Marauder Semi-auto power tune mods

Jump to latest Follow Reply
sorry for the delay here, thought I hit submit first thing this morning. 


The misfires were immediate, very beginning of first string. First shot fired and the trigger went slack like the hammer did not catch when it bounced back. Pulled the mag and pulled the charging handle back to cock. Inserted the mag and now had two pellets in the chamber (I realized the bolt did cycle completely after this.) Pulled the trigger and got the 700fps double pellet second shot. Failed to cycle on this shot also, but it was the bolt that didn’t cycle (probably because of the 2 pellets I guess) so I pulled the mag, pulled back the charging handle, dry fired, replaced the mag, used forward assist, fired this pellet, another incomplete cycle (sorry I don’t remember this time what the specific failure was) so I pulled the magazine, cocked using the charging handle, fired, and reinserted the magazine. I pulled the mag 3 times total and then everything worked fine from here on for the rest of the first string. Recharged to 3000 and everything worked fine but the fps dropped as the shot string shows. 


just had time to take everything back apart. The reg is either still at 2/3 out from stock or 1/3 in from stock if it moved the other direction. The set screw turning in (lower) could explain the dropping then constant 920 fps right? 

It held air fine and everything looks good in disassembly. From the pictures I took of the reg over the course of these tests it really looks like it is turned out, not in. I am going to try to turn it back in 
D373B91C-C6AE-4194-9BD5-59D6F5500D5E.1641708244.jpeg
59B7EAA1-99E4-4B6E-A892-DDD6BA3F63FB.1641708247.jpeg


to 1/3 over stock, loctite, and try again. I’ll post results when I have them. 

Adding pics of the regulator, the red is the factory set point and the blue I added to keep track. Over the course of these experiments. 

 
Upvote 0
It sounds like you may be approaching some of the limits. The hammer bounce system is probably driven more by the pressure in the plenum, so that limit is approximately 2300psi. The bolt cycling is probably driven by the overall force of the shot, in this case, FPE. The wall may be 35FPE.

When you go to the larger plenum, you will be able to drop the reg setting down to achieve the same power. I think that will get the hammer cocking back in its operating range. But, you might run into the same wall of 35FPE on the cycling. Might be able to increase mag spring an adjustment or two. A full mag of heavier pellets takes more time to move than lighter ones, too.

You might try testing some more to see if it repeats and you are at/near the limits. But, think going to the larger plenum is the next big step. Unless you still plan some porting, in which case would want to test with this configuration before going larger plenum..

I should have mentioned getting a height measurement on the reg, before adjusting, so you could tell when it has gone past 360 degrees. 

Locktite is probably not the best for trying to hold polymer adjuster. I may try a very small drop of plastic bonder epoxy. Just hope it doesn't spread into the threads and become un-adjustable. ;) Is there much metal there, such that you could tap it for a shallow set-screw?



PS: For the SAM specific parts you purchased, could you post or email/IM them to me?




 
Upvote 0
Upvote 0
That is exactly what I was thinking across the board. Measured the total height of the reg at zero last night. A little grub screw is a great idea! 

I wanted to return to what was functional and take smaller steps until the regulator shows up to increase the plenum size. I’ll send you my parts list and the data in a spreadsheet format later today. Thank you again for all the help getting here!

Here is the +1/3 regulator and 7 turns in on the hammer screw summary (noticed the same high shot fps outliers after mag change again with this and turned up the hammer spring for the next set):

Shot count: 39
Low: 923
Hi: 970
Avg: 944
Spread: 47
STD Dev: 9.8

Same regulator and 8 turns HS:

Shot count: 10
Low: 958
Hi: 974
Avg: 962
Spread: 16
STD Dev: 4.7


Same reg and 8.5 turns HS:

Shot count: 30
Low: 951
Hi: 981
Avg: 964
Spread: 30
STD Dev: 5.3

Edited for accurate HS information, probably need more coffee
 
Upvote 0
(noticed the same high shot fps outliers after mag change again 



I have been thinking about what may be causing that, but the scenerio doesn't align with the hammer adjustment. I was thinking that after the mag load and release of the T-bolt w/assist, the bolt and pellet is fully seated. On cycling the bolt and pellet did not seat as far in the barrel, partially blocking the barrel to probe port. I couldn't remember if this has a round or U-port to the probe.. Even if it has a U-port the pellet tail may be blocking.

