Upgrading an older Marauder to work like the Field and Target gun

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Saltlake58

Member
Apr 9, 2015
2,907
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Utah, United States
First, I want to thank Tom Holland (XbowSniper) for incredible amount of help and support during the upgrade process.

I started this whole escapade to make my Marauder work better by purchasing an Audrius regulator several months ago. It sat for a while till I had time to install it and start to tinker. Never could make it do what I wanted for a number of reasons including needing to undo some long-forgotten tinkering that got in the way.

To make a long story short, here goes:

I returned the gun to stock and undid all previous tinkering. Then installed the regulator at 2200 PSI, tested, installed at 1800 PSI and tested, installed at 1300 PSI and tested, and nothing worked. Shot count DROPPED significantly.

Tom got involved about this point. He recommended about 1600 PSI, and a couple upgrades to pull it all together. That actually helped and got me to 40 shots per fill at 830fps, which was my goal.

Tom then recommended some upgrades that included a new, lighter hammer spring, lighter valve spring, and a high flow transfer port. Also recommended keeping my stock hammer and valve, and to set the valve wide open with 5 turns. All good advice.

He also recommended polishing the air tube where all the punch outs are to keep from scalping O-Rings. I did that by purchasing a shotgun cleaning kit and wrapping enough duct tape on one length of the rod to give me about ¾ inch across and taped 1000 grit sand paper to it. After I got that smoothed off, I switched to 1200 grit and left it there. Incredible difference on the inside of the tube and the hammer should slide much more consistently. I also polished the bottom of the hammer as it was pretty rough with machining marks. Slides easier now!

All parts came from Hill Airguns and cost under $30 for everything. Valve Spring, #255 Hammer Spring, and the high flow transfer port all came within 3 days of ordering.

Went back to setting the regulator at about 1550 to 1600 PSI, installed the springs and transfer port, set Hammer Spring and Hammer Striker at ZERO, with Transfer Port at 5 turns.

Instantly, out of the gate, 835 fps average. Best part was 65 shots per fill between about 807 fps and 845 fps. After 65 shots it dropped off the regulator. when testing with pellets weighed and sorted to 1/100 of a grain, FPS variance dropped to 4 FPS on a magazine. I'm instantly very happy!

Total upgrade was under $125 including the regulator. Excellent investment if for nothing else than economy of air. If you hand pump, that’s twice the shooting for the same pumping!

I plan on spending time tonight optically centering my scope and getting ready to sight the gun in again. After that, to the range to see how accuracy is affected. Hopefully for the better.

Thank you, Tom, and everyone else on the forum for help along the way getting through this. It’s incredible what the Marauder can do. It’s a great platform to work with.


 
It may be a week or more before I can shoot some groups. Working on returning my scope to optical center and after that, I'll mount and zero. Once the gun is back in working shape, I'll shoot groups.

Also, found a major leak. Turns out I mangled the Fill Valve assembly (yet another stupid thing that turned into a learning lesson.) replacement part is on the way. One thing I like about Crosman guns is that the parts are relatively inexpensive. The fill valve assembly was $20, also ordered a new hammer and some other parts for under $40. Should be here in a few days. It was a pretty good leak so maybe it'll get more shots per fill?? Maybe not. But in any case, I'll post groups when able.

Many thanks all, 
 
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Saltlake,

Keep in mind that the threads where the fill adapter is on the end of the tube, the fine threads are very sharp. What I have done is run a little fine sandpaper (wet or dry type, about 600-1000 grit) and run it past the threads. Just a few light passes, this will take the sharp edge off the threads. I also show the finesse involved in the installation of the fill valve assembly in my rebuilding video. Keep in mind that this fitting does not have to be wrenched down tight, just tighten by hand, then a little extra oomph, and that's it. I also show this in my video as well. I would not do the sandpaper thing with the regulator and other parts still installed. You'll want to get all of those ultra fine crunchies out and away from all this stuff.

Good luck again,

Tom Holland 

Field Target Tech 
 
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Well, my problem was just a touch different. I literally ripped / unscrewed the fill nipple from the rest of the assembly, which isn't supposed to happen. I had replaced the o-ring with one that turned out to be too thick, it jammed into tube, so I had to use a vice to unscrew it. Damage to the fill assembly was fairly extensive on the outside, but I thought it still worked on the inside. Another OOOOOPS along the way (I do a lot of those, but luckily with Airguns, you can recover!) I intended to replace the entire assembly anyway due to the cosmetic damage on the outside 

Turns out that when I reassembled it, I didn't use enough thread lock, so it's leaking at the nipple.

I think the threads on my gun are OK for now. Next time I tear it apart, I'll knock the edges off, but for now, all seems working as I want. Scope is now mounted so after I mow the lawn, maybe some time to start the sighting process! Leak is slow enough to get some work done. From there, shooting some groups.
 
