Has any SAM owner's here done transfer port work or anything else to their gun to get more power out of it to shoot heavier pellets? I'm maxed out at 835-840 fps with Hades 15.89 grain pellets, but I would like to be able to run it faster to have a range of power to tune with and use heavier pellets or slugs.
Marauder Semi-auto power tune mods
- Thread starter Airgun-hobbyist
- Start date
Ask the resident Crosman "Representative" AGN member to inquire if it's gonna affect semi auto function reliability b4 doing anything the alter the factory engineering.
I'm assuming you still want it to function as a semi auto?
I'm assuming you still want it to function as a semi auto?
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Even without considering the SA action, the F&T Mrod, which it is based on, is not an easy power mod gun. The primary reason is the small plenum. The reg is between the valve and the gauge. The SAM TP is 0.140" ID and that is normal Mrod valve exhaust. So it would need barrel, TP and valve exhaust to be opened. My experience, based on the similar designed Fortitude, only minimum gains will be made, even if you up the reg pressure slightly. It needs more plenum space.
As Odoyle mentioned, the bigger issue is going to be the SA action. The power mods are going to play into how it works. Changing the plenum pressure will effect how the hammer cocks. So far, that seems robust, and haven't had one occurrence of not latching. It works on hammer bounce, so changes to hammer or valve spring, along with hammer weight, might be needed. The bolt cycles just from the power of the shot and the bolt spring. A higher power tune, probably needs a heavier spring or more pre-load. Current SAM production uses a blind pin for the bolt. You would have to drill a hole in the top of the breech to drive it out. Crosman says that hole will be forthcoming in new production.
Now all that being said, I do plan to mod mine at some point to get a 30fpe gun. That will not happen until the schematic is released, and I can buy the unique SAM parts. I learned my lesson on the Fortitude. It will be an overall balancing act, and do not expect to be able to tune it back to oem specs.
As Odoyle mentioned, the bigger issue is going to be the SA action. The power mods are going to play into how it works. Changing the plenum pressure will effect how the hammer cocks. So far, that seems robust, and haven't had one occurrence of not latching. It works on hammer bounce, so changes to hammer or valve spring, along with hammer weight, might be needed. The bolt cycles just from the power of the shot and the bolt spring. A higher power tune, probably needs a heavier spring or more pre-load. Current SAM production uses a blind pin for the bolt. You would have to drill a hole in the top of the breech to drive it out. Crosman says that hole will be forthcoming in new production.
Now all that being said, I do plan to mod mine at some point to get a 30fpe gun. That will not happen until the schematic is released, and I can buy the unique SAM parts. I learned my lesson on the Fortitude. It will be an overall balancing act, and do not expect to be able to tune it back to oem specs.
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@Odoyle Yes, I still want it to function properly, but with 100 more fps from it's current ability. I will see if the designers will give me those answers They have been forthcoming with answers on this gun thus far.
@FuzzyGrub Thanks for the insights. Based on what I have read of the design, it did seem that everything in the system might need to be adjusted with different spring pressures and tuning but only if it is reworked a great deal. I am hoping for just a slight port job just to make it more efficient in airflow to gain the additional adjustment range.
@FuzzyGrub Thanks for the insights. Based on what I have read of the design, it did seem that everything in the system might need to be adjusted with different spring pressures and tuning but only if it is reworked a great deal. I am hoping for just a slight port job just to make it more efficient in airflow to gain the additional adjustment range.
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IMO, you will not get 100fps by opening the ports. It is probably low risk, taking the barrel, TP, and valve exhaust to 0.160", though. The valve is unique to SAM, so be careful. The TP is the same as the 25 cal, so can order more of those. Also, be careful with barrel, it's not the exact same as Mrod 22 barrel.
I will tell you, that some saw fps decrease or stay same after same mods to Fortitude. I'll be interested in your results, and would also like to see some pictures of the valve.
I will tell you, that some saw fps decrease or stay same after same mods to Fortitude. I'll be interested in your results, and would also like to see some pictures of the valve.
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@FuzzyGrub I'll get you pictures of the valve and other components when I tear into it. I still need to figure out if it de-gasses the same as the standard Marauders and make or buy that tool.
