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 Post subject: QB78 or 79
PostPosted: Tue Jan 30, 2018 6:23 pm 
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Joined: Tue Sep 22, 2009 9:57 pm
Posts: 64
Location: Aurora, ON, L4G7X4
I cannot recall seeing 25cal barrels for these? What are the closer fits eventually with some lathe rework?
I made some nice mods on my 22cal following the threads here @ AF, got to a point of pretty consistent speed of 740@800psi with 21g pellets.
I have two more 1200 psi and two 1800 psi tank regulators but afraid to mount, not really interested for higher noise level but more into jumping into a next OD and weight in size. Still winter long way to go, enough time to prepare the boy for longer ranges.


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 Post subject: Re: QB78 or 79
PostPosted: Tue Jan 30, 2018 7:46 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8936
Location: Coalmont BC
QBs are not available in .25 cal, it would be a custom job.... The standard QB78 has a 14mm barrel, the Deluxe (and I believe the QB79) have 15mm OD barrels.... Lothar Walther's standard .25 cal barrel is 23.8" long (about 2.5" longer than a QB) and is 16 mm OD.... It could be turned down to fit inside the receiver, and would still clear the main tube, although it might hit the knurled nut at the front (worst case, file a small flat on the bottom of the barrel to clear it).... Also, you would have to modify the barrel band, or make a new one for the larger OD barrel.... In addition, you would need a larger bolt, and of course the barrel would have to have the chamber, leade, port and loading tray machined at the breech end, and crowned at the muzzle....

I would not run more that 1400-1500 psi regulated pressure, because you need to protect the gun with a 1.8K burst disc on the output side of the regulator (do NOT change it out for a 3K).... and 1600 psi or higher will blow the disc (it may even blow at 1500)....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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 Post subject: Re: QB78 or 79
PostPosted: Tue Jan 30, 2018 9:38 pm 
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Joined: Tue Sep 22, 2009 9:57 pm
Posts: 64
Location: Aurora, ON, L4G7X4
Thanks rsterne
I have the archers repeater upgrade kit installed I believe that barrel is 15mm. The barrel is raised from the cylinder way too much to my liking, I would need to solve that sooner or later. Not sure if the 16mm barrel you mentioned will have the port hole close enough to QB's but without having a closer look I must admit I will pass that purchase.
I may go then for a heavier 30g+ pellet with a pressure jump from 800 to 1200 psi. With a 21 grain pellet I would probably brake or come too close to the sound barrier and I don't want to go that way.


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 Post subject: Re: QB78 or 79
PostPosted: Tue Jan 30, 2018 9:44 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8936
Location: Coalmont BC
The LW barrels are "blanks", supplied "in the white".... That means they have a rifled bore, with a choke at the muzzle, but NO other machining done.... and are plain steel, not blued.... Pretty much all aftermarket barrels are supplied the same way.... The only way you will get something that you can bolt into your gun is to buy one already machined to fit it.... I don't know of any to fit QBs....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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 Post subject: Re: QB78 or 79
PostPosted: Tue Jan 30, 2018 9:53 pm 
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Joined: Tue Sep 22, 2009 9:57 pm
Posts: 64
Location: Aurora, ON, L4G7X4
A friend of my have a machine shop with couple CNC's and one old lathe, I may be able to take care of the fit to the breach block, but the internals I just finished and no spare parts to play with ports.
btw, wanted to upload some pics from my project but this forum seem to me working a bit different...
figure it out :)

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 Post subject: Re: QB78 or 79
PostPosted: Wed Jan 31, 2018 12:47 am 
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Joined: Sat Nov 05, 2016 10:52 am
Posts: 2612
Location: Caronport, Saskatchewan
Cool! Neat idea [emoji846]
That's pretty good velocity you are getting at 800psi! You must have opened things up quite a bit inside.

Sent from my LG-H812 using Tapatalk


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