QB79 HPA with .177 LW retrofit

[nervoustrigger]

Hi guys,

I was rummaging around in the shop a few weeks ago and came across some lonely QB79 parts, and remembered that I have a .177 Lothar Walther barrel in the closet that came from a Precision Airguns clearance back in 2015.  I dug it out to have a look:

As you can see, it was intended for a springer.  The breech end is a stepped arrangment and there is no leade or port.  It's exactly 3" shorter than an OEM QB barrel, and only 12mm diameter compared to 15mm.  The straightforward thing would have been to chop off the stepped portion but I didn't really want to give up any more length than I could help, so I took some measurements and determined that I could build it back up with some brass tubing and threadlocker.



I also ordered some carbon fiber tubing with a 12mm ID and 1.5mm walls for a 15mm OD which would conveniently allow me to use the OEM barrel band. 

Seeing as how this barrel had been in the closet for 4+ years, I was in no rush so I ordered what I needed on Aliexpress and put it out of mind until the parts arrived.  Meanwhile I dinked around with the new mini-lathe in the shop and watched a bunch of videos by Frank Hoose and This Old Tony, in hopes of working up the courage to start drilling and cutting when the stuff came in.

Fast forward to last week, everything was in hand and I got to work.  I threadlocked some sections of brass tubing to the end and let it cure, then loaded it into the lathe and used a gauge pin in the bore to index off of and dialed the 4-jaw chuck until I had less than 0.001" total indicated runout (TIR).  Then I turned down the end carefully to achieve a snug fit to the receiver with zero slop.

Then I added a couple of divots to secure it to the receiver with grub screws.  Then drilled the barrel port.  All was going great so far.  Unfortunately I didn't write down my order of operations.  The next step should have been to drill and ream the leade but I got distracted and notched the end to create the little loading tray.

Oops.  Now there's no material on one side to keep the drill from wandering off center when cutting the leade.  I thought about it and decided to take a stab at making a wooden guide block that the bit would bite into before engaging the steel.  Realizing that twist drill bits only really cut at the tip and not the sides, I thought it might work but still considered it a long shot.  I proceeded slowly, stepping up one numbered bit at a time, then used a reamer to cut the last couple of thousandths.  I couldn't see the work as it went so I had my fingers crossed when I finished and removed the block to inspect it.  You can imagine my relief when I held it up and found the leade and loading tray nicely centered on the bore.

Next up was to cut the O-ring grooves.  Another first for me...making a cutter from a HSS blank.  Bench grinder for the shaping and then diamond hones and wet/dry paper to put a polish on the cutting edge and it was ready to go:



I have to say it was very satisfying to bring it into the workpiece and see it peel off material like an apple peel.  I may add a chipbreaker gullet but other than that, I don't think it could have worked any better.

With all the metal cutting done, it was time to bond the carbon fiber sleeve.  I degreased everything and applied some Loctite 638 to both pieces and slipped them together.  After setting up for a couple of hours at room temperature, I put it in the oven at 175°F for 5 hours to accelerate the cure.  Then a smidge of shaping and it was ready to marry up to the receiver:



Today I assembled the rifle.  The idea was to tune it to something in the ballpark of 12fpe.  Not looking for a hotrod, just something accurate and hopefully not too pellet picky with the choked barrel. 

Here's what it looks like assembled:



I lucked out and hit the 12fpe straight away with a 1000psi regulator setpoint.  I mounted the scope and got it roughly zeroed and started testing pellets at 25 yards.  The first 5 pellets all grouped anywhere from good to excellent:



These 5 from left to right:

• boxed CPH - 0.31" CTC (1.18) MoA)
• boxed CPL - 0.19" CTC (0.73 MoA)
• Baracuda Match - 0.33" CTC (1.26 MoA)
• Baracuda Hunter Extreme - 0.48" CTC (1.83 MoA)
• JSB 10.3gr - 0.31 CTC (1.18 MoA)

I'm pretty happy with it so far.  Definitely appears to have potential.  Considering the barrel has less than 100 pellets through it so far and I haven't tested many types yet, I think the best is yet to come.

[Motorhead]

Excellent ... I also put a .177 LW into a QB79 HPA.  That barrel came from a Daystate airwolf swap.
They shoot GREAT making quite the little shooter from an otherwise just ok shooter

[Ribbonstone]

Nice job on that one...not the most fun barrel breech shape to duplicate.

