How bad/inefficient can you design a PCP rifle?

[Chickenthief]

Mr. Hollowpoint has tested the Umarex hammer:



Why wont the video link work???

And it strikes me that they only boast 705fpe on the box and can hardly get that. Pre production they claimed 800+fpe for years.



But he shoots two shots on a fill and it drops below 24-2600psi from 4500psi (@ 18:20 in the video).
Lets just say 750psi/52bar per shot from a 480cc bottle, thats 25 liters of air per shot and at best getting 660fpe. The Texan will get 660fpe using less than half of that amount of air.



225gr: 527ftlbs
 255gr: 551ftlbs
 270gr: 516ftlbs
 345gr: 581ftlbs
 350gr: 563ftlbs
 385gr: 567ftlbs
 445gr: 650ftlbs
 450gr: 577ftlbs
 500gr: 635ftlbs
 525gr: 623ftlbs
 550gr: 660ftlbs

Is this due to "bad" design or is it a trade off for the light cocking force?

[rsterne]

That's better than my DAQ .308 Exile as delivered, it was 0.38 FPE/CI.... There are a few other Big Bores that are less than 0.40 FPE/CI as sold.... If the Hammer is getting 660 FPE from 25L (1524 CI) that is 0.43 FPE/CI.... Horrible, yes, but not the worst by any means.... 

Pretty much any PCP which keeps the valve open until the bullet exits the muzzle to get maximum FPE will be under 0.50 FPE/CI.... 

Bob

[Chickenthief]

Learnig something new every day :-)
Thanks for the info.

[Acetek2]

It seems from watching a disassembly video of The Hammer not much thought was put into efficiency for reasons that may include cutting costs. I am referencing "Umarex Hammer Isssues" Posted by Will Roman's Air-gun World. In the video, the plenum is rearward at 51:42, nearest the stock and is regulated from the front tube. I mean...............it dumps that plenum at stated 3000 psi? Seeing that the breach seal is being blown out of the gun from quasi manufacturing quality doesn't make the impression any better. My thoughts anyways........