The Marine Corps Times reports that the USMC has decided  to pass on the US Army upgrades to M4

Key Highlights:

• As the Army moves to field more than 10,000 conversion kits designed to make the 5.56mm M4 deadlier and more reliable, the Marine Corps says it has no plans to update its inventory. Upgrades will integrate a heavier, more durable barrel, strengthened site rails, a piston-charged operating system and the ability to fire in full automatic mode — fixes designed to address complaints about the weapons’ lethality and reliability. The plan calls for distributing 12,000 conversion kits in the short term, effectively turning existing M4s into improved versions of the special operations M4A1, said Army Brig. Gen. Peter Fuller, commander of Program Executive Office Soldier. An additional 25,000 M4A1s and 65,000 conversion kits would be purchased through additional contracts.
• “We’ve been looking at our small arms for a long time, you know,assessing the effects on the battlefield, knock-down power, killing power, those types of things,” General Conway, Commandant of the Marine Corps said. “We are never going to be a carbine Marine Corps, OK. We’re never going to go completely to the M4. We’re a rifle Marine Corps. We believe in long-range shooting skills, and those skills are just not as resident in a carbine as they are in a service rifle.”
• U.S. combat troops have complained about the stopping power of both the M16A4 and M4 in recent years, particularly in Afghanistan, where combat is frequently in open fields and valleys that require powerful, long-range shots. In response, the Corps began replacing its conventional Cold War-era 5.56mm M855 ammo this spring with an enhanced 5.56mm Special Operations Science & Technology round that uses an open-tip design common in sniper ammunition. The Corps also is considering a new, lead-free Army round fielded recently, the M855A1, and will evaluate both options in coming months.

SFTT Analysis:

• This article pre-dates the Army’s recent decision to retro-fit all of the Army’s M4 inventory, but at least here, we get the rationale on why the Marine Corps passed on this conversion.
• If this report is accurate, the Marine Corps has ceded the argument that they want to replace the M16A4 due to “cost”.