Military.com:

Preliminary results of an Army test to see how the service’s M855A1 5.56mm round performs in Marine Corps weapons show that the enhanced performance round causes reliability and durability problems in the Marine M27 Infantry Automatic Rifle, service officials say.

The Marine Corps in March added the M27 and the M16A4 rifles to the Army’s ongoing testing of M855A1 Enhanced Performance Round at Aberdeen Proving Ground in Maryland after lawmakers questioned why the Army and the Marines use two different types of 5.56mm ammunition.

“One of the reasons we were doing that test was because of congressional language from last year that said ‘you two services need to look at getting to a common round,’ so we heard Congress loud and clear last year,” Col. Michael Manning, program manager for the Marine Corps Infantry Weapon Systems, told Military.com in a Dec. 15 Interview.

Lawmakers again expressed concern this year in the final joint version of the Fiscal 2017 National Defense Appropriations Act, which includes a provision requiring the secretary of defense to submit a report to the House and Senate Armed Services Committees explaining why the two services are using different types of 5.56 mm ammunition.

[ … ]

The Army replaced the Cold War-era M855 5.56mm round in 2010 with its new M855A1 EPR, the result of more than a decade of work to develop a lead-free round.

The M855A1 features a steel penetrator on top of a solid copper slug, making it is more dependable than the current M855, Army officials have said. It delivers consistent performance at all distances and penetrates 3/8s-inch-thick steel at ranges approaching 400 meters, tripling the performance of the M855, Army officials maintain.

First of all, my former Marine Daniel laments the transition from the SAW to the IAR.  It’s all part of the softening of the USMC.  They should still be deploying the SAW.  But let’s assume that whatever problems they’re having with the IAR, they would have with the SAW too.

About this being a better round, I think the Army is lying.  That isn’t what I hear.

The Army M855A1 had a LOT of problems in development. Wearing down barrels, damaging the chambers, requiring new magazines because of the feed angle

Folks, they threw ballistics to the wind, didn’t consider what’s best for killing, and decided to go all green with their ammunition (this isn’t the only area they did this, witness the push for solar panels on military bases with the use of defense dollars).

And about this, commenter Fred tells it like it is.  “It’s green, why won’t you understand that? It’s green for everyone’s benefit especially the children. What is wrong with you people who can’t understanding destroying whole countries in a friendly, environmentally sound, and loving way is green?

Lets wreck this whole motherfuckin’ city and blow it up and kill millions of people but, let’s do it in an environmentally responsible way.”