We don't know. As Jurgen Brauer writes in "The U.S. Firearms Industry: Production and Supply", "No comprehensive economic studies of the US firearms industry have been attempted in recent decades. Primarily, this would seem to be due to the paucity of credible data and the difficulty of accessing it. This is true for data pertaining to both the market as a whole and individual companies."

The best data we have comes from the Bureau of Alcohol, Tobacco, Firearms and Explosives, which each year publishes its "Firearms Commerce in the United States" report. That report is extremely limited, however. It has a lot of gaps in the data ─ secondhand sales is perhaps the biggest one ─ and it doesn't have much historical depth. The ATF's usual reports only go back to the 1980s, when modern recordkeeping standards were implemented. Before that, figures have to be gleaned from microfilm and microfiche, and that's an incredibly intensive process.

In fact, I know of only one organization that does that on a regular basis. The Violence Policy Center in 2000 and 2002 published "Firearms Production in America," a document that attempted to identify the production per manufacturer per year, an attempt that partially failed. Despite that, the report is valuable for our purposes because it contains one of the few tables of domestic American firearms production between 1946 and 1998. It footnotes that table (Appendix Four in the link just above) with the simple label "Figures obtained from Bureau of Alcohol, Tobacco and Firearms," which doesn't help any researcher much, unfortunately.

What we do see in the table is that domestic production is surprisingly low through the period you're asking about. While that table deals with production, not sales, we know from Brauer's paper and ATF figures that imports were an extremely small fraction of the American market until the later 1980s and 1990s. What was made in the U.S. was used in the U.S.

The table also obscures other sources of firearms that might have entered the civilian market. Since it only talks about production, it doesn't account for the vast quantities of firearms available through surplus sales and auctions after World War II. It also doesn't account for unregulated sales of pre-existing firearms.

As Brauer points out, it's titanically difficult to track sales through economic data, since many (if not most) firearms firms were or are privately held and didn't report sales data. Social data is extremely limited as well. We know that (particularly since the start of the 21st century) firearms ownership is on the decline in the United States, even as sales stay near historic highs. Looking back to 1959, however, a Gallup poll conducted in July found that just 49 percent of Americans said they owned a gun in their home. Today, that figure is down to 41 percent. The mix of guns has changed along with that decline. There are fewer long guns used in hunting and more handguns, used for personal defense.