Oops! My Benjamin 397 has valve lock!

by B.B. Pelletier


The Benjamin 397 (left) is a powerful multi-pump. Obsolete 397 carbine at right.

Today, we have a critical report about airgun maintenance and operation. So, if we’re being critical, let’s start with the title. It’s a It’s no one’s fault — let’s all get along title. It should read, Oops! I really screwed up! And when I say “I,” that’s exactly what I mean!

About a month ago, a friend of mine — who shall remain nameless, unless he repeates what I am about to tell you — received a new Benjamin 397 multi-pump pneumatic. Hurray!

I went over all the operational and maintenance steps carefully with him — pump it no more than 10 times per shot, always store it with one pump in it, use Pellgunoil on the pump head etc. — and then turned him loose with his new rifle. Last week the rifle came back to me with the complaint that it didn’t fire pellets anymore.

I must have looked like that old plumber who knows just where to tap the pipe to get the system going again, because before I even examined the rifle I told him it was over-pumped and therefore valve-locked. Then, I took the rifle and opened the pump handle, which sprang open with a lot of force. Yep — it’s valve-locked, all right!

I listened carefully to the story of how it couldn’t possibly have been anything that he did wrong. I’ve heard that same story a hundred times before; but like a compassionate priest, you have to let them confess everything as you listen in silence. On about the third go-round, I got the real story.

It seems he was at work, shooting his new gun with a buddy who was also shooting his own multi-pump. Remember, folks, we’re talking Texas, here. Depending on your job, shooting at work isn’t that uncommon. Perhaps not at a funeral home or at a fast-food franchise, but there are a lot of outdoor jobs where shooting is possible and not objectionable.

They were shooting at a metal sign that the buddy’s gun wasn’t able to dent very much, but the 397 put a big ole’ dent in it. However, something wasn’t right! It seems the other guy’s pump gun was much easier to pump than the 397. What was wrong with the 397?

What was wrong with it was that it wasn’t a Crosman 760, like the other guy’s gun! At least that’s my guess. I’m still waiting to hear what the other guy’s gun was.

So, his new gun was harder to pump, but it was also a lot more powerful. MAYBE he wanted to see if the 397 would go all the way through the sign, thus vexing his friend, which is the tradition whenever two guys shoot together. He pumped it ALL the way up, being VERY CAREFUL not to exceed the 10-pump limit, as I’d instructed him. But that time it fired only weakly.

He handed his rifle to his friend, who then pumped it up again, also being VERY CAREFUL not to exceed the 10-pump limit, because the owner was watching him. This time when the trigger was pulled, the gun just went CLICK and no pellet came out. So, now he knows that his gun doesn’t work anymore.

At least he stopped when it got to this point. He didn’t keep loading pellets and pumping it a couple more times just to be sure. I have seen owners do that before.

He brought me the rifle and asked if I could possibly help him. I told him there are two ways to go about this. One is to wait a couple months and hope that the gun leaks down enough that the valve is no longer locked. If the gun had not been properly oiled with Crosman Pellgunoil, that might have been a possible solution. But it was well-oiled, and I didn’t think it would leak down in even a year!

I decided to go the other way. I would remove the extra air mechanically by partially disassembling the gun and rapping on the valve stem with a heavier hammer. That’s how the repair center fixes guns that are over-pumped. Or, at least it used to be! This is where the “old plumber” became a student, again.

I discovered that the new 397’s design is vastly different from what I was used to. You can no longer do what I just said because the gun is not designed to allow it. The new design is much cheaper to build and easier to repair — except when the gun is over-pumped. I’ll describe what I did and what happened as a result — and I don’t see any other way of doing the job.

Poor photos today
I apologize for the poor photos that follow. I was working on the gun and getting dirty, so I used the flash on the camera to make the work go faster. That’s why everything is so over-exposed.


What appears to be the stock screw also holds the valve inside the pressure tube. If the rifle is pressurized, this screw will be under pressure from the valve body trying to move! If this is the case, remove the bolt before you loosen this screw!

