It is no secret that the 7.62x51mm NATO cartridge continues to be the most widely used cartridge for combat sniping among NATO countries and likely throughout the world. But that dominance has been challenged recently by the adoption by more and more countries of rifles that use the extremely capable 338 Lapua cartridge. The USA has actually taken a different path to enhance the capability of the 7.62NATO and has adopted the venerable 300 Win Mag for its modern long range sniping rifles. The 300 Win Mag in its current form has a history of military sniping use in the USA of nearly three decades now, but most people do not know the history of the development of the 300 Winchester Magnum as a sniping cartridge. We thought it would be worth while to take the time to explain the interesting history of the 300 Winchester Magnum and its use as a sniping cartridge. We have attempted to provide a brief, semi-thorough historical account of that history here.
To begin, let us cover a very short history of the cartridge itself. The 300 Winchester Magnum, which we will refer to simply as the 300WM, was introduced by Winchester in 1963 as a magnum class cartridge that would fit in a standard length and sized action. The cartridge is based on the .375 H&H magnum case that has been shortened, blown out, and necked down to .30 caliber. Because it is based on the 375 H&H, it means that the case also has a belt near the case head and is referred to as a “belted magnum”. The head spacing of the barrel is traditionally done off of the belt and not the shoulder which can make it a bit more difficult for 300WM rifles to get the best accuracy, though specialty and production gun makers have their own means of overcoming this challenge. The 300WM remains a very popular choice among hunters even with the advent of more powerful 30 caliber cartridges like the 300 Remington Ultra Mag (RUM). This popularity of the 300WM is for a good reason as it offers plenty of power for big game hunting of all types and there are plenty of rifle and ammunition options available.
The 300WM shoots the same 30 caliber projectiles as the 308/7.62 cartridge, but at a much higher velocity and typically with heavier weight bullets, and this has even lead to the 300WM winning its fair share of 1000 yard competitions and Wimbledon Cup Championships. The legendary sniper Carlos Hathcock used a 300WM to win his Wimbledon Cup in the 1960’s before he went on to become a sniper in Vietnam. Because of its long range capabilities, the 300WM had caught the eye of the military on a number of occasions for use as a sniping cartridge, but it was not until the 1980’s that it was examined seriously as a candidate for a sniping rifle.
The Developmental Years
The story of the 300WM use for military sniping begins in the 1980s and with the US Navy. The Navy had been looking at several different cartridges for use with both their competition shooting team(s) and for sniping use (USMC and Naval Special Operations). Initially they actually had played with some wildcat cartridges as well as others and none of them really met their fancy. In the late 1980s, their attention switched to the 300 WM for a number of reasons including the fact that it was commercially produced in large quantities and commercial weapons suitable for military use were easily procured. As we mentioned above, the cartridge also had a track record of success in long range match competitions. Beyond the US Navy shooting team, the other primary interested party was the Naval Special Warfare Forces, in other words, the SEALs. The Navy decided that a single configuration of the 300 WM cartridge would be developed to satisfy both parties.
The Navy set out to develop this new loading to satisfy multiple requirements that included:
- Projectile had to be consistent with the Law of War obligations (No “dum-dum” or expanding bullets)
- Chamber pressure had to be within SAAMI limits at 70F, 125F, and -40F
- Velocity was to be maximized while staying within those SAAMI pressure limits
- 10″ extreme spread at 1000 yards was desired, 15″ extreme spread was required
The interesting thing about this original load was that in an effort to increase case capacity and to reduce the bullet jump, they decided to use a max overall case length of 3.50″, which is in excess of SAAMI overall length specifications, but yet it would still fit in the magazines of most 300WM rifles. Additionally, the round was intended to be used in McMillan M83, McMillan M86 and Remington 700 bolt action rifles.
