Analysis: .277 Sig Fury - Inside MDT

Posted by David Henry on 2023 May 4th

Analysis: .277 Sig Fury - Inside MDT

.277 Fury

Alright, if you haven't heard the news, the .277 Fury is a center-fired rimless bottleneck rifle cartridge announced by Sig Sauer in late 2019. It's a hybrid three-piece case with a steel case base and a brass body connected by an aluminum locking washer to support chamber pressures of 80,000 PSI. I know what you're thinking '80,000 PSI in a rifle cartridge? That's pretty crazy!' And that's the reason for the design of the three-piece case. They have the brass as the bottleneck portion so they can expand to the chamber and make a tight seal and the steel case base to hold all that pressure inside the chamber as that rocket takes off.


Sig Sauer designed the cartridge for the US Army's next-generation squad weapon program. This cartridge was announced for nonmilitary use along with the Sig Cross (a bolt action magazine-fed rifle) in December 2019 as a short action cartridge with increased internal ballistic performance. In 2020, it was accepted by SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) as a new cartridge. In 2022 Sig announced that they intended to chamber the MCX-SPEAR rifle in the .277 Fury commercially.

Sig claims the cartridge performs superior to the 6.5 Creedmoor, exhibiting up to 9 feet less drop at 1000 yards while delivering 25% greater energy. Sig has listed a Sig Fury Hybrid Elite bonded polymer tip .277 ammunition firing off a 150-grain bullet at 2,833 feet per second with a 16-inch barrel. Stretch that out to a 24-inch barrel, and you're over 3,120 feet per second. The energy produced from this round in a 16-inch barrel is over 2600 foot-pounds, and the 24-inch is over 3200. This is no joke! It's a serious contender in the short-action cartridges.

There are a few other options that Sig offers for this .277 Fury, such as; an elite ball full metal jacket that comes standard with the elite match brass case and pushes 135-grain bullet at over 2700 feet per second with a 16-inch barrel. They also list 130-grain soft-point hunting bullets.

For the extra velocity that Sig is getting out of their hybrid case, the .277 Fury is awesome, especially if you want to run it in a short, barreled rifle. Their example of a 16-inch rifle barrel running over 2700 feet per second with a 135-grain bullet is pretty impressive. As an avid reloader, seeing that 80,000 PSI makes me a little nervous. But Sig is doing a lot of maneuvering to ensure they design a case capable of holding those pressures and being approved by SAAMI. This might be a winner!

Sig XM5/XM7 Rifle

Sig XM5/XM7 Rifle.

The US military thinks it's a winner because they awarded Sig a few contracts with this cartridge. In April 2022, the US Army announced they selected the Sig XM5/XM7 rifle and the .277-fury ammunition to partially replace the M4. Just for a little insight, the ammo Sig produced needed to match the accuracy and penetration to pierce body armor out to 500 meters and use a 6.8 mm projectile. The .277 Fury was Sig's concept and was designed for the program, which worked out for them. The round was accepted by SAAMI in 2020. Then the round, along with the company's XM5/XM7 and MX250 LMG rifles, were adopted by the US Army in 2022.

I previously mentioned the pressure of 80,000 PSI- just for a little contrast, the 5.56 NATO is another round, roughly 75% that of the .277 Sig round at 60,000 PSI. How about the 6.5 Creedmoor or the .308? They have only slightly more pressure than the 5.56 at 62,000 PSI. Even the big magnum cartridges like the .338 Lapua at 60,000 PSI don't come close to the pressures allowed in the .277 Fury.

SIG 277 FURY will feed from a short action AICS magazine. Pictured is an XM5/XM7 with an AR-10 style magazine.

SIG 277 FURY will feed from a short action AICS magazine. Pictured is an XM5/XM7 with an AR-10 style magazine.

I don't know about you, but Sig is creating some waves in the military arms category. First, the release of the P320 took over many of the sidearms of the military and law enforcement, and now the Sig Spear, or XM5/XM7, chambered in this revolutionary cartridge pushing insane velocities with super high pressures. With the advanced case designs, Sig is pushing the boundaries and making the next-generation rifle just one step better than the last. It's awesome to see innovation in cartridge technology to increase performance. This is another cartridge that I might have to look at, as it would be fun to play with those kinds of pressures and see exactly what we could do with a custom build.


If I were to build a Sig .277 right now, I would start with an MDT XRS with the XRS enclosed forend, M-Lok Arca Rail, and CKYE-POD. I would drop in a Falkor 7EVEN short action with a 16"Hells Canyon armory Ultralight SUMMIT Carbon Barrel. Then I would use a Triggertech Diamond Two-Stage trigger. Next, let's look at the glass. A NightForce ATACR 4-16x42mm F1 with the Mil-XT would be sweet sitting in an MDT one-piece scope mount. I would use the MDT .308/6.5 Creedmoor Metal AICS 12-round mag. Then last but not least, let's top it off with a Mission Silencers 1.5 LPR (Long Range Precision). What would you build?

Author would start with an MDT XRS for his SIG 277 FURY build.

Author would start with an MDT XRS for his SIG 277 FURY build.



I have 20+ years in the automotive industry- first managing shops in the northwest for over 13 years and now as a factory rep for Hunter Engineering. I love my family, my faith, and my firearms. I've shot competitively in the PRS southwest region for two years. I also compete in long-range AR-15 competitions at least once a month and am an avid reloader. I have written for Ballistic Magazine's 'Ballistic Best' precision rifle edition for two years. My other hobbies include photography, videography, woodworking, and knife-making. You can find me on Instagram @davidinthesun


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