The new 397 valve is held in the gun by the single stock screw. That screw fastens the trigger group to the action, and there’s no way to rap out the air the way I described it earlier. I did an internet search and discovered there were no instructions on what to do! In fact, everyone dances around this design almost as though they don’t understand it, though I’m quite sure most of them do. It’s so much simpler than the guns I’m used to. When a gun is over-pumped, there seems to be no good way of depressurizing it — other than to remove the single screw I just described and let the air blow out. But before you do, be sure to remove the bolt first!


Remove the two sideplate screws and the sideplate and cocking plate will come off (right and left, respectively in this photo). Then, you can remove the Allen screw from the bolt.


Once the Allen screw is out, the bolt slides out of the receiver.

I didn’t know it while I was doing it, of course, but when the stock screw backed out sufficiently far, the air exploded out of the gun as the valve moved within the pressure tube. It caught me by surprise, but in retrospect I can’t see a better way of doing the job. If anyone knows of one, I’d like to hear what it is.

In retrospect, I should have removed the bolt from the gun before removing the stock bolt. To do that, remove the two screws that hold the sideplate to the left side of the action, exposing the Allen screw on the bolt that cocks the hammer. Then remove the Allen screw, and the bolt slides out of the action.


The action can be removed from the stock when the one Phillips screw is loose. The screw is captive inside the stock and doesn’t show here.

At this point, I finished the disassembly, checked all the parts to see that they were okay, which they were, and assembled the gun again. There’s a trick to assembling this gun. The pump arm must be swung forward to allow the valve to go forward enough for access to the screw hole. If you do that, this is an easy pneumatic to assemble. If you don’t — good luck!


You’re looking through the screw slot in the triggerguard at the brass valve body and its fastening screw hole. How many people would realize that their one stock screw is holding all this?


This picture shows why you cannot just rap out the air anymore. The rear of the pressure tube is blocked by the back of the trigger assembly, which has to be removed to gain access to the valve.

And how does it work?
The rifle now works fine, but I’ll run a little test to see how fine. I’ll shoot the gun through a chronograph on six pumps, and keep increasing the number of pumps until there air remains in the gun after the shot. Then, I can tell the owner what the exact maximum safe number of pumps are for this specific gun. That’s another great reason for owning a chronograph!

Checking the velocity
I decided to use Crosman Premiers in the 7.9-grain weight for my test pellets. This is what the gun now does.

Pumps…Velocity…Air remaining?
6………….613………..No
7………….650………..No
8………….688………..Yes! A soft pop was heard.
9………….713………..Yes — a second shot went 555 f.p.s.

Chronograph reveals what happened
It’s easy to see what happened to this rifle. I told the guy that 10 pumps was the maximum, because I thought that was what the owner’s manual said. But it isn’t! Crosman has folded the Benjamin rifles and Sheridan rifles together, and now they all top out at 8 pumps. So, I was responsible for the owner over-pumping his gun! Several years ago, when the Benjamin and Sheridan brands were different, the Sheridan stopped at 8 pumps but the Benjamins stopped at 10. But those days are over. Now they all stop at 8. So — shame on me! Apparently this is my week for confessing my sins.

What if you don’t own a chronograph?
But you don’t care about that! You care about your own air rifle, and, since you don’t own a chronograph yet, how can you determine the exact number of pumps that are maximum for your rifle? It’s simple. Do what I did above and increase each shot by one pump. Then cock the rifle afterward and fire it again without a pellet. Listen for the pop of escaping air. When you hear it, back off one pump and that is the maximum number of pumps your rifle can handle.

Just to be safe, pump your rifle to the newly established maximum number of shots five times and shoot it. After the fifth shot, cock the gun once more without pumping it and fire it again, listening for a pop. Sometimes the amount of air that remains is so low you cannot hear it, but after a cumulative five shots, you should be able to hear it very well.

Lessons learned
I got the tables turned on me this time. And I also learned how easy it is to work on these new Benjamin rifles. And you readers got to watch everything over my shoulder, plus you got a new way of testing the maximum number of pumps for your specific pump rifles if you don’t own a chronograph. I would call that a good day’s work!


Benjamin 397C: Part 3

by B.B. Pelletier

Photos and tests by Earl “Mac” McDonald

Part 1
Part 2


The Benjamin 397C (right) is noticeably shorter and smaller than the 397 long gun. It’s three inches shorter and more than a full pound lighter than the rifle we know today.

