Marksman model 70 breakbarrel air rifle: Part 6

Marksman model 70 breakbarrel rifle.

Part 1
Part 2
Part 3
Part 4
Part 5

History of airguns

This report covers:

• Erase, erase
• Shortify da spring
• Attach the barrel
• The piston seal
• Lubed the spring
• Off the track
• Holes out of alignment
• However
• End cap and trigger assembly installed
• The stock
• Oh, no!
• BB fixes it
• Discussion
• Summary

Oh, boy, have I got one for you today! Thank the Lord that BB is as flawed as he is, because he can tell you something the first time and then come back and tell it all over again — the right way! Brew up another pot of coffee, because this one is gonna be good!

Erase, erase

As you know from Part 5, the Marksman 70 was completely apart. Last Saturday I cut the mainspring like we discussed and assembled the rifle. And in doing so I learned a lot about how this strange breakbarrel goes together. And it goes together unlike any other air rifle I have assembled. If you ever have to take one of these apart, this report is worth what your entire year’s subscription to this blog cost you!

I will pull a quote from Part 5 and criticize it for you today. But I started with a rifle in pieces, so that’s where this report will start.

Shortify da spring

The first job was to remove the bent end of the mainspring. Remember that?

The Marksman mainspring was bent on the end that goes over the spring guide.

You guys talked A LOT about how I should do this, and I didn’t comment. But here is my view. I want to keep as much of the spring as possible, and I plan to heat and crush the last coil and grind it flat, so the last bit of bend can be preserved. Therefore I cut a little below where the bend begins.

I used a cordless Dremel tool with a cutoff wheel to cut the spring. We know it is hardened, plus it is made of good steel, but the cutoff wheel zips right through it. It took less than a minute to cut.

The cordless Dremel made short work of the mainspring. Gotta love that tool!

My neighbor, Denny, was over to see how a spring gun goes together (and he had to see this one — oh, the shame!), and he stayed and helped me.

My bench grinder isn’t mounted to my workbench yet, so we went over to Denny’s and he ground the end on his Shopsmith sander. 

The end is ground, but the last coil needs to be collapsed.

Back to my shop we traipsed and put the spring in a vise. Just the last two coils were sticking out of the jaws and I heated one spot on the last coil to red hot then Denny whacked the end with a  hammer. It’s now reasonably flat.

Denny told me to quench the last coil, so I dunked it in my coffee. It worked, plus it heated the coffee a bit!

Now I did that job exactly backward. I should have collapsed the coil first and then ground the end. Live and learn.

This spring is not ground as flat as I would like. But for the testing I have planned, it will do.

Attach the barrel

Now I attached the barrel to the spring tube so the piston could be installed. The cocking link on the barrel has to attach to the piston before the spring puts any pressure on the piston, or it will never go together.

Remember to lube the thrust washers on each side of the base block (the block that holds the barrel) and the pivot bolt with moly grease. And grease all sides of the cocking link shoe that connects the cocking link to the piston, before you connect the link to the piston.

The piston seal

Did some of you think the piston seal in this rifle was leather? It’s not. It’s synthetic, and it is still flexible enough to work.

The Marksman 70 piston seal is synthetic and flexible enough to work okay.

The piston now slides easily into the spring tube. I lubed the seal with Vortek grease lightly. Before sliding the piston in I felt every surface of the cocking slot and all the other cuts in the spring tube and there were no burrs. This one is slick!

Lubed the spring

Okay everyone — how much Tune in a Tube grease did I put on the mainspring? Not very much! I took a couple pictures, so you could see.

That is how much TIAT grease I put on the entire mainspring. Just a whisper!

And, to show you what a whisper of TIAT looks like as it is applied, here it is going on the outside of the spring.

About half the grease is on the front half of the mainspring. Look at the threads that grease makes!

Okay — the piston is in and the mainspring is lubed and in. Now the rest of the powerplant gets assembled.

Off the track

And here is where the train left the tracks. Old BB is not as smart as some of you give him credit for. He’ll take the credit, but know that he sometimes makes mistakes. A LOT of mistakes.

I won’t bore you with the whole story. Rather, I will summarize. BB tried to push the bushing (remember that part?) that backs up the mainspring into the spring tube with the end cap. He did so because that’s the way other airguns go together. But NOT THIS ONE!

In fairness to BB, Denny who was standing right there watching, was a patternmaker for White Farm Equipment and Vought Aircraft, and he knows how things have to go together. He was standing right there with BB, looking and seeing that, when the bolt hole for the mainspring bushing lined up with the hole in the spring tube, the screw hole for the scope ramp on the other side of the spring tube was a third of its diameter off-center.

