Marksman model 70 breakbarrel air rifle: Part 13
Marksman model 70 breakbarrel rifle.
This report covers:
- Scope test
- The scope
- A soft obstruction
- Sight in
- The test
- Predator Polymag
- Test changed
- Where is the mount now?
- Air Arms 16-grain domes
Folks, today I have a special report that taught me many different things. Are you ready to learn with me?
Several readers asked me to test this rifle for accuracy with a scope mounted, now that it was shooting both smoothly and powerfully. I wanted to tune the rifle next, but I relented and mounted a scope. And, as long as I was doing that I thought I would also address an issue that reader Pacoinohio has been having with a peep sight walking backwards off his rifle. Oh, boy, do I have a lot of good stuff for you today!
The scope is one that UTG no longer offers. Boy, am I glad I have one! It is a 2-7X44 Mini SWAT with long eye relief. It’s clear as a bell and the reticle is as fine as frog hair.
This scope was already in 30mm rings that were shimmed. I felt it would be easy to get on target. But the ring bases are Weaver, so I used the UTG Weaver to 11mm dovetail adaptors. I felt that would show everyone how well this stuff works.
The Marksman 70 has two scope stop holes on the scope base that is screwed to the top of the spring tube. Since the scope has a long eye relief, I put the scope stop in the forward hole.
The mount is attached to the rifle’s scope base.
A soft obstruction
I know for a fact that putting a loose steel pin in the stop hole and then sliding the mount back to jam into it will hold the scope and mount rigidly. But I thought that today I would do something a little different. I used a soft-cast .22 long rifle lead bullet instead of a steel pin. This is one of the bullets I cast for the reloading .22 rimfire series, which isn’t finished, by the way. I reckoned the soft lead would give us some idea of how hard that mount is sliding back. After the test we could examine the bullet to see how deeply the mount had dug into it.
I just dropped the soft lead bullet into the scope stop hole.
Then I slid the scope back until the rear ring base was jammed against the bullet. Then the scope was tightened on the rifle’s scope base.
Oh, boy! We gonna learn us some stuff today!
I sighted in at 12 feet. It took 4 shots to get the scope to the point where I could move back to 10 meters. Then it took another 5 shots to complete the sight-in at 10 meters.
Obviously I am shooting the rifle at 10 meters. I want to keep today’s test close to the test I did in Part 12, so we can make comparisons. That also means I am shooting 5-shot groups. The rifle is rested directly on the sandbag.
The first pellet I tested was the JSB Exact Jumbo Heavy that in Part 12 gave us 5-shot groups that measured 0.357-inches and 0.391-inches Today with the scope five of the same pellet went into 0.461-inches between centers. It’s in the same ballpark as the others that were shot with open sights, but not quite as small. Lesson one is a scope doesn’t always make the rifle shoot better.
The next pellet I tested was the 16-grain Predator Polymag. In Part 12 I shot three 5-shot groups with these. They measured 0.431-inches, 0.552-inches and the third was 0.639-inches. Today he first four pellets went into 0.334-inches. On shot number 4 something fell off the rifle and landed on the shooting bench. The soft lead bullet I had placed in the scope stop hole had sheared off! Shot five opened the group to 0.727-inches.
So, the nine sight-in shots plus the five shots in the first group and the four in this group (another nine, for a total of 18 in all) were what it took to shear off that .22-caliber lead bullet. That’s a lot of force when you think about it.
Well, we got us a brand new test with this turn of events. There is no way I can continue to run this test and call it right. And as far as I’m concerned the first group is not valid either, since the mount was moving while it was being shot. So, I decided to make some lemonade!
Where is the mount now?
I photographed the mount base before the last 5-shot group.
This is where the scope mount is before the last 5 shots.
Air Arms 16-grain domes
I had two more pellets to test with this rifle, but because of what happened I only shot one of them. I have run out of .22-caliber RWS Superdomes and when I tried to order them a few weeks ago they were out at Pyramyd Air. I bought three tins today, but we will have to wait for them to come to me. So instead I tried that Air Arms 16-grain dome.
Five of them went into a group measuring 1.196-inches between centers. But look at how low they hit! And take a look at the scope mount after those five shots.
After five shots this is how far the scope mount slid.
Well, we certainly learned a lot today! First we learned how much force a sliding scope mount has. It can shear a solid lead cylinder.
As a corollary to that lesson this report should show that if you do use my steel pin idea, go as large as possible (as close to the scope stop hole’s size) to spread the force. A thin bar in the hole of this rifle would probably leave dents in the side of the stop hole.
Next, I hope we learned that a scope doesn’t always make an airgun more accurate. Of course that lesson won’t be completed until I can run this test again without the scope moving. So I better hold off making pronouncements.
Finally, I hope the last two pictures that show how much the scope mount moved in five shots demonstrate the need for a scope stop.
I had planned to run this test once and then move on to tune the rifle. But with what happened today I definitely need to re-run today’s entire test. We’re getting to see this Marksman model 70 quite a lot, aren’t we?