Barrels are fine. But.. the forward profile is a little different, The HK has a taper to it. As is the flash suppressor end. Threading is the same. It just looks different. The CETME triple rail is different, but should still work. The CETME trunnion is not compatible, bolt head is different. A great source for CETME and HK91/G3 parts compatibility is RTG. The link is
http://www.robertrtg.com/cetmeinfo.html (Robert is a great source for HK parts). Pic are from the top. CETME demilled, HK G3 w/triple frame, bottom is Santa Barbara in the White.
The ammo advisory is because the commercial ammo is made to internal specs based on the civilian SAMMI standards. The Milspec is made to the NATO standard. The case base on NATO rounds are thicker. Some sporting ammo can have the base ripped of on extraction in a delayed roller system. Plus the civilian ammo has more internal room for powder than a NATO round, which can lead to either a over pressure from the extra powder or the bullet being seated to far into the casing with the same net result.