As far as opening up the ports and smoothing flow around corners there, in theory, the system shouldn't lose power but it may not cycle the same. The way I understand it the action was designed to utilize the wasted hammer bounce rather than air reserves. But having less restriction on air flow may change that effect, so we'll see. The videos of the standard Marauders show that adjustment to flow can start with opening the brass port through the side adjuster screw, and that is as good a place to start as any.
As far as opening up the ports and smoothing flow around corners there, in theory, the system shouldn't lose power but it may not cycle the same. The way I understand it the action was designed to utilize the wasted hammer bounce rather than air reserves. But having less restriction on air flow may change that effect, so we'll see. The videos of the standard Marauders show that adjustment to flow can start with opening the brass port through the side adjuster screw, and that is as good a place to start as any.
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Airgun-hobbyist,
I have found the fastest way to degas the SAM is to just dry fire until empty. Once it gets low on air it will do a full auto like air dump. Unscrew the gauge to release the last 50 to 100 psi. Also, there is no VMS adjustment on the SAM. Hammer bounce to cock hammer and flow through TP and pellet back pressure cycle the spring loaded bolt probe.
I have found the fastest way to degas the SAM is to just dry fire until empty. Once it gets low on air it will do a full auto like air dump. Unscrew the gauge to release the last 50 to 100 psi. Also, there is no VMS adjustment on the SAM. Hammer bounce to cock hammer and flow through TP and pellet back pressure cycle the spring loaded bolt probe.
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@vdwb I had to look up what a "VMS adjustment" was. You are correct. That hole in the air cylinder showing off the brass underneath on the SAM doesn't have any adjusters in it like the tuning videos of the standard Marauder show. This is my first Marauder (SAM) so I am learning by researching the Marauder videos and threads, and should have looked more closely at my SAM before posting (right after watching videos).
So, it looks like I am back to simply messaging the ports to make what airflow we do have be more efficient in going around corners and increasing the volume a little. Would you think that the SAM would benefit from a stronger preload on the adjuster? It is not maxed out, but gains are minimal now with the tension on it. I have not had any bad cycling or the like, so everything is good there.
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I look at hammer preload on a reg'ed gun as to a way to tune to the particular plenum/reg setting, vs a "power adjuster".
FWIW: The current spring is 0.48" OD X 1.5" L w/0.055" wire. I haven't measured the hammer throw, but it is less than the standard Mrod of about 0.9".
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Here's a picture to check out of the SAM air tube internals... Complete with de-pinging rubber bushing, regulator, plenum spacer and valve assembly. 
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I did this and it did the auto air dump, but it left some pressure on the plenum side of the regulator. When releasing the valve assembly it pushed it out and locked up as I removed the last holding screw. Some heavy down pressure with a rod while releasing the screw worked to free it up. I made a de-gassing tool today to push on the hammer weight and dump through the barrel.
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Taking the valve and transfer port from .140" to .156" and having radiused the corners on the pellet probe and barrel ports netted a 30 fps gain. With this mod it's pushing 15.89 grain Hades at 870 fps. Shot count remained the same and cycled without missing a beat.
Adding a 90° ccw turn to the regulator killed my high shot count, but I was not looking for that type of efficiency. The added regulator pressure netted an additional 30 fps. Now it is pushing the Hades at 900 fps. It still cycled consistently, oiled well, including the magazine.
All testing was done with full hammer spring tension setting.
Adding a 90° ccw turn to the regulator killed my high shot count, but I was not looking for that type of efficiency. The added regulator pressure netted an additional 30 fps. Now it is pushing the Hades at 900 fps. It still cycled consistently, oiled well, including the magazine.
All testing was done with full hammer spring tension setting.
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You can forget my post in the other thread. 
Thanks for posting this info.
On the regulator, the hole on top, furthest to the left, is that a set-screw hole to lock-down the reg setting?
Any pictures or details of the valve disassembled? C clip style? etc
A full string with 18g JSBs to see if preload is too much/little/just right, with an indication of reg off point.
