Cartridges: 7.62 NATO Long Range Match Cartridges - Part 2

We are very pleased to bring you this three-part series regarding the development of the 7.62 NATO cartridge for long range match shooting. In a departure from our usual practice, there is significant load data contained in this series. The government arsenals and military teams using and developing these loads had pressure testing equipment, plenty of expendable rifles and plenty of replaceable recruits that they loved a bit less than their mothers did. Just about every load mentioned here other than the basic arsenal match loads will generate excessive pressure and cause damage to your rifle and can certainly injure the shooter. Read and enjoy this for its historical value but please have the common sense to realize that duplicating these loads today with canister grade powders is dangerous and should not be attempted. - GAS -

7.62 NATO Long Range Match Cartridges
By Frederick Salberta

The first long range load for the M14 that that saw wide scale issue was based on the Western 180 gr. FMJ match projectile. First utilized by the AMU before 1967, the typical load was simply a substitution of the Western projectile for the LC M118 bullet. The average peak pressures in the M118 was around 44,000 cup; with a slight increase in the amount of IMR 4895, the velocity could be pushed up closer to 2630~2640 fps without exceeding the safety margin of the M14. The exact load was never standardized, but added no more than 0.5 gr. to 0.7 gr. of IMR 4895 to get the effective muzzle velocity of the load up to around 2,630~2640 fps. Sometime in the 1960s the 180 gr. Sierra HPBT (old 9 degree boat tail bullet) was substituted for the western FMJ projectile. With the slightly better ballistic coefficient of this bullet and the slightly higher muzzle velocity, these loads would remain above 1220 fps at 1000 yards under most match conditions. This became the preferred solution of the Army, National Guard and Army Reserve teams in the pre 1975 era.


The Marine Corp does not seem to have done anything other than utilize M118 with some form of 180 gr. bullet substitution for long range until 1968 or 1969, when two new loads seem to have come out of the Marine Corps shooting team. The first load was a Sierra 168 gr. HPBT on top of 39.0 grains of IMR3031 for short range. This load was found to be very successful for matches where it was allowed. It would eventually be loaded by Federal in the mid 1970s for the Marine Corp team; becoming the Federal Gold match load in 1990 (though bumped up to 41 grains of IMR 3031, with a subsequent shift to IMR 4064). The second load used the same powder charge with a Sierra 190 gr. HPBT bullet, which was used for 600 through 1000 yards in the M14. With a muzzle velocity of approximately 2,450 fps, it remained supersonic to 1000 yards. This load was very accurate with the light barrel Marine match M14 of pre 1975 vintage; though it was considered hot enough to make the brass one-time use. The pressure with this load was well above any accepted pressure level, being closer to the blue pill proof cartridges. The load was very hard on the rifles, and not all rifles would shoot it well. Nonetheless under typical summer temperatures this load was the over 600 yard to 1000 yard match load.

The Navy continued to use the 7.62 M1 Garand after 1967. The Air Force closed down the Air Force M1 rifle build program in 1969 while still retaining the 7.62 APG (Air Force Premium Grade) Garand. Both teams continued to use these rifles through 1975. Both had access to IMR4475 loaded lots of M80 ball, loaded and clipped especially for use in the M1 7.62 conversions. The Navy found that by pulling the 148 gr. bullets and substituting a Sierra 168 gr. HPBT over 42 grains of IMR 4475 that such a load shot very well out of the M1 barrel up to 600 yards. Shooters from the period credit this load as being part of the reason the Navy 7.62 conversions were quite competitive with the Army and Marine Corps M14 match rifles at 600 yards. It was not suitable for longer ranges.

The Air Force developed a load suitable for the 7.62 APG M1 which featured the use of the Sierra 190 grain projectile over top approximately 43.6 gr. to 44 gr. of IMR 4320. This load achieved something close to 2,500 fps out of a 7.62 M1 and remained supersonic out to 1000 yards. It was an accurate but very stout load that placed severe stress on the op-rod design of the M1. Bent op-rods were not an entirely unexpected outcome when shooting this load in an M1. Given the use of the slower IMR 4320 powder, the load was not suitable for an M14 rifle with its gas port location closer to the chamber than that of the M1.

If special loads were not available, the 7.62 M1 rifles would shoot good lots of M118 well out to 1000 yards; the 1:12″ twist 24 inch M1 barrels keeping the load above the transonic region due to the extra length. However by the middle 1970s most of the lots of M118 issued at non-national match events were loaded with ball powder; these lots did not group well at either 600 or 1000 yards.

