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Temperature issues arise for lead-free slug

The Army is scrapping the latest design for its eco-friendly 5.56mm ammo after some of the bullets began to show trajectory problems when exposed to hot temperatures.

Army ballistics officials halted production of the M855A1 Lead Free Slug ammunition in mid July, launched an investigation and decided to replace the bismuth-tin alloy slug with another material, said Lt. Col. Jeff Woods, product manager for Small Caliber Ammunition.

“We are currently evaluating alternate lead-free materials, and we will resume qualification once a selection is made,” Woods told Army Times.

In the M855A1 LFS bullet’s design, the bismuth-tin alloy sits beneath a steel penetrating tip. A copper jacket encases all but the point of the bullet. The round was designed to work specifically with the M4 carbine. Army officials have maintained that the new round will provide more “consistent performance” than the current M855 round and perform better against hard targets.

The problem surfaced when some of the bullets did not follow their trajectory or planned flight path.

“During ballistic testing of production LFS cartridges, we noticed that some projectiles occasionally varied from the intended trajectory,” Woods said.

The plan was to start issuing the first of 20 million rounds in August, replacing the standard M855 lead round.

One thing the Army is sure of is that “this will delay fielding of the new round,” Woods said.

This is not the first hiccup to occur in the quest for lead-free ammunition, a program the Army has invested tens of millions of dollars in since the mid-1990s.

The first attempt featured a tungsten-nylon bullet that didn’t perform well and proved almost as harmful to the environment as lead.

This new wrinkle in the program appears to be linked to “higher temperatures,” but ballistic officials would not describe the specific temperature at which the problem occurs.

Sources familiar with the program said that the bismuth-tin alloy softens under heated temperatures, causing the round to perform inconsistently.

“It’s the slug; that’s where the problem is,” said Ken McKee, who works in the quality assurance department for ATK’s Small Caliber Ammunition Systems at the Lake City Army Ammunition Plant in Independence, Mo.

He also said that the timeline for the current lead-free slug design may have been too ambitious.

“We had a delivery schedule; this kind of knocked a hole in that,” McKee said. “It was a very aggressive schedule to begin with.”