It does look like with the shorter valve that I would need to cut a plenum spacer for using a Huma reg w/gauge port, in a "standard" Mrod air tube.
Or, like what I've done in the Fortitude, create a bridge to get past the vent hole. The standard gauge block w/plug, and plenum spacer, and Huma should work.
Bothe would give a larger plenum and be able to drop reg point some.
Thanks for posting this info.On the regulator, the hole on top, furthest to the left, is that a set-screw hole to lock-down the reg setting?
Any pictures or details of the valve disassembled? C clip style? etc
A full string with 18g JSBs to see if preload is too much/little/just right, with an indication of reg off point.
It does look like with the shorter valve that I would need to cut a plenum spacer for using a Huma reg w/gauge port, in a "standard" Mrod air tube.
Or, like what I've done in the Fortitude, create a bridge to get past the vent hole. The standard gauge block w/plug, and plenum spacer, and Huma should work.
Bothe would give a larger plenum and be able to drop reg point some.
You can forget my post in the other thread.
On the regulator, the hole on top, furthest to the left, is that a set-screw hole to lock-down the reg setting?
Any pictures or details of the valve disassembled? C clip style? etc
A full string with 18g JSBs to see if preload is too much/little/just right, with an indication of reg off point.
It does look like with the shorter valve that I would need to cut a plenum spacer for using a Huma reg w/gauge port, in a "standard" Mrod air tube.
Or, like what I've done in the Fortitude, create a bridge to get past the vent hole. The standard gauge block w/plug, and plenum spacer, and Huma should work.
Bothe would give a larger plenum and be able to drop reg point some.
Per your inquiry in the other thread, yes, the regulator appears to be set and fall off at about 2250. But it still does not fall right off. It is a slow decline.
On the valve body... It is a C-clip that holds the cap in place. Inside is a spring and poppet valve only. The two holes furthest left are threaded holes where the action/receiver block screws come down into the valve. The hole low and right, 1 of 3 around the body, lock the valve body in place within the tube.
To make more plenum space with stock components you would have to strategically machine metal off of the valve body and regulator, as well as cross-drill holes in the plenum spacer. But even then, because of how everything is located in there, very little room is left for gaining the extra space. If you can get more space with using the Huma regulator please let us know how you go about it.
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You wouldn't have to use a Huma, but using the OEM reg would require drilling a new vent hole. You would use the oem gauge block and the oem reg would be upstream of it.
I don't seem to have a Mrod Huma reg with gauge port hole not installed in a gun. If I had one out, I'd post for better clarity.
It would go: VALVE => SPACER => GAUGE BLOCK BRIDGE => HUMA
Note1: Spacer cut to length that would allow Huma gauge to align with air tube gauge hole.
Note2: Gauge block bridge would be a modified for plenum volume, oem gauge block or Hill with a BSPP plug that is "below deck".
If you happen to go back in, for some reason, I'd like to see some length measurements and would be able calculate plenum volumes.
I don't seem to have a Mrod Huma reg with gauge port hole not installed in a gun. If I had one out, I'd post for better clarity.
It would go: VALVE => SPACER => GAUGE BLOCK BRIDGE => HUMA
Note1: Spacer cut to length that would allow Huma gauge to align with air tube gauge hole.
Note2: Gauge block bridge would be a modified for plenum volume, oem gauge block or Hill with a BSPP plug that is "below deck".
If you happen to go back in, for some reason, I'd like to see some length measurements and would be able calculate plenum volumes.
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FuzzyGrub,
I do like your solution. Bridge the old reg vent hole, use the gauge block air tube hole to vent the reg, and pitch the gauge for now anyway.
Very interesting thread!
Nugria
I do like your solution. Bridge the old reg vent hole, use the gauge block air tube hole to vent the reg, and pitch the gauge for now anyway.
Very interesting thread!
Nugria
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I measure 1.75" increase in the tube length in the SAM over standard Mrod. I calculate that would work out to 10cc more than a Huma regulated standard Mrod.
A standard mrod with Huma looks like it would have a larger plenum than what the SAM has, but can't tell by how much. So it should supply more than enough plenum to support 30fpe. Now, I wouldn't want to drop the plenum pressure to below 1600-1700psi, or will be too close to the point where it goes full auto.
