Compatible with these barrels:
TR50: https://mcsus.com/products/hdr50-tr50-20j-steel-tuning-barrel-kit
TR50L: https://mcsus.com/products/hdr50l-tr50l-20j-steel-tuning-barrel-kit
HDP TP50: https://mcsus.com/products/hdp-50-20j-steel-tuning-barrel-kit
HDP TP50 Compact: https://mcsus.com/products/hdp-tp50-compact-steel-tuning-barrel-kit