Air pressure vs impact

[old sparky]

At the last field target shoot I missed the first 55 yard targets. I thought my shots were good. I couldn’t see my pellet impact so I didn’t know if I shot high low or didn’t see some wind. Yesterday I was marking up my scope for ranging and found out I was shooting almost a inch low at 55 yards. I had was sure nothing changed with my scope, no wind to speak of so I kept shooting the same hold at aiming points wondering. I wish I had keep track of the number of shots but I didn’t. After about ten shots I was shooting closer then I started hitting my mark. I checked my air and now was at 215 bar I started at 225 bar. Is that normal. Without shooting thru a chronograph I figure my velocity is slower at the higher fill then gets to the 215ish and then will stabilize. I knew 210 bar is marked on the rifle as the sweet spot but didn’t know my 55 yard impact could change that much above 210. I have started all my shoots at a higher pressure to be sure I had enough air. Comments?

Thanks Jim

[Terry Vanpool]

Well since you didn't tell anything about what gun you are shooting I will make some assumptions and guess you are shooting an unregulated Daystate but the same applies to all unregulated guns. In order to know what the sweet spot is you will have to shoot a full shot string across a chrono. Pick an area of the string where you can keep within a 20 fps extreme spread. You cannot rely on the recommended fill pressure marked on the gun. With a starting pressure of 225 bar you may be 50 fps or more below the peak of the shot curve and that will explain your low shots.

[Motorhead]

Exactly the subject of thread from a few days ago ... some good reading 

https://www.gatewaytoairguns.org/GTA/index.php?topic=139040.msg1398028#msg1398028

[old sparky]

Oops! I’m shooting a Daystate Huntsman.177
I couldn’t get my chronograph to pick up my pellet. So I’m guessing about velocity change. I am interested in further testing, also how many good shots I can get before refilling. Thanks for the link. I haven’t figured out looking thru the “Gates”

[Terry Vanpool]

Hey Jim,
The reason I could guess your gun is "been there done that". On mine I start at 2900 psi and get 45 shots in the 20 fps window. You won't get a full match out of it so don't try by overfilling the gun. You can't go by my numbers so you still need to get a full string measured so you will know where you are at.
BTW, my Huntsman Regal is capable of competing with anything accuracy wise in Hunter class FT. You just have to refill mid-match.