Mauser 300SL target rifle: Part 2

by Tom Gaylord
Writing as B.B. Pelletier

Mauser 300SL
Mauser 300SL. There are three finger scallops along the cocking lever.

Part 1

A history of airguns

This report covers:

  • Velocity
  • Hobby
  • Disassembly
  • Tuning tip
  • Build quality
  • It worked!
  • Oil the piston seal
  • Velocity after lubrication
  • Qiang Yuan Training pellets
  • Sig Sauer Match Ballistic Alloy pellets
  • Trigger
  • Impressions

I’m diving right into the Mauser 300SL. Today will be velocity day, plus I will try to treat the mainspring(s) with Tune in a Tube. Lots to do, so let’s get started.


If I don’t test the velocity of the rifle before trying to tune it I know many readers will be upset, but I’m only going to test a single pellet. That will give us a before/after comparison with Tune in a Tube. However, the way this rifle vibrates, there is no way I’m not going to try to calm it down. It’s supposed to be a target rifle anyway, so raw velocity is not important.

If Tune in a Tube does not do the trick, as reader Dom predicts (because of the design of the powerplant), then I may try to tune it further — either with a trick he mentioned or some other way.


I shot the RWS Hobby pellet for the velocity test before lubrication and the average was 576 f.p.s. That is right at the low end of where a target rifle should shoot. The velocity spread went from a low of 566 to as high of 580 — so 14 f.p.s. That’s not bad at all!

The vibration was slow and not painful, but it was distracting. I couldn’t shoot a gun that vibrates this much for very long! And now I had a starting velocity to compare to.


I removed the stock to see the state of lubrication as the gun came to me. The mainspring(s) was/were dry. I also got a look at the trigger assembly that is welded to the spring tube. It appears straightforward and I believe I now know what each of the two adjustment screws does. Dom tells me there are two springs in the gun as well as a leather piston seal. So, not only do I need to lube the mainspring — the piston seal also needs some oil. That should increase the velocity, if anything.

Mauser 300SL spring
The mainspring and piston were dry.

Tuning tip

When I took the action out of the stock I thought about the newer readers who have no experience doing things like this. I wanted to give them a little tip. Usually (but not always) the triggerguard is attached to the stock by a wood screw and attached to the action by a longer bolt. The head of the longer bolt is almost always larger because that bolt gets tightened more than the smaller wood screw needs to be. You can leave the wood screw in the triggerguard when disassembling the rifle

Mauser 300SL screws
On the left is the bolt that passes through the triggerguard and goes into the spring tube. Next to it is the wood screw that goes through the rear of the triggerguard. It doesn’t need to be removed to take the action out of the stock.

Build quality

I saw a clue to the build quality when the action was out of the stock. The underlever is attached by a bolt that has a locking screw that fits into notches cut into the bolt head. It’s a 1930s design, and it’s also the kind of build quality that many airgunners long for.

Mauser 300SL underlever screws
The underlever pivots on a bolt that’s locked in place by a second screw.

All is not perfect however. The action rocks fore and aft when it lies in the stock. That’s proof that the bedding (inletting) is not correct. And it can be a deterrent to accuracy. In fact, it almost always is, because as the bedding screws change tension the action moves in the stock.

It worked!

Once the gun was apart I saw places to apply Tune in a Tube. I put in a lot, because it has to spread all around to all the parts on the inside. Then I put the stock back on and fired the first shot. Dom — you really need to get some of this stuff, because it calmed the gun down on the very first shot!

There was still a trace of vibration at this point, but I would say 80 percent had gone. The rifle had  passed from being offensive to tolerable. In fact I find myself now criticizing the trigger because the vibration is out of the way.

Oil the piston seal

I remembered the piston seal too, and filled the loading tap with silicone chamber oil, then rotated it closed and stood the rifle on its butt for a hour. The oil runs straight back to the piston seal this way and should rejuvenate the leather. If there is a velocity increase, it will be due to the oil and not to the Tune in a Tube grease.

Velocity after lubrication

After the Tune in a Tube grease and pistol seal oil were applied, I went back and retested the rifle with Hobby pellets. This time they averaged 593 f.p.s., with a spread from 586 to 599 f.p.s. The average increased by 17 f.p.s. and the spread was 13 f.p.s., or 1 f.p.s. less than before. I attribute all the gain to oiling the piston seal. I have to add that the rifle became increasingly smoother as I shot it, so the grease is still spreading around. Remember the Tune in a Tube directions say to shoot the gun 30-50 times to distribute the grease. I have not done that yet. You are watching it as it breaks in — shot-by-shot. Now, let’s try a couple target pellets.

Qiang Yuan Training pellets

Qiang Yuan Training pellets are wadcutters that weigh 8.2 grains. They can be remarkably accurate in some target spring guns. In the Mauser 300SL they averaged 534 f.p.s. The range went from a low of 528 f.p.s. to a high of 544 f.p.s. That’s a 16 f.p.s. spread. The rifle was remarkably smooth with them.

