EDIT: .357 Pellet Slinger

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    Well, I’ve started gathering parts for a 6mm (or .243) Marauder build. I’ll post picks when I find a replacement for “Photo-I like fucking people-bucket”, so apologies for that. Why am I doing a 6mm? Well, I’ll have a .257, and I didn’t want to build another. I just wanted to build something different. Anyhoo, here’s a rundown:

    -28″ OAL TJ 6mm barrel, 0.237″ lands and 0.243″ grooves, with a 10″ twist. OD is custom ground to a hair under 14mm so that I can sleeve the barrel with a 18mm OD x 14mm ID carbon fiber tube. I’ll have the end threaded 1/2″x20 for an LDC.

    Armada breech. This will be modified so that the 18mm barrel sleeve will fit snug. The shroud will be recessed into the breech by 1.25″, which is as deep as I care to go, because of the breech screws.

    Bottle conversion block from Oldpro. I’ll be shortening the Mrod’s main tube to 11.75″ for the bottle conversion.

    Ninja 4500 psi input, 3k psi output reg. I’ll be using an aluminum 450cc tank I found on Aliexpress. It’s the only tank I can use with the reg’s threads.

    Cothran powerhouse valve

    TSS and MDS spring/hammer from Oldpro. Ease of tuning and easy cocking effort in combination with the Cothran valve.

    This thing is for both long range target shooting and general varmint shooting. I’m having someone design a very light weight stock that uses an Evanix Sniper’s stock, can use AR15 grips, and incorporates a trigger guard. This should be a relatively lightweight rifle. Bipod will mount to the bottle via an adapter I can get from Dr. Bob in the UK.

    For ammunition, I’ll be casting my own, using a 4-cavity Arsenal mold that Jack Bowman designed. It’s a scaled down Lyman 257420. Mold should drop cast boolits at 60 grains. I’ll be sending it off to Eric at Hollowpoint molds so I can have two cavities modified to HP. Should be nice and devastating on prairie dogs and woodchucks :8:

    Well, that’s the basic rundown of the build… I’ll post pictures as I progress through the project.


    Not too much of an update, because other than ordering parts, nothing has really been done yet. Other than research of course. But:

    I have my barrel and CF sleeve in hand. Barrel from TJ looks great as always. The CF sleeve fits beautifully!! I think I should be able to get away with using a “thimble” for the chamber area, as the Armada breech will be getting modified to fit the CF sleeved TJ barrel. I can only recess the barrel so far without running into the front breech screws. Having a thimble will make machining the barrel so much easier. We’ll see what’s up with it. 6mm is only .243 so I shouldn’t have a problem since the breech is made for a .50″ O.D. barrel in .25. I should have more than enough material for the bolt o-ring groove.

    A little note about the Armada breech- I’m going to see if I can somehow machine in a “J-slot” so that the probe can push the boolit far enough into the thimble/barrel to clear the transfer port, but retract back for increased flow. I’m gonna cross my fingers.

    I have a Ninja 4.5k psi input/3k psi output tank valve, with a 4.5k psi aluminum 480cc tank that I was going to use. But the set up would be front heavy. I really wanted to use a CF tank from Tony at TT, but there were no valves that I wholly trusted that fit the CF tank (I know about JDS Airman…). So I was content with this set up because I had to be. Months go by and Oldpro has designed a 4.5k psi intake tank reg that is both externally adjustable and it has the correct threads for the CF tank!!! Needless to say, I’ll be getting one for this build. I have a left over CF tank from a .30 Condor build I’ll be using with the new tank reg. I’ll probably use the current valve I have as a tethering valve, once I find a large enough tank. Probably one of those 90+ cu in tanks. I want to be able to have more available shots w/o having to lug the HUGE 97 cu ft tank with me in the field.

    A member from another airgun forum is designing an Aluminium main tube for the Marauders, which would drop over a pound of weight over a factory tube. I’m debating on whether or not I want one. I’m pretty sure I’m going to stick to my factory tube, since I already have it…

    I’m now working on my own stock, not having someone else build one for me. Actually, the stock might be able to be used across multiple platforms, depending on the inlet block. If I make it right. Not sure how I’m going to go about this stock build yet. In the end, since I’m using the same overall stock design for multiple projects (McMillan A4), I’ll probably send the patterns off to an airgun stock builder to keep, so others can benefit from my efforts. I shouldn’t run into copyright or patent issues with McMillan because the stocks should be just different enough to be a completely different product.

