I had one guy that ordered a 2-pcs. Blank-Barrel-Assembly in 7.62x51mm/.308 cal. tell me that he was having problems with .308 Blanks "chambering" fully.
I went ahead and ordered new chamber-reamers (both 8x57mm and .308 cal.)....and then ordered different "surplus" Blanks.
What I found out was that (again) not all "surplus" .308 Blanks are loaded the same....."AND" that not all .308 "surplus" Blanks are even made the same.
When checked against the SAAMI Spec. Books that has not only cartridges-specs. ....but also manufacturing-spec. for "chambers"....I found that some "surplus" Blanks are slightly too larger in OD (Outside-Diameter) as the photos below show.
What does this mean (?).........??????
What hapens is that the larger diameter POF Blanks start into the chamber and slow down as the bulleted-shape-crimp starts to jam into that smaller area (forcing-cone) in front of the chamber......this basically will jam and stop an MG34/SA34 from running.....and some MG42/SA42s.
Well, to insure that your MG34/SA34 (which does have a slightly longer "lock-up" time than the MG42) you may have to slightly alter the area infront of the chamber (called the "lead") which is a transition-area between the chamber to where the rifling (land & grooves) starts. (A 5/16" drill at .3125" should do the trick......"but" you may not want to use that same barrel-assembly for anything but "Blanks".
The MG34/SA34 also needs to use the larger "L" shaped Feed-Tray-Spacer to help guide the Blanks down into the chamber "and" not allow them to raise up at the front and jam against the top-front of the feed-tray cut-out.
Regards, RichardS in MI.Blanksguy2001@chartermi.net
PS: Maybe someone can post photos and measurements for the plastic-Blanks.....which will run better "if" you use a 2-pcs. Blank-Barrel-Assembly. It has less weight just trying to move that short rear-section/piston.
.....and I will be making more of these 2-pcs. Blank-Barrel-Assemblies up in .308 cal shortly.....e-mail me if interested.