Once a large production batch of anything is running, the marginal cost for making additional units drops to effectively zero, even though the raw materials costs stay constant. So, the margin on the 10,000th unit of 1 lbs of powder is cheaper than the 5,000th unit, and much cheaper than the 100th unit. And you're right... no one has to sell a pound of powder for $1 cheaper, because the demand is such that they already sell every pound they can economically make at the current price, and making more would likely increase manufacturing operating costs and even might require a significant capital investment in new equipment. CCI made an announcement a few years ago when there was a shortage of available rimfire ammo... they were already running three shifts in their plants and would not invest in additional production capability because they didn't know how long the increased demand would work, and didn't want to be stuck with a huge capital investment that would become surplus to their needs in the near term. Who can blame them? What happened in the market instead is the increased availability of foreign-made .22 ammo... Wolf, Aguila, etc... into the US market because the cost per round was cheaper than building US facilities that would likely become superfluous in a year or two. That's capitalism... trying to get the most efficient use of money to maximize profit.
If demand exceeds supply, then supply will increase until it matches demand. Demand can be increased by reducing the price of goods... more people buy computers now that you can get a decent PC for under $1,000 then they did back in the 1980s when they were several thousand dollars. Similarly, once demand equals supply an ammo company could increase demand by lowering the price. How much .22 ammo would you buy if, say, Federal put their bulk .22 LR on sale for 50 cents a box, $5 a brick?
Re small businesses not making profit, this only works if they're not making profit by leveraging tax policy, e.g., depreciation, taking tax credits, etc. Businesses have to make a profit, in real terms (not tax terms), to stay in business. You can't make up losses by increasing the volume of unprofitable trade.