Fitzpatrick said the bill's requirement that all magazines have serial numbers adds enough production costs to make it worth leaving. He also said smaller magazines can be easily connected to each other — magazines can be hooked up to make a 60-round magazine, for example — and the company fears it would legally liable if people were to do that.
Democrats have tried to ease Magpul's fears, amending the bill to make clear that the company can still manufacture magazines of any size, as long as they're sold only out-of-state, to the military or law enforcement.
Republicans who oppose the restrictions argue Democrats are sending mixed messages about gun control to keep a company in Colorado.
"It's being hypocritical. These things are either bad or they're not," said Republican Rep. Brian DelGrosso.
Magpul argues that limiting magazine sizes will not reduce gun violence, and that criminals will find ways around laws, including going to other states to buy larger magazines. Magpul officials note that some of their products sometimes end up in California, which limits magazine sizes to 10 rounds.
"The solutions that people want to bring up are hardware solutions," said Magpul Director Duane Liptak. "And they want to talk about this physical piece of equipment that's not inherently evil. It's not inherently good. It's a tool like anything else. It can be used for good, and it can be used improperly by people who have evil in their hearts."
Supporters of the proposals say Magpul is bluffing and that a move would prove too costly.
"I don't think Magpul is about to pull out," said Bill Hoover, 83, whose grandson AJ Boik was among the 12 killed in the theater shooting. "It's going to cost them a bundle of money."
Fitzpatrick said his company is serious.
"It's not really a threat. It's a promise," he said.
Sens. Lois Tochtrop and Cheri Jahn are the two Democrats voting against the bill. Both say they don't believe it addresses the main problem — mental health — and Tochtrop also cited Magpul's potential departure.
"I think we really need to address that problem. Look at the cause, not the tool," Tochtrop said.