Before we begin today’s report, I’d like to give you an update on two projects. First, I’ve replaced the trigger in the RWS Diana 34 P rifle, so I’m ready to do the T06 trigger evaluation. It was the easiest trigger replacement/piston removal I’ve ever encountered! I used to think Weihrauchs were easy to work on, but now that Diana has gotten rid of the T01 trigger that had a couple small things you needed to know how to do, replacing a trigger in one of their rifles is about like putting batteries into an airsoft AEG. I did the whole job in 20 minutes, start to finish, which included set-up and clean-up time. A lot of the credit for that goes to the Air Venturi spring kit that was in the gun, because the mainspring is not under a lot of pre-compression. I’m sorry to see that product go, because it made a world of difference in the performance of the gun.

I was so pumped with the success of the trigger swap that I tackled the Slavia 631 next. It’s also easy to take apart, and you won’t believe the improvement that just lubrication has brought. A 35-lb. cocking effort is now down to just 21 lbs.! I had guessed it could drop to 28 lbs., but that was way too conservative. I also got rid of 80 percent of the vibration, but that’s something I will save for the next report. Since the rifle is now so different from the way it was, I’m going to retest the velocity for you in a special report.

There’s lots more to tell about both projects. This was just an update to let you know how things are going. And, wprejs, this week I’ll pack the harmonica rifle and send it to Vince. Now, let’s look at today’s test.

Let’s take a look at the accuracy potential for the Benjamin 397C that Mac’s been testing. There’s been a lot of interest in this little rifle since this report started, and practically nobody knew of the gun’s existence before now. Even so, it was produced so recently that there’s still a good chance of finding one in near-new condition and still in the box, so this is one of those sleeper opportunities that abound in this hobby. As I finish this report, you have to ask yourself what it is that you like about airgunning; because if it’s finding rare guns for very little money, this carbine is one to look for. And, you need some references like the Blue Book of Airguns to help you find things like this.

The test
Because this is a multi-pump pneumatic, there are some things we need to know before we look at the targets. The number of pumps that were used for every shot. Mac shot the carbine off a rest at 25 yards, and each shot got the maximum of eight pumps.

The way this gun works, some high-pressure air will always be trapped in front of the pump piston head after the pump stroke is finished. All the air does not go into the reservoir, even on modified guns.

As the number of strokes increases, the amount of air trapped in front of the piston head increases, so naturally it’s always the greatest when using the maximum number of strokes. When that happens, the air pushes back on the piston head, forcing down the pump lever, which is the carbine’s forearm, just a little. When you shoot, the air pressure inside the reservoir drops instantly and the tiny bit of high-pressure air in front of the pump piston head pushes its way into the reservoir. That allows the forearm to return to its relaxed position, and the shooter feels this as the whole gun settling. It’s a trait very common to a multi-pump, and it allows some movement of the gun with the shot.

There’s nothing a shooter can do about this movement when it happens; when it does, the pellet is already out of the barrel. The slight movement should have no effect on the accuracy of the gun. However, I want you to remember this discussion, because it had an effect on the outcome of the test.

Mac notes that the little carbine is hardly a bench gun, and we wouldn’t expect it to be at just 4 lbs. Sometimes, light weight and overall shortness can be a detriment to accurate shooting, as these little rifles are so twitchy (sensitive to how they are held).

You’ll remember from Part 1 that there is a Williams peep sight on this gun. Mac installed the hunting aperture, which has a larger hole for more rapid target acquisition. Peep sights with large apertures are quicker to get on target than regular notch sights, but the downside is you give up some precision to get the speed. I love the way an M1 carbine gets on target in an instant, but nobody will ever confuse it with a target gun because the large aperture reduces it to a minute-of-person weapon.

Accuracy
The first pellet Mac tried was the 7.9-grain Crosman Premier  dome that’s usually one of the most accurate pellets in these multi-pumps from Crosman, Benjamin and Sheridan. But this day there was no joy as five pellets went into a group measuring 0.93 inches.


Crosman Premier lites were disappointing, producing a 0.93-inch group for five shots at 25 yards.

Next, he tried RWS Hobby pellets, which he also thought would be wonderful. They disappointed as well, with a five-shot group that measured 0.77 inches at the same 25 yards.


