Working my way through Volvo's QB78 Deluxe. I keep wanting to call it a Tech Force, probably because my AR2078a carries that name laser engraved on the breech.
Here's what I've been doing:
Cleaned up then blackened the aluminum riser plate.
Made a new bolt handle from a piece of tool steel--with 1/4-20 threads as I've done before.
The old bolt handle.
And here's the new handle again with a 1" rubberized ball. Spoiler. The rubber ball handle is a fail.
Then spent a few minutes deburring the barrel shank o-ring grooves.
Softened all the sharp corners that were chewing up the o-rings.
Recut the crown.
QB78!
My old friend, flex hone.
This is the easiest way to clean up and remove all the burrs left from the machining.
Original locator stud and stock nut had to go. It's not you, it's me. It's me not having a suitable notched peg-spanner on hand making this so damn inconvenient every single time the rifle is taken down. It's you for not being a commonly encountered fastener. It's definitely you.
This is what I went through to make my life easier.
Found this in the scrap box.
A 1/2" diameter 6061 aluminum rod that already had M8x1.25mm threads in one end.
M8x1.25mm low profile socket head cap screw. LPSHCS.
And a scrap of 1" diameter aluminum for a screw cup.
The 1" diameter aluminum was first turned down to just slip into that gaping hole in the underside of the stock.
Shave a bit off, test fit. A bit more, test fit... Measure? Bah. I had enough aluminum to wing it.
Through drilled with a 5/16".
Counterbored for the head of the 8mm fastener.
Parted off.
Cleaned up, deburred, chamfered.
Checking fits and clearances.
Through hole in the stock is too small to take the 1/2" aluminum rod.
Carefully lined up the existing hole on the milling machine.
Changed bits and opened up the hole.
Here's the screw cup.
Yep.
Bolt will fit like this...
Still didn't feel like measuring. Slid the 1/2 aluminum rod through the stock until it bottomed on the screw cup. Grabbed that Sharpie marker in the background and marked the rod where it'll stop against the gas tube.
The rod will need to be approx 1/8 to 1/4" shorter than this marked length.
Cut and faced the rod.
Drilled and tapped M6x1mm.
M6x1mm Socket head cap screw. SHCS
Cut the head off. SHCS
Into the 6mm screw holder.
Some Loctite.
Now I have an oversize locator stud.
The 6mm thread screws though the gas tube and retains the valve retainer ring.
The 8mm end fits the stock bolt.
Detour.
Dropped the cocking pin from the hammer. Heard it bounce and roll. It still hasn't turned up. Made a replacement.
Back on track for my project to make the stock nut "convenient". The irony isn't lost on me.
OK, the LPSHCS stock nut and a couple really thin steel washers.
Assembly time:
New o-rings for the barrel shank.
Installed the bolt with the rubber handle that doesn't make the cut.
Trigger unit
Tank block, barrel band & barrel.
More new fasteners.
There's the end of the 1/2" locator stud. Just barely recessed below the counterbore.
Sometimes this works OK. Sometimes nope.
Looks good.
Then I tried cocking it and remembered why that rubber ball bolt handle didn't make the cut with my AR2078A.
The "Cock on Close" operation of the bolt action leaves a little to be desired. It's awkward biomechanically. The rifle is off your shoulder and you shove the bolt forward against spring pressure as you try to hold the rifle stationary. When the bolt is completely forward, you rotate it down to lock it closed. That soft rubber ball squishes and flexes as it adds vagueness to the awkward cocking motion.
Try this again:
This essentially got the rifle assembled and functional. I didn't really do anything additional to the trigger except replace the blade.
Try this again:
Sorry, no unboxing video, it came in a bag.
Steel. 1/4-20 threads. McMaster-Carr.
Blackend.
This essentially got the rifle assembled and functional. I didn't really do anything additional to the trigger except replace the blade.
Still figuring out sight options and need to send more pellets downrange. Volvo likely had a specific role in mind for this rifle. I'm thinking it was backyard garden pesting in the suburbs. I'm considering some alterations to better fit my needs and add more convenience.
I'll have something up in a couple days. Thanks for checking in.
