Standard-capacity magazine ban introduced in the House
You should probably let your Congressperson know to OPPOSE the new legislation, even if you have already told them to oppose new gun control in general. It helps to provide specific instructions about individual pieces of legislation.
This bill is being introduced by one of the usual suspects -- Carolyn McCarthy. It's worth noting that the legislation would ban the sale or transfer of magazines capable of holding more than 10 rounds, but not the simple possession -- at least according to the article. However, since magazines are not registered nor tracked by serial number, it would be impossible to examine a particular magazine to determine if it violated the law or not. Anyone could be prosecuted for "transfer" on the word of an informant -- or for including a few magazines along with the legal sale of the firearm they are designed for. It would be impossible to prove whether any magazine in your possession was a legal, pre-ban magazine that you had not sold or transferred.
There are millions of these standard capacity magazines in circulation for a wide variety of firearms. Each and every one would place its owner into substantial legal jeopardy should this bill pass. Remember, that's what they want. The more legal uncertainty that comes along with being a gun owner, the more risk it takes to maintain the capacity of self-defense independent of the State, the better.