Benjamin Marauder .25 ports drilling size

I agree with Scott's comment. He has a ton more experience than I do but his comment is consistent with my experience. Our guns are a system of parts and modifying a few of the parts will do a lot less than modifying the entire system.

My Prod shoots at about 18 fpe now instead of the stock 12-13 fpe. To get there I changed the size of the transfer port, the hammer spring tension and the fill pressure (I just went to 3000). I can make 20 fpe but only got one magazine out of that tune. The transfer port was the big limitation to airflow in my opinion at about .080. I think the largest I used was .120. I think it has a .111 in it right now. Could it make more than 20 fpe, I am sure it can. But the reason I only get 1 magazine out of my 20 fpe tune is it doesn't store much air. If you went to 25 or maybe even 30 fpe, would you only get one or two shots? Seems likely. I get about 3 magazines at 18 fpe and I am good with that. The velocity falls a little quicker on the last half of the last magazine but if I need the shots they are available. They are just going to hit a little lower.

I tried to take my P35-25 to 50 fpe. It likes JSB 33.95 grain MKII pellets and I wanted to get them over 800 fps. I got there but it is currently detuned to about 760 fps. I drilled out the barrel port and the passage from the valve to the barrel port from about 75% of the bore size to 85%. That got me about 15 fps. Probably was not worth doing. I may try reducing the size of the valve a very small amount, my guess is that will do more but I think I will also need to reduce the length. What I did that was worthwhile is put on a larger plenum. That got me about 60 fps to about 775 fps. I then fiddled with the reg pressure and managed to get to 800 fps or a little more but when the weather changed the hammer spring was no longer strong enough to open the valve. Velocity fell to about 550 fps. So I've detuned it slightly back to about 760 fps. I would like to try a pin probe on it but changing that is not easy on a P35. So my most likely next step if there is one is to decrease the valve head size by about 1/32 of an inch adjusting the length as necessary to have the pin protrude the same. I will need to have a spare valve on hand before I would feel OK doing this. Reducing the valve head size will both flow more air and also make it easier for the hammer to open the valve (the air pressure on the valve head is more of the resistance for the hammer than is the valve spring).

I think it is fine to mess around with our guns this way as long as we consistently degass before opening up the air storage area but we need to have realistic expectations of what to expect. Most of us would probably be money and certainly time ahead to just buy a different gun. But when I am in the right mood messing around with one of my guns is fun too.

anonymous_.457 said:

Not really. Go watch airgun lab marauder air tube 10,000 psi test.

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That was on the custom Prod tubes he made for the doubt tube. I doubt the stock rifle tubes will handle that much nor should they ever see that high.

I wouldn't want to go over 3500 without knowing that'll happen on the steel tube. It's not super thin, but still.

Stubbers said:

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Is that a broken record?

anonymous_.457 said:

Not really. Go watch airgun lab marauder air tube 10,000 psi test.

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I know the alloy tubes were tested to 10,000 psi or close and failure occurred by the tube ripping/shearing, the valve moved back and the pressure relieved. They were using oil, not air for the hydro test. Working pressure for my Marauder rifles is 3,000 psi and not a bit more, be they steel or aluminum or hybrid. Aluminum does have a cyclic life, steel does not generally unless taken beyond yield. I would say that 3,800 psi on the M-Rod is asking for trouble. If that valve were to blow out of that air tube you would get hit potentially by a 1.00 inch caliber slug. There was a video floating around where a valve did go through some fellers leg and it was ugly. It was not a Marauder but the point is that those three screws into the valve are all that seperates you from a donut size hole in your face!

I like the Tim Hill items. I have one of his valves and I like it a lot and the gauge block and a few other things. I do not like his hammer. Being lighter it either requires mods to the valve or a heavier spring and more preload on the poppet to make any power. It may bounce less but it still bounces. Installing the Tim Hill kit is not going to get 100 fpe.

The stock Marauder can handle 3850 fill pressure for many lifetimes without any deformation on the tubes/valve screws ect provided they're all up to oem spec...the issue more so is the oem poppet head material will see a ton more wear and won't last as long, accelerated wear on other o-rings, and potential valve lock.

Frankly that is the least educated approach to take to increase your air rifles power output without extensive knowledge understanding how or why it is safe or not safe..."lets just over fill it"...luckily in OP's case he is still within a reasonable margin for safety...

The interwebs is chock full of information on modifying Marauders. This kid Connor has been around for over a year now, and still lacks basic understanding of how porting works through an airgun's valve...we all learn differently, but I have exhausted my abilities to teach via text, hopefully one day cross sectional / surface area equivalency from valve entry, to valve seat, to pellet base will make sense to him in terms of valve porting. Heck, that is just the tip of the iceberg when it comes to airgun mods and tuning.

I enjoy helping others but I do not enjoy talking to a brick wall. So anything said here is really for other readers, lol.

-Matt

What I have observed on the valve retaining screws is that they can loosen up from cycling I assume. I started using Vibratite and since then no loose screws. Well, not in my guns, elsewhere perhaps .

Another potential problem as we increase power on the M-Rod is recoil. When I dial up 60 fpe there is noticeable recoil from the .25 and especially with the heavy pellets. The breech is attached with four (or in a Gen 1 three) tiny screws and no recoil block. The 3 or 4 breech screws also resist bolt cocking forces and hold all of the scopes and lights and barrel and all that other stuff to the air tube assembly, they get a good workout . Those screws will loosen up so they get careful installation and Vibratite.

And finally, the breech will begin to flex much beyond 60 fpe. I think that is one of the reasons that JSAR went to a high rise breech for their M-Rod side lever. It is much stiffer than the OE part. Hitting the OE breech with near 4,000 psi I am going to expect some flexing as the breech tries to lift off of the air tube. Those four little screws are holding both shear and tension loads. The valve retaining screws are in shear only.

I fully appreciate that I spent $ getting my rifles up to my requirements and had a lot of fun doing so and I am still learning. Yes, I would love to get the new M4 or that BRK Ghost but I will have to sell some blood or kidney or something to get one. And they are just a starting point for more $$, especially the FX guns I see.

The M-Rod is an excellent platform to learn on and have a useful rifle that can last essentially forever. The reason is that it is all metal, traditional and over built despite some glaring faults that hopefully someday Crosman might address in a Gen 3. Or not. Probably about the time FX learns to build a gun that can hold POI .

Stubbers said:

The interwebs is chock full of information on modifying Marauders. This kid Connor has been around for over a year now, and still lacks basic understanding of how porting works through an airgun's valve...we all learn differently, but I have exhausted my abilities to teach via text, hopefully one day cross sectional / surface area equivalency from valve entry, to valve seat, to pellet base will make sense to him in terms of valve porting. Heck, that is just the tip of the iceberg when it comes to airgun mods and tuning.
-Matt

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That guy Connor has done nothing but work on Mrod platform for a year, and still doesn't get it.

The really bad thing is that there was tons of Mrod platform content on older forums that I wish I would have downloaded and saved,but foolishly thought it would be online forever, so I didn't.

Guys like Connor are trying to do things that have been done 10's of 1K's of time, and acting as if they're first to ever do so, but can't get it right.

What's a transfer port?

anonymous_.457 said:

Is this a joke?lol.

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Yes!

anonymous_.457 said:

Ok good.lol

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Is it like a point of entry? Like where frieght goes thru? Lol