Qb78 deluxe .177 … 70+ accuracy.

[skorec]

May be light wind,  low riflescope magnification ( 12x ) or still not perfect barrel crown case so bad accuracy.
Have you  better  accuracy at long distances ?

[Smaug2]

If you're talking about accuracy at 70m, that's not bad, for .177. .177 starts to de-stabilize after about 50m and is really effected by the wind.

If you want to shoot at 70m, you'd be better served by a .22 or .25.

12X scope is a limitation too; it limits how precisely you can see the target and stay lined up on it.  The reticle "becomes thicker" at that range. I was shooting at 37 yards yesterday with 10X, and even with a fine reticle, it was pushing it. I switched to my other rifle with a 24X scope and it made a difference.

At any rate, the last thing I'd blame is the gun. The other three things all have their contribution.

[skorec]

The wind has stoped and the gouping at 73m is closer a litle bit.
1" at 78 yard. 

[nervoustrigger]

That's really good for .177 at that distance.   Chairgun shows that an imperceptible amount of wind (3mph) will push the pellet 4 inches at that distance.  A 1" group is fantastic!  Well done! 

The wind must have really been calm at the time you shot that because you can see the group size is defined by vertical stringing.  What sort of ES are you getting?

[nervoustrigger]

By the way, the other reason I'm asking about the ES is because 252m/s (827fps) seems really slow for 1500psi.  It should take only an infinitesimal amount of lift and dwell at 1500psi to achieve that velocity.  Either that or you've had to choke off the porting considerably.  If the former, your ES may be suffering because the valve is just barely being knocked open and that leads to a higher shot-to-shot variation.  I assume this is a regulated setup, in which case it would work better to reduce the pressure and adjust the hammer strike to get back to your desired velocity.

[skorec]

Sorry I do not know what is ES.  I have just maximize diameters  on air transfer way ( but  not jet the valve itself  ) and I have added 4mm spacer to original hammer spring. Also filc filter is still inside the valve body because I stil use sometime  CO2 too.

Shooting was done by connecting to Ninja 4500 to 1500 air presure regulator as you can see on the picture.

[nervoustrigger]

ES is extreme spread.   Since you are working with a regulated setup, you can just chronograph 10 or 15 shots and look at the min and max velocity.  The min should be within 1% or 2% of the max.

You have a good point about the filter limiting flow but I think that's only part of the reason.

Based on my experience with the QB platform, a 4mm hammer spring spacer is probably barely cracking the valve open at 1500psi.  That is, with ever thicker spacers, I expect the velocity would climb quite a bit.  But don't fool with it yet, just get some chronograph numbers and see what that tells us.

[skorec]

ES is extreme spread.   Since you are working with a regulated setup, you can just chronograph 10 or 15 shots and look at the min and max velocity.  The min should be within 1% or 2% of the max.

You have a good point about the filter limiting flow but I think that's only part of the reason.

Based on my experience with the QB platform, a 4mm hammer spring spacer is probably barely cracking the valve open at 1500psi.  That is, with ever thicker spacers, I expect the velocity would climb quite a bit.  But don't fool with it yet, just get some chronograph numbers and see what that tells us.

Thanks,
I have not been concentrating on velocity changes  too much but differences was about 2%.
In according too short spring spacer a need to notices that if I shoot without the air line connected  to ninja regulator output  the ES was “
1.   1500 PSI  250 m/s
2.   1350 PSI  240 m/s
3.   1200 PSI  230 m/s
4.   1100 PSI  220 m/s
5.   1000 PSI  210 m/s.

In according to this I  was planning   not to use the spacer at all.

[nervoustrigger]

Okay, got it.  I agree, you are seeing increasingly higher velocity as you increase pressure so that suggests you have enough hammer strike.  And your ES of about 2% is right in line with a properly configured regulated setup.  Seems like we've reasonably ruled that out as an explanation for the vertical stringing.

To be fair, one group isn't enough go gauge a trend.  Just keep an eye on your groups to see if there is a tendency to have one type of stringing over the other.  Obviously that's easier said than done because the tiniest bit of wind will have a profound effect on horizontal stringing at those distances.

[skorec]

Jason,

This group  is going  to be   my best group at 78 yards for the time.  Just a little bit better group I made  by using my AA S 510 .177 carbine from the same BR place by using the same 4,52 Heavy pellets with a little bit higher speed . Interesting is that 1:LW 17,7 chocked barrel seems to be more choicy  for pellets as  QB deluxe barrel .
 
Thanks that you  have noticed me for a wind . I was forgetting on it by these new 78 Yards BR shooting place.
 
I hope that some guys add here also better .177 long distance groups .

[skorec]

I have checked  accuracy again  . 
Interesting is that the  last  barrel re crowed tool not see right at all after I have stoped  recrowing.

[skorec]

Do you know which is exact  caliber of JSB premium pellets ( 4,50 or 4,51 or 4,52 or 4,53 ) ?
They shoot a little bit to right than standard Exacts 4,50 mm