My New .177 FX Crown Has A Low POI On First Shot Just Like My .25

[milacik]

It is a workaround, not a fix bear in mind. You adjust different part, components of the gun to negate/compensate for the issue. Ultimately MP44 is doing the right thing sending back as the root cause has to be addressed.

 

[jking]

Or.... my thinking is now that the gun needed the HS tension adjusted this way to begin with. If the gun would have been in this tune condition there would have been no POI drop. I don't think in my case the regulator has much to do with it but I think I still might need to back off the regulator and keep my Heavies shooting around the 850-860 range.

jk

 

[milacik]

Nah the original poster said the reg output creeps up by what 8bar just by sitting there. Plus POI moves reproducibly as a result of that. If he wants to keep the shotcount and to keep the current quietness/efficiency he has to have the reg fixed in the first place. 

the workaround will be a compromise, giving up on these other things. Some people can accept that and obviously it is easier to work around as as the adjustment of hst is ‘nothing ’ just a turn of a knob on that gun. the fix itself is a major operation.

 

[skorec]

Try tuning it to the velocity knee...that is, just a shade under its maximum velocity. That will make it less sensitive to regulator creep. It's the same principle that applies to conventional (unregulated) PCPs, how they maintain a tight ES over a fairly wide pressure range.



I'm not familiar with all the knobs you can twiddle on the Crown but typically the way this tune is accomplished is by increasing the hammer spring tension until the velocity no longer increases. Let's say your max velocity was 920fps. What you would then do is back off the hammer spring tension until the velocity fell to about 97% of that maximum, or about 892fps in this example.



If that happens to place your rifle at a velocity where your accuracy is not optimal, you can restrict the transfer port to bring it down to the rifles preferred velocity.

Excellent explanation.

YES it is probably also the reason why to prefer velocity adjusting via air choking front of hammer spring preloading.