As pressure to act on a proposal to expand gun background checks in Pennsylvania builds in the state legislature, an error published by Harrisburg NBC affiliate WGAL is providing fodder to the bill's opponents.

Pennsylvania currently only requires buyers of handguns to undergo a criminal background check. Purchasers of long guns such as shotguns and rifles -- including military-style assault weapons -- can buy these weapons without a background check in “private sales.” H.B. 1010 would extend the background check requirement to long guns.

Gun violence prevention group Ceasefire PA recently visited the legislature to lobby for the bill. In support of the bill, Ceasefire PA has argued that the proportion of murders with firearms other than handguns in Pennsylvania has more than doubled since 1998 and that long guns are disproportionality used to kill police officers.

In a September 16 article, WGAL sloppily attempted to share Ceasefire PA's argument for expanded background checks, but instead misstated the nature and year of the claim that Ceasefire PA has made:

Cease Fire says FBI figures show the number of murders committed with long guns has doubled since 1996.

In fact, Ceasefire had argued that the proportion of murders committed with guns other than handguns has increased. According to a September joint report from Ceasefire PA and Center for American Progress Action Fund, FBI data indicates that this figure has increased since 1998 from 8 percent to 21 percent:

Now prominent gun bloggers are seizing on the line from WGAL's story to accuse Ceasefire PA of inventing statistics.

WGAL was first cited by Bob Owens, a gun blogger who has in the past endorsed calls for anti-government violence and expressed a desire that Media Matters “feel threatened.”

In a blog titled “And Then They Came For The Bolt-Actions” -- an apparent allusion to Martin Niemöller's famous poem about Nazi incrementalism -- Owens quoted language from WGAL and wrote, “It will probably come as a surprise to no one that Ceasefire PA is dramatically lying with their claim.”

Owens purported to debunk the claim with FBI statistics about the total number of murders nationwide with rifles and shotguns since 1996. But if Owens would have checked Ceasefire PA's actual claim, he would have seen that it was about proportionality and limited to the state of Pennsylvania.

Shall Not Be Questioned, the most prominent Pennsylvania gun blog, quickly picked up Owens' mistaken claim with a post titled, “Catching CeaseFire in a Lie.”