It will still be a balancing act.
A standard mrod with Huma looks like it would have a larger plenum than what the SAM has, but can't tell by how much. So it should supply more than enough plenum to support 30fpe. Now, I wouldn't want to drop the plenum pressure to below 1600-1700psi, or will be too close to the point where it goes full auto.
It will still be a balancing act.
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Howdy! Extremely helpful thread. Fuzzygrub your input is exceptionally on point. Changing the tune of the marauder SAM will be a balancing act. And it is hard for me to guess the relative importance of the variables. It looks like the easy things to change are:
The only way I can see to adjust the power easily is is adjusting the hammer spring setting. Not ideal from a tuning perspective but maybe better than nothing.
A few questions for the experts here. Fuzzygrub can you weigh in on this please?
The regulator (as stated above in this thread) has an adjustable nylon plug. I cant see how screwing this in or out would adjust spring tension inside the regulator. Unfortunately I did not clock a shot string over the stock setting to see where it drops off now, but 1900-2250 psi seems pretty consistent with my experience with the rifle. Degassing by dry firing did not get “full auto” until well under 1500 psi (meaning that is where the pressure was too low to fully cycle the bolt and or the hammer, as they operate independently in this set up.) Under gassing this system seems like it could cause a number of problems during use so I am not going to run this under about 2000. I hope. This regulator is the same part number as the marauder field and target model I think if that helps.
So, best guess, is the nylon screw going to do anything or do I need to pull the regulator apart to see if shimming is required?
Is there any harm in drilling the valve outlet, transfer port, and breach inlet to about to 5/32”? The existing size of the inlet hole in the bolt probe is exactly 5/32, or .155” and the other ports are slightly smaller.
Will using higher Regulator pressure (maybe 2500, but no real idea about reg adjustment and output) require a a stiffer bolt return spring? I tried some heavier pellets and the FPS dropped pretty dramatically making me wonder if the bolt was opening too soon releasing pressure before the heavier 25.5 gr pellet was up to speed. Low pressure and the tiny plenum probably don’t help either.
Based on this gas powered semi automatic action, it seems like a stronger bolt spring might help a lot as there is a balance of pressure to drive the pellet out the barrel and the same pressure cycling the bolt. Too much spring pressure would cause cycling failure also, pretty easily from the looks of things.
Any thoughts on doing several of these at the same time? I realize that would not be as valuable to the community as having each individual change documented to answer the relative priority question. Although drilling is easy it also can be undone so I will probably skip that. Using a spacer to get a larger plenum by relocating the reg upstream of the Gauge Block seems easy if I can make the spacer.
Happy to post pics and measurements if that helps anyone. Thanks for any feedback in advance
- Hammer Spring Adjustment
- Regulator Pressure
- Plenum Size (regulator location)
- Transfer port size
- Bolt Return Spring type
The only way I can see to adjust the power easily is is adjusting the hammer spring setting. Not ideal from a tuning perspective but maybe better than nothing.
A few questions for the experts here. Fuzzygrub can you weigh in on this please?
The regulator (as stated above in this thread) has an adjustable nylon plug. I cant see how screwing this in or out would adjust spring tension inside the regulator. Unfortunately I did not clock a shot string over the stock setting to see where it drops off now, but 1900-2250 psi seems pretty consistent with my experience with the rifle. Degassing by dry firing did not get “full auto” until well under 1500 psi (meaning that is where the pressure was too low to fully cycle the bolt and or the hammer, as they operate independently in this set up.) Under gassing this system seems like it could cause a number of problems during use so I am not going to run this under about 2000. I hope. This regulator is the same part number as the marauder field and target model I think if that helps.
So, best guess, is the nylon screw going to do anything or do I need to pull the regulator apart to see if shimming is required?
Is there any harm in drilling the valve outlet, transfer port, and breach inlet to about to 5/32”? The existing size of the inlet hole in the bolt probe is exactly 5/32, or .155” and the other ports are slightly smaller.