    I’m still going to be using the Cothran valve that I have. A better version has been made by Oldpro, but I don’t want to waste the money I’ve spent. Also, the gun will be regulated, so that’ll go a long way in making the gun more efficient. The Cothran valve in it’s standard configuration is set up for max power, and has a power curve to match. First shot highest, with a progressively lowering velocity across the powerband. Oldpro’s has a bit better flow, and is more tunable. But, I’ve been wanting a Cothran valve since they first came out, and again- this will be a regulated gun. So I’m not too worried about it. Plus, it gives me an excuse to build another Brod! :rofl:

    Anyhoo, that’s about it. Like I said, not much of an update. I guess this post will be more like a journal, cataloging the 6mm build. As always, I’ll keep whoever’s interested enough in reading this updated, as I make progress.


    No pictures or real update- I did make a slight change though… I’m going to get a Wicked Air Rifles Cobra tank block- it’s both a bottle adapter and a regulator in one piece. It can also use a M18-1.5 threaded tank. It’s even more simple than using that externally adjustable tank reg. Plus, that adjustable tank reg isn’t out yet, and the Cobra block from WAR is currently available. Other than that, I’m still gathering all the small parts needed for the build.


    I’m thinking about going bigger with the tank, I’ve found a source for a 1L (1,000 cc) CF tank. The only problem (other than price) is that the O.D. is 85mm. The standard size CF tank is around 60mm. I’m not sure I’ll have enough room for the larger bottle. I’m asking around though. I’m gonna cross my fingers. 1L of regulated air? You bet I’m going to ask around to see if it’ll work!!


    The 6mm Mrod build turned into a 9mm Mrod build. I’m turning the 6mm build over to Wicked Air Rifles, as their Flex rifle is pretty much what I want, and will be much better than a bottle converted Mrod.

    I’m not wasting the parts I’ve gathered so far though, as I’m going to take the same basic plan, but build a .357 Mrod. One major change is that I’m not going to bottle the Mrod. I am going to use a longer (and lighter) main tube from JSA. The new main tube will be 30″ long, which is the same length as a factory Mrod tube, with a TT extension. No gauge block, which should give a tiny bit more volume… I’m not worried about a gauge anyway… It’s a .357 with a Cothran valve- not a regulated 12 fpe plinker :rofl:

    I’ll keep y’all posted.


    Felt like posting… Here’s a short list of parts and a snippet of the build plan:

    Armada .25 breech– modified to have a 18mm CF barrel shroud recessed 1.25″ into the breech. Breech will also be modified for a larger TP for the .357, and also have a J-slot so that I can retract the probe for firing. It gives full-bore flow without obstruction. I’ll also be upgrading the bolt locking lug to a 10-32 screw. The bolt would also have to have a o-ring on it, because there’s no room in a .5″ O.D. .357 barrel for an o-ring inside the chamber, like the Mrod has.

    28″ OAL .357 barrel from TJ Enterprises– with a 26″ twist and a 14mm O.D. Muzzle threaded to M14x1.5 for an LDC. Will get a CF sleeve w/a 18mm O.D. to stiffen up the thin barrel.

    Jefferson State Air Rifles main tube, 30″ long, no gauge hole– Its the same length as a factory tube w/a 6″ extension, but has a tiny bit more volume due to no extension end cap (where it attaches to the factory tube) and no gauge block. It also saves over a pound of weight.

    Cothran Powerhouse valve

    MDS Hammer from WAR

    TSS Kit from WAR

    Boyd’s Pro Varmint Stock– It’s relatively cheap and it’s a ready-made stock. Plus I can easily add an adjustable comb.

    That’s about it for the major parts. Most everything else will be factory parts to keep the build cheap.

    My goal for this gun is to have the same performance or better, as the Bulldog. I’ll be happy with 200 fpe. If I get more, cool! I’ll only be shooting cast boolits from this build- 136 gr BBT from NOE. I don’t care too much about shot count either, as the Cothran valve doesn’t really allow too much tuning. So maybe 2-3 consistent, full-power shots is fine by me. If I can get more, cool… But that’s not my goal. I just want a powerful .357 slug shooter w/o having to buy another platform. I already have most of these parts “left over” from the 6mm build, so I may as well use them for something cool!! I’m hoping this turns out well!!


    Not much of an update- just some thinking…

    I’ve changed my mind a bit about the build, and this is going to be a bottle gun. Been crunching some numbers with some guys on another forum, and we all came to the conclusion that there’s just not enough air for more than two (with a small ES) or three shots. After some thinking, I just don’t think I’ll be happy with 2-3 shots off tether. This is supposed to be (mostly) a hunting gun… So I’d like more shots than that… Long story short, the WAR Cobra regulator/tank block is back on the menu… I’ll be using a left over TT CF tank as well.

