Modified side lever AR2079B to hpa

[rloftus]

I wanted to try a .177 caliber rifle for target shooting, and I wanted to show a few steps with what I came up with.  I ordered a side lever AR2079B rifle, and intended to set it up for regulated air.  I hoped to obtain about 900 fps with 10 grain pellets, and I hoped rsterne’s modification would develop enough air in the QB79 platform with limited reservoir capacity.

When I received the rifle, most was what I expected except for one thing – the barrel was horribly bent to the left.  When I later removed the barrel, from the breach end to the muzzle showed an offset of .192 inches when tested on a gauge block.  That kind of dampened my enthusiasm, but I decided to proceed as planned.

I reset the regulator to 1300 psi and installed it on the gun.  With that setting and without other modification, the gun would shoot 10 gr JSB’s at about 600 fps.  Forget trying to hit a target with that barrel!

From there, I pulled the gun apart and performed the modifications shown below.



The first modification was rsterne’s air chamber modification.  I cut down the valve assembly and installed the mounted spring return to the rear block.  I changed the valve by machining down the rear collar, and notched it for tightening down the o-ring for a more secure seal.  The valve was streamlined and a notch was cut for the spring seat at its base.  With silicon o-rings installed on the valve and block, everything is leak free.

The next big thing is the cock on opening modification.  The first step is drilling a 3/16 hole as far back as possible on the hammer behind the original hole.  I had to press in a 3/8 inch spacer into the hammer so the new hole has a solid base. I had to remove about .25 inches from the hammer spring guide to clear the 3/8 block in the hammer.

 The hammer is very hard, so a hardened bit is recommended.  With the cocking pin placed in the new hole, the bolt is moved back enough when cocked for good pellet feeding as shown below.



The final change for the cock on opening is the modification to the magazine end plug.  I placed the RVA screw in the center of the plug and tapped it 10-32.  From there, I carefully tapped the existing vertical hole through the plug with a Helicoil 10-32 tap.  The Helicoil inserts are exactly the right length to fit up to the edge of the RVA screw hole, and provide a very secure fit for the 10-32 upper 1” screw and .5” lower screw.   The action on this gun is very nice, and the cock on open is very smooth up to the hammer lock on the sear.  The no tension entrance of the pellet gives you a good feel for seating into the barrel, and a desirable bolt lock when toggle is closed.

I should mention the transfer port area of these airguns.  I prefer to shallow mill the valve and breech areas to .25 od, and use Nylaflow .25 x .190 tubing for the transfer seal.  It is good to pay attention the alignment of the barrel and breech, and the bolt probe as well.  On this gun, the bolt probe inlet was so tiny and not completely cleared, and I am sure this alone had a huge impact on performance.  The modified probe is shown below.



Now fixing the barrel.  I was tempted to buy a new one, but thought I would try working on the bent barrel to see if I could straighten it out.  After about 20 trips to the press, the flat plate, and then the lathe, I had the barrel down to a few thousands.  From there, I put the gun together and extended the stock so that I could shoot it.



I sighted the gun at about 12 yards, and did the chronograph testing to see what it would do.  With the RVA screw turned in so the gun would just cock, I would get about 940 fps   with JSB 10.34 gr pellets.  As I backed the RVA screw out, the velocity slightly changed until I reached about 900 fps, and I used that as a fixed point for this gun.

Next, shooting my normal 50 yard target.  I shot twice and could see I was quite close so finished a 5 shot group.  I carefully adjusted the scope to the new center and shot 5 more pellets at the target.  I couldn’t really see where these hit, so I walked up to see what had happened.



I was just blown away – I’m just not that good a shot, but it sure looked like the gun had some real promise.  Anyway, it seemed good enough to finish the stock and complete the gun. 

Here is the fore-stock being made.



And epoxyed together before sanding and finishing.



And here is the finished product.  Kind of an ugly duckling at that.



There is some real satisfaction completing a rifle like this and making something better than can be purchased at the price.  Even if it does not turn out well, there is much to be learned for the next effort.  Very much part of the airgun attraction!

[Tomg]

Very nice work buddy!
Love the additions to the stock, makes it look a bit more grown up!

T

[wilsonj1018]

congrats bud, I miss my old qb I built quite badly.
Josh

[rsterne]

Well done !!!

Bob

[renowntwo]

Nicely done.

[nervoustrigger]

Excellent work, I like what you have done.

Having built several QB HPA conversions for folks, I know what you mean about the feeling of satisfaction that comes with making them shine.  From the factory they are very much diamonds in the rough, and even with my rudimentary metalworking skills, I have gotten excellent results from each and every one.  A .22 cal tuned to 33fpe with JSB 18.1gr is my everyday hunting and pesting rifle...shooting from a table, headshots on squirrels at 65 yards have become routine.  I love it.

I do have one question for you regarding your barrel.  Other than straightening it and porting it, did you do anything else?  Polishing, leade work, crown, etc.?

[rloftus]

Thanks everyone!

Jason, how could a barrel be so bad, and be good at the same time.   While the pellet impressions looked good after straightening the barrel, I really wasn't expecting much in the way of performance.  No other barrel modifications except for cleaning with a few patches.  I am pretty happy with the way it turned out, and again, this is now my most accurate airgun.  The second is the reverse bottled qb78 .22 rifle I described earlier, and it has an unmodified barrel also.   Just great performance from these airguns when set up properly!

Roger

[rewinder]

Nice write up on a project well done and thought out! Nice machining and woodworking .

I did a similar rework on my 79 with a repeater breech, but I like the looks of your stock. would like to get the target stock, How did you attach the forarm to the stock?

[rloftus]

Rewinder, I epoxyed the parts together with high strength (not 5 minute) glue.  It is very important to cut small channels in the surfaces to be bonded together, and use a cotton flox epoxy filler mixed in to greatly strengthen the the bond.   Without flox, I doubt the bond would be permanent under the very worst circumstances.  You mix the flox into the epoxy until it is fairly thick, but will still flow well over the pieces to be bonded.  Done properly, the joint should be stronger than the wood itself!
 
Roger

[rewinder]

thanks for the info, I've used micro balloon epoxy filler, I just googled to find out what the flox is.

I like that you can pop the stock off and not interfere with the gauge.

 think this will be my winter project, and it won't put the 79 out of commission while working on it

[Ribbonstone]

Very nice rifle, with much nicer stock treatment than my old conversion.  Used a long tubed AR2078, and don’t mind the “hanging bottle” feel of it, but your final product looks much better.




Been a few years in use, no real problems once it’s  set up right. Haven't decided about the side-lever version, although I"d welcome your thoughts on that.  The QB barrels really can be very good, hanging in there with the “big boys”.

[rloftus]

Ribbenstone, the side action is a delight!  I carefully shimmed the pivot point so the toggle is very tight, and with the RVA and bolt pivot set as shown, the pullback to sear engagement is very light.  Pellet entrance is very well enhanced as well.  The whole thing really works much smoother than  my AT44-10 side lever.

I an really thinking about converting my bolt action reverse bottle QB78 to a side lever also.  There would be quite a bit of machining to change the bolt probe from the .177 side action setup, but I really think it would be worth it.  There is quite a bit of bolt tension in the cock on open setup on this airgun and the side lever option would completely remove that.

I guess I am looking at another project!

Roger

[Ribbonstone]

Lot of airguns about the place, but only one side lever.  Really haven’t made up my mind about side levers.  Can see where it might be easier to cycle (better leverage) but I’ve just been too conditioned to reach for a bolt.

I'll think on it, use that side lever a bit more often than i do.