This may be a good check with the stiff wire through the load assist hole. Measure how far the bolt is closed on the start and compare to the gun cycled shots. The difference, if there is any, won't be allot.

 
Upvote 0
Thanks, It seems like that was more pronounced when the reg was dialed down and the FPS were on the low end. I have been pushing that in every time I change a magazine and not after so that would make a lot of sense. I will get some measurements of the bolt through the hole in the load assist. 


Any chance this is related to pellet seating depth somehow? 
 
Upvote 0
I received my SAM valve yesterday. I was looking to use it on a reg'ed gun to get a larger plenum. I measured/calculated out an increase of 7.3 cc's using an aluminum tube standoff.

SAM VALVE

One thing I found out after porting to 0.187", for a 25 cal, is the poppet stem hole is slightly larger than a standard valve. The SAM must be using some of that air leakage to help reset the hammer, along with hammer bounce.




 
Upvote 0
I wonder what that means in terms of overall efficiency? Funny I just picked up the valve and noticed it is possible to move the stem a little with my thumb for the first time. I though it was going to be air forcing the valve stem back into the hammer to assist bounce to get it latched but a little direct air pressure might help too. I wonder if that means I could use a heavier valve spring without problems? The limitation still seems like the bolt/probe set up. Too much pellet weight or air seems to muck up the timing with the magazine spring beyond about 35fpe. so the next test is plenum size. And about that…I received a Lane regulator thinking the install would be very straightforward using the kit components. I opted for the lane instead of a Huma based on the fill speed of the respective systems. The people at both shops were exceptionally responsive and helpful. The Huma used on my last Bulldog project still works great. There are some pics of the Lane package and the measurements to see if I could use the gauge block with a plug to seal the stock regulator vent in the air tube. Unfortunately I needed to learn about 1/8 NPT vs BSP standards the hard way, and stripped the gauge block and the supplied Lane plug. So I am out of commission until a new gauge block comes in. The Lane setup with integrated gauge port will add significant volume to the plenum, so the suggestion was to drop the pressure down to 130 bar. Fortunately removal and adjustment of this regulator will not take complete disassembly. 


A other discovery while I had the thing apart last time, my hammer spring setting of 8 turns out was really 7.5 or so and then just spinning around. 7.5 turns in is all I have on the threads. 

Anyway sorry about the delay. I will post some numbers as soon as I get this sealed up and shooting again. Will probably start with the 130 bar setting and 6.5 turns of Hammer Spring, unless There is a better suggestion. 


Another question for the experts, I found an MRod tube on sale under a pyramid for 50$ So I bought it. Any ideas on how different this is from the SAM? As long as I am experimenting it would be nice to have an air reserve gauge on the side of the rifle or maybe both gauges on the side if I need to start drilling one of these, although the original intent was to not drill the air tube and not try to overpower the magazine and bolt timing. Let me know please? 










95115521-E961-4D58-A62E-BCD441CB1F70.1642393093.jpeg
D5279CC4-BAA5-4CEF-8C3D-0B77F8F4EE1E.1642393095.jpeg
74F6C6D1-16D0-4192-BF32-42FC9CCAD53A.1642393096.jpeg



 
Upvote 0
Yep, the threading is close, but no cigar. You need a BSPP plug for the gauge block, correct?

The SAM valve spring is very stiff and goes into coil bind before the poppet stem reaches the back of the valve. Any heavier spring will require making a slightly deeper pocket in spring guide. Not much, if any to gain to be had there.

The standard Mrod tube is a couple inches shorter, and gauge is in a different location, which means different stocks. The SAM air tube is very close the F&T (oem reg'ed) Mrod, but my understanding is that it is different. According to the older HAM articles, the slots changed. I haven't verified, but highly suspect that the sear slot is shorter and doesn't extend down to the back of the valve, like the "standard" Mrod does. It would be a big air leak for pushing the hammer back.






