc

Please do a search or two because, honestly, this has been asked literally dozens of times.  Visit both caliber specific forums and that will help a lot.  Just sort through the personal biases and sort the facts.
I favor the SOCOM and have 4 of them and am building a fifth.  I initially wanted the Beowulf but chose the SOCOM for the following reasons.  Over the past decade of using it my decision has only been reafirmed.
.458 S:
Headspaces on the shoulder so crimp and case length is less critical.  A short case is not a ruined case.
Bullets from 100 to 600 gr.  Over 100 choices of .458 bullets from Midway alone, and that does not include a bunch of smaller bullet makers like Lehigh.  
Uses UNALTERED AR mags.
Uses standard AR parts.  Standard buffers and springs.
CAR or handgun gas, stay away from midlength gas because the rifle gets the best performance from fast powders and they do not often work well with midlength gas.
The bottleneck case feeds smoother and is less affected by feed lip differences.

Same thing here as far as ammo at Academy, only possible issue is that .450BM uses .451 projectiles, which are handgun projectiles, so your selection will be lightweight and most are not designed to perform at the much higher velocities.

That use to be true but is not any longer with the advent of the .460 S&W (.450 Bushmaster) and .500 S&W (.50 Beowulf).  That was a huge reason I went to the SOCOM over the Beowulf because there were no bullets in .50 caliber that were designed for such high (relatively) velocity and the .460 and the .500 had not even been dreamed up yet.  With the introduction of .500 and .460 bullets with heavy jackets the worry about the bullets blowing up is no longer an issue.  But there still is nowhere near the variety of bullets offered in .500 caliber as there is in .458, enough for most shooters, yes, but still not anywhere near the variety as in .458 caliber.

All of the 458 bullets can be swaged down to 451 if you so desire, they work fine for the 450B.

I went with a .50 Beowulf for several reasons...I like the idea of having a true .50, I already have a Grendel so it needed a sibling, I've dealt with Alexander Arms in the past and they are fantastic people (especially Bill), there are plenty of .50 caliber choices for reloaders, there's more variety of Beowulf ammo than I could ever need, the ammo isn't any harder to find than any other big bore during these times (it was was quite easy to find before the shortage and will be afterwards), it's TONS of fun to shoot and when people ask what you are shooting they reaction is way cooler when you say it's a .50 caliber Beowulf.  There are probably a lot more reasons for me choosing the .50 Beowulf than the others but that's all I can remember at the moment.  Also mags are not an issue despite what anti-Beowulf will tell you, plain old unmodified 5.56 mags work just fine.  You'll find a lot of people who are against one or the other will include a lot of b.s. in their "why this is better" rants.  There are more kinds of .50 Beowulf ammo than the normal person would ever need (I've got several different types in my safe right now).  There are more different types of reloadable bullets than you would ever need so it really doesn't matter if one has more than the other.  Pick whichever appeals to you the most because they all are capable of making big holes and there are plenty of choices for reloading any of them either.  

Last time I took mine out we shot it at a distance for the the first time and it was banging the 100 yard steel like a gong without even touching the scope.  I was absolutely amazed by it's performance at 100 yards so I can't wait to see what she does at 200 yards (probably it's max for hunting).  It'll be my choice if i'm ever in big bear country or get to hunt giant moose or buffalo or Yeti's.  Personally I think it's the best of the bunch but they will all put a big hole in a pig so it just depends on which you prefer, you are going to get  big boomer out of them all.

Brandi is correct..The 50 Beowulf overall would be your better choice..i have owned and reloaded both calibers and  I sold my 458 Socom..The 458 brass and factory ammo is extremely hard to get and.Brand new factory ammo cost double the amount vs the 50 Beowulf..the ballistics are very close to each other but the 50 Beowulf has the slight advantage using  factory ammo around the same weight ..please check the link with manufactures testing both of them.. http://alexanderarms.com/images/2013catalog/index.html#p=26 ..Also whomever said that the 458 socom has more bullet choices was telling the truth if he or she were to say that several yrs ago........but in todays market this isn't so ..Things have changed dramatically with more than 30 different choices of 50cal bullets available..some of the large manufcaturers like federal, Winchester, hornady, speer . Remington, Power Belt ,Sierra , berrys manufacture  and, Barnes have been making bullets for 50 cal guns that can hold up to velocity tolerences over 2000fps....In all reality you really don't even need more than 9 choices of bullet types if  you are an average hunter..If you decide on a caliber for large and dangerous game..both the 50 beo and 458 Socom will do the job just fine..but if you want something a little bigger and wanna save some money and you are not a reloader the 50 Beowulf would be the way to go..Here is a pic of my 50 Beowulf  10.5" SBR  http://imageshack.com/a/img196/4670/vp7z.jpg http://imageshack.com/a/img802/2366/ve7d.jpg http://imageshack.com/a/img547/2589/cztl.jpg

Voonman:  the original poster here, say, who built your upper?  I am leaning towards he Beowulf and want the upper to be 10.5" regardless of the caliber.  Is Alexander Arms the only company making these uppers now?