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Saltlake,

Cool, looking forward to see the results. I tore my Marauder apart, and brought it to the range to screw with, and had something odd happen. As I loaded pellets into the breech, (using a single shot tray) they went kinda tough, like something wasn't aligned properly. Shot a few shots, and a pellet got jammed into the barrel. This is a barrel that has never been shot, so my next order of business is to tear it apart (again) and find the problem. Hopefully, it's not a barrel quality control issue, I'll have to investigate.

And the plot thickens.....

Let you know what I find

Tom Holland 
 
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Just got back in from initial tests. Best I could do was a group about the size of a quarter at 50 yards. Doesn't sound very good, but if you remove me from the equation, I think the gun can do much better. I'll get my lead sled out for the next round. That'll take my shakiness out of the equation and really tell me how the gun is doing. Best group was also with JSB 18.3's.

I hear you on the barrel issue. The new fill assembly Crosman sent doesn't leak but it does lose at least 200 PSI when disconnect the fill hose. The valve doesn't close immediately, and the first time I filled it, thought I'd lost the whole tank of air. It did seal, but was took much longer than usual. I tore my old one apart and am stunned at the simplicity of the valve assembly, and since I actually have two old ones, took the older one apart. Different design between the two. Fundamentally they are the same, but the valve in one uses a stem 1/16th of an inch thick, and the other is probably 1/4 or 3/8 inch thick. The larger one works better by the way.

Good luck with the barrel, keep me posted on what you find. If it's a QC problem, that doesn't bode well for Crosman's processes, hopefully it's something else, but not sure what it could be.

even with the slow seal I'm getting 50 shots per fill, which was way above my original goal, but if I can get back to 60+, it'd be sweet. I ordered a 5 pack of one way valves from China for Paintball guns. Should fit (checked and threads are supposedly the same). Hopefully one of the valves will close fast.
 
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Saltlake,

I fixed it. Kinda dumb-dumb move on my part. Something that I wouldn't have thought.

When you get a new barrel from Crosman, you have to put the little o ring inside the breech part of the barrel, it does NOT come with one, as I found out.

What was happening was the pellet went into the breech crooked, and got hung up on the groove where the o ring should go. I strolled 800 feet away to my local hardware store, bought a wooden dowel to knock the pellet out. Took a pick set, and extracted all of the lead shavings out of the o ring groove, cleaned it, and lightly greased and installed a new o ring. Hand pushed the pellet using the bolt, and ran the pellet down the barrel with the dowel. I can safely say it works after doing this several times.

I can also attest that this barrel might need a little more lapping/polishing, as I slid the pellet down the barrel, it was looser in some spots, and tighter in others. It also is a 100% choked barrel, despite what anyone says or tells you. The last 3 inches of pushing the pellet through, clearly indicated that. 

Put it all back together, shot about a dozen shots through it, flawlessly.

Sometimes it's the simple stupid things. How many times in history has a $.20 o ring cause catastrophic damage to stuff?

The Crosman valves are simple, generally, if they leak, there is usually a piece of fly crap on the valve seat, or the oring, if not maybe a bad o ring on it. I usually find that if I take it apart, clean it in alcohol, let it dry out, put a light wipe of grease on it, it'll seal better. They are pretty good valves, but can be finicky if they get a little crud in them. I usually have several spares in my range box, just in case.

Keep me posted, at least we both got them up and running.

Tom Holland 
 
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Want to further the shot count ... LIGHTER HAMMER

Have set up & tuned dozens of .177 M-rods at the >20 ft lb limit ( 10.3's @ 900 ) that get 80-95 shots on a 3k fill.
Click to expand...


Motorhead - absolutely right -

I lightened the hammer spring and valve spring and polished the hammer for smoother movement. Peak shots per fill was 65, but I had a leak so severe I probably lost 5 to 10 shots to the leak during the test. It also comes down to money. The lighter Hill Hammer is over $60 and I just don't want to spend that right now. Just getting to 50 or 60 shots per fill will do for me, for now.

My gun's a .22 and using 14.3 Premier Domes as a baseline mostly because I have several extra tins. I am also testing against JSB 18.3's and so far those results are good. Goal is around 20 FPE to 22FPE, so much more work to come. It's been fascinating to work with the gun, and this is a learning experience!
 
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signal3 - will do. It'll be a couple days before I get another chance to shoot. Had a couple things working against me on Sunday, like the caffeine and sugar overload (my eating habits are terrible), and I was using a new shooting bag instead of the bi-pod I'm used to. Still trying to figure out how to use the bag, it's the Caldwell Tack Driver bag, really nice, but was having trouble getting the gun to cradle in the bag correctly. I'll either use the Lead Sled or the bi-pod I'm used to for the next session, and no caffeine when I shoot. Got to remove all human variables possible to really see how the gun operates.