 
Upvote 0
Sounds like I bought the “bargain” spare air tube a bit too early. And yes you are correct, I needed a BSP thread plug for the SAM gauge block. And a gauge block now that I stripped the stock one learning that thread lesson… the little gauge adapter is NPT for the gauge and BSP at the block. Maybe I can just use low melting temperature aluminum welding rod to fill in the thoroughly stripped threads on the the gauge block to finish the spacer. 

I sold my F&T marauder on eBay and it arrived to the buyer with the stock snapped in half at the grip. When that all worked out I ended up making my son do a little woodwork with me and that is the stock in use on the SAM now. I saw another MRod stock at pyramid for under 100$ and was tempted to grab it, and maybe I should. If it is possible to make a Frankenstein SAM with the stock marauder tube. At least we would know what the differences are between models. 


For now I just want to seal the stock reg bleed hole and then can do a little testing with lower pressure, less hammer spring, and bigger plenum and see if that helps get above 35 fpe but I am kind of guessing the bolt magazine combo timing is going to limit me pretty close to where we are now. 
 
Upvote 0
8F108D7D-D83D-4C8A-AAE3-FE6DB27869E5.1642653900.jpeg
325D200C-EB14-41B9-A3CF-B5B4D46BD3CC.1642653907.jpeg
285EBF23-8057-4FC1-A4AC-4BFD588140C1.1642653909.jpeg
2A32731C-C726-41D6-891E-5C5DC7BCBC74.1642653911.jpeg
Well a little update. I spent some time baffled about why I kept turning the reg pressure up, seeing it on the gauge, and the fps just kept running at the same place. Or even lower than previously. Then I noticed a little grease coming from between the pressure tube and the breech (I smeared a ring around the TP on assembly to see if it was leaking). Then I found one of the gaskets that seal the TP on the floor next to where I was shooting… so I have a lot of shots that don’t mean very much but I am way less confused. And if that gasket is removed it looks like the rifle runs at about 820 fps with 14.3 gr pellets… 



The cause of the problem, opening the TP further to 0.170 or so was enough that one of the small tips that fits inside the sealing gaskets top and bottom fell off. So this is not really a surprise. Im going to try replace the stock aluminum TP something plastic tubing. Most of the path is encased in aluminum in the breech but the risk of popping a gasket out still exists. Seems like this is the new bottleneck. 


I have a spare stock TP so it is easy to drill this again. Maybe in from each side and a little smaller to keep the rim intact. But so far opening the TP pathway was the most impactful so maybe a good area to explore and see if the thing cycles at stock pressures. I’ll post what happens…

Some other thoughts so far from the early testing before the gasket popped out. Cranking the HS up to the max seemed to fix the misfire problem. Need to repeat this with the TP sealed to be sure though. 

The Lane moderator fills fast. I can’t out shoot it. 

It is easy to adjust compared to stock. This only takes removing the filling assembly to pull the regulator. 

The gauge and regulator markings appear spot on making adjustments. 

Is it possible to replace the Hammer Spring with something stronger? 









 
Upvote 0
Found some aluminum spacers. Will try to drill one out to 0.175 (or about the same diameter as the hole in the gaskets) and cut to a little longer than the stock TP and give that a shot instead of messing with plastic. The stock ID is 0.165 and the stock OD is 0.255, just a bit smaller than the stock TP OD of 0.262. So, I’ll try this and skip the plastic thing mentioned above… 



3C334251-CD94-47B4-AD8D-D7307E830F63.1642659089.jpeg

 
Upvote 0
You will need to turn the ends down and use the rubber gaskets to seal. Basically same constraints as oem. It will leak like a sieve if you try to just butt seal aluminum to valve and barrel.

Above 0.160" I use poly icemaker tubing with 0.187" ID. It takes patience though. The ends have to be perfectly square and length has to be just a slight bit of compression to seal, but not too much to start it to collapse. many time, you will have to make a new one, when you take it back apart.

I thought the probe inside diameter was the bottle neck? What did you get for a measurement?



The hammer spring is 1" shorter than standard Mrod, but I don't remember the wire size. I also don't know the cocking distance, to determine if a spring will go into coil bind and not even cock. Otherwise, Mcmaster-Carr has some 0.48" OD X 1.5" Length springs to look at: MC SPRINGS

As I said earlier, I think something else is causing this. Were you able to determine if bolt position was different from manual cycling vs gun action cycling? Are all the shots high if you do only manual cycling?

