As far as I could tell and IIRC, the blast shields that fell off at 400 and 500 rounds were the result of an installation/frame problem -- i.e. not erosion related. So, I'm guessing it will take 300 to 500 rounds to start to see anything.

The gun I'm working with has had 174 rounds fired to date (since the new frame/blast shield). A2400 - 26 rnds, H110 - 52 rnds, HP38 - 6 rnds, and VV N110 - 90 rnds. I took the pictures today for future comparison purposes:






I don't see any erosion at this point. The second photo shows what looks like a shallow depression in the area you would expect to see erosion. I couldn't feel anything with the figer nail or a plastic pick -- it might be light shadow and/or residue that didn't get cleaned off or stress from where the front of the shield was bent to fit under the barrel extension.

Paul