Marksman model 70 breakbarrel rifle.
This report covers:
- History of this report
- A word about the washers
- The lesson
- Shot cycle
Today we add shims to the Marksman model 70 mainspring, to see what that does.
History of this report
This Marksman model 70 breakbarrel air rifle was made in the 1980s by Weihrauch from both their parts and the BSF parts that they acquired when they purchased the company. In past reports we have seen many of the rifle’s strange design details.
We have also tested the power of the rifle as it came from the factory, then again, after the canted spring portion was cut away. Then once more after another large portion of spring was removed to get the rifle to almost no mainspring preload. Let’s look at the performance of those past reports now. The same RWS Hobby pellet that I have used in every previous test will be the pellet I use today.
10-shot average with extreme spread
Fac. Vel………..Cant spring cut……..More spring cut
715 (15 f.p.s.)….746 (12 f.p.s.)……….606 (22 f.p.s.)
28 lbs……………..22 lbs………………….20 lbs.
So that is where we were. To add preload to the mainspring, I shimmed it with common flat washers. I used 8 washers that together add about a half-inch of preload.
Eight washers were about a half-inch high.
A word about the washers
The washers I used were common flat washers with a 3/8 hole. The hole wasn’t big enough to go over the spring guide but it did go over the piston rod. So the washers went into the piston. That did add some weight to the piston.
Luckily the 3/8″ washers fit over the piston rod.
These washers are stainless steel. I had no choice in that. They are punched out of sheet steel, so one side is rounded and smooth and the other side is flat with tiny ridge marks. I put them into the piston with the flat side down (going into the piston first) and the rounded side toward the mainspring.
I lightly lubed each washer with thin grease, so they would slip and slide when the gun fired. I have no idea if that’s good or not. It just seemed like the thing to do.
When I last cut the mainspring the preload on the spring was still about 3/8-inch.
This is how much preload remained on the mainspring from the last spring cut.
And this is how much preload that half-inch of washers made.
Let’s look at what this amount of preload did to the rifle’s performance. Remember, a lot of mainspring was removed and those washers that added the space back in don’t add anything to the power of the spring, other than what the preload offers.
Ten RWS Hobby pellets averaged 689 f.p.s. The spread went from 682 to 694 f.p.s., so a difference of 12 f.p.s. The cocking effort is now 26 lbs. Let’s see how this compares to where we have been.
10-shot average with extreme spread
Fac. Vel………..Cant spring cut……..More spring cut……..half-inch preload
715 (15 f.p.s.)….746 (12 f.p.s.)……….606 (22 f.p.s.)………689 (12 f.p.s.)
28 lbs……………..22 lbs………………..…20 lbs………………….26 lbs.
The lesson today is that if we had remained with the spring after the cant was removed by the first spring cut, the rifle would now average around 746 f.p.s. and require 22 lbs. of cocking effort. Adding shims to the short mainspring brought back 83 f.p.s. of velocity that was lost when the spring was cut the final time, but the cocking effort increased by 6 lbs.
Looking at it from the other side, cutting the mainspring and adding the shim removes 57 f.p.s. of average velocity (from 746 to 689) and adds 4 pounds of cocking effort. From a performance standpoint, shimming the shorter spring hasn’t returned all the power that cutting the spring took away.
The rifle now shoots dead calm. It’s as nice as Michael’s Winchester 427, which is the smoothest spring rifle I have ever tuned. It just goes “Thuck” when it fires — not even “Thunk.” With Hobbys it’s nice and smooth but with H&N Field Target Trophy pellets there is a tiny buzz at the end of the shot. It’s almost unnoticeable.
Don’t worry about any of this because this mainspring wasn’t going to remain in the rifle anyway. It’s old and tired. A fresh new spring will probably do wonders for performance. But as long as we are here I think I will shim the spring one more time to see what that does.
48 thoughts on “Marksman model 70 breakbarrel air rifle: Part 10”
Intriguing. Could you possibly fit the washers in the rear of the spring so there is no weight added to the piston? How much weight did those washers add to the piston?
As you read, it would be impossible to put the washers on tyhe other end because of the size of the hole in them. The spring guide is much larger. Coul;d each one be drilled out? Yes, but that’s a huge job.
Those washers added about 30-40 grams to the piston. That is a guess. I can weigh some and get back to you.
If anything, the washers there made the gun more powerful for heavier pellets, but the buzz I got with the Field Target Trophy pellet negate that.