1975 saw the old 5-V target (36 inch 5 ring) give way to the LR 10X target (20 inch 10 ring). In the same year the M14 was allowed to utilize a heavier barrel, which had different harmonics than the older light weight barrels, along with epoxy impregnated stocks. M14 accuracy went from struggling to hold 1.6 to 1.7 MOA at long range to approaching 1 MOA or even less on a consistent basis. M118 loaded with ball powder was very much the limiting factor in scores with these rifles. While the post 1972 lots of WC846 had much of the calcium carbonate eliminated and hence showed much less tendency to foul the middle of the bore with persistent carbon, the long range accuracy was not even close to acceptable for use on the post 1975 10-X MR (600 yard) and LR (1000 yard) target. In response, from 1975 on the preferred powder to be used in M118 intended for match use was IMR 4895, though some lots were still loaded with WC846. It would appear that M118 used in the National Matches (with one exception) from 1975 to 1979 was loaded with IMR4895. Even these lots showed accuracy far less impressive than the pre-1968 lots, as the bullets utilized were right off of the production line, instead of being carefully selected as was the pre-1968 practice. Scores suffered.

In response in 1980 Lake City began developing a more accurate 7.62 NATO cartridge for match use. The primary focus was on bullet quality with examples from Lapua, Nosler and Sierra being tested. The result after two test NM lots was the M852 match cartridge, which utilized a Sierra 168 gr. match projectile and 42.0 gr. of IMR4895. This load showed a nominal velocity of 2,550 fps at 78 feet, which corresponds to an actual muzzle velocity of approximately 2,600 fps at the muzzle of the M14. The new load was very successful, as the accuracy variability between lots diminished. While the new load showed accuracy similar to the old pre-1968 M118 NM lots, the load was not suitable for long range use, that is at distances over 800 yards, as it went subsonic around 860 yards. This was primarily due to the lower BC of the Sierra 168 gr. (~.441G1) vs. the 174 gr. Lake City projectile (~.514G1); therefore, for Palma or events past 800 yards, M118 or service team developed handloads remained the only solution available.

After the adoption of the M852 match cartridge in 1981, the last lots of M118 Match were loaded in 1982. After 1982, the M118 was referred to as M118 Special Ball denoting that it was no longer intended for match use, but rather for use by snipers. Lots loaded in 1982 and 1983 were still loaded with a nominal charge of 42 grains of IMR 4895. In 1984 the powder type was changed to WC846, the regular ball powder used to load M80 ball, all lots loaded after this date use WC846. Shooters forced to use this ammunition were very disappointed in the special ball characteristics and felt that the accuracy of all lots of this ammunition left something to be desired.

The Army teams continued to use the “old model” (9 degree boat tail) Sierra 180 gr. projectiles. This load gave both supersonic performance at 1000 yards with accuracy similar to the Sierra 168 gr. bullet. This load could be easily made through bullet substitution on M852 cartridges, though in most all cases the rounds were hand-loaded using new components by the respective service teams. The powder used in these loads was typically IMR 4895 or IMR 4064. In the post 1975 M14 rifles, the team loads tended to shift to the use of IMR4064 for bullets weighing over168 gr., based on the respective team experiences. There was no standard load but the reported loads were typically a low of 42.8 to a high of 43.2 grains of IMR4064 (180 gr. Sierra). These loads produced nominal MV of around 2,620 fps to 2,650 fps in an M14 with an un-eroded throat. In order to avoid damage to the gas system on the latter load, a small gas relief hole was typically drilled in the M14 gas cylinder lock screw. These loads continued in use until 1988 or 1989 when Sierra changed the 180 gr., bullet to a 13 degree boat tail, which effectively lowered the BC of this bullet and made this bullet uncompetitive at long range. Special lots of the old 180 gr. Sierra bullet remained in Army long range match use past the year 2000. The 185 gr. Berger saw use once supplies of the old Sierra 180 gr. dried up after 1998.

The old 190 gr. Marine Corp load was not as successful with the new stiffer barrels post-1975, so the Marines began to experiment with hot 168 gr. loads. They developed a special load utilizing the 168 gr. Sierra bullet, but with a heavier charge of powder in order to get the velocity to approximately 2,800 fps. Several different loads were developed, but the most successful load was the famous “G-4” load. This utilized a virgin Lake City case, with crimped-in Lake City primer and 44.2 gr. to 44.5 gr. of IMR4895 under a Sierra 168 gr. Matchking. This load was strictly a fire once and discard the case proposition as the pressure of this load was far above the peak pressure allowed for 7.62 NATO ammunition. Additionally, rifles set up for this load had the gas cylinder lock screw drilled with a different size gas hole and special attention to the rear of the chamber to ensure ideal support of the case in the head/web area. These loads were not suitable for use in any rifle not specifically set up to shoot them. Nonetheless with a muzzle velocity of 2,800 fps this load could keep the 168 gr. Sierra bullet supersonic at 1000 yards with acceptable accuracy.

