Lou Cornicelli peered intently through the scope of his rifle, then squeezed the trigger.

The shot exploded with a crack, slamming into a most unusual target: A sheep carcass suspended by straps in a field about 160 feet away.

Several workers removed the carcass and replaced it with another, which Cornicelli also shot.

In all, the Minnesota Department of Natural Resources big game manager fired several different types of bullets from different guns into 35 sheep Tuesday at Carlos Avery Wildlife Management Area near Forest Lake. They were among 75 killed sheep used in a first-of-its-kind study to examine the fragmentation of lead bullets.

The sheep were stand-ins for whitetail deer, and the test results are meant to give Minnesota's 500,000 deer hunters guidance this fall about which ammo poses the least risk of lead contamination.

"The goal is to simply give hunters some recommendations on bullet selection,'' Cornicelli said.

Other states, too, are eagerly awaiting the results, he said.

The sheep will be X-rayed and tested for lead at the University of Minnesota's Veterinary Diagnostic Laboratory in St. Paul. Some also will be given CT scans, which will provide a three-dimensional image.

The study was prompted by the discovery this spring of lead fragments in venison donated to food shelves in North Dakota, Minnesota and Wisconsin. Twenty-two percent of the 1,239 samples tested in Minnesota had lead fragments. Distribution was suspended, some venison was discarded and the venison-donation programs were thrown into turmoil.

That Minnesota's deer hunters and their families and thousands of food shelf users might be consuming even small amounts of lead, a toxin, has become a major concern.

The DNR offers general recommendations in its fall hunting regulation booklet, issued this week, on how deer hunters can avoid lead contamination. The bullet study will give hunters information about specific ammunition. Bullet fragmentation is believed to vary widely, depending on the type of ammunition and gun used.

The $35,000 study is on a fast track because of the deer hunting season in November. "We hope to have recommendations for hunters in the next 30 days,'' Cornicelli said.

He knows the study may be controversial, even among hunters.

"It's not some anti-hunting conspiracy,'' said Cornicelli, an avid hunter whose own venison was found to contain lead. "Our intent is not to ban lead [ammunition] or force the use of one bullet over another; it's merely to allow hunters to make their own informed decision.''

Some all-copper bullets were included in the tests. The DNR says hunters who want to avoid any lead contamination could switch to non-lead bullets, which are much more costly. But lead is overwhelmingly the No. 1 metal used in bullets, and a large-scale conversion to nontoxic ammunition would be expensive and difficult, manufacturers say.

Study has some limits

The sheep were "cull animals'' destined for a rendering plant, Cornicelli said, and were destroyed before testing.

"We couldn't use deer -- it's not the right time of year,'' he said. "We wanted to use something that would approximate deer, and these do.'' Eight deer killed as part of a recent bovine tuberculosis culling program in northwestern Minnesota will be included in the study.

The bullet study is limited, Cornicelli acknowledged, because officials simply couldn't duplicate all the variables involved in deer hunting, including distances, shot placement and gun types.

Cornicelli used a .308-caliber rifle, a 12-gauge shotgun and a .50-caliber muzzleloader to fire seven different types of bullets and a shotgun slug into the sheep carcasses, positioned to their side, from 50 meters (164 feet).

Five basic types of high-caliber bullets were used. Two are designed to expand rapidly on impact: a lead soft-point, the most common bullet, and a ballistic-tip, which has a plastic tip, lead body and copper jacket.

Two others were "controlled expansion'' bullets designed to expand more slowly and retain more weight. One was a lead-bonded bullet -- lead fused inside a copper jacket -- and the other was a copper bullet with a lead core. The fifth was the all-copper bullet. A lead shotgun slug and two muzzleloader bullets were also tested.

Lead fragments from an initial inspection of some X-rays were widespread with the rapid-expanding bullets, said Marrett Grund, DNR farmland deer manager and study leader. Many lead fragments are too small to be seen with the naked eye, and lead powder -- left by some bullets -- doesn't show up on X-rays.

Minnesota officials found lead in venison that showed no fragments on X-rays, meaning X-rays alone won't detect all of the lead.

Grund, a longtime hunter, said the lead issue has been a surprise for wildlife managers and researchers, as well as hunters. "When I say surprised, I mean surprised we've never thought of this before,'' he said. "It never dawned on me that it might be an issue.''

He has two young children who regularly ate venison -- until the lead issue surfaced.

As for this fall: "I'll likely use a copper bullet,'' Grund said.

Doug Smith • 612-673-7667