QB78 .177 MV- okay @ 600fps?

QB78 .177 MV- okay @ 600fps?

Joined: June 9th, 2016, 11:17 pm

January 27th, 2017, 7:17 pm #1

New .177 QB78 bought 12-2016. Totally stock. Tested using a chronograph. First CO2 cartridge, getting ~600 fps w/Crosman Premier HP 7.9 gr, want to know if this is reasonable or abnormally low- I've seen reports of QB78 velocities being higher but little/no info on what, if anything, has been done to these guns to get the higher MV. All that I have done is clean the barrel prior to shooting it the first time.

Thanks in advance, Mark
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Joined: November 17th, 2006, 3:51 am

January 27th, 2017, 10:55 pm #2

How cool was the rifle (lets assume it was whatever the air temperature was)?
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Joined: March 28th, 2002, 6:54 pm

January 28th, 2017, 2:03 am #3

New .177 QB78 bought 12-2016. Totally stock. Tested using a chronograph. First CO2 cartridge, getting ~600 fps w/Crosman Premier HP 7.9 gr, want to know if this is reasonable or abnormally low- I've seen reports of QB78 velocities being higher but little/no info on what, if anything, has been done to these guns to get the higher MV. All that I have done is clean the barrel prior to shooting it the first time.

Thanks in advance, Mark
There's lots you can do to bump the velocity up, the archives here are full of tune tricks, but this kit from Archers..http://www.archerairguns.com/QB78-XP-Tu ... unekit.htm is a great place to start as a newbie 78 tuner.
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Joined: May 22nd, 2016, 9:38 pm

January 28th, 2017, 6:36 am #4

New .177 QB78 bought 12-2016. Totally stock. Tested using a chronograph. First CO2 cartridge, getting ~600 fps w/Crosman Premier HP 7.9 gr, want to know if this is reasonable or abnormally low- I've seen reports of QB78 velocities being higher but little/no info on what, if anything, has been done to these guns to get the higher MV. All that I have done is clean the barrel prior to shooting it the first time.

Thanks in advance, Mark
...a stock QB78 .177 should do about 625 fps.

But what the other fellow said: CO2 is highly sensitive to cold temperatures.
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Joined: June 9th, 2016, 11:17 pm

January 28th, 2017, 8:11 am #5

New .177 QB78 bought 12-2016. Totally stock. Tested using a chronograph. First CO2 cartridge, getting ~600 fps w/Crosman Premier HP 7.9 gr, want to know if this is reasonable or abnormally low- I've seen reports of QB78 velocities being higher but little/no info on what, if anything, has been done to these guns to get the higher MV. All that I have done is clean the barrel prior to shooting it the first time.

Thanks in advance, Mark
It was around 60-65 deg. F. when I tested the MV. If 625fps is about "normal" @ 75 deg. F, my gun is about where it should be, maybe a touch low, so I guess I can live with 600fps @ the temps I was shooting at. Thanks everyone.
Last edited by cobalt327 on January 28th, 2017, 8:15 am, edited 1 time in total.
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Joined: November 17th, 2006, 3:51 am

January 28th, 2017, 2:41 pm #6

...rifle won't cool down super fast, so if you set it in a warm room for a half, then quickly chronograph a couple of shots.

Good news is that all the QB's so far have gotten a little faster as the moving parts "mated up" and ran smoother.
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Joined: June 9th, 2016, 11:17 pm

January 29th, 2017, 2:28 am #7

According to a very reliable source, Steve Archer of Archer Airguns, "The muzzle velocity of QB78-type guns varies by about 2 fps per degree Fahrenheit". So my gun is right where it should be. Guess I'll have to find something else to worry about!

Thanks for the help, everyone. I appreciate it.

Mark
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Joined: January 9th, 2005, 1:46 am

February 7th, 2017, 8:23 pm #8

Yes, 600 FPS for a stock QB78 in .177 caliber is right on the nail for muzzle velocity at 65 degrees F.

And yes, my experiments showed a difference of around 2 FPS per degree F in temperature change.

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