Headspacing

[G.T.]

Hello to all! I'm not a gunsmith, hardly even a mechanic.. but I've always had a suspicion that the best way to learn, was to do? The second best way is to listen closely to those who did! Soooo, I'm going to relate a recent experience with re-barreling a Luger with a standard P.08 4" military take off barrel... excellent bore, and very nice overall... I removed the .30 Luger barrel without incident, good so far... Then I installed the used original 9mm 4" P.08, went on perfectly, so good so far....
Drop in the "GO' gauge, closes fine... Drop in the "NO GO" gauge and closes fine! What? Wait a minute, NOT GOOD! How come, What? Why?.... Need to dig further...

First observation, toggle assembly seems very loose?.. Most of the play is in the two forward pins, the breechblock pin and the middle toggle pin... I HATE to work on the middle toggle pin as sometimes the small middle toggle pin retaining pin becomes a work monster all by it's self! So, what to do, well the rear pin seems fine, but we'll put in a pin that is as new and fits pretty tight, then, we install a breechblock pin that tightens things up a few thousands as well? As we are being timid, we hope the middle toggle pin is good enough?... Re-test with the "NO GO" and find you have to push a little, but it will still snap closed on the "NO GO".. Good enough? Let's go the range and see!
First round, perfect! No issues, problems, works fine... Halfway thru the first mag full, I see one of the empties has a black primer hole? I load up another mag, as I'm determined to see if this is a problem or just a fluke? At the end of the second mag! Kaaa Boom! we got trouble! I could feel it, and the gun jammed... I cleared it and was ready to continue, and thought, stop you fool... pay attention?... So, knowing it needed improvement, home I went...
Well, the result was, on the brass I collected, one of the pierced primers had flattened the primer as well? Also, it broke the fining pin retainer head off, and pushed it thru the back of the breechblock!! Not only that, but it also lifted the breechblock metal on both sides of the extractor, failure was on its way, a few more rounds and we would have probably had a catastrophic failure...
Soooo, after a little thought, I replace the breechblock with a nice original, breechblock (at my expense, and also the firing pin retainer, also at my expense!) and totally re-pined all the of the toggle train with original oversize pins!!! Wala, head space came back to normal, (probably .004" over "GO"?) range test 100% normal...
Off and away back to the owner! I also replaced the solid firing pin with a fluted one, and would have liked to see if this would have happened at all with the later pin? But, I'm short on breechblocks and not really interested in ruining more, at least for now?... … BTW, the difference between the "GO" & "NO GO"
is approx. .020" I now think, if you have play in your chamber, it better not be more that .010" past "GO" or more than half way between the gauges?... Less is MUCH better, and very tight on the "GO" even better yet!!! Hope this enlightens some of you! No place for the timid here! Best to all, til...lat'r....GT....