One area I thought to look at, was the hammer and bolt cocking pins. They are suppose to clear each other. Next time you have the breech off, see if there are any contact marks.



Bigger plenum at the same reg setting should have produced more power with the same porting as you had (0.160") If not, something we need to understand is going on. Does the bolt need more back pressure?
 
Upvote 0
@acmillerus You should be able to make a shim for the hammer spring to give it a bit of tension to experiment with for some additional power. You should be able get a quality spring from Century Spring right to the new specified size you need if you can't find it at McMaster Carr or the like.

It looks like you are drilling the ports right out to that 80% value of transfer port to barrel inside diameter. Those numbers should be good. I can't wait to see them.

One thing I did with my internal moving parts was polish them to a mirror finish where there was any evidence of dragging/friction on another part. Also, I have noticed that the gun doesn't seat a new magazine's first pellet the same unless (when I cycle in a new magazine) I pull the loader all the way back and let it slam it's full weight into place as it would under the shot cycle. It may be that the barrel's rifling lead may need machined to a sharper ramping angle to facilitate easier loading.
 
Upvote 0
Got the TP situation fixed. It is smaller than previous but didn’t want to drill off the ends again and end up stuck back there shooting orings. Now the the TP seems fixed and stable, cycling is a problem. Starting at about 2050 PSI the rifle will not cycle. It is not destroying magazines, it is now munching pellets. It seems to double load and jam every shot. Tried adjusting the hammer spring downward and quickly reached the place where the hammer would not catch. The bolt would cycle there, seemingly normally, without making the farting sound and double loading. It seems like more valve spring might help, but this is also past the point where it is possible to balance increased power and cycling. The shots that leave the barrel are flying 860-880 fps. 


Robert at Lane recommended 130 Bar or about 1850 psi to start, but if 2050 psi is running in the 880 ballpark and not cycling I’m not sure there is any reason to try lower pressure as that would just mean lower power, so not the goal. 


it seems the Crosman engineers developed the small plenum to keep the bolt/magazine and hammer cycling all coordinated. The Lane regulator is really nice but the increased plenum volume seems to create additional problems. There is an extra valve here to experiment with, but given the functionality of the higher PSI lower plenum volume with larger TP pathway it seems like going back to that might be the best bet. 


John if you have any ideas they would be very much appreciated as always. You already managed to get me pretty far down this path without anything going really off the rails so thank you again for that and thanks again to the OP for opening the topic and providing great feedback. 


If shimming the valve spring or the hammer spring might help let me know? It looks like everything else internally is working correctly. 


I’ll get 10 single shots as a string to get a better average and see what that looks like…
 
Upvote 0
The small plenum was due to constraints of using existing parts from the F&T. John did his best to enlarge the plenum by making the valve and gauge block smaller.

I wouldn't jump to the conclusion yet, that the latest problems are plenum related. I know of a GTA member that fixed a leaky TP gasket, and started having cycling problems. This was an otherwise stock gun, and he was going to return to crosman for repairs.

Did the sequence go like this?:

- Installed Lane reg at the recommended 1850psi setting, and power was the same? I assume the hammer and bolt were cycling fine at this point?

- Raised the reg pressure to 2K psi and power was still the same? Hammer and bolt cycling fine?

- Opened TP to 0.170" and power was still the same? Hammer and bolt cycling fine? Then found broken TP part.

- Replaced the TP with Crosman or homemade TP? Opened to what ID?

- Now the cycling and hammer not cocking started? Does the 1st shot shoot fine, then misfires from then on?



If so, then I suspect something else is amiss.

Did you get a chance to look at the bolt and hammer lugs to see if there was any indication of them hitting each other. If either has started to back out, that would happen.

How does the barrel O-ring look? Probably worth replacing. -009, any pieces of pellets blocking the top of the TP? A piece of the broken TP or O-ring?

How does the probe tip look? No rough edges from hitting something?

I'd also re-lube the T-handle, and bolt.

What is the new plenum size?

Also, check where the bolt retracts into the breech, for pellets jammed in there, or pieces of. Probably best with a small mirror. That happened on my first SAM.








 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu