D460 low fps tried breech seal and spring...

[splitbeing]

Diana 460 .22 14.3 CPHPs going 780.

Changed breech spring. Tightened up the ES a bit.

Changed the breech seal. Old one looked fine. No real difference, maybe 3 fps.

Opened up the gun. Piston seal looks fine. Spring is straight. Lube is good.

Any ideas? My expectation is low 800s.

[Robert 5mm]

Is this a new to you 460 and do you know it's history.

I would start from scratch and put in new spring and piston seal after what you already did.


After your post : I would get new spring and piston seal.

[splitbeing]

Got it new a handful or more years ago. It hasn't been shot much. Maybe 1000 rounds.

[Roadworthy]

How tight is the piston seal?  You've probably not shot the gun enough to "break it in".  If the seal is too tight your velocity will be low.  If it's too loose your piston will slam against the end of the compression tube.  Ideally I like to try for three to five pounds of force to move the lubed piston seal on the piston through the compression tube.  I will turn the seal until I have the desired amount of resistance.

[splitbeing]

How tight is the piston seal?  You've probably not shot the gun enough to "break it in".  If the seal is too tight your velocity will be low.  If it's too loose your piston will slam against the end of the compression tube.  Ideally I like to try for three to five pounds of force to move the lubed piston seal on the piston through the compression tube.  I will turn the seal until I have the desired amount of resistance.

Thanks, Thomas. I'll try that.  The piston does seem a bit tight. I'm putting it through it's paces, shooting a lot, hoping it breaks in. If it stays low, I'll open it up again and relube with 3 to 5 lbs of force to move the piston in mind.

[Mark 611]

That's too much pressure for a piston seal! need needs to like 2lbs of force

[lefteyeshot]

Too much lube?

[HectorMedina]

Diana 460 .22 14.3 CPHPs going 780.

Changed breech spring. Tightened up the ES a bit.

Changed the breech seal. Old one looked fine. No real difference, maybe 3 fps.

Opened up the gun. Piston seal looks fine. Spring is straight. Lube is good.

Any ideas? My expectation is low 800s.

Have you tried other pellets?

I am not a fan of CPHP's, as the basic Premier design is based on a head seal AND rifling guide.
IMHO, too much to ask from a single section of the pellet; and, DIANA barrels tend to be on the "wide" side.

IMHE, the efficiency of an airgun can vary as much as 10% when comparing pellets (same barrel, same powerplant, same pellet weight).

Which means that the ENERGY difference for pellets of the same weight, but different design can be up to 10% more/less efficient than others.

Since energy is a function of the SQUARE of the MV, then you can expect differences of as much as 4.9% in MV, and you are looking for 2.6%, so a simple change of pellet COULD be the solution.

If you are thinking that you should use the CPHP because of the "HP" do remember that the little dimple is a production shortcut to make the heads more even and uniform. It was never intended to be a true "hollow point" (as in "expanding" ammo).

Personally I do not fret for differences as small as that. As the old Guru once said: "He who lives by the chrono will die by the chrono".

IF CPHP's are being dead on and consistent for you at that power output, stay with it. Learn the trajectory and use the stability of the "lower" speed as your advantage.

I am shooting 9.56 / 4.51/ 0.177"s out to 55 yards at 720-730 fps and have found that the stability and consistency gained more than outweigh the few fps that would be allowed by the rules.
Some of the best World Class competitors shoot at 740 fps, even with lighter pellets (8.44's)  because at LONG range (55 yards), the behaviour of the pellet is consistent and uniform.

Just some thoughts

HTH, and keep us posted!






HM

[Razor62]

I had a friend bring me his 460 that he purchased as a refurb because it wasn't shooting very consistently at all. What I discovered was that over time, several pellets had been dropped into the sliding breech area apparently without being noticed. Each time that this happened, the cocking lever was returned to the home position which resulted in the pellet being mashed up into the face of the receiver tube. Eventually, there was enough lead there to keep the breech seal from seating completely.
The video below that I made shows the issue better than I can explain it.

[splitbeing]

Thanks for the comments and suggestions.

I went into the gun again. The piston went in with what I guess is a few pounds of pressure.

 Although the piston and seal are lubed, I can still hear the piston seal when cocking most times. I think the moly behind the seal needs more time to do its work.

I did not find any smashed pellet lead but did look. Thanks for the tip. I like your videos.

750 fps is a fine shooting speed for the cphps. So going with what works makes sense to me.

I like thehandling of this gun. The grips are nice and with a scope the balance is right where I want it.

I found a video by wisconsin airgunners with helpful info. The author doesn't know much about spring guns. However, his 460 is putting out the same fpe as mine. Maybe the newer 460s in .22 are 18/19/20 fpe guns now?