The M38 SDMR Squad Designated Marksman Rifle was introduced into service with the US Marine Corps in 2017. Despite the separate designation, it is not a new weapon nor even a special version, but nothing more that the M27 Infantry Automatic Rifle, converted with a special “Squad Designated Marksman” kit. This SDMR equipment kit includes the 2.5-8Х Leupold TS-30A2 Mark 4 MR/T variable power daytime telescopic sight, a sound suppressor, made by the Knights Armaments co, and a detachable lightweight folding bipod.
The M37 rifle retains its select fire capability and uses same 30-round magazines as ‘standard USMC issue’ M27 IAR. This approach greatly simplifies logistics at the squad level, allows the squad marksman to blend in with his squad mates as not to draw unnecessary attention of the enemy, and allows marksman to fight as an ordinary foot soldier if required. Downside of this approach, as compared to a widespread concept of a more powerful squad marksman rifle, introduced by Russians in 1963 with the Dragunov SVD and now pursued by many other weapons such as British L129, is that 5.56mm M38 SDMR rifle lacks the range and the punch of a full-power 7.62mm round.
To give an idea, at 600 meters the M38 SDMR delivers roughly 270 Joules of energy with 5.56mm Mk.318 ammunition (bullet weight 4.01 g / 62 grain, muzzle velocity 910 m/s), and about 435 Joules with 5.56mm Mk.262 ammunition loaded with Match grade bullets (projectile weight 4.99 g / 77 grain, muzzle velocity 818 m/s). For comparison, the 7.62x54R 7N1 round, when fired from the Dragunov SVD rifle, delivers about 930 Joules of energy at the same range. Furthermore, both 5.56mm rounds feature relatively soft lead core that lack penetration against barriers and body armor, while 7N1 and many other 7.62mm DMR rounds feature steel cores. So, like any other weapon system in existence, the M38 Squad Designated Marksman Rifle is a trade-off, where lighter weight, greater firepower at short range, simplicity of logistics, training and maintenance took preference over longer effective range, and better penetration and lethality.