RWS Hobbys that usually do well were only so-so in the 397C. The group measures 0.77 inches.

Finally, Mac tried the pellet he likes the best for most air rifles in .177 caliber — the RWS Superdome. But try though he might, five of them grouped only 0.84 inches at 25 yards. Then, he had a thought.


RWS Superdomes that Mac likes didn’t do so well, either. This group measures 0.84 inches at 25 yards.

Inspiration!
Remember that forearm that moves on every shot? Mac noticed it, too, and was holding the rifle with his off hand close to the triggerguard, the way you’re supposed to hold a breakbarrel. He decided to throw caution to the wind and rest the rifle with the forearm lying on the flat of his palm. He just knew that the moving forearm would throw him off, but he tried another five RWS Superdomes and discovered the secret. That’s the perfect way to hold this little carbine! Five pellets went into 0.24 inches at the same 25 yards.


Mac discovered the secret hold! Resting the forearm on the flat of his off hand made this spectacular five-shot group with RWS Superdomes. It measures 0.24 inches between centers.

What this test tells us is that conventional wisdom isn’t always right. This reminds me of the time when I decided to hold my Beeman C1 carbine with a super-light hold to see how bad it would group and wound up discovering what I now call the artillery hold!

The bottom line for this little gun is that Mac loves it. He likes it most for its size and weight, and it’s the gun he most often hands to guests when they want to do a little shooting. Offhand, it shoots much better than these groups might suggest, and Mac doesn’t worry about the loss of velocity. As long as everyone has a good time and can hit the targets, everything is fine.


Benjamin 397C: Part 2

by B.B. Pelletier

Photos and tests by Earl “Mac” McDonald

Part 1

The Benjamin 397C (right) is smaller than the 397 long gun.

We’re continuing our look at the Benjamin 397C that we started recently. It seems this model caught a lot of people off their guard, as the responses agree that not many people were aware it had even been made. In Part 1, I made reference to a comparison between this carbine and the 397 long gun, but I hope you understand that Mac is testing just this one gun. I’ll refer to the 397’s performance through the published specs and what I know of the gun. I invite any readers to add their comments as well.

Beautiful wood
Milan commented on the fine wood of the 397 rifle shown in Part 1, and I guess I should have said more than I did about it. Benjamin traditionally bought the wood for their rifle stocks from Stover, Missouri, and lucky owners often got beautiful stocks through the luck of the draw. The factory never made any attempt to segregate the wood by grain pattern.

I owned one Sheridan Silver Streak with a gorgeous crotch grain stock that would have added 50 percent to the price of any firearm it had been on. The wood on my current Blue Streak is pretty nice, too. So, good wood goes hand-in-hand with both the Benjamin and Sheridan names.

Velocity day
Today is velocity day, and it’s when we find out what has been sacrificed to shorten this carbine. Mac did several tests to help us understand how the multi-pump powerplant works. For starters, he pumped the gun different numbers of strokes and obtained the average velocity for each set between 2 pumps and 8. Let’s begin there.

The pump lever must be pulled down and forward like this for every pump.

All the following shooting was done with 7.9-grain Crosman Premier pellets in .177 caliber.

Pumps
Velocity
Low
High
Spread
2
325
318
331
13
3
407
401
412
11
4
466
462
471
9
5
511
509
513
4
6
544
538
549
11
7
576
573
582
9
8
596
593
598
5

We can learn some things from this data. First, notice that as the number of pumps increases, the velocity jumps get smaller. This demonstrates the diminishing returns that are common to all multi-pump pneumatics.

Another thing to take away from this is that the rifle is more stable at certain numbers of pumps than at others. Five pumps, for example, vary by only four feet per second across all ten shots, while six pumps vary by almost three times as much. What you can learn from this is that each rifle is very particular in how it behaves and you really need to know your rifle well. However, I’ll let you in on a little secret. In all the testing of both Benjamin and Sheridan multi-pumps that I’ve done over the years, I’ve found that five pumps is sort of a magic number for all guns. Fo some reason, they all seem to do well with five pump strokes.

And another thing. If Mac didn’t have a chronograph, none of this testing would be possible. Just one more useful thing you can do with them.