Since the previous accuracy testing shows that this rifle’s barrel seems to prefer the light to middleweight pellets there seems no need to add additional weight to the piston. No need to weigh those washers since you are going to change the spring anyway. If you weren’t going to change the spring the weight would be significant because that would indicate the amount of weight a tuner would have to shave off the piston. The question now in my mind is how are you going to proceed with the new spring? Definitely this rifle needs preload of at least an inch to an inch and a half. You should avoid shortening the spring too much because the addition of washers to increase the tension then increases the weight of the piston affecting the behavior of the rifle on firing. Cut > Collapse > Grind flat. And remember that spring guide on reassembly.
He can buy custom springs. He can give them the wire size, number of twists and length or he can give them I.D., O.D. and length. It just depends on whom he goes with.
I have one that I intend to do this very experiment with. It has a violent firing cycle, even after the over-application of TIAT. If I can bring this beast down to where it can be handled and have good accuracy above 12 FPE, I will be tickled.
B.B. would the result be any different if the washers were inserted behind the spring? I would think velocity would increase because the spring would not be pushing a “heavier” piston.
Off topic, are .177 JSB Exact RS pellets the same as Air Arms Falcon pellets? Does anyone know for sure? They are both 7.33 grains and look identical to me.
Ah, Siraniko, you read my mind!
Air Arms owns the dies on which their pellets are made. The pellets are very similar and there are others besides.
Yes, there would have been a difference in performance. The velocity of the Hobby likely would increase. If a tuner was going to leave those washers in, the tuner would likely lighten the piston to compensate.
Glad we are back to airguns! Springers even.
Wondering if a new spring will change the lovely shot cycle? Proves spacing can increase performance. Maybe make the amount of spring left in there work harder?
PS it would be great if you could change springs. One a long thin spring with lots of preload, and a short, stout spring. Hopefully the would produce about the same amount of energy, but I would love to know the differences in shot cycles…
I still want to shim this spring once more before we advance.
I am thoroughly enjoying this series and am eagerly awaiting the next installment.
Me too! 🙂
You can only go up in wire size by so much as you are limited by I.D. of the compression tube and O.D. of the piston shaft and the spring guide. Now there are sproingers that do not use a piston shaft. With those you have various options, including gas sproings.
Now to answer your question, going with the assumption that both will be compressed within the same length, the stout spring is going to give you a shorter shot cycle. It will also likely produce more power as the pellet will not likely start moving until the piston bounces, while with the light spring having a longer shot cycle, the pellet very likely will start moving before the air is fully compressed. Also, the thinner wire will put out less work.
Designing a nice sproinger is a lot more difficult than many think, including the manufacturers. A lot of R&D and practical experience goes into making a fine sproinger. Most do not bother. With them it is a numbers game. How many of these can we sell? What is our profit margin? How cheaply can we make these? Will improving the trigger cost us more per airgun?
I’m enjoying this series, too and have been shooting the Cometa whose spring I shortened to just more than zero preload and am enjoying it more now than when at full power. The sizable steel tophat weighs more than an ounce, but I’m away from home and I don’t remember the actual weight. I want to do the opposite of what you’re doing and make a new tophat out of nylon or delrin, to reduce the weight and hopefully reduce the forward lunge when the piston stops. I don’t have the plastic yet, or it would already be done.
It sounds like you’re saying that the shot cycle is calmer with the additional weight of the washers in the piston than it was before you put them in. I wonder if the added weight slows down the piston after being released from the cocked position enough to make a difference in the “snappiness” that might be felt with a lighter, faster piston? We have to think about changes in the behavior of the system at both ends of the shot cycle, don’t we? I’ll also try putting some washers in mine to see if it becomes smoother before I make a new tophat. It will be an easy and inexpensive experiment, that’s for sure! Neat-o B.B.!! Thank you!
Yes! This is definitely neat-o! 🙂
You put that one more washer in and you might be getting closer to coil bind with this cut spring.
Usually the gun won’t cock when you get to that point. But sometimes they still will cock but if they have a automatic safety the safety won’t set.
Just something to be aware of if you start stacking washers.
And another thing if you want to eliminate some of the weight of the washers you could make a nylon spacer the size of your stacked washers. And that will calm and quiet the gun down a little more over using the stacked washers and the nylon spacer can stay up in front of the spring still.
I wonder if BB has access to a lathe and a block of nylon?
They do make nylon washers.
Don’t know but if I remember right I seen different nylon spacers at the big name hardware stores.
I have seen them.