Sig Sauer Match Ballistic Alloy pellets

Next, I tried some Sig Sauer Match Ballistic Alloy pellets. These are surprisingly accurate in many lower-powered airguns. In the 300SL they averaged 681 f.p.s. and the velocity spread went from a low of 670 f.p.s. to 691 f.p.s. And the rifle became even smoother.


When the rifle was out of the stock I got a good look at the trigger. It’s housed in a sheet metal box that’s welded to the spring tube, so no modularity. But the parts look simple and relatively straightforward to work on. I think I can at least lubricate them and adjust the two screws properly.

Mauser 300SL trigger
The trigger appears straightforward and accessible.


I’m starting to think this rifle will be all right! The vibration is nearly gone and I think I can adjust and lubricate the trigger to get it smoother and lighter than it is now.

I will start testing for accuracy next, but I’ll also show you more of the rifle, plus I’ll make those adjustments to the trigger that hopefully make it better.

Ultimately I want to try this rifle with a real peep sight, if my eyes will focus. If not there is a dovetail that can accept optics. We shall see!

31 thoughts on “Mauser 300SL target rifle: Part 2

  1. LOL! You most certainly have been converted to being a member of the choir in singing the praises of Tune-In-A-Tube! It really is so easy to use and works quite well as long as you follow the directions.

    I do so like the quality of the construction of this air rifle. This is the quality that I look for. That is why with proper care, someone will be enjoying this air rifle another hundred years from now.

    When you mentioned the action rocking back and forth in the stock, the thought came to mind that perhaps the wood has shrunk some from drying out as it has aged over the years. That could certainly cause some of this issue. I would personally be tempted to have the stock steamed to se if that cured the issue.

    • RidgeRunner,

      Steaming the entire stock is something thing I have not heard of. I have heard of steaming sections but the entire stock? How is that accomplished? I would suppose bedding the action to the stock using some other material to fill in the gap to eliminate movement is an alternative. Although the pressure applied when replacing the screws might end up cracking the stock though come to think of it.


      • Siraniko,

        A friend of mine is a cabinet and furniture builder and has a cabinet set up to steam larger pieces of wood. One could make such a setup for stocks using a large diameter pipe section.

  2. There doesnt seem to be a way to engineer the vibration out of dual spring designs without a liberal application of grease, and I include early BSA’s in that too.
    Strange concept really, the dual spring, and as mentioned before there is a kit for the FEG/Relum that converts it to a meteor spring with Delrin guides and top hats with rotation washers to simplify and smooth things. The difference with this rifle is that I’ve never seen this design in 177. The 22 normally produces around 9.5 fpe and can be tuned to around 11, you would imagine the 177 to lose 10-15% of efficiency due to calibre, if all other mechanicals are the same (not a given) so you would imagine around 620fps in good condition.
    Tip for tap condition check, three pieces of masking tape, one over the port and one each over each side of the rotating tap, fire it with a pellet, anything flies off…and you have a leak.
    If so, take out tap, with a small art brush paint a little epoxy adhesive very thinly on the tap, replace it, sit it on your lap while working the tap and watching the TV for an hour (don’t stop!) carefully remove the tap and leave it on the side to dry overnight, a little clean up with OO grade wire wool, grease and replace
    Tune in a Tube isn’t available in the UK, but I think I know what it is, most of these things are pretty workaday, I worked a while in the lubrication and fuels industry and the marketing smoke and mirrors is an eye opener (I have 10l of “Ballistol” in my shed)

  3. I don’t hold out a great deal of hope on the accuracy front. At least not “target level”
    Certainly, you were doing pretty well to get 5 shots under an inch at 25 yards with the Relum Tornado
    It was still good value though, it retailed at around 25% less than a BSA Meteor

    • Mind you, when these rifles were popular, the pellets were terrible, especially the cheap ones that the same broke teen that had bought a mad Hungarian underlever could likely afford!

  4. As usual with tap loaders, wadcutters are often a poor choice, I’d give JSB Exact. H&N FTT (or the Beeman equivalent FTS I think)…or even “our flexible friend” the RWS Superpoint for shorter ranges.
    You want the transition from tap to barrel to have as few edges to “pick up” on as possible

      • I think. Knowing it’s lineage, that the term “target” was maybe stretching things a bit, however, even in budget 22 Relum clothes they weren’t inaccurate as such (no worse than any taploader) and the little break barrel Relum Telly was notably accurate so we know FEG can make a barrel. After all they did a lot of manufacturing for CZ/BRNO too.

  5. Early dual spring BSA’s are assembled with the windings opposing each other, I can’t remember with FEG, but the idea is that coils are less likely to trap each other both when cocking and firing. A lot of people reassemble them incorrectly…..just a thought

  6. BB— My Beeman C1 was loose in the stock when I got it. It rocked back and forth so much, that the trigger guard screw was bent. I glass bedded this rifle, at the tang and the screw holes. It worked. the action no longer moves, and the rifle is very accurate. A shim at the tang might good for a quick temporary fix. —-Ed

  7. BB, you tested a 177 Relum Supertornado back in 2009, and got very similar velocities
    I feel they are around 70-100fps low and the rifle should produce around the 8fpe range, the springs are probably a bit old and set

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