Tag Archives: Air Venturi

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1
Part 2
Part 3

My rifle is actually a BSA Super Meteor.

The last report on this BSA Super Meteor was on October 15. That’s how long it’s been since we saw this gun in print. But in the background, I’ve been doing lots of things that I’ll share with you today.

The last time we looked at this rifle, I was taking it apart and getting a lesson on how it was built and what was wrong with it. To summarize for you, this BSA Meteor is made from folded metal, in the same way Daisy BB guns are made. And the piston head was attached to the piston by means of an E-type circlip that was incapable of standing up to the stress. I can tell that by the damage that was done when that clip let go — but more because the Brits have invented a much better solution for fixing this gun today, when it does break down — and all of them are going to break!

I sent my order to T.R. Robb in the UK for a replacement piston head, o-rings and spacers. The problem is that when I sent in that order I didn’t pay attention to the fact that the same order button also got a piston head for a BSA Scorpion pistol, which is larger than the Meteor head. Well, guess which one Mr. Lysdexic ordered?

That’s right, I ordered the Scorpion piston head. And a couple days later, when I realized what I’d done and contacted T.R. Robb, they had already shipped the order. But to their credit, they sent a second piston head — this one was for a Scorpion, too. That’s right! They sent me 2 Scorpion piston heads and no Meteor head! But I’ll give them credit for trying to help me, for being very generous and refusing my offer to pay for the second head, and for being very prompt in shipping both heads. I had them in less than 10 days.

So, blog reader David Enoch — I now have a spare BSA Scorpion piston head that I believe you said you needed. The price will be right, too. You’ll pay what I paid, which was nothing.

Lots to see here. The replacement piston head is the shiny one on the left, the darker original is on the right. Obviously, the replacement part is larger and has to be cut down to fit. The blue spacer and 2 o-rings are just some of the soft parts that came in the kit. There were a total of 4 o-rings of different sizes and 2 more spacers of varying thicknesses. They allow you to set the power of your airgun, and they also allow for differences in the tolerances of different guns.

When I saw how large the piston head was, I knew it wouldn’t fit. I asked my friend Otho to cut it down for me on his lathe. He also had to cut the o-ring channel deeper at the same time.

Silly me — I thought that would solve everything. So, Otho took the head and had it back to me in a week. Then, I assembled it to the end of the piston and tried to insert the piston back into the spring tube. But it wouldn’t fit! I’d taken it out several weeks earlier, and now it wouldn’t fit back inside! It was like that pair of blue jeans that used to fit, before they suddenly and quite mysteriously shrank. I hate it when that happens — especially to jeans I’ve worn for years!

I took a more critical look at both the spring tube and the piston. Glory be — they’re both made of folded metal like a Red Ryder! Except that Red Ryder spring tubes are generally round, while both of these pieces had variable shapes, with a tendency toward the oval.

The tail end of the piston. Here you clearly see that it’s folded metal, tack-welded at each end.

At least that’s the theory! Here you see the weld at the piston head end has broken. Wonder why the piston is no longer round?

And, on the other side of the piston, opposite the broken weld, the solid metal has also cracked! Here you can see the nut that now holds the piston head to the piston body. It’s not about to break off like the circlip did!

Looking at just the condition of the piston gives you an idea of the shape this rifle is in. I don’t think the design of the rifle caused all this damage. I think people continued to try to cock and fire it after the piston head separated from the piston, and they hammered it into the mess you see here.

I examined the interior of the spring tube very critically at this point and found a lot of metal galling (shiny areas that indicate the scraping of metal against metal without lubrication). There was also a fair bit of surface rust. I also found that some of the folded metal edges of the spring tube that hold the trigger parts were bent into the interior of the spring tube and were blocking the passage of the piston. I fixed those with a Dremel tool, but the inside of the tube was too deep to reach.

I showed the spring tube and piston to Otho, who agreed with me as to the extent of the damage. He felt he might be able to clean out the tube with a tool that holds strips of abrasive paper and is spun in an electric drill. I don’t own that tool, so I was only too happy to let him have a go at it. He also said he could tack-weld and refinish the piston where it was separating.

So, Otho came to the rescue once more. And he was true to his word, because a week later I got back the tube and piston, ready for assembly. But that wasn’t the end of the rifle’s problems!

Otho welded the broken piston and dressed it round again.

Otho also welded the back side of the piston where it was cracked.

Loose barrel pivot
I had discovered that the barrel wobbled from side to side when I first got the rifle. And a little research online told me this is a common problem with Meteors from the 1970s. Apparently, when the forearm stock screws are tightened, the shape of the stock allows them to pull apart the action forks that hold the barrel breech. It’s a design flaw of the rifle, and the solution is to not over-tighten those screws. But how to fix it — since the barrel pivot is a pin, rather than a bolt? Well, this is something I know how to do.

I chucked the forks in the padded jaws of my bench vice and closed the jaws on the forks. When there was some inward tension on them, I hit the outside vice jaw with a 2-lb. ball-peen hammer, which sent a shock wave into the metal of the action forks and realigned their crystalline structure. Or at least that looks cool when I write it. I haven’t got a clue what really happens! All I know for sure is that when you do this, the metal takes a set in the new position, and now the action forks are about 5 thousandths of an inch smaller then the breechblock of the barrel that has to fit between them.