[RDB]

Nice work Jason! Should get tons of fun shots. Im curious how the jsb 8.4 do in that barrel. 177 and 12 ft.lbs just seem to go perfect together.

[Ribbonstone]

HAve managed 195-205 12 foot pound shots per 13CI bottle fill with set ups a lot like that without anything too complicated being done.

[nervoustrigger]

Scott, thanks for the reminder about your QB.  I plan to look it up this evening and read over it again.

Robert, yeah I don't know how much time I put into but I sure am glad it turned out to be a good barrel!  It would have put a damper on the holiday weekend if it ended up spraying pellets.

Rod, I'm with you on the 8.4gr JSBs or Air Arms.  Those have been very good pellets in a lot of rifles. 

We visited with family for a good part of today but I did get a little trigger time.  First was a quick run of 5 random pellets this morning:



These were also at 25 yards.  The RWS Supermag wadcutters deliver a devastating impact on house sparrows and chipmunks so I'm glad to see them grouping well.  The H&N FTT did excellent.   CPHP did pretty decent too.  It was beginning to look like the barrel would group anything so I threw in the Remington domes and the Crosman Destroyers.   Those two have been hot garbage in every gun I've tried.  This time was no different.

Later on this afternoon when we got back home, I decided to pull the barrel band just to see how it would behave:



It seems to like it fine so I'll probably leave it like that for a while and see how well it holds the zero.  The JSBs did great as usual.

[skorec]

Jason , your`s  "brass tubing and threadlocker"  is seriosly good and very usable idea  .

I have not changed  the origin QB78 barrel because after re_ crowning is shooting very well .  CO2 let me less power therefore I use much lighter .177 JSB Express pellets.  They are more accurate for short distances probably because shirt stabilization is higher/quicker.

Fore longer distances I am using another AGs and only If I need to use QB78 for longer distances I use 1500 PSI air and JSB Heavy
https://www.gatewaytoairguns.org/GTA/index.php?topic=125568.msg1228415#msg1228415

[Mr. Panther]

I always enjoy reading your posts on these QB's. Keep up the good work! looks like it all turned out perfect.

[Machinist]

The order of operations can bite you for sure.  Problem is you can't put the metal back.

But in the end, it all worked out. Nice job!

Steve

[Gippeto]

Run mine without a barrel band as well. 16mm choked blank fitted to the receiver sans oring grooves...uses a sleeve transfer port, and separate delrin loading tray for screw access. Cleaned/trued the factory flow through bolt and using it. The lack of barrel band has not been a problem...but it's a bench gun, not a field piece.

Nice shooting btw  ...mine likes the JSB 10.3's as well...Barracuda Match are a close second though...JSB's on the left, Barracuda's on the right. 25yrds, 20ftlb tune. Red dots are 1/4" diameter, 5 shot groups.

Al

[Ribbonstone]

HAve only rebarrled 2 QB's,so certainly not an expert on the subject...and I never did have myown mill.

Think I did learn a few things from the first one (and I didn't have the bushing to deal with...good thinking on that one).

Ignoring the loading ramp until last helped me.  Got the ouside turned to nice fit, cut the o-ring seats, get the port drilled, get the locking set screw fixation points drilled, and get it "chambered"....then mill (or cut/grind/file) the loading ramp.

Just seemed easier for me to deal with a round solid barrel shank than to deal with a 1/2 round shank.


I've NOT rebarreled most of them.  Some of the issue barrels didn't no matter what I tried....one worked out well after  cutting off the offending  section of muzzle or breech, and a couple I'm quite happy with as they came.

But is a Forest Gump type choice....a good barrel is a good barrel no matter who made it....but like blindly reaching into a chocolate box, it's a pretty random choice.  Known barrel makers take most of the random out of it.

Hope you have as much fun out of yours...have kept two HPA conversions (a long tube and a short) for a lot of years (10?) and intend to keep them going for as long as I can still manage to shoot.
DSCN1706 by Robert Dean, on Flickr


Do have most of the parts to another HPA conversion....have a used .25 Hatsan AT44 barrel that shot well....and the use of a full sized lathe (as well as a tiny small sized lathe at home to make the little parts). 

