#Fabrl

When I started the Modern Intermediate Calibers series, I did not expect it to grow as large as it has. The initial plan was for 7 major calibers, which grew into well over 20, and the spinoff Modern Personal Defense Weapon Calibers, which itself will have at least 20 entries.

Among the interesting concepts that were tested in the mid-late 20th Century is that of an extremely light for caliber, very long bullet made in part of a lightweight material like aluminum and plastic. The 7.92×40 CETME, which if I can find a specimen I will cover later on, is one example, but starting in 1972 the now-closed Frankford Arsenal began experiments on 5.56mm cases loaded with super-long projectiles with von Karman ogives, with the aim of creating a lightweight round using a low-density projectile and an aluminum case. Original testing was conducted with full-length 5.56mm cases and two lengths of bullets, but eventually a shortened brass case and a 37gr bullet with the same shape as the shorter initial test bullet was created. As a solution to the problem of burn-though with aluminum cases, the Arsenal developed a plastic insert called a “flexible internal element” (FIE), and the brass cased rounds developed for ballistic testing also had FIEs. This shorter round in both aluminum and brass cased forms was called the 5.56x38mm FABRL, which stood for “Frankford Arsenal – Ballistics Research Laboratory”, and this at some point was made into a backronym for “Future Ammunition for Burst Rifle Launch”.