The best replacement for rpd is rpk.

The best alternatives to rpd are rated as following:
★★★★★  rpk
★★★  aug
★★  hamr zombies
★★  mg4
★★  m60
★★  rsd
★★  hamr
★  m240
★  l86
★  lsat
★  aug mw2
★  galil
★  m249
★  aug hbar
★  m249 saw
  aug hbar mw2
  m60 cod4

Your alternative for rpd is not listed? Suggest!
Speaking about rpd, one probably shouldn't forget about extended mags.

Other search terms related to rpd and their ratings are:
★★★★★ extended mags
You have in mind a companion for rpd and it is not yet here? Propose!



Google Trends

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rpd
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