The last thing we can learn from this data is that a ninth pump stroke is probably not going to give any more velocity than eight strokes. In fact, it’s more than likely that the ninth stroke will actually make the rifle shoot slower than it does on eight. You can see that coming by looking at how close the average velocities are between seven strokes and eight. There’s an increase of only 20 f.p.s., while the difference between three and four pump strokes is 59 f.p.s.

What about nine pumps?
So, should you even try a ninth stroke? The answer depends on the gun. Most guns will not shoot any faster on nine pumps than they do on eight, but a few will. The gain might only be five f.p.s., but it will be a gain, nevertheless.

Most rifles will not increase, though, and after the shot when they’re cocked and fired again without pumping any additional times, you’ll hear some air exhaust. So, the ninth pump stroke was a waste of energy.

Bear in mind that the higher number pump strokes put a greater strain on the pump mechanism of the earlier ones because of the additional effort that’s needed. These guns have been designed to last virtually forever on eight pump strokes, but as you exceed that number the additional wear will cause them to wear out. When I was a kid, I used to hear adults brag about how they pumped their old Benjamin rifles up 30 times and they shot just as hard as a .22 rimfire. That’s hogwash! I can prove they won’t work that way, and if they really did pump their guns 30 times, which is next to impossible, they probably broke them.

Mac did pump his gun nine times for this test and he found that the velocity did go down by a few f.p.s. He didn’t keep a record of how much it dropped, so I can’t tell you that, but the rifle did exhaust air when it was cocked and fired again without pumping it again.

Velocity test
For this test, Mac started all over again. He didn’t re-use the velocity from the first test. This test was done at 8 pumps for every shot.

This time, Crosman 7.9-grain Premiers averaged 595 f.p.s. and ranged from 593 to 598, for a spread of five f.p.s. At the average velocity, the muzzle energy is 6.22 foot-pounds.

RWS Hobby pellets averaged 631 f.p.s., ranging from 626 to 638 f.p.s. That’s a spread of 12 f.p.s. The average muzzle energy was 6.19 foot-pounds.

RWS Superdomes averaged 596 f.p.s., with a spread from 592 to 602 f.p.s. The average energy was 6.54 foot-pounds.

Well, that should settle the question of what happens when a pneumatic is shortened. The velocity drops as the barrel gets shorter. The longer 397 rifle would get between 725 f.p.s. and 775 f.p.s. with 7.9-grain Crosman Premier pellets; and at an average of 750 f.p.s., the energy would be 9.87 foot-pounds. That gives you a good comparison between the long gun and the carbine.

Some readers have commented that the Benjamin 397 is already a smallish air rifle and wondered if it is really necessary to make a carbine out of it? I guess that’s a good question, because the longer gun has been in production for almost two full decades while the carbine lasted only four years. But Mac insists this is a very handy airgun, so I guess it’s one of those personal taste choices. If you look at the photo at the top of this report, you’ll note that even the pull length has been scaled back by an inch, so the carbine is undoubtedly best suited to shooters who either want or don’t mind a short-pull rifle.


Benjamin 397C: Part 1

by B.B. Pelletier

Photos and tests by Earl “Mac” McDonald

Today, we’ll begin a look at a strange duck. It’s an airgun model that is still current, but this variation is a relatively little-known offshoot that, because of its nature, is a completely different airgun. I’m referring to the Benjamin 397C. I linked to the Benjamin 397, which is the parent model and is still available for sale, because the “C” or carbine version of this multi-pump pneumatic isn’t made anymore. It was made and sold between 1994 and 1998, but not a lot of them were made. That’s the gun we’re studying today — the 397C that’s different than the longer 397, as this report will show.


The Benjamin 397C (right) is noticeably shorter and smaller than the 397 long gun. It’s three inches shorter and more than a full pound lighter than the rifle we know today.

Mac bought two brand new 397Cs at an airgun show several years ago. He has since gotten rid of one, but he holds on to the other because he’s grown to like it so much.

The carbine is 33 inches overall with a 16-inch barrel. The length of pull is a short 12-1/4 inches, but it’s comfortable for most adults in the offhand position. It weighs 4 lbs. 4 oz.

