What PCP in .177

BSA Scorpion. I am pretty sure you can use discount codes for them at PA or AD or look for them to go on sale. I have the Scorpion SE in .177 and its very accurate and holds 1/2 groups at 50 yds pretty easy. The BSA Scorpion is also very easy to add a regulator to and with the 232 bar fill will give you allot of shots for the size of the rifle.
 
ahh sorry missed the under 600 part. yes limited then. The walther pcp can be had for under 600?

under 600 really put a dent in your options, the rotex can be had for under 600 after that then just the gamo pcp's that i would recommend. 

I would rather have a good barrel with a bad trigger vs a bad trigger and bad barrel but with a slow reg.

tbh might as well go even lower then and grab a diana stormrider for 199$ and then save up for something better. 
 
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I have a little 1720t that I’ve added a LDC to. It’s accurate, light, fun and not expensive.