I've really enjoyed working on the Marauder, I've made mistakes, had to replace parts, installed some upgrades and generally, learned how a PCP works, so when I tinker on other guns I'v got a foundation. Great mentally stimulating project! Lots and lots of support from AGN as well. Great organization and people! 
 
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OK, finally back out shooting for a few minutes. Still getting 50 shots per fil between about 815 and 835 fps. If you limit the string to 48 shots, it's more like 825 to 835 fps. Very happy!!!

Now, for groups. Just to let you all know how I managed this one, here's the setup:

  • Broke in the regulator with between 500 and 750 rounds. Audrious regulator purchased on eBay for about $70. That was just firing over a chronograph into a box filled with rubber mulch. BORING, but well worth it.
  • Gen 2 Marauder about 7 years old. Crosman barrel (no, I haven't upgraded),
  • Hill lighter valve spring $10
  • Hill 252 Hammer Spring. $10
  • Hill HFTP Transfer Port (bit of plastic tube, works really well!) $6
  • Adjustments to the gun are Hammer Spring Zero (0), Hammer Stroke Zero (0), and Transfer Port wide open at 5 turns.
  • Hammer is Crosman stock, though polished a bit. Polished the internal tube so the hammer would travel more consistently
  • Scope is BSA 4-14x44 FFP, scope still needs minor adjustment to the right.
  • Stock trigger, no adjustments, still factory set
  • Pellets are JSB 18.3 grain that weigh 18.2 (yes, I weighed them), head size is unknown.
  • Distance about 48 yaards
  • To remove shooter from the equation as much as possible, Caldwell Lead Sled was used instead of a bipod or bags.

While the cost of the upgrades that made it into the final setup was a touch under $100, I probably spent over $200 trying different things here and there. Also, firing 500 shots across a chronograph took a lot of air. This was only possible due to recent purchase of a compressor. If you try this, have lots of air available.

Now, for the best 5 shot group of the night:

1557628211_3687505165cd78533e0c7f5.08915774_IMG_20190511_202248071.jpg
1557628224_15900759475cd7854018fe31.81070287_IMG_20190511_202238602.jpg


So yes it is a dime size group at 48 yards. My fantastic Harbor Freight $10 digital calipers say it is about 1/2 inch center to center, or about 13mm. If I thought it would hold at 100 yards, it could be a 1 MOA gun, but my experience with the Marauder is that the pellet will become unstable somewhere after 75 yards. I may try it, but for now, it's my 50 yard gun!

Yes, I'm HAPPY with the results. Thanks everyone on AGN and thanks Tom! Couldn't have done it without you!

Edit - Adding one bit of clarity. The 830 FPS was with 14.3 grain Crosman Premier Domes / Hollow Point. The group was JSB 18.3 Jumbo's. The 18.3's run about 750 to 760 FPS. Little slower, but with these results, I think I'll leave it alone.


 
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Finally got a day at the range today. Drove through driving rain, hail and gusting winds. Rain was flooding the areas around the range and a couple cars in the parking lot were in a foot of water. Storms are supposed to be hit and miss today, so went inside and paid for access and took a chance.

By the time I got back to the car to drive to the rifle range, the rain was letting up, and when I set my targets, pretty much done. Light drizzle here and there, but otherwise, no wind, no rain. I was the only person on a 20 lane range, except of course the 4 range masters.

At 50 yards, with my Marauder and new regulator setup, I shot Crosman 14.3 grain premier domes, JSB 15.89 grain and JSB 18,1 grain at 50 yards. minimum 10 shot groups, but Results were interesting.

Crosman Premier Domes, 3 inch groups at 50 yards. Needless to say, didn't waste much effort with the Dome's after that.

JSB 18's, really surprised me and not in a good way. 2 inch groups.

The JSB 15.89's did the best with 10 shot groups of .8 inches according to my fancy Harbor Freight calipers.

All that got me to thinking, maybe the 18 grain pellets need more speed to stabilize, so back to the chronograph I went. At the current settings, I'm getting about 770 fps, so a little slow by most standards. One turn on the Hammer Spring got me up to 780, and two turns to 792. That's where it stopped. No matter how many turns on the spring, no more speed, meaning where I've got the regulator set is a tad low to send the 18 grain pellets any faster than 790'ish.

Well, back to trial and error. I'll be adjusting the regulator up from the 1600 PSI currently set at to something closer to 1800. That should give me a bit more room to "tune" the speed of the pellet, cause 20 fps isn't much range. I might need to buy that lighter Hill hammer as well. Did someone say something about this being an expensive hobby?

Could be a couple more weeks before I shoot a major test again, but it'll come. Have fun.
 
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