Something I noticed throughout your testing so far is that you used Hobbys for the velocity tests, but did not use them in the accuracy testing. Yes, you used the RWS Meistermabuggers, but they are a little heavier and tend to be better made, Yeah, this is probably being picky, but sometimes I just have to be that way. Picky, picky, picky.
Something else I forgot in my comment above about the coil bind and cocking still but the safety won’t set. Your possibly not engaging the sear all the way. It could be a accidental mis-fire if the gun gets bumped.
Definitely do a bump test in multiple ways in a safe direction to see if the gun can accidently discharge.
Been to long
When I was competing in field target I was at a national competition. The great shooter from new York . Can’t remember his name. Shoots with his father.
Anyhow he introduced me to buying washers from McMastercar. They sell them in different thickness and they are machined to exact thickness and are hardened steel. Black, shiny and with oil they allow the spring to rotate.
That was Ray Apelles, who shoots with his dad, Hans. I will look into it.
Yes that is correct. Ray is really a gentleman.
I was shooting with DIFTA and he would often show us how it’s done. In one competition he finished low in the standings. I figured he was having a bad day. No he was shooting field target with open sights just to see how he would do.
Fun to experiment eh BB?
I used to shim the spring on our Slavia 618s to just below coil-bind to boost the meager 350ish fps as much as possible. Once I had determined the length needed I would make an aluminum spacer to fit properly.
One thing I really like about PCPs is their tuneability. Having had my “find the best pellet for the gun” perspective changed to “tune the gun to the pellet of choice” approach I see that stack of washers as an opportunity to fine tune the springer velocity for best accuracy. Might be something for the springer enthusiasts to try out.
Hey Hank…like you could do with a pressure adjustable Gas Spring. You could also change the length of the compression tube Spring length (preload) for “normal” spring piston powerplants with a mechanical external adjuster. A port to add or remove piston weights, a tunable Transfer port. There are so many things that the manufacturers COULD do! But then would the typical buyer just screw it up resulting in lots of frustrated buyers generating returns?
I have helped a great number of adjustable PCP/Gas gunners get back control of a completely self inflicted adjustment disaster.
K.I.S.S. for the Masses?
Yeah, adjustability is a double-edged sword, a boon for those who know and a curse to those who don’t.
See that with the FX Impact all the time. Regulator, hammer spring and valve dwell adjustments are readily accessible. The first thing that people do is crank everything to the max, then they complain that the gun is not accurate followed by trashing the design because it leaks. Go figure eh?
Don’t know, mine came from the factory properly tuned (33 fpe) to stack .22 18.13 JSBs at 40 yards (in spite of me 😉 ). Zero problems after thousands of pellets. Tuning for different pellets is easy if you take you time to balance things properly.
I used to polish a half-venturi in to the transfer port of the 618 (from the piston side) to improve air flow but didn’t change the size.
The manufacturers could do more but that adds to the cost. I always enjoy working on springers – amazing the improvements a bit of spit and polish will gain!
A problem they ran into at Theoben was people charging the adjustable gas sproings so high they would literally burn up and melt the piston seal. BB had a melted down one a while back.
I would love an adjustable gas sproing, but there are too many mental midgets out there for a company to offer them.
There is an adjustable Theoben gas sproing in the HW90.
Yes but I already own all the Gas Spring break barrel I will probably ever own. I doubt I will be buying anymore airguns since every niche (THAT EXISTS at this point) is filled and lots of overlap in some spots.
I will however be buying ammo in great quantities and other accessories! LOL!
I do like to tinker, but I like my rifles working properly much more, so I shoot them and don’t tinker ;P
Still enjoying the SAM & Fortitude!
I like shooting much more than tinkering! I wish I still had Armourers to turn my guns over to and keep them running 100%, ammo, range time and all of it free of charge no less! There was this pesky Unlimited Employment Contract though….
Yes, that contract did have some serious drawbacks, did it not.
You said that all of the possible niches were filled in your collection. How is your antique airgun niche doing?
About half of my airguns are older than BB, you or myself. The majority of my airguns are at least fifty years old. There are very few less than ten years old. Most of those young’ns I would trade in a heartbeat for the right deal.
I enjoy dancing with the old gals. They all have there own little special dance steps and some of them can dance with the young’ns and put them to shame.
Well I see another report coming.
Once you figure out the right length for your stack of washers get a nylon spacer then see which one is smoother and more consistent.
