Relevant: https://www.jns.org/israel-begins-shift-to-domestic-ammunition-production/

Small arms and their ammunition were mostly domestically produced already long before this war, dating back as far as the 1930s, before the nation was even founded. I haven't been able to find any numbers, but I'm pretty certain that domestic arms manufacturer Elbit is responsible for the bulk of the IDF's small caliber ammunition supply:

https://elbitsystems.com/pdf-category/company-brochures/land-systems/ammunition/

I know you were implying that it's America who sent these over, likely in an effort to blame America, but in reality, in regards to ammunition, it's mostly artillery shells, bombs and interceptor missiles that are delivered from the US. Israel can and does produce all of these things, but chose not to do so to the full extend of their capabilities in the past out of both convenience and because Uncle Sam insisted. Like the above article says, the issues Ukraine is facing with fickle allies makes Israel, just like Ukraine, look inward and, just like in the past (see the development of their own tanks, fighter jets, missile shield, drones, robots, etc. - many of which started when partners suddenly stopped being reliable) intensify efforts to produce weapons domestically. Some of Israel's current dependency on the US in particular actually happened against at least partially their will: The F-16, the workhorse of the IAF, was practically forced onto Israel by America (because the American defense industry feared Israeli competition), resulting in the shuttering of an advanced domestic fighter aircraft program of their own that was meant to replace the ageing domestic Kfir. High costs were another factor, but who knows what would have happened if the Reagan administration hadn't flexed their muscles.