Finally, all the faults had been corrected, as far as I knew. The piston now slides into the spring tube with only a little friction, not unlike a Weihrauch piston in a Weihrauch gun. It was time to assemble the rifle!

Otho and I both think whoever designed this Super Meteor Mark IV was a genius at eliminating cost and making one thing do many jobs. The way this air rifle is designed should be a study in an engineering course, but the students would first have to know how others had done the same things with other spring-piston powerplants. At every turn, you can see the embodiment of the Spartan design.

And the parts that need to be hard are hard! I mean glass-hard! There’s no wear on any of the trigger parts, or on the piston, where it’s held by the sear. The boys at BSA knew what they were doing.

Since there had been so much metal galling in the spring tube, I first lubricated it with Moly Paste before any parts went back in. The molybdenum disulphide particles will bond with the metal surfaces and will not wash out over time. I applied this paste (which is a thick grease) with a swab made from a long thin dowel rod covered with a paper towel on one end.

This simple swab can be used to clean the inside of spring tubes/compression chambers, as well as to lubricate them.

After the inside of the spring/compression tube was lubricated, I also lubricated the outside of the piston head and piston tail with the same moly paste. I’d like to say a word about the piston head now. The kit of parts I was sent had 3 spacers of differing thicknesses. Any of them will work, but each gives you a piston head of a different length when it ‘s fastened to the piston body.

The way the Meteor is designed, adjusting the length of the piston head controls the power of the rifle. A shorter piston head will give a longer piston stroke and therefore greater power. I don’t want power. I want a smooth rifle that’s easy to cock and is also easy to shoot. So I went with a thicker spacer on the head.

Now, I lubricated both the piston head and the tail with moly. The center of the piston body can be left dry because it’s narrower than the ends and will never touch the inside of the spring tube.

The piston head is lubed with moly paste. No precision is required for this application because this stuff spreads as the gun is cocked and fired. The other end of the piston got the same treatment before it was slid back into the spring tube.

Once the piston was in the tube, I coated the mainspring with Beeman Spring Gel and slid it into place inside the piston. Don’t look for that product anywhere — it’s obsolete. It was a viscous silicone (Beeman only says it’s a synthetic in their catalog; but given where it’s going, I’m pretty sure it’s silicone) grease that dampened vibration without slowing the gun much, if any. So, pretty much any viscous silicone with the consistency of toothpaste should suffice. Or, you could do it the old-school way and just use a lithium-based grease.

The powerplant went together the same way it came apart; but the barrel, which was the next item, was harder to install because the action forks were now smaller, thanks to my repair. Nevertheless, the barrel did go into the action forks of the spring tube (I “buttoned” it in using the baseblock to spread the forks slightly), with the cocking link locked inside the piston and lots of moly grease on all metal surfaces that touch.

When it came time to close the barrel, I got a small surprise. It seems the spring-loaded chisel detent (the chisel-looking thingie that holds the barrel shut when the gun fires) was sticking out so far that the barrel wouldn’t close! Examination revealed that the detent is held in the baseblock by the pivot pin that passes through. How in the heck was I going to do that?

Well, if you think like a redneck cheapskate, which I am trained to do, you insert the pivot pin partway, lever the chisel detent back as far as it will go and then tap the pivot pin home. I could have closed my eyes for this maneuver, it went so smoothly. Obviously, I’d discovered something that the original 28-year-old BSA assembler, Trevor, could do 175 times in an 8-hour shift back in 1978.

From there, the only big task was to get the mainspring back inside the spring tube all the way. It only stuck out the end of the tube less than an inch, but it also had to go another full inch into the tube, where it would be held by a crosspin that’s profiled on one side to capture the base of the spring guide. It’s easier to just show you.

This is the side of the assembly pin that fits inside the base of the mainspring guide and holds it inside the rifle.

This 58-cent tool was made from a 4-inch plastic sprinkler pipe in about 20 minutes. With the action in the mainspring compressor, it pushes the washer at the base of the mainspring, while allowing the crosspin to be inserted through its slot. It isn’t beautiful, but it worked both times I used it and looks like it will hold up for dozens more jobs like this.

And the pin is back in place. The contours on the other side of the pin have meshed with the base of the spring guide.

I showed you these parts and the trigger parts in the earlier reports, namely in Parts 2 and 3. So I’m covering ground that I’ve already explained. When I took the rifle apart back in October, I didn’t have to use a mainspring compressor; but to get the mainspring back in place and insert the crosspin, I did. And it was easy.

And the remainder of the airgun went together exactly as it should. I have a theory. Whenever something goes together easily, it means I’ve left out something. I’m in my wetsuit but have forgotten to put on my briefs! I remember learning how to disassemble and assemble the M1 Garand rifle. I thought I could never learn, but a few weeks later I was stripping it like a pro. That’s the way BSA spring rifles are, I guess. You’d like them to come apart in 30 seconds without hand tools, but they don’t. However, once you’ve been down the path a few times, I’m sure the job seems simple.

The proof
This is the part I dreaded. Sure the parts were back together, but who was to say they were where they should be? Only cocking and firing the gun would tell me that. So I did. And it did! Hurrah!

The only task left to do is to clean the barrel. I had close to 2 months to do that while it was off the rifle; but to tell the truth, I wasn’t sure if I would be able to get the gun back to functioning again. No sense doing a great job on a barrel I’ll never use. But now the gun is working, so the next report can be about the velocity.