Between 223 and .500, expanding bullet, with minimum 500 fpe:
https://www.legis.iowa.gov/publications/search/document?fq=id:1291400&q=Senate+581
NEW SUBSECTION. 9. There shall be a January antlerless
deer only hunting season in a county whenever that county
has unsold antlerless deer licenses available in its county
quota as set by the commission by rule. The commission shall
establish the season dates. Licenses shall be available for
sale beginning the day after the close of the late muzzleloader
season until either the county quota allotment has been sold or
until the end of the season, whichever occurs first. A January
antlerless deer only license issued under this subsection is
valid only in the county identified on the license. A rifle
with a barrel length of at least sixteen inches and firing
centerfire ammunition propelling an expanding-type bullet with
a maximum diameter of no less than two hundred twenty-three
thousandths of one inch and no larger than five hundred
thousandths of one inch and with a published or calculated
muzzle energy of five hundred foot pounds or higher is the
approved method of take for this season.
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