First off, let's remember that the NRA dates back to around the civil war... So it's hardly unexpected that there has been some changes in its view over the years.

For a very long time (until 1977) the NRA wasn't terribly political. While it did participate in input into things like the National Firearms Act of 1934, it's hard to say that this was "lobbying for restrictions". It was merely input into legislation.

During the 1970's, organizations like Handgun Control, Inc. started coming up that outright advocated for wide scale gun control, with the end goal of a total ban on all civilian gun ownership. In response to this, elements of the NRA membership became increasingly concerned that the NRA was becoming a conservation organization, and abandoning its pro 2nd amendment mission. These elements took control of the NRA at its convention in 1977. After 1977, the NRA has never advocated for more gun control, although it has advocated for existing laws to be enforced.