QB78/79 - RVA How To?

[sr1sws]

I've looked around and it appears that the 'typical' QB7x RVA is drilled off-center to miss the bolt/screw tying the trigger group, air tube and breech together.  I saw one that was described as drilled on center with bolts/screws entering from top through receiver and below - unfortunately there were no photos.

So, is there a 'how to' documented that I simply failed to find?  If not, suggestions are greatly welcomed.

Oh... I did install a cock on opening mod that uses a tight fitting plastic (possibly Delrin) spacer behind the cocking block/spring guide.  As it is very tight, it would seem that it should not cant under the off-center pressure from the typical RVA.

Thanks for any suggestions or tips!

Steve

[nervoustrigger]

Hi Steve,

I am accustomed to the off-center RVA approach and have applied it to several QBs.  If you prefer to do an on-center RVA, I will not attempt to talk you out of it.  However, if you are looking into it on the basis that the off-center type causes the spring guide to cant and produces erratic velocity...well, that is not borne out in my experience.  Just as an example, the 30-shot string that UCChris posted a few weeks ago was produced with just such an RVA:

Code: [Select]

30 shots
High:  857fps
Low:  853fps
ES:  4fps
SD: 1.38

That is consistency a $1500 rifle would be proud to deliver.

[sr1sws]

Hi Steve,

I am accustomed to the off-center RVA approach and have applied it to several QBs.  If you prefer to do an on-center RVA, I will not attempt to talk you out of it.  However, if you are looking into it on the basis that the off-center type causes the spring guide to cant and produces erratic velocity...well, that is not borne out in my experience.  Just as an example, the 30-shot string that UCChris posted a few weeks ago was produced with just such an RVA:

Code: [Select]

30 shots
High:  857fps
Low:  853fps
ES:  4fps
SD: 1.38

That is consistency a $1500 rifle would be proud to deliver.

Thanks Jason.  Obviously the off-center version is much easier to pull off.  I believe that's the route I'll go.

Thanks!
Steve

[Millipede]

do you need the cock on opening mod for the RVA to work right?

[sr1sws]

do you need the cock on opening mod for the RVA to work right?

I *think* so... maybe someone with definite knowledge can chime in.  The native cock on close setup of the QB7x series seems weird - I'm not sure I fully understood it or why it would have been designed that way.  Cock on open (the version I have anyway) would have only added 1 spacer but eliminated at least one machining operation and a pin.

In retrospect, it appears easy enough to do yourself, other than drilling the striker, which is surface hardened.  Supposedly you can grind a flat through the case hardening and then drill it.  I wanted a 2nd hammer anyway - as I flat-sided the new one and wanted to be able to go back to stock if it didn't work the way I wanted it to.

Steve

[rloftus]

You can use the helicoil setup as described here for a centered RVA.  This makes a nice modification that I use on all my QB78 and 79 models.

http://www.gatewaytoairguns.org/GTA/index.php?topic=75939.msg722511#msg722511

Roger

[sr1sws]

Sweet Roger, I'll check it out.

Thanks!!
Steve