The US didn't enter the war until December 1941.
In the official, and legal sense, the declaration of war was Dec 8th, 1941. However, we had been producing arms as a "neutral nation" for some years before that, both building up our forces for the conflict we could see coming, and selling arms to foreign nations to support their war effort.
When the British Home Guard was drilling with shovels and rakes and pitchforks due to a lack of arms, private American citizens sent some of their personal guns to England to help arm them against Nazi invasion.
And the British were buying (or being "loaned") everything from the US arms industry they could get.
I don't know whether it was a US Govt. order to shut down or lucrative military contracts with bigger profits that halted the production of civilian firearms. I'm inclined towards the latter.
Don't discount the fact that patriotism played a HUGE factor. The change over to wartime production (which was far from instantaneous) wasn't entirely driven by govt orders, or the profit motive alone. The American public was mad as hell, even those pushing isolationism either changed their tune or just shut up entirely after that Sunday in Dec.
Over a fairly short period of months, virtually every industry in the nation that could contribute to the war effort set up to do so, and it wasn't entirely for profit. Sure, they made money, but there was a bit more to it than just the desire to make money.
And, while general production of civilian arms was drastically reduced, it wasn't completely eliminated, other than by the choice of the people running the different factories. IF govt contracts were being met, and the factory had spare production capacity, some did produce small numbers of guns for civilian sales. Savage did this, and likely some of the others too.
Brings up one of my greatest worries, factories ultimately "win the war" by out producing the enemy. In each passing year we are losing our ability to manufacture anything at all.
I'm sure the US could, in time of great need create/recreate the industrial capability we once had, IF we have the time. And that the biggest worry, with modern tech, weapons and delivery systems, we're unlike to have the time, unmolested, as we did in WWII.
The two great advantages the US had during WWII was first, the bulk of the raw materials we needed were available "locally", and second (and far from unimportant) was that our factories and our civilian population was far removed from the war fronts (generally) and did not face the threat of direct enemy attack the way European nations were.
..factories ultimately "win the war" by out producing the enemy.
While there is truth in this, its not the entire story, just one big part of what wins the war. The other parts are that the war materials have to get to where they are needed, and used successfully by our troops, and having those troops is also a vital part.
Everything civilian didn't get complete shut down for the war effort, many things did, others were just drastically reduced. Here's a tidbit, even after the ammo makers "dropped everything but military production" they still made some .30-30 ammo.
America could manage without an abundant supply of new hunting rifles, but without ammo, they aren't good for much. Being able to get a box of .30-30 might be the difference between eking by on ration allowance or being better fed for a lot of families.