The Navy utilized Crane and the NavSea group to do the research and development on this load and they put it out for bid and awarded the initial contract to Federal Cartridge for a 180gr FMJ load at 2950 fps. The testing requirements were 8″ extreme spread at 600 yards and 3.5″ at 300 yards, but due to constraints this was changed to 2.3″ at 200 yards. The initial Federal load used a 180gr Sierra MatchKing HPBT bullet with the tip spun shut to be considered a FMJ. The accuracy and velocities were within spec and the first lot was procured and fielded in 1988.
Unfortunately, it was discovered by the marksmanship teams, and then verified by the Naval Special Warfare personnel, that the tip of the bullet was causing the bullets to become unstable after 800 yards and that at 1000 yards the bullets were tumbling. Additionally, the Navy JAG ruled that the projectile was not acceptable for combat use based upon the appearance of the open tip design, despite the burnishing. So it was back to the drawing board to come up with a new solution for a 300WM sniping cartridge.
As an interim solution and test, some Lapua 185gr bullets were pushed into place of the same loads that had the 180gr SMK bullets and an average velocity of 2930 fps was obtained at 70F. This load also produced acceptable accuracy with an extreme spread of 9.1″ at 800 yards and 15.4″ at 1000 yards and a bonus was that it actually dropped 14″ less at 1000 yards than the 180gr SMK. This lead to the awarding of a contract to HSM in Missoula (now Stevensville) Montana for a 300WM load using the Lapua 185gr (D46) projectile and IMR4350 powder. The average velocity actually ended up being about 3000 fps with very good accuracy at 200 yards, but the pressures exceeded SAAMI spec at 125F and the 800 yard accuracy was not adequate. At this point the Navy decided to try and develop a better projectile for lower pressures and better long range accuracy. At the same time, the Army JAG ruled that the 168gr SMK bullet was acceptable for combat use because the open tip was not intended to increase the wounding capability and was for accuracy only. All of this lead to the development of the Sierra 190gr MatchKing bullet to be used instead of the Lapua 185gr D46.
Several different loads were tested using the new SMK 190gr bullet with several different powder types to determine the best velocity, pressure, and accuracy combination. The two powders that provided the best results was Reloader 19 and Reloader 22 and the resulting load included commercial brass and match primers using the Sierra Match King 190gr projectile. In 1992 this load was approved and a procurement action was initiated. The average velocity or the initial 20,000 tests loads was 2937 fps with very acceptable pressures and accuracy (2″ mean accuracy at 200 yards). At that point the type classification tests were conducted and passed and the cartridge configuration was defined by HS/2024/C91/621 and was authorized for use in combat by snipers on 23 Nov 1993 by both the US Army JAG and the US Navy JAG. The cataloging information was assigned as A191 and it is this load that is the foundation of the 300WM sniping ammo for the USA. The US Navy shooting team had improved performance with the load and the special operation snipers and others have had good success with the A191 load in combat at ranges out to, and even beyond, 1200 yards. The Federal Gold Medal Match 300 Win Mag load with 190gr SMK is an example of a commercial equivalent of the A191 military load and has become a popular long range load in the civilian market as well.
Improving the Foundation
There were various rifles used by the Special Operations crowd chambered in 300WM, but nothing that was widely adopted until after the war on terror began. The USMC used their Mk13 Mod5 300WM rifles and the SEALs had their various custom built platforms as well. Then the US Army got into the mix on a larger scale with the adoption of the M2010 converted sniper rifles chambered in 300WM. It was at this point that once again Crane and the NavSea group took charge on developing a Product Improvement (PIP) on the A191 300WM cartridge. Initially they were tasked with developing a .338 Lapua load to extend the range of US snipers to 1500 yards and beyond. After testing various configurations of the 300WM and the 338 Lapua, as well as discussing it with industry experts, they determined that they could meet the new objectives with the 300WM instead of the 338LM. What were those stated objectives? They were as follows:
- Extend the effective range from 1200 yards for the A191 to 1500 yards.
