You should read Freedom's Forge. I've read a ton on the history of Lend Lease and this is simultaneously the least academic and best written. I can give you some more highly regarded writers who are much less enjoyable to read, they all say the same thing. Which is not what the popular press shows. -XC PS - FYI, ammo is produced Olin, Alliant, L3, and a host of small subcontractors. Most military small arms ammo is actually of lower average quality than civilian ammo (for a host of reasons). Most military tactical ammo is stockpiled for 18-24 months of war-rate usage. The USAF seems to be the exception on that one - I understand that we were almost bingo on some JDAM's during the height of the Iraq war. Otherwise our major material losses are so very slight, relative, it's not exactly like we're having Barbarossa style problems in resupply.
I'll check out Freedom's Forge. I just finished Churchill's The Gathering Storm last week actually, and it impressed upon me the cost to Great Britian from not only taking a passive political role, but a passive armament role leading up to WWII. I have real doubts that we will have to go into a full mobilization in the next couple of decades, but, who knows with that crazy Euro... Even so, the Big 3 infrastructure was a massive advantage to the War effort. I'm sure Boeing is "Too strategic to Fail" as well.