458 brass is not that hard to get . just place an order and get in line when they make a run it will come to the door .

^^^ This^^^

^^^And That^^^

If the 458 was more available I would go that route, but with such limited sources of ammo and brass I would opt for the 450B as the Hornady ammo is plentiful and relatively cheap.

My upper is built by Alexander Arms..It was originally 12" but I was not comfortable with that length..so I gave it to my master gunsmith and he put my barrel on a lathe and cut it down to 10.5"..there was no need to open up the gas ports or change the buffer spring..everything still worked great without and jamming or failure to feed or eject..I am glad I went this route...My Beowulf is my number one choice for dangerous game when I go hunting..By cutting it down another 1.5" i only lost 30fps in velocity... Here are some links with uppers readily available in stock..  http://www.midwayusa.com/product/171578/alexander-arms-ar-15-pistol-a3-upper-assembly-50-beowulf-1-in-20-twist-12-barrel-matte-with-m4-handguard-pepper-pot-muzzle-brake-10-round-magazine?cm_vc=subv1316928   .... https://www.saodind.com/uppers-specialty/ar-15/ar-15-sbr-upper-10-5-inch-6-5-saod-upper-detail

voonmam:

Does the rail system on yours fit "over" the stock railed gas block or did you have to change it out for a low profile gas block?  What rail system is that?  I like the looks of it and would probably go with that but a little longer if they make them as I am going to stick with the 12" model and go with the Tank Brake.

MadDog

Hi Mad Dog

The Bilevel rail system I have on mine is made by A.R.M.S and it is a midlength rail that fits over a low profile gas system  ..They make there rail systems exclusively for the US military ..Barret Firearms  and of course the public ..Ive seen black water snipers use this on there missions..it holds zero very well and is probably one of the most durable rails you can buy on the market.. The problem I had with buying it was the price I had to pay..They are pretty expensive.  .Brand new they run about $450 for the bilevel S.I.R Rail system..Here is the link to there website.. you can find the various sizes that will suit your needs..  http://www.armsmounts.com/default.asp?mode=products&sub=rails  ....Also in my previous post I posted a link to where you can purchase a 12" upper that is currently available in stock from Midway USA..Also Just to give you an idea on 50 Beowulf Factory ammo prices vs 450 bushmaster and 458 socom look below

458 Socom 300Gr 20rds priced at $65.99      http://www.midwayusa.com/product/531624/sbr-ammunition-458-socom-300-grain-barnes-tipped-triple-shock-x-bullet-lead-free-box-of-20

50 Beowulf 350Gr 20rds Priced at $26.99     http://www.midwayusa.com/product/721544/alexander-arms-ammunition-50-beowulf-350-grain-hornady-xtp-jacketed-hollow-point-box-of-20

450 Bushmaster 250gr  20rds Priced at $30.99      http://www.midwayusa.com/product/979384/hornady-custom-ammunition-450-bushmaster-250-grain-sst-flex-tip-expanding-box-of-20

http://alexanderarms.com/images/2013catalog/index.html#p=26

voonman:

I can't see your gas block.  Is it the stock railed block that Alexander Arms used on their uppers or is that too big to fit underneath?  If you swapped it out for a low profile, whose did you use?  Isn't the inside diameter of the gas block something like .906"

MadDog

I had mine custom built by alexander arms using a low profile gas block.The standard railed gas block is too big and it would not fit under the ARMS Sir Rail System.For you to get this done..you have to call alexander arms directly to custom build it and let them know what you want..because they don't advertise it on there website..the diameter is 0.907

This is mine...Alexander Arms Lower, the upper was sold to me as an AA upper but was not marked AA (although it may be one of AA's first made uppers when they were just coming out which would be cool) regardless it is so accurate looking at the target the first time made me question what just happened but, fortunately, I've found she is just plain accurate.  Mine is mostly stock except I added a King Armory KA-0450 muzzle brake, a Daniel Defense free float rail and a Leupold VX-R Hog 1.25-4x20 with FireDot scope, Magpul CTR stock with LimbSaver recoil pad (not shown).  It is an awesome shooter and unbelievably accurate.

There are a lot of different things you can do with your Beowulf..i made a little sbr bug out kit..this is my Beowulf before I cut the barrel down in its pelican kit..

https://www.youtube.com/watch?v=zHTMl91Fpjo