Are you getting a full stroke???????????????

[mikeiniowa]

Was working on a 78 today and noticed as I reassembled it that the striker wasn't getting a full stroke, problem turned out to be that it was hitting the inside plug (#0200) , took it apart again and started measuring parts, the pin wasn't hitting the front of the cut out in the bolt either, in fact there was at least 20 thousands more stroke to be had at the very least before the pin would hit anything. I did some testing with a stock plug installed and with one that had been shortened by 20 thou., does it make a difference? not to much with a stock rifle, possibly a 5 fps gain. I'll be checking it once I get all the parts modified for a full power tune and see what if any change there is.

[Jaymo]

Hmm, I hadn't though of that. Then again, I haven't even gotten started on tuning mine.

[DanoInTx]

I know on the B50/51 PCP's you can get higher/lower power by adjusting the screw in the front of the hammer that actually strikes the exhaust valve.  By increasing the gap between hammer and valve stem power goes up, by decreasing the gap power goes down.  Increasing gap gives the hammer more room to pick up speed, I couldn't think of a reason why a QB78 would be any different.