[HKPRO]

Finally something new--433/437 (.300 Blackout version of the 433) will be the subject of a mag article on All4Shooters. Preview pic showing size of the 437 SBR next to a MP5 SD:

View attachment 282642

Also note altered controls and what appears to be a new pattern of bolt catch/release.

Does that mag well look long enough for .300 BO to you?

 

[BarnOwlLover]

I thought that .300 Blackout was based off of/intended to have the same OAL as .223/5.56mm NATO?

Better quality pic of the 437 9" SBR vs MP5 SD: