I finally got a Luger.....nothing unusual, just a reblued 1914 DWM shooter that I probably paid $100 or $200 too much for. But it looks good (other than poor aftermarket grips), is "mostly" matching, and most importantly, is "mine"

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This is what's going on:
If you slowly bring the toggle forward, spring tension will not completely close the breech. To close it the last 3/16"- 1/4" or so, you have to lightly push down or tap on the toggle. It will only "spring" closeed the last 1/16". If you release the toggle from the fully rearward position, the centrifigual force will fully and strongly close the breech. With the breech fully closed, you can pull the toggle with VERY LITTLE tension fealt (if any) until the breach is open 3/16"- 1/4". I've never owned a Luger, so i don't know if this is normal op's or not.
I took it to the range to test fire it and had issues with the Breech and Toggle. After the first shot the sight picture looked "odd". The cause was the breech wasn't fully closed. Pushed down on the top of the Toggle (very little pressure was needed....more of a "tap") to close the breech the last 1/8" and fired again with the same issue. Every time I fired I had to close the breech fully to fire again. I also did the masking tape to the back of the frame to check for any battering by the rear of the Toggle. I was suspicious due to some out of place bare metal marks/nicks at the Frame/Toggle area. My suspicions were correct and the tape was usually mashed to goo or transfered to the Toggle at the previously nicked spots after just one shot. I only fired it 15 times, 5 rounds each of Winchester White Box, Blazer Brass, and Federal....all of them caused the same issues with the breech not fully closing and the Togggle/Frame contact.
I suspect I may have a weak or short mainspring. Or do you think I may have other issues?
The guy i got it from has a 3 day inspection period, and my first instinct is to send it back. But I got to thinking that if it's just a mainspring issue, I can take care of it for a $15 spring kit as opposed to paying to ship it back AND bite the original shipping cost which would combine to between $50-$60.
Your thoughts and or advice?