Period-24 glider gun is a true period 24 gun discovered by Noam D. Elkies in 1997. It uses four large period-4 oscillators (two of them variants of fountain, the other two adjoined by common casing) to hassle two T-tetrominos, which react together to produce gliders. The form on the right is a reduced variant found by Karel Suhajda. The eater 1 can be replaced with a unix for compacting purposes, such as in earlier versions of the period-48 glider gun.
No more than five days after the initial discovery, Elkies found a method to double the period of the gun, resulting in the first known period 48 glider gun. A smaller version was found in 2016 by Tanner Jacobi, using Rich's p16 to double the period.
In January 2019 a smaller period-24 gun was assembled by Tanner Jacobi and Matthias Merzenich, based on the dueling banjos oscillator (see animation below). It was further reduced in November of that same year due to the discovery of a new p6 domino sparker by Dongook Lee. Both of these variants have been used to create period-48 LWSS guns, and the former gun was in turn used to create a pseudo-period 16 glider gun.