From NRA-ILA:

The term “sporting purposes” is undefined by federal statute and has been subject to several reinterpretations by the BATFE and its predecessor agency.  BATFE and anti-gun administrations have exploited the lack of a clear definition of “sporting purposes” to bypass Congress and impose gun control through executive fiat. The most recent (and perhaps most infamous) example of this was the Obama administration’s attempt to ban a highly popular form of ammunition for the AR-15, America’s most popular rifle.

More from NRA:

“This important legislation would prevent arbitrary ammunition bans like the one attempted earlier this year by the Obama Administration,” said Chris W. Cox, executive director of the NRA’s Institute for Legislative Action. “With the support of America’s law-abiding gun owners, the NRA was able to beat back Obama’s attempt to ban ammunition used by millions of law-abiding Americans every day for target shooting, hunting, and self-defense. This legislation would fix the law to protect us from similar government overreach in the future.”