If you can’t find one that will work give me the dimensions and I will make you one and send it to you free of charge. 🙂
I was reading a different blog on airguns (Connecticut Custom Airguns) and came across an anti-bounce piston device. It seems to work on the same type principle as a dead blow hammer. It is only tangentially referred to and described, but caught my eye? I wonder if it will come to a point where you could buy a piston for an airgun that would drop in and bring a new experience to a rifle? Maybe even a device and spring for a drop in modification… Interesting where technology can go with the efforts of resourceful enthusiasts.
Webley made such a piston in the 1990s for the Beeman C1. When the piston bottomed out a rubber washer squished out and hugged the walls of the compression chamber. It did nothing at all in reality.
These are fun to talk about, but they just don’t work. Now, I haven’t tested all of them. There could be one that works.
BB, If I cut down my Synergis barrel to about a foot long, will I get more velocity? I dont know if the barrel is chocked or not, and there seems to be a square nut on the breech end for what I dont know, an oring in there? If I did that, it would put the cocking handle in front of the end of the barrel, what I dont like, but the rifle would have a quicker lock time? (pellet out of the gun sooner)That would make it a tanker springergis… By sqeezing the the two welded halves of Bandits trigger group housing, cold setting, there is now no side to side play with the tigger. Nice light target trigger now. I thought piston bouncing was more of a PCP/co2 issue. I use an Oring tune for that, and for the springers you change the weight of the pellet. If a spring piston didnt bounce, how would I know if its tuned just right or not. They could just machine a detent for the piston, but that would cost xtra.
Shortening the barrel of the Synergis may work. Take note of the new Springfield M1A cocking lever. It is short when stowed and extends when you use it. Maybe you could make something similar for the Synergis.
The barrels for the Air Arms TX200 and Hunter Carbine are only ten inches long. The shroud and baffle system makes them look longer and allows for the longer cocking lever.
RR, with an aftermarket shroud on it, its looks far more menacing than it really is. It doesn’t really need one. Now, I have xtra parts lying around.
Live and learn,
I don’t know, but please don’t do it. The gain would be minor, on the order of 20-30 f.p.s. I imagine.
Since PCPs and CO2n guns don’t have pistons, how could they bounce?
BB, thanks, I dont need to do it, maybe I’ll just paint the plastic stock then.
Yeah, hammers go with orings, but they do both bounce. Is it ok to use high magnafication scopes with both eyes open? It seems to work ok.
I dont want to make a bad habit permanent.
I have used up to 80X with both eyes open.
Some PCP are claimed to do that PING thing and folks do VooDoo stuff with things called “debouncers” to the air tube to keep it from happening.
Still others believe the hammer bounces multiple times on some PCP/Gas guns waste of air they say.
It has been proven that some airguns do strike the valve multiple times, wasting air. The Marauder is bad about that. Crosman even puts a debouncer in them now. The “slingshot” striker that Daystate developed is designed to eliminate that bouncing.
As far as the “pinging” goes, I believe that is caused by the sudden changing of the air pressure in the reservoir creating a vibration in the tube. the “voodoo” that many use is a plastic bushing that fits snugly in the tube to reduce that vibration. An insertable regulator may do the same thing.
Yes hammer/striker bounce happens. It doesn’t NEED TO with a balanced valve, (pressure/volume metering system) regulator and/or plenum. Oh, forgot one: Dump Valve! The only thing that causes it is a mismatch of forces for the desired projectile acceleration.
The ping happens when the valve is not in the air tube and/or no plenum is used. DAQs don’t PING, bottle guns don’t ping, Condors, Talons, Texans don’t PING…why take up charge volume with a “fix” that isn’t needed? I know, I know, COST!
Now for your earlier question about the more “mature” Ladies: i lust after only one…
The rest of my airguns truly fill my needs and i hope they will all become fine Ladies and family heirlooms. I hope they will get lots of active shooting and LOVING care until they just can’t anymore…then they should go to places of honor on a wall.
BB, that shim might get you 20fps. Just say’n. Also, I found out about the plastic threaded co2 charging caps with the metal inserts you use an allen key to tighten, almost all co2 guns have them(?) They are junk, they crack, and the insert just spins. On my co2 Luger, they wisely chose an all metal design for that. Its the only co2 gun I have that still works, because of that feature. That one and the Sheridan EB. Its too bad because the broom handel Mauser was an extemely accurate bb gun, and both mags failed because of those caps. I was thinking about a rifled barrel SAA, but
I don’t need anymore co2 parts.
Buy, and learn.
For the last week or so all the photos on this blog are like, faded out. What’s going on?
Really like the series on the Marksman 70. I like ANY sproinger series, but the Marksman 70 is especially fun!
St. Louis, MO