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Store » All Pistol Cases

#3055 - 12.7x42mm Brass (Magnum Large Pistol primer)

The 12.7x42mm is a powerful big bore cartridge designed for use in AR style rifles. The brass case is essentially a lengthened 50 AE (1.650 long) with a rebated 7.62x39 style head. This brass case is designed to use a large magnum pistol primer.

.50 Beowulf®, Beowulf®, .50 Beo® and Beo® are registered trademarks of Alexander Industries Inc., and are in no way affiliated with Starline Brass®

**WARNING** In firearms that use a floating firing pin (such as the AR-15 and its variants), dropping the bolt on a chambered round could lead to a slam fire. It is important that these firearms are loaded from the magazine so that the bolt loses inertia when it strips a round from the magazine. It is also important NOT to use sensitive primers that aren’t designed for use in an AR, as this increases the chance of a slam fire.



  250 for $192.50
$0.77/each

  500 for $355.50
$0.71/each

  1000 for $687.50
$0.69/each

* Starline Brass does not sell any loaded ammunition. What you are purchasing are brass cases only and will need to be loaded into ammunition in order to be fired from a firearm.


Average rating

4.7 / 5


Rate This Product

Rating breakdown

5
86%
13
86%
4
6%
1
6%
3
0%
0
0%
2
6%
1
6%
1
0%
0
0%
Kevin Weiland
HOMESTEAD, FL
January 24, 2021
Product Review
This is a great alternative to Alex. Arms. Brass.
Michael Mabe
Walnut Cove, NC
July 20, 2020
Product Review
I have reloaded quite a few of the same cases more than 15 times so far. These cases are really top quality as is all of Starline's brass that I have used. If you're going to reload, invest your money in quality brass. And in my opinion, Starline is leading the way in manufacturing top quality brass.
Jeff W.
Santa Maria, California
March 03, 2018
Product Review
Best brass for a reasonable cost. Dont over crimp the 50 Beowulf rounds, i had a couple of split cases when i first started loading the caliber (happened with both S.L. & A.A. brass). No issues after backing off the crimp. Starline brass is holding up well after multiple reloads. I recommend starline brass to everyone that handloads. Keep up the good work and reasonable pricing, you will have many more life long customers!
Roy Vanas
Muskegon, Michigan
October 12, 2017
Product Review
I recomend Starline Brass for loading .50 Beowulf rounds. I have ruined a few cases during the loading prossess because of my errors not the brass. I check every case before starting for any imperfections and during and inbetween prossesses and have never found a single manufacturing error. When I do find a flaw it has always bee because of my doing.
Peter Hofius
Excelsior, Minnesota
June 13, 2017
Product Review
Bought 250 11-12 years ago. Have reloaded them numerous times and am down to 211 cases. They are starting to separate at the base.. Couldn't be my max loads. Figure that in another 5-6 years I may have to get another 250. Starline has the best brass of all calibers I've ever used.
Larry Dixon
Tecumseh, Kansas
April 27, 2017
Product Review
the Beowulf brass has the great quality that all other brass I have purchased from Starline over the years I give it 5 stars
Neil Tillett
Bartlesville, Oklahoma
September 24, 2016
Product Review
I have been building and shooting 59 Beowulf for more than five years. I use star line new brass on it and many other calipers. 50 Beowulf is longer than 500 SW. Don't try to modify the SW case. It's not worth the effort and the cost is the same! Get the Beowulf brass and load it and go! It has proven to be accurate and durable brass! Thanks Starline
Mark Austin
Madison Hgts., Michigan
June 16, 2016
Product Review
I've never had any trouble with Starline brass. I've reloaded it countless times. I have no idea why Jeff F of Houston, Texas thinks that 500 S&W brass is cheaper (it's not) . 250 cases for $170 is about $14 a box. I think it's reasonable \_0_/
Dale Balzer
Fargo, North Dakota
June 15, 2016
Product Review
Called Alexander Arms to ask about this brass, they told me that Starline Brass is one of their suppliers for the brass that they use and sell. So, yes, this is great brass. Especially if the manufacturer uses, sells, and recommends it.
Randy Oldfield
Newport, Washington
May 19, 2016
Product Review
Recieved in only a few days - looks wonderful
Dwayne Deininger
Sumter, South Carolina
May 18, 2016
Product Review
Almost 5 Stars but it seems like I get at least 4 to 5 per box of 50 that crack after first time they are shot. I dont blame Hornaday its just what happens when a small rim case is expanded to that dia
Lane W
college station, Texas
May 28, 2015
Product Review
I never had any issues with the brass I got from starline brass I've reloaded for my Beowulf from day one and re used the brass more times than I can count its very good
Jeff Fox
Houston, Texas
January 23, 2013
Product Review
Way to expensive for what this isnt. The death of this cartridge. Get some 500 S&W cartridges and trim the rim. Way cheaper. At this price it's laughable, almost shameful. 2 stars, good quality, horrible price
Bob D'Ambro
Mechanicville, New York
December 30, 2012
Product Review
First time reloading,brass measured up great,no problems
Andy Lunemann
Pinedale, AK
December 02, 2012
Product Review
Great product all under max lengthe Loads well no damaged rims. Re loaded several times and no signs of wear yet.