Neither the Army nor the Marine loads were ideal, but in the pre-1995 world that was what was available. In 1995 Sierra developed a new .30 caliber match projectile, the 175 gr. Matchking. This bullet was simply nothing more than an improved version of the old Lake City 174 gr. projectile with a slightly improved ballistic shape resulting in an advertised BC (G1) of .496. One of the features on this bullet was smooth transition from supersonic to subsonic velocity, so that the typical “fan pattern” seen with the 13 degree Sierra 168 gr. boat tails when entering the subsonic realm was largely eliminated if the bullet was fired from a high quality barrel and the side winds were not excessive.

A 1991 US Army Judge Advocate General (JAG, the Army’s legal arm) decision held that certain hollow point projectiles were not subject to the Hague Convention’s prohibition of such projectiles for use in warfare, as long as the purpose of the “open tip” was to provide better accuracy or ballistic shape, instead of to enhance bullet expansion. Following that ruling, the US military saw the new Sierra bullet as an ideal candidate for an updated M118 load for match and sniper use.

The result was the 1995 adoption of the M118LR cartridge. Due to the arsenal’s preference for ball powders for uniformity of loading on high-speed machinery, the new cartridge utilized WC750 ball powder. The first published powder charge for this load was nominally 42.8 gr. of WC750. The load used a Lake City case and the Sierra 175 gr. Matchking projectile. The nominal velocity was 2,600 fps at 78 feet, from a 22″ barrel, which correlates to a velocity of 2,660 fps at the muzzle of the M24 bolt action rifle with a 24″ barrel.

The powder charge was increased to a nominal 43.3 gr. of WC750 in 1996. This load gave a higher muzzle velocity, on the order of 2,700 fps at 78 feet from the 24 inch barrel of the M24/M40 sniper rifles. This correlates to an approximate muzzle velocity of 2,750 fps from a 24 inch barrel. The higher velocity gave better performance and less wind deflection. By the middle to late 1990s, the Army, Marines and Coast Guard were using bolt action sniper rifles based on the Remington 700 design, which eliminated some of the restrictions on the cartridge that the M14 design had imposed. As the M14 was seen as largely obsolete, the new updated cartridge did not have to meet the gas port pressure requirements of the M14. The last lot of M118LR known to be loaded with theWC750 powder was LC-99C173-013 in 1999.

In 1999 the powder type was changed to Alliant Reloder 15. The new nominal charge was 44.3 gr. of RE-15 powder, which produced a muzzle velocity of approximately 2,750 fps from the 24 inch barrel of the M24/M40 with a velocity at 78 feet of approximately 2,700 fps. The reason for the change has not been definitely published, but seems to have to do with some improvement in either temperature stability or accuracy. In any case neither of these cartridges variants was intended for use in the M14, though the early lots of M118LR (those loaded with 42.8 gr. instead of 43.3 gr. of WC750) were suitable for the M14, although hard on the rifles due to the high gas port pressure. Indeed the Marine Corp prohibited the use of the M118LR cartridge in the M14 DMR rifle until 2002

Between 2001 and 2003 several events occurred which lead to a reassessment of the M118LR cartridge. First with the start of the war on terror in 2001 the Marine Corp and Army began to issue the M14 in a Designated Marksman Rifle (DMR) role. The lack of sufficient M852 ammunition in the supply system (last lots were loaded in 1994 or 1995) and the lack of long range accuracy of the M118 special ball cartridge meant that these troops were looking for a substitute cartridge. The Navy had already tried using the M118LR cartridge in their match M14 rifles in the all-Navy matches in the spring of 2001 due to the lack of remaining M852 stocks (last issue of Navy M852 occurred in 2000). Though the lots of M118LR they issued were from 1995 and presumably some of the earlier lower pressure lots, the Navy found the M14 rifles not to be damaged and the accuracy was very good. As a result, it appears that in 2002 both the Army and Marines began using M1118LR in their M14 rifles for the DMR/SDM role.

With the start of the Gulf War II in 2003 the high temperatures encountered in Iraq (in excess of 115 degrees F) began to produce some M14 op-rod failures due to excessive pressure at the gas port. Both the Army and Marines found the range marking on their scopes to be off of calibration with the higher velocity M118LR loads in such desert conditions. The result was a decision to reduce the load to a more moderate level.

