BSF S70 air rifle: Part 2
by Tom Gaylord
Writing as B.B. Pelletier
BSF S70 rifle is the father of several famous Weirauch models.
This report covers:
- Today’s the day
- Oiled the piston seal
- RWS Hobby
- Crosman Premier 7.9-grain
- What’s up?
- Cocking effort
- Trigger pull
Today’s the day
Today we find out how honest that Freimark is on my BSF S70 rifle. If you don’t know what Freimark is, read Part 1.
The Freimark is a German airgun mark that denotes a gun that does not exceed 7.5 joules power at the muzzle. That’s 5.53 foot-pounds. That would be a 7-grain RWS Hobby pellet moving 596 f.p.s. That will be our line in the sand.
From my experience with the BSF line, the S55/60/70/80 rifles (same powerplant in all of them) are above 7.5 joules all the time. That doesn’t mean there can’t be some that were made below that level, if German law allows. UK law states that if a model of an airgun can produce over 12 foot-pounds, then ievery one of them must be accompanied by a Firearms Certificate (FAC). They do not allow lower-powered versions of the same model gun to avoid that requirement. In other words, once a certain model needs an FAC, all of that same model need an FAC, regardless of what power they generate. But like I said, I don’t know how the German law reads.
Oiled the piston seal
This rifle has a leather piston seal that needs frequent lubrication. I oiled it with silicone chamber oil and then fired it several times. It did detonate a couple times, then it settled down to shoot normally again. It was ready to test.
I jumped right in and tested with the lightest lead pellet that was likely to be around when the BSF S70 was new. A 7-grain RWS Hobby would suffice. Ten Hobbys averaged 657 f.p.s. in this rifle. The spread went from 638 to 669 f.p.s., so 31 f.p.s. At the average velocity this pellet generated 6.71 foot-pounds, or 9.1 joules at the muzzle. Oops — it was over the line. Close, but on the wrong side of the limit.
No judgement yet. Let’s continue and see what happens.
Crosman Premier 7.9-grain
Next up was the 7.9-grain Crosman Premier pellet. This is a good weight for a powerplant of this power level, and the Premier is also accurate in many airguns. Ten Premiers averaged 644 f.p.s., which was faster than expected — given what the Hobbys did. The spread went from 618 f.p.s. to 670 f.p.s., a whopping 52 f.p.s. difference. At the average velocity this pellet generates 7.28 foot-pounds, or 9.87 joules of muzzle energy, which puts it ahead of the Hobby. The theory says the lighter pellet will generate more energy in a springer, so this one is running counter to that.
At this point I noticed that all the stock screws had loosened. This is a common problem with spring guns of this vintage, so you have to watch for it. After they were all tightened, the rifle was noticeably calmer when fired.
Next I tried the RWS Superdome pellet. Weighing 8.3 grains, it is the heaviest pellet I tested in the S70. This pellet averaged 623 f.p.s. at the muzzle, with a spread from 612 f.p.s. to 641 f.p.s. That’s a total of 29 f.p.s. At the average velocity this pellet produced 7.29 foot-pounds or 9.88 joules at the muzzle. That was the highest energy seen in this test — from the heaviest pellet! Something was backwards, because springers are supposed to do best with the lightest pellets.
Why is this BSF S70 so much less powerful than the other one I tested for you years ago? That one averaged 866 f.p.s. with Hobbys and produced 11.71 foot-pounds or 15.88 joules at the muzzle. You may remember that in Part 1 of this report I said I suspected this one might shoot slower because it didn’t appear to have been worked on. The first rifle had an optional peep sight that Air Rifle Headquarters would install, and I had the feeling that they had sold the rifle.
Until I look inside I won’t know for certain whether this rifle has been worked on, but the cocking effort for this rifle is 25 pounds, while the effort for the first rifle is 34 pounds. That’s quite a difference! But, is it enough to account for the difference in power? I don’t know. I normally believe a more powerful mainspring does not add any power to a spring piston airgun, but that may not be correct. Or, there may be other modifications to the first gun that account for the additional power. Until I look inside both rifles, I won’t know.
Okay, it was time to test the trigger pull. BSF triggers are noteworthy for wearing in to the point they become unsafe. I’ve seen it several times. They get to the point that they have to be adjusted as heavy as they will go and even then they are on the ragged edge of unsafe.
This trigger acts like it’s brand new. Unfortunately it is single-stage only, which gives you no feel for the release. You just keep pulling until the rifle fires. There is no creep, but you do feel the trigger blade move as it is pulled. It turned out to be much heavier than I estimated. It broke between 5 lbs. 7 oz. and 5 lbs. 10 oz. I estimated something around 3 lbs. So, I guess the pull is very smooth. I have no desire to adjust it any lighter.
Where we are now is we know the rifle exceeds the legal German limit for power for a Freimarked airgun. But it is not as powerful as the other BSF S70 I tested several years ago. I think that probably means this rifle is stock — exactly as it came from the factory — while the other one has been modified. Maybe I will use the new Rail Lock mainspring compressor on both rifles to find out!
Accuracy testing comes next, though. I will start at 10 meters, using the open sights that came with the rifle.
I have to say this. While this BSF S70 isn’t as smooth or as light as a Diana model 27, it is in the same category, when it comes to quality. A shooter could do a lot worse than to shoot one of these.