Will using higher Regulator pressure (maybe 2500, but no real idea about reg adjustment and output) require a a stiffer bolt return spring? I tried some heavier pellets and the FPS dropped pretty dramatically making me wonder if the bolt was opening too soon releasing pressure before the heavier 25.5 gr pellet was up to speed. Low pressure and the tiny plenum probably don’t help either.
Based on this gas powered semi automatic action, it seems like a stronger bolt spring might help a lot as there is a balance of pressure to drive the pellet out the barrel and the same pressure cycling the bolt. Too much spring pressure would cause cycling failure also, pretty easily from the looks of things.
Any thoughts on doing several of these at the same time? I realize that would not be as valuable to the community as having each individual change documented to answer the relative priority question. Although drilling is easy it also can be undone so I will probably skip that. Using a spacer to get a larger plenum by relocating the reg upstream of the Gauge Block seems easy if I can make the spacer.
Happy to post pics and measurements if that helps anyone. Thanks for any feedback in advance
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FWIW: I still haven't tried to modify mine, so my comments are only that.
To me, the key issue will be the bolt cycling. If you go up on pressure/flow, it will need more spring. At what point are you out of that operating window? I don't know yet. I do know that stock guns have cycling issues and that the "window" is probably small. The problem is compounded by the fact the bolt and spring can not be removed from the breech without drilling a hole and punching out a blind pin.
Without doing so, don't know how much work there might be to go with a heavier spring. Is there room? Unlikely. Something will most likely to need machining. The only option i have thought of, without going "all in", was trying to use the load assist spring tension. That push button only puts added preload on the spring. You can push it in "too" far and the end of the button will catch and stay. yes, you can pop it back out.
Until a pioneer blazes this trail, and documents it, I highly recommend only changing one thing at a time. If you want to be that pioneer, I'll try to guide you through the mountain pass, from a safe distance.
1. Stock Gun - Complete Baseline String Use Crosman domes
2. Test Load Assist button string, did it cycle fine?, did fps go up?
3. Change TP to 0.160" - what power gain and test cycling, test without and with load assist pushed in.
4. Raise regulator pressure 200psi, test again - some complication with this reg and set-up. Not as easy as it should be.
5. If no issues, raise reg another 200psi, and repeat
6. If no issues, raise reg another 200psi, and repeat. Don't bother going higher than this.
Goal is to see what power changes do to cycling and do it in a way that is easily reversable.
Note: When you start having cycling problems, It will quickly damage the mag. Be prepared and have a number of mags on hand.
Note2: Every time you adjust the reg higher, the hammer spring preload, needs to be raised.
To me, the key issue will be the bolt cycling. If you go up on pressure/flow, it will need more spring. At what point are you out of that operating window? I don't know yet. I do know that stock guns have cycling issues and that the "window" is probably small. The problem is compounded by the fact the bolt and spring can not be removed from the breech without drilling a hole and punching out a blind pin.
Without doing so, don't know how much work there might be to go with a heavier spring. Is there room? Unlikely. Something will most likely to need machining. The only option i have thought of, without going "all in", was trying to use the load assist spring tension. That push button only puts added preload on the spring. You can push it in "too" far and the end of the button will catch and stay. yes, you can pop it back out.
Until a pioneer blazes this trail, and documents it, I highly recommend only changing one thing at a time. If you want to be that pioneer, I'll try to guide you through the mountain pass, from a safe distance.
1. Stock Gun - Complete Baseline String Use Crosman domes
2. Test Load Assist button string, did it cycle fine?, did fps go up?
3. Change TP to 0.160" - what power gain and test cycling, test without and with load assist pushed in.
4. Raise regulator pressure 200psi, test again - some complication with this reg and set-up. Not as easy as it should be.
5. If no issues, raise reg another 200psi, and repeat
6. If no issues, raise reg another 200psi, and repeat. Don't bother going higher than this.
Goal is to see what power changes do to cycling and do it in a way that is easily reversable.
Note: When you start having cycling problems, It will quickly damage the mag. Be prepared and have a number of mags on hand.
Note2: Every time you adjust the reg higher, the hammer spring preload, needs to be raised.
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