Here is a test fire session of one of our clients Ed K's new baby! This video is at 600 frames per second. Notice the flame ball and then sometimes no flame but lots of unburnt powder residue. Shows the flash hider is trying to do it's job but kinda tuff on a 9" barreled belt fed! RDTS's 21 UBF (Universla Belt Fed) does a great job of firing Russian TULA ammo. Almost the same as Wolf, same factory I believe? We have a problem on occasion with Wolf ammo with lite primer strikes as their primer's are pretty hard. The TULA has no problem and at $250 a 1000 the price is right! RDTS sets up the gun to run nicely with TULA but in doing so most NATO brass won't eject due to the slower powder burn. Russian ammo tends to burn with more pressure. If the RDTS 21 UBF was set up for NATO ammo with the 9" barrel it would beat itself up and run at a higher RPM with the TULA. We figure our clients would rather burn $250 a 1000 TULA ammo rather than $500-$600 a 1000 NATO out of a 9" firebreather! As was noted the RDTS 21 UBF can be set up for both, again resulting though in a high rate of fire and more wear with the TULA.
When we change to a 17.25" stock 21 barrel and locking piece change it seems to be OK with both types of ammo. Still slightly higher RPM with TULA but not as bad and capable of using NATO also. Our goal at RDTS is to build a 21 that is reliable and fun to shoot along with having a high round receiver life. Look for the video of the RDTS 21 UBF with the 17.25 barrel and Suppressor doing a 50 pull! Sound signature is that of a 22 LR rifle (10/22 Ruger).
FFL/SOT since 1981