By Dan Shea

In the 1970s-80s, there was a movement in the U.S. to create rifles in .50 BMG (12.7x99mm.) .55 Boys rifles were converted, the magazine and barrel were close to the dimensions, 20mm Lahtis were as well, and a few extremely dangerous designs were showing up at civilian shoots with the incumbent accidents. Gunny Carlos Hathcock had famously made three kills at 2500 yards with “Ma Deuce” in Vietnam (only one confirmed), an M2HB with a craft-made mount from the SEABEE chop shop, for his 8-power Unertl optic. This author has seen cobbled together .50 cals all over the world from the revolutionary groups in South America to communist guerillas in Africa, mostly from the 1950s-60s. But it wasn’t until 1983 when a shooter/inventor named Ronnie Barrett showed up at the Knob Creek Machine Gun Shoot in Kentucky with his M82, that the idea of a semi-automatic .50 BMG sniper rifle could be taken seriously. At the time, this author was blown away by the functionality of Ronnie’s design, and I’ve had a long history with these rifles; shooting, training, armorering, supplying, use in the field OCONUS… and on this visit to the factory, I spent a few days with Ronnie and Barrett’s engineers with the intent to bring you this technical article on the M107A1- introduced in 2011- about what makes the M107A1 what it is today, an advancement beyond the M82A1 and M107.

By 1989, Ronnie Barrett’s M82A1 rifle was making serious waves in military circles; the Swedish Army ordered 100, and various “OGAs” (other government agencies) were taking notice and buying them. In 1990, the U.S. armed forces were making special buys, the Israeli Defense Force and others were lining up. The M82A1 was a hit with operators; it did a job they needed done, better than any other small arm. It had amazing range and impressive terminal ballistics. The U.S. Army adopted the M82A1 as the M107 in 2005 (with a longer rail and other mods), and Barrett immediately started on a quest to lighten the system, improve the recoil pressures, and make the new design suppressor friendly – the M107/M82A1 cannot reliably or safely use a muzzle sound suppressor. More on that below.

NIOA ACQUIRES BARRETT FIREARMS

M107A1 : THE GREAT LEAP FORWARD

Typically, in the firearms industry, we discuss aluminum using the 4-digit system- there is also a 5-digit system which is more precise but not prevalent. 7000 series aluminums use zinc as their main alloy element. The next three digits indicate an agreed-on mix of other alloy metals. The common example in firearms manufacture, especially AR-15 type firearms, is 7075, a WWII Japanese alloy mix adopted by the U.S. and others. It has a lot of advantages, one of which is its ability to 11% stretch without cracking. The second nomenclature for this would be “T6” which is a temper. 7075 T6 aluminum would have 5-6% zinc, 2-3% magnesium, and 1-2% copper, as well as some other small metal quantities. The zinc and magnesium making the alloy heat treatable. The “T” designations are temper processes for heat treatable aluminum alloys. In this case, T6 means that the 7075 was “Solution Heat Treated” then artificially aged. Solution Heat Treating means to heat the alloy just under its melting point, and some planned lower percentage alloys dissolve into the aluminum, creating a “solid solution.” The material is quickly quenched and preserves the new metal structure. 7075 age-hardens naturally, so if welded properly, the heat-treating recovers.

Why discuss this? Because Ronnie Barrett wanted to lighten the M107/M82A1 system and the first place to start is the upper receiver – a very large component. Barrett did not choose 7075 T6; it would be the wrong temper for the job. It’s difficult to extrude into the needed shape, it suffers a lot of internal stress which can cause deformation in processing, and it would not have the structural strength to match the cold-rolled 1045 steel in the M107/M82A1 upper. 1045 is a medium carbon steel that is very strong, with a high yield point (about 45,000 PSI). A lot of machinery parts, bolts, gears, shafts, etc. are made from this. It’s a good steel, especially for a long channel like the M107 upper.

Trying to match that strength with an aluminum alloy that can be extruded in long shapes to cut to length and machine is difficult and “7075 T6 isn’t it.”

Barrett’s engineers developed a scientific testing method with weights and distances to match the yield point of 1045 steel with a reasonable thickness, extrudable aluminum alloy, and they decided on 7075 but with a T6511 temper. The T6511 temper adds stress relief by stretching along with the solution treating and artificial aging. Perfect for the job; extruded, machinable lengths that won’t distort in machining.

The new 7075 T6511 upper receiver is finished with a type-3 hard-anodizing and then an oven-cured Cerakote finish, which matches durability with the M107/M82A1 1045 steel finished with a manganese phosphate parkerizing.

Front is the M107A1 showing the optic rail is milled into the aluminum extrusion, with allowance for a bolt-in-place rear back up sight. Rear is the M107 steel optic rail bolted in place, with the rear back up sight mounted on the rail. The optic rail on both the M107 and M107A1 is angled at 27 MOA. 

This new upper receiver was just the first of the techniques used to lighten the M107 system and create the lighter, suppressor-friendly M107A1.

As part of the lightening process, the bipod yoke, yoke mount, and the internal shaft of the bipod are made from titanium for the M107A1. The foot for the bipod legs is plastic for the M107A1. The M107A1 has plastic flat feet, the M107 has steel spiked feet, and the 82A1 has steel flat feet. Note the quick release pins must be put in from the rear, as recoil forces can dislodge them if they are inserted from the front.

