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QB79 vs. qb79 repeater velocity differences....Doesnt make sense

December 27 2016 at 9:47 AM
VAF  (Login VAFarmer)
YC

Can someone explain to me what gives the qb79 repeater a 100fps velocity increase over the regular qb79 ( .177 ).

It seems to me that the increased dead space would make for less velocity/

Is 700 fps attainable in .177 on the standard version and 88 gram carts?

Thanks in advance ya'll.

God bless,

Farmer

 
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Steve888
(Login Steve888)
YF

Here's Why It Makes Sense...

December 27 2016, 1:35 PM 

Farmer,

The QB79 Repeater uses a different bolt to that of the standard QB79. The Repeater bolt is based on the XP Tune bolt and that - together with the superior breech seal compared to the single shot factory gun - is the cause of the higher muzzle velocity in the Repeater. There's over 20 different parts in the Repeater when compared to the factory, single shot QB79...

Answering your question about 700 fps muzzle velocity in a standard gun is somewhat complex. The muzzle velocity of any gun will vary with the pellet weight. And, with any CO2 gun, the temperature makes a big difference also. For example, the muzzle velocity of QB78-type guns varies by about 2 fps per degree Farenheit. So a gun shooting a specific pellet at 600 fps at 65 degrees F will shoot the same pellet at about 640 fps at 85 degrees F.

The muzzle velocity numbers we quote are with "real world" medium weight pellets - 7.9 Grains in .177 caliber.

I'd say that it might be possible for a .177 factory gun to - just - reach 700 fps with the lightest possible (eg 4 Grain) alloy pellets shot at 90 degrees F +. But with an unmodified gun shooting medium weight pellets in average temperatures, no.

I hope this helps,

Stephen Archer
Archer Airguns Inc.
http://www.archerairguns.com




 
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VAF
(Login VAFarmer)
YC

Thanks for the explaination......should I then

December 27 2016, 2:05 PM 

infer that if the factory Qb79 (single shot) were to be given that XP bolt and the same upgraded breech seal that it would do ~700 fps as well?

God bless,

Farmer

 
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Doug Wall
(Login DougWall)
YF

Re: Thanks for the explaination......should I then

December 27 2016, 7:50 PM 


 
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Steve888
(Login Steve888)
YF

Yes, That's Correct.

December 28 2016, 10:14 AM 

Farmer,

The XP Tune Kit will give approximately 700 FPS with 7.9 Grain pellets at around 65 - 70 degrees F when fitted to a .177 caliber QB78 or QB79 single shot air rifle.

Doug, thanks for providing the link to more details!

Please note that although the XP Tune Kit bolt and the Repeater bolt are very similar, they are not interchangeable as they have slightly different designs in ways that are not significant to muzzle velocity.

Stephen Archer
Archer Airguns Inc.
http://www.archerairguns.com

 
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