Breech-seating tests – Part 1

by B.B. Pelletier

Today’s test was inspired by the velocity test I did with the Belgian Hy Score 801 rifle I reported on a few weeks ago. You may remember that rifle shot much faster with the pellets seated deep in the breech. Because there was a breech-seating tool built right into the rifle, seating deep came naturally, but it got me wondering whether deep-seating is something we ought to be doing most of the time. Several readers did tests that showed no improvement with higher-powered spring rifles, so I guessed the technique only worked well on lower-powered springers. After you see today’s results, though, I think you’ll be scratching your heads, just as I am.

To keep this test inside a reasonable time limit, I decided to test two different rifles with two different pellets. I chose the new Air Venturi Bronco and a Slavia 631 I have because these two are close in power but also separated to some extent. I knew the Slavia was the slightly more powerful rifle and wanted to see what difference that would make.

For pellets, I chose Crosman Premier 7.9-grain pellets and RWS Hobbys. The Premiers are heavier than the Hobbys, plus they’re made of harder lead. The Hobbys have wider skirts, so we should be able to see if any of the pellet’s design matters to this test.

First the Bronco with Premiers
The Bronco went first with unseated 7.9-grain Premiers. I seated these pellets flush with the breech and pushed them tight so they wouldn’t fall out. That’s not a problem with the Bronco, but with some guns the pellets do want to fall out unless you press them in hard. This is especially true of some models made in China.

The unseated Premiers averaged 548 f.p.s. with a spread from 542 to 551 f.p.s. The rifle felt smooth shooting these pellets.

Then, I seated the Premiers with a Bic-type ballpoint pen, known in Europe as a Biro. The pellet seats about an eighth of an inch into the bore, and the pen stops when the tapered point contacts the diameter of the bore. You are simple pushing the writing end of the pen into the pellet’s skirt, which pushes the pellet straight into the barrel. So, every seating is the same. The average velocity for seated pellets was 527 f.p.s. with a spread from 522 to 529 f.p.s. The firing behavior was smooth once more. Thus, we see that the consistency of velocity remained when the pellets were seated deeply, but the average dropped about 20 f.p.s.

Now, the Slavia 631 with Premiers
The Slavia 631 averaged 600 f.p.s. with unseated Premiers, with a range from 594 to 606 f.p.s. Once, again, the pellets were pushed in hard with the thumb, though the 631 doesn’t have a problem dropping pellets from the breech. The firing behavior was full of a lot of vibration and some forward recoil. I probably would not have noticed it in any other test, but after shooting the smooth Bronco it really stood out.

When the pellets were seated deeply, they averaged 534 f.p.s. with a spread from 529 to 545 f.p.s. So, the velocity spread opened up when the pellets were seated deep, and the average dropped 66 f.p.s. As with the unseated pellets, the vibration pattern was full of vibration and forward recoil.

Now, the Bronco with Hobbys
With RWS Hobbys, the Bronco averaged 553 f.p.s. In fact, only one shot of 10 went any other velocity, and that one went 554 f.p.s. From a performance standpoint, the Bronco likes Hobbys a lot.

Deep-seating brings a big surprise
When they were seated deep the Hobbys averaged 515 f.p.s. with a spread from 493 to 547 f.p.s. Not a performance that you would think was any good except for one thing. These deep-seated pellets shot so butter-smooth that it felt like Ivan Hancock had personally tuned the rifle. All firing impulse went away. Curiously, the gun started to produce smoke with every shot. That’s what I meant when I said the results of this test were puzzling. If I hadn’t been chronographing them, I would have thought that I’d found the most ideal situation for the Bronco, which gave me an idea for the future. Since I have two more accuracy tests coming for the Bronco, I’ll include Hobby pellets and will try them both flush-seated and deep-seated to see what they do on paper.

The Slavia 631 with Hobbys
The Slavia 631 averaged 659 f.p.s. with Hobbys seated flush. They ranged from 653 to 667 f.p.s. The firing behavior of the rifle was very harsh.

When the Hobbys were seated deep, the average velocity was 564 f.p.s. with a spread from 545 to 573. So the rifle lost 100 f.p.s. on average and the velocity spread opened up considerably. Once again, though, the rifle became much smoother-shooting. I didn’t notice any dieseling with these pellets seated deeply.

I don’t know about you, but this little test has really caused me to think about the deep-seating situation. I note, for example, that both rifles shot faster with flush-seated pellets. I thought the Bronco might be faster with deep-seating. That leads me to wonder how representative the little 801 really is. Is it possible that unless a gun has a very small swept volume in the compression chamber that flush-seating is usually the best was to go? Is that even a true statement? I don’t know the answers to any of this yet, so it appears there are a lot of things that need to be studied.

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