This was done in late 2003 or early 2004, when the M118LR nominal change was lowered to 43.1 gr. of RE-15 from 44.3 gr. of that powder. This is the nominal load, assuming use of canister grade powder; however, most lots disassembled show an actual powder charge of about 42.8 grains of RE-15. The result was a 40 fps reduction in the velocity at 78 feet to around 2659 fps, which correlates to a 2,709 fps velocity from the 24″ barrel of the M24 or M40 rifle. Out of an M14, the muzzle velocity will be around 2685 fps. This load, though slower than the earlier lots of M118LR, can be used in the M14 with minimal risk to the rifle or gas system and it is this cartridge that is intended to be used with both the Army and Marines new M14 based EBR/EMR and M110 rifles.

Although this cartridge remains the current M118LR standard, it apparently still suffers from excessive velocity variation as the temperature changes and less accuracy than might be desired for truly precise shots at mid-range to long-range distances. The specification for M118LR requires 14 shots in less than 8 inches at 600 yards. To correct that difficulty, in 2008 the SOCOM/Navy sponsored a new developmental project to enhance the accuracy of the M118LR cartridge while maintaining its suitability for use in the M14, SR25 and M700 Remington rifle designs. As such port pressure consistency was a primary concern. The contract was given the Federal Cartridge Company, which for a long time has made a series of match cartridges under the “Gold Medal” brand. These were developed from the custom loads designed for the Marine Corp MTU in the 1970s (the IMR 3031 39 gr. match load). By this time IMR 4064 was the powder of preference for the Gold Medal match cartridge line. One of the areas considered by Federal Cartridge Co. was the case itself, with a more uniform neck concentricity tolerance than Lake City brass and beefed up web to cartridge case head interface being part of the finished cartridge design.

The result, when it was standardized as the MK316 Mod 0 cartridge, was a Federal modified case (Drawing number 8347636), Federal match primer, Sierra 175 grain Matchking and 41.75 grains of IMR 4064 powder. According to the published sources this load will produce a muzzle velocity of 2640 fps out of a 24 inch barrel. The load as produced by Federal is claimed to produce under 1 MOA out to 1000 yards from an appropriate rifle. With the IMR powder the shift in velocity is only 20 fps from 0 to 100 Deg C, with the Standard deviation in velocity over 40 rounds being 15 fps or less. In contrast the M118LR loaded with RE-15 powder will see a 50 fps rise in velocity for a 50 deg rise in temperature.

The MK316 ammunition is essentially the finest possible mass produced match ammunition, comparable to the hand loads utilized by the various service MTUs. The cost is higher than M118LR, with a government cost of 78 cents per round for the MK 316 Mod 0 rather than 55 cents for the M118LR (2009 prices).

In 2009 the NRA allowed the AR-10/SR-25 to be used as a service rifle for NRA competitions, which includes the Palma and 1000 yard matches. While the AR-10 was capable of exceedingly high accuracy, the 20 inch barrel put a further constraint on achievable velocities so crucial to 1000 yard performance. By this time the less than ideal transonic performance of the Sierra 175 gr. Match King had been shown by the performance of the M118LR cartridge fired from the AR10 rifle when these rifles were utilized in 1000 yard matches. In high winds the M118 LR cartridges show poor performance once the velocity drops below 1226 fps; therefore, performance on the 900 and 1000 yard lines can be problematic in high winds as the 20″ barrel of the AR10 simply does not generate the muzzle velocity needed to keep the 175 gr. Sierra above that threshold. Something new was needed to make the AR-10 with its 20″ barrel competitive in 1000 yard matches.

Initial attempts to achieve supersonic performance at 1000 yards revolved around the Berger 155 gr. match bullet on top of a load of Varget above 45 grains in a 1:11″ twist barrel. This load seems to have not achieved all that the AMU expected in terms of velocity at 1000 yards. Recent information indicates that approximately 45 gr. of Varget is being used with the Berger 185 LR gr. bullets out of a 1:10″ twist barrel. Recent match results indicate this load is very accurate and remains supersonic at 1000 yards out of AMU prepared AR 10 rifles. While suitable for limited military match use this load is far too hot for general service adoption. There is no doubt continued development on this cartridge for match use, just as the AMU has continued to develop loads for the 5.56 M16 match rifles.

Copyright 2012, F.R. Salberta, used by permission.
Part 3 of this series will contain summarized load information.
 
We are very pleased to bring you this three-part series regarding the development of the 7.62 NATO cartridge for long range match shooting. In a departure from our usual practice, there is significant load data contained in this series. The government arsenals and military teams using and developing these loads had pressure testing equipment, plenty of expendable rifles and plenty of replaceable recruits that they loved a bit less than their mothers did. Just about every load mentioned here other than the basic arsenal match loads will generate excessive pressure and cause damage to your rifle and can certainly injure the shooter. Read and enjoy this for its historical value but please have the common sense to realize that duplicating these loads today with canister grade powders is dangerous and should not be attempted. - GAS -
 

All contents Copyright 2012 The Rifleman's Journal