Design limitations
Because the 397C is a carbine and must be shorter than the long gun model, by definition of what a carbine is, it must also suffer the limitations that come with it. As regular readers of this blog know, pneumatic guns derive their power partly through the length of their barrels. Just as in the 19th century, a firearm rifle with a longer barrel was often more efficient and got more power from the same load than a shorter rifle when all things were equal, so any pneumatic will suffer from a power loss when its barrel is shortened. This is one time when physics will not give in to design.

Additionally, the pump mechanism and air reservoir were also shortened to make this carbine, so these two facts will affect performance as well. The bottom line is: don’t shorten the barrel if you want to get maximum efficiency from a pneumatic powerplant, anymore than you would shorten the barrel of a black powder rifle and not expect a similar power loss. Heck, for the same reason, the U.S. Army has discovered to its chagrin that the compact M4 carbine hamstrings the performance of the 5.56mm round that’s standard in the M16.

Design benefits
On the other hand, carbines are much handier to hold and to use. Mac pointed out that his 397C is a delightful airgun that he pulls out often when guests come over to shoot. Everybody likes the compact, light feel of the gun; and until you shoot it over a chronograph, you don’t notice the power loss. All things considered, Mac likes the carbine size over that of the full-sized rifle.

Because it comes from an older period in the life cycle of the 397, this carbine has the rocker-style safety that has a tab on either side of the receiver. It’s called a rocker safety because when the action is out of the stock you can see that the safety mechanism rocks from side to side as the Safe and Fire tabs are pressed.


The 397C has the old-style rocker safety that shooters love.

Like all other Benjamin pneumatics, the 397C is almost completely ambidextrous. The bolt is on the right side and cannot be switched, but the gun’s simple lines and the way the safety works combine to make it easy to operate from either side.

Like the full-sized 397, the carbine is recommended for a maximum of eight pumps and no more. Being a multi-pump, it can get along with fewer, depending on the situation. Three pumps for indoor target practice at close range and five if you want to shoot farther. Mac measured the effort required for the pump strokes and found that it takes 10 lbs. at stroke number two, 18 lbs. at stroke four, 24 lbs. at stroke six and 30 lbs. at stroke eight. That makes it somewhat easier to pump than the full-sized rifle, which requires about 35 lbs. for the eighth stroke. Of course, that means that less air is being compressed with every stroke.

Williams peep sight
Many of you know that Mac likes peep sights on his rifles, and Benjamin multi-pumps are made at the factory to accept them. When he purchased the gun, it had the Williams peep sight that is made specifically for Benjamin and Sheridan air rifles.

The Williams receiver sight is specially made to mount on the Benjamin and Sheridan pneumatics.

Two maintenance procedures
One thing the readers of this blog should have learned by now is that most CO2 and pneumatic guns require frequent oiling to keep the interior seals fresh and doing their job. But a quirk of marking on the rifle confuses many owners. The air intake hole has the words AIR HOLE DO NOT OIL stamped next to it, and many owners assume that means they are not to oil the rifle at all. In fact, oiling is one of two maintenance procedures that keeps the rifle operating for many decades. But you don’t oil through the small air hole. Instead, you extend the pump handle as far as it will go, which draws out the pump piston head as far as it can come. The pump head gets the oil. Three or four drops of Crosman Pellgunoil on the pump piston head every six months will keep the rifle working properly for a long time.


When the pump handle is opened all the way, the pump piston head comes as far out of the pump mechanism as possible without disassembling the airgun. Put three or four drops of Crosman Pellgunoil on the piston head at the end of the pump slot and then work the pump handle back and forth to spread the oil to the inner walls of the compression chamber.

The second maintenance procedure for this rifle is to always store it with a pump of air in the gun. That keeps both the inlet and firing valves shut against airborne contamination, and the seals will stay fresh for many years.

Mac promised to test both velocity and accuracy for us in the weeks to come. We’ll have a chance to look at this less-common type of Benjamin pneumatic and compare it with the longer rifle of today.

The 397C is another example of a rare type of airgun that’s still relatively unknown and still available for a good price. While it may not be your cup of tea, it gives us all hope that the field of airgun collecting is not just reserved for those with deep pockets and access to vintage airguns.