M82A1/M107 top, M107A1 bottom: Some of the most important changes that were made were in the recoil system. Barrett’s M82A1/M107/M107A1 operate on the short recoil principle; i.e. the bolt and barrel are locked together and travel in recoil a specified, short distance/time until pressures have dropped, then unlock from each other and recoil and return separately. The first thing to notice in this picture is that the barrel springs in the M107A1 have a larger wire diameter but have a smaller overall outside diameter. Due to the smaller outside diameter of the barrel springs, the barrel spring relief cuts in the barrel were removed to aid in making the barrel stiffer. The M82A1/M107 barrel has the two deep grooves, the M107A1 barrel does not. Second, the impact bumper – the plastic cylinder behind the barrel key – is longer on the M107A1; this shortens the stroke for the barrel recoil. The (return to-) battery bumper is the same for all.

Top in each picture, is the M82A1/M107 bolt carrier assembly, bottom is the M107A1. Note there are several more cuts/wells in the M107A1; this is for the bolt extender, which is critical for suppressor use.

SOME BALLISTIC TALK ON .50 BMG & TRANSONIC SHIFT

Shooting at long ranges requires extensive understanding of exterior ballistics – from the projectile uncorking from the barrel, to striking the terminal end, as well as all the environmental factors that are constantly changing. There is a lot of information out there to digest, and we don’t have time or space to explain it all but there are a couple of things relevant to the subject of this article to start with. First, the Barrett rifles were designed to fire military ball ammunition back in the times when that was all there was. M33 Ball with a 660-grain (42.8 gram) FMJ boat tail bullet with a mild steel core. Fired in a 45-inch barrel from an M2HB machine gun, its muzzle velocity was 2,910 fps. In today’s world, there are many options – solid, turned, very accurate bullets, of 750 grains and other weights. These are designed for accuracy at long ranges, and are fired from 20-, 29-inch or other barrels but not the 45-inch barrel of “Ma Deuce.” Thus, velocity comparisons must be apples-to-apples – barrel length, rifling twist, etc. to understand at what distance the supersonic projectiles will drop into the zone approaching the speed of sound – the transonic region – and below, the subsonic region. Larger projectiles like .50 Browning Machine Gun (BMG) rounds are less affected by environmental pressures than smaller diameter/weight projectiles; but there is still an effect on accuracy.

When people are discussing calibers in comparison and make statements like “.50 BMG destabilizes as transonic at 1320 meters,” it’s inaccurate. There might be a combination of barrel length, bullet weight, etc. that does, but the U.S. M33 from a 45-inch barrel goes transonic in the 2200-meter range according to longtime military data, however today’s ballistic calculators show it at 1500 meters and a 750-grain AMAX bullet may go transonic much further from a 29-inch barrel. There is much more to it than simple calculations. A skilled shooter knows more than just the math, he reads the wind and everything else in the theatre he’s firing through and into. Hitting targets well beyond that theoretical transonic distance is both science and art, and is done frequently – look up “The King of 2 Miles” competitions.

WEIGHT:

• Weight M107A1 unloaded: 28.7 lbs (13 kg)
• Weight M107   unloaded:  32.7 lbs (14.8 kg)

BALLISTIC PERFORMANCE WITH M33 BALL AMMUNITION:

• 20-inch (508mm) 1:15 in. (381mm) 2,550 fps (778 m/s) Transonic at 1300m
• 29-inch (737mm) 1:15 in. (381mm) 2,799 fps (853 m/s) Transonic at 1,450m
• 45-inch M2HB:  1:15 in. (381mm)  2,910 fps (890 m/s) Transonic at 1,500m

FEEDING THE BEAST

One of the hardest parts of designing a firearm, is feeding the rounds into the chamber properly. It’s pretty basic on a straight-pull single-shot rifle, but when you go semi- or fully-automatic, there are many forces that come to bear. It’s not just a case of presenting the cartridge properly to the feed ramp, it must be done fast enough so that, as the bolt goes into recoil, the spring consistently presents the next round for feeding. Spring fatigue is also an issue. This can be a lot trickier than it seems, and it does explain why many firearms inventors adopt existing magazines, such as the M16 style for 5.56mm. In Barrett’s case, he had to deal with the length and weight of 10 rounds of .50 BMG cartridges, a much different animal than the 5.56mm.

MARKINGS

SUPPRESSING THE M107A1

Barrett and other knowledgeable people continually warn against firing the M107/M82A1 with a suppressor – it just isn’t safe. But some users have done this. There are a number of references in this article regarding upgrades to M107A1, and they all add up to: The M107/M82A1 system is not designed for suppressor use, which changes recoil forces, time of locking and unlocking, pressures, velocities, etc. While these rifles are robust, and some have successfully fired them, Barrett cannot guarantee their product with suppressor use. That is what the M107A1 is for – it has been purpose engineered to withstand these forces. I’ve had several people tell me about using a suppressor on the M82A1, each unaware of the real dangers involved and one manufacturer who explained his suppressor “worked” as is, and when pressed, he had made modifications to the rifle that would void his warranty and frankly, I did not see how they addressed the issues involved. It’s best to purchase the proper rifle for suppression, the M107A1, which is properly engineered for this. There have been charging handle impacts damaging the upper receiver, and broken bolt handles. One thing to remember – the recoil forces of putting a suppressor on an M82A1/M107, can easily warp the bolt latch into failure. That is a negative event…

The arrowhead muzzle brake designs used on the M107/M82A1 work very well for mitigating the recoil force with  rearward gas energy; approximately 70% reduction in recoil. In order to make the M107A1 suppressor-friendly, the design had to change so there could be a quick mount suppressor, which is the round one in the three photos here.

We at Small Arms Defense Journal hope that this focus on the Barrett M107A1 and its technical upgrades helps you in understanding the quality of this product. We have long experience with the Barrett systems, and there are quite a few misconceptions about why the M107A1 was needed- hopefully, this helps the readers and users understand the great leap forward the M107A1 is for the .50 BMG Sniper systems.