RMAC 22 rifle
This is the actual rifle I’m testing. I won the lumber lottery with this one!

Part 1
Part 2
Part 3

History of airguns

This report covers:

  • The design
  • First thing
  • Complete the loading
  • Save the bullet
  • Nowhere to be found
  • Sound of the discharge
  • Success — sort of
  • Use a board!
  • Third time is the charm
  • Measure the ball
  • Summary

Today I hope to test the velocity of the RMAC .22 caliber breechloading black powder rifle. I say I hope because last time I couldn’t get a buckshot out the barrel. I will be doing things to improve my chances today.

The design

Let’s take a moment to look at the design of this rifle. It sure isn’t a redneck-engineered project. Look at the end of the breech that aligns with the barrel.

RMAC breech
Look at the exit hole of the breech. Not only is it rounded like the rest of the breech, the edge of the hole is contoured, top and bottom, to fit the rear of the barrel better.

Now look at the rear of the barrel that the rotating breech aligns with. That contoured barrel is not the product of, “Git ‘er done!” technology.

0RMAC barrel
The rear of the barrel is contoured to fit the rotating breech.

First thing

Okay, today’s test is meaningless if I can’t get a bullet to come out of the barrel. So, that is the first thing that has to be done.

Remember that last time I went with a light load of Pyrodex P, a replica black powder that’s equivalent to 3F. Today I will use real 4F black powder. And I will use more of it. Instead of 3.2-3.3 grains, today I’m charging the rifle with — well, I really don’t know. It’s more than 5 grains of powder and less than 6.5 grains, but I’m not loading by weight. I’m loading by volume. I’ll show you.

RMAC powder scale
Here is 6.4-grains of 4F black powder.

RMAC too much powder
That is too much powder for this rifle because a ball has to fit on top of it and then be rammed deep enough that the breech can be rotated into position behind the barrel.

There is no mechanical advantage when you use that ball-seating tool. Sure, the powder will compress a little, but only a little. It turns out that filling the powder chamber about three-quarters full is the ticket.

RMAC powder right
That is about the right level for the powder. It’s almost 6 grains — maybe 5.8 grains? See those grains outside the chamber? Brush them away or they will also burn up when the rifle fires.

Then the ball is placed on top of the powder and three-quarters of the ball will still be outside the chamber. This is where the ramming tool goes to work. Since there is no mechanical advantage, you just press down hard. It’s handy to have a rubber hammer close by.

RMAC ball seated
This view doesn’t show it but the top of the ball is about level with the edge of the breech. It should just clear the barrel.

Complete the loading

Now it’s time to punch out a cap, load it into the cap cover, put the cover on the rear of the breech turret and rotate it into position.

Save the bullet

The whole point of this drill was to catch and save the lead buckshot, to be able to measure it when it came out of that .20 caliber barrel. Last time it didn’t make it out of the barrel, so this time with almost twice the powder, plus a finer grade of powder, I expected big things.

I shot into a pug of duct seal, hoping the bullet would remain inside. No such luck! The bullet went all the way through the pug and out the back. Fortunately I backed the pug with my office bullet trap that has two more inches of duct seal, huge chunks of fused pellets everywhere and a steel plate in the back.

RMAC pug front
The ball from the rifle made a clean hole through the pug of duct seal.

RMAC pug back
…and went right out the back. That wasn’t expected.

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Nowhere to be found

And the ball disappeared in my bullet trap, mixed in with thousands of smashed-up and fused chunks of lead pellets left there from testing. Or maybe the ball was so deformed by hitting those lead chunks that it isn’t recognizable anymore? I couldn’t find it.

Sound of the discharge

Because I was using almost twice the powder this time, I recorded the discharge again. You may recall in Part 3 that it registered at 114.6 decibels. Today the first shot registered 117.5 decibels — the loudest sound I have ever recorded.

RMAC discharge
The RMAC rifle isn’t quiet! This is the loudest sound I have ever recorded.

Success — sort of

So the first shot was a partial success, because the bullet came out the muzzle. But in every other way it was a failure. I wanted that bullet and I never found it. I reloaded the rifle to go again.

This time it was easier to load the powder because there was no weighing or measuring. Just fill the chamber to the three-quarters mark and you’re done. I actually over-filled it, so I dumped some out and then added just a bit more to get it where I wanted it.

Use a board!

So a thin pug of duct seal didn’t stop the bullet. How about a board? I got a 2-inch by 6-inch plank and put the duct seal behind it. However when I fired, the bullet didn’t go all the way through the board. The board was at least 10 years old and had hardened over time. According to my ELECTRONIC caliper, the base of the bullet is about 0.491 inches into the board, so the whole bullet made it about halfway into the board. This board measures 1.463-inches across. Even though it’s a 2-inch by 6-inch board, that’s the rough measurement, not the finished measurement. And this is a finished board.

RMAC board
The bullet didn’t go all the way through the board. I had to lighten the image a lot to show the hole. Now you know where the term “powder burns” comes from.

Third time is the charm

I’m learning a lot about how this RMAC rifle works. And I will say that every shot has been positive. There have been no failures to ignite. Unlike the Daisy VL that I tested for you, I think this one may turn out to be good!

I realize that it looks like I’m going extra slow, but that’s mostly because I’m learning the gun. Now let’s see if we can catch a bullet!

I reloaded the same as before, but I probably put just a little too much powder into the chamber. That’s not dangerous, but it makes it difficult to ram the ball low enough to be able to rotate the breech. Hence the rubber hammer!

I did have to tap on the wooden end of the ball rammer with the rubber hammer to get the ball low enough to be able to rotate the turret in line with the barrel. And then I shot the third time. Success! The ball went through the pug again, and into a part of my bullet trap where there are no large chunks of lead.

RMAC breech second pug entry
The entry hole in the second pug. Once again you can see the powder burns.

RMAC second pug exit
The exit hole from the second pug.

RMAC ball in trap
The ball went about a half-inch into the duct seal of the trap without hitting any pellets. It was easy to remove.

Measure the ball

In part 2 I measured a number 4 buckshot ball for you and found the diameter between 0.231 and 0.239-inches. My question, as well as yours, is how does that .20-caliber barrel swage that ball down in size? When I measured the cylindrical part of the recovered ball it was very consistently 0.2195 across, The fat portion measures 0.232 to 0.28 inches. That’s from slowing down so fast in the duct seal.

RMAC recovered ball
The recovered buckshot ball. The fat end at the top was the front of the ball. Notice the rifling.

Summary

I wanted to test velocity today, but this ball recovery test took longer than anticipated. But I now know how the rifle likes to be loaded and maybe that will give me more consistency when I do test the velocity.