He listened as BB told him that, at Weihrauch, a 21-year-old girl named Heidi had put this rifle together at the factory in less time than it took BB to tell him about it. We laughed, we joked, we sat down. How can the end cap screw hole in the top of the spring tube be a third off-center when the large bolt hole in the bottom of the bushing is aligned?

Holes out of alignment

Let me remind you that I had seen the problem when I took the rifle apart, but I didn’t know what I was seeing. Here is what I said in Part 5.

“Well, when the (bushing) bolt came out of the hole, the inner hole popped off-center a few millimeters and stopped (not enough tension on the end cap), so something else was holding the end cap in.”

Denny and I stood up again and tried reversing the bushing. Was the bolt hole drilled off-center? It sure didn’t look like it, but BB was out of ideas. How can that end cap hole not line up when the hole in the bushing is aligned?

We sat back down. Then, after just a minute Denny smiled and I knew he had figured it out. So it was something that was possible to figure out! Then BB figured it out a minute later.  The bushing and the end cap are separate parts!

THE END CAP DOES NOT PUSH THE BUSHING INTO THE SPRING TUBE!!!!!!!!!

The bushing goes into the spring tube on its own and gets attached to the spring tube with the large bolt, before the end cap ever enters the tube! That bushing holds the mainspring under tension. And, now that I had cut off a hunk of the mainspring, it was very easy to push in, against the spring. I used a deep wall socket to push it into the spring tube and slightly compress the spring.

So, when you disassemble this model rifle, do what I just said in reverse. Take the end cap and trigger assembly out first, before you remove the bushing bolt. This is what the assembler, Heidi, at the Weihrauch factory knew. Old BB had to learn it the hard way.

I pushed the bushing back in and installed the bolt that holds it in place. The other end of the same bolt is the threaded hole where the front triggerguared screws into.

However

I was not yet out of the woods. Take a real close look at the picture above and see if you know what old BB did wrong — again. I tell you, with “expertise” like mine, there are probably three or four reports in this one simple job!

End cap and trigger assembly installed

With the bushing in place it was easy to slide in the end cap that also houses the trigger assembly. The plate that fits in the top of the spring tube popped in and the scope rail screw hole aligned perfectly — BECAUSE THE END CAP WAS UNDER MY CONTROL AND NOT UNDER PRESSURE FROM THE MAINSPRING!

When the end cap can be positioned wherever you want it, the screw hole lines up perfectly.

The stock

The stock now goes on and the job is done. Wow! This rifle cocks so easily! And it shoots dead calm. BB Pelletier has done it again! Ta-da!

Oh, no!

Have you found it yet? The thing BB did wrong? Did you cheat and read ahead to the answer? Shame on those who did that!

With the rifle assembled old BB saw one part still laying on his workbench that should probably be inside the rifle — the spring guide! Yes, in his haste to see if Denny was right about the bushing and end cap, old BB Pelletier forgot to put the spring guide into the rifle. The mainspring was resting directly against the bushing.

BB fixes it

Denny went home, probably laughing. BB stopped for lunch and dinner and to spend some time in the air conditioning. Then he came back out to the garage, disassembled the rifle and put in the spring guide (lightly lubed with TIAT) and had the rifle back together  — all in about 20 minutes. Now the rifle cocks a little harder than it did a few hours earlier, but still much easier than before I took it apart. In Part 3 it cocked with 28 pounds of effort. Now, with the shorter mainspring and the spring guide in place it cocks with 22 lbs. of effort.

It shoots smooth, though the rifle still lunges forward when the piston comes to a stop. I have to say, I like it as it is. Gotta check the velocity next.

Discussion

Learn from my mistakes. If you have a Marksman rifle to disassemble, you may encounter the same things I have talked about today. Watch for that bushing! Never saw one quite like it, but no doubt there are more out there.

Why does the rifle shoot smoother? Well, first of all, the bent part of the mainspring is no longer there. That took care of a lot of the vibration. The TIAT grease probably helped, but maybe not as much as we have seen with other tunes. But, as little as I applied, it probably didn’t take anything off the velocity.

Summary

This isn’t the way I will leave this rifle unless, by a strange quirk of fate, it has gained 50 f.p.s. That would be RWS Hobbys going out the spout at 765 f.p.s.  I did what I did today so we can assess the effects of mainspring spring length on velocity.

Dale Evans enjoys her sunbeam that arrives at 9 a.m. most mornings.

Tom Gaylord (B.B. Pelletier)

Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

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