Lets see if the long nights of winter keep that urge to use up the parts.

[Motorhead]

Jason,

Wanted to add , mine too does GREAT with Crosman 7.9 dome ( Boxed ) and also the original H&N Sniper Meds running +/- 12 ft lbs.

[K.O.]

Nice job Jason...

I think the barrel is an old AirForce barrel from when they quit using the L.W and switched to Smooth Twist... at least that was what they were sold as  thru AOA, think it was in 2015...

19" long and just a smidge under 12mm od...stepped exactly the way yours is... would love to get it machined for  the Little Dianna Storm... the larger of the stepped portion fits the storm breech just a touch more secure than the stock Chinese barrel...it also fits the barrel band just a touch better than the stock barrel...

it really wants the barrel...Keeps saying it is fate and it has a German name it should have a German barrel..  

Seeing your 12ish fpe results has me wondering how well the L.W. barrel would do at 20ish fpe...

a pic muzzle end of both barrels in post #3...  https://www.gatewaytoairguns.org/GTA/index.php?topic=151471.0 

I think it is just that I really do not like the oddball o-rings that spa uses that stops me...

[Ribbonstone]

Cut different o-ring seats...use different O-rings?

[nervoustrigger]

Hey thanks guys, this little rifle sure is turning out to be a lot of fun.

Peter, I agree on the OEM barrels.  Most of them are remarkably accurate with the right pellet.  In this case I was just looking to try something new and have an excuse to use the lathe.

Cole, it's good to hear from you sir!

Steve, thanks for the words of encouragement.  I'm definitely learning as I go.

Gipetto, that's some really fine shooting!  I would be over the moon if mine would do that with the right pellets.  Was that shouldered or with both a front and rear rest?  Indoors out outdoors?  So far I've only practiced with a front rest and the stock shouldered so I'm contending with pulse and respiration but I'm very happy with it so far.

Robert, I remember you saying you rebarreled one in .20 cal with a HW blank if memory serves.  What was the other one?

Scott, thanks for the heads up about the boxed domes.  Actually in the initial post I tried a group at 25y with some die D and got a sub-MoA @ 0.19" CTC   The photo shows a tin though so that detail is easy to miss.

Kirby, thanks for the info on the barrel being an Airforce.  Definitely looks the same, down to the undercut on the smallest step.

[nervoustrigger]

I haven't had an opportunity to do a ton of pellet testing but suffice it to say it seems to like a whole lot more than it dislikes.  That's fantastic...exactly what I was hoping for.

Here's a few more pellets at 25yds:


I won't say I wasn't trying but I wasn't taking my time and all of them were pretty respectable.

Later on I wanted to try the Baracuda Match again, this time at 30 yards (typical pesting distance).
 


Sweet!  Flirting with MoA.

I'm kinda eyeing the RWS Supermags though.  An accurate wadcutter at 12fpe is a beautiful thing for pesting and I have about 15,000 of them in the closet!

[tronickero]

nice work jason as always!!

the last week I also received my new lathe/mill combo ....When I have time I will start uploading my works but I need to study better the videos of "this old tony" but is difficult because my english listening is bad

Success in ur proyects Jason!

Tron

[Gippeto]

Indoors and off the bipod. I shoot from the bench choked up on it with the butt against my shoulder and resting on my offside hand.

This is close, but he's using a rear bag...same idea though.



Al

[nervoustrigger]

Tron, thank you sir!

Gipetto, well the indoors makes me feel a little better   Those groups are still really impressive.  Great shooting!

[Ribbonstone]

"Other" one was a .25...then fitted to a PCP tube and run at 3K...but the machining wasn't my work.

The "other-other" one was a little co2 short barreled carbine that used the issue barrel.  Bore was pretty cursty for the first 1 3/4" (so I cut off the breech end)and kind of crusty at the muzzle (so I cut off 1 1/2"from the muzzle)...and retro fitted the good looking/good feeling/good measuring middle section.  I still shoot that QB...but as an HPA conversion.



So long as I'm on that subject...that .25 from Roy at MountainAirguns….made me believe that the "lead"(or the equivalent of a "chamber" in firearms terms)may not be really all that needed. Shoots great, and all down the loading platform can still see the lands of the rifling.