- Decrease the effects of wind on the projectile
- Use a flash reduced and temperature stable propellant (-25F to +165F)
The team that was put together to develop the new PIP load obtained prototype ammo for the 300WM using the 210gr Sierra MatchKing VLD, 220gr Sierra MatchKing and prototypes for the 338 Lapua using the Lapua 250gr Scenar, Sierra 250gr MatchKing, and Sierra 300gr MatchKing projectiles. Once these loads were ready the accuracy was tested at 1000 yards as well as pressures and velocities measured.
The accuracy on all five of the loads were similar, except for the 300gr 338 load which did not perform well. But what the team noticed was that the 220/210gr 300WM loads had a similar velocity retention as the 250gr 338 Lapua loads. This should really not come as any big surprise since the 30 cal 220gr MatchKing has a BC that is similar to the 250gr 338 cal MatchKing. With the velocities in the mid 2800 fps range for both the 300WM with 220gr bullet and 338 Lapua with 250gr bullet, the velocities and drop are similar for both the 300WM and 338Lapua. The big 300gr 338 Lapua did do better at long ranges, but accuracy was the hold up on that particular load.
When they evaluated the results of the tests and compared them to their stated objectives for the PIP, they decided that the objectives could be met with the 300WM and at a significant cost savings over going with the 338 Lapua. The cost savings would come not only in just the ammunition expenses, but the 300WM could be used in all of the existing 300WM rifles that were in the system at that time. The decision was finalized to adopt the 220gr Sierra MatchKing bullet as it was less sensitive and finicky compared to the new to the market 210gr MatchKing VLD bullet. The accuracy with this new load was comparable to the A191 and all the other benefits were recognized from the stated objectives and a contract was awarded in June of 2009.
The new Product Improved (PIP) cartridge was adopted as the Mk248Mod1 in October of 2008 and then was superseded in March of 2009 with Revision A which modified the test specifications to comply with SAAMI specifications instead of military specs. The specs indicate the use of non coated brass and match primers. The propellant is Hodgdon H1000 with flash reduction additives. The max Cartridge Overall Length (COL) is specified as 3.500″. The specified velocity at 70F is 2850 fps +/- 50 fps. The chamber pressures are to be no more than 68,100 PSI. There are also both 300 and 600 yard accuracy requirements using 10 round groups. The loads must average about 1 MOA at those ranges using ten, 10-shot groups. This is all done from a 24″ test barrel. Note that both the COL and pressures are ABOVE the SAAMI max specifications. SAAMI specifies 3.340″ for the max COL and 64,000 PSI for the max chamber pressures but since the Mk248Mod1 is intended for military rifles only, they decided that it was acceptable.
As a comparison of the Mk248Mod1 versus the various other sniping cartridges, we include a basic ballistic chart below with the rifles zeroed at 600 yards and with the bullet drop listed at various ranges. You can see how much better the new Mk248Mod1 load does versus the A191 and how well it compares to the 338 Lapua Mag using both the 250gr Sierra MatchKing and 300gr MatchKing bullets.
|338LM 250gr SMK||+27″||0″||-168″||-335″||-747″|
|338LM 300gr SMK||+28″||0″||-159″||-309″||-656″|
With modern powders, some commercial ammunition makers such as HSM and Choice Ammunition, have been able to get the same, or very close, performance while keeping the pressures and OAL within SAAMI limits. Other makers such as RUAG have loaded nice loads with the same bullet, but about 100 fps slower than the 2850 fps of the Mk248Mod1, in order to maintain accuracy and safety. This load would still provide an excellent long range load even with the lower velocity.
The military Mk248Mod1 loads started arriving in combat zones in early 2011 and by all accounts it has been an excellent performing round for the 300WM with great long range capability. It appears that all of the objectives of this load have been met. The Special Operations crowd continues to use some additional unique cartridges such as the 338 Lapua, 416 Cheytac and 300 Norma, but the new bread and butter for the US military long range cartridge is the 300 WM and specifically the Mk248Mod1, which makes an excellent complement to the 7.62x51mm NATO M118LR rifles and capability.
Much of the information from this article came from the Crane and NavSea Group publicly available documentation and history.
Sniper Central 2017