    As far as the JSA custom main tube, I think I’m going to go with an 18.5″ long tube. That length, when combined with the Cobra reg and CF tank; the end of the tank should be 1″ shy of the threaded muzzle, which will allow me to thread on an LDC. The 18.5″ length will also get me the largest possible plenum (around 170 cc). Hopefully I can meet my goal of 200 fpe w/a 136 gr cast boolit. Not sure how many shots I would get, but it would be more than 2-3, that’s for damn sure!

    With all the weight basically in the front now, I’m really considering going a weird direction with the stock… Possibly converting a full metal airsoft EBR. I’d just be using the stock. It may tip the balance of the rifle back to the rear of the gun… I dunno.


    Edit number 5 billion! :biggrinn:

    Okay, After reading some posts from another shooter/tinkerer, I’ve decided to make the .357 Brod a dedicated pellet shooter. 130 fpe is the max energy goal. I just feel like this power level is more appropriate for what I’m trying to do and the base platform I’m using. Also, cost is a factor- this is supposed to be a “spares build”, so I decided to err on the side of cheap and what I have on hand.

    Also, this project gives me something to do while I save up for a Bulldog. Oldpro (alongside others) has designed a high power balanced valve for the Bulldog. Another person has put together a larger reservoir kit for the Bulldog. I will modify a Bulldog into a more powerful, dedicated .357 slug shooter. Can’t waste this .357 AG bullet mold, can I? :rofl:

    Anyhoo, a few changes:

    Gen1 Brod conversion block– not a Cobra Reg. WAY cheaper. Just under $100 vs. $350
    – Going to use my TT CF tank instead of buying a larger one. I already have it, so again, cost was a factor.
    Modified Mrod maintube. Again, it’s cheaper than a new custom tube. $0 vs $150+
    – Modified Armada lower receiver for a stock… maybe unmodified, dunno yet. It’s only $25!! I already have all the other parts from AR builds. This also works with the “spares build” idea…
    – Modified Ninja reg clone. Because it’s cheaper than a Ninja, but more importantly, only a clone reg has threads to fit the M18-1.5 threads of the CF tank.

    I think that’s about it- All the other parts and modifications will remain the same. I’m fixin’ to buy the barrel on monday or tuesday. My reg should be in in a week or so, so I can break that down and make my modifications to it. I’ve also been able to talk to a machinist to make the needed modifications to my breech, bolt and barrel. The project is humming along quite nicely! It’ll be up and shooting before we know it!


    Well, I called TJ last Monday- I won’t be able to order anything until at least July 1st, but I’ll wait until the 9th or 10th. I’m headed out of town. It’s fine- it gives me time to break down the reg and take out the pin valve, and set the pressure where I want it.

    I received my Armada lower receiver and my clone reg. Both seem to be good parts. The Armada stock seems a bit loose around the trigger group. The reg threads into the tank nice, and the reg also threads into the Mrod tank adapter well. Everything fits nice together!

    Still waiting on my shortened tube- not in a rush at all… it’s free after all.

    Now to just gather the AR parts I’m going to use, and basically just twiddle my thumbs until I can get that barrel ordered. Then I can send off the breech, barrel and bolt off to be machined/modified.


    One step closer!

    I received my modified Mrod tube… I was debating between a 12.75″ and an 11.75″ OAL tube… I decided on the 11.75″ OAL tube. I’m glad I did! I feel the 12.75″ would have been too long for the Armada chassis and would have looked kinda goofy… Not that I really care about looks, but still. I test fit everything together, and it all goes together with no problems! I still haven’t cracked open the reg yet, so I’ll have something to work on while waiting for TJ to get back up and running.

    All I have left to do is:

    Order/Machine the barrel
    Modify the breech
    Make/modify a bolt
    Sleeve the barrel

    Then it’s just assembling and tuning it… Oh man, I can’t wait!!


    Nothing really new, I am going to order the barrel come monday though…


    I finally have my barrel on order!! The end is near!


    Since there have been so many changes to this project, I’ll go ahead and narrow down the parts and such in this post…

    Armada .25 breech. Will be modified to fit a 18mm CF barrel shroud. Also, the transfer port will be opened up if needed, so that I have a full .257″ port from the valve to the barrel.
    Armada chassis. Because it’s the cheapest, most modular stock choice. It’s $25 and fits all of my left over AR parts.
    Cothran Powerhouse valve
    Shortened Mrod tube. 11.75″ OAL, no gauge hole.
    Carbon Fiber tube. 18mm OD, 14mm ID. Barrel sleeve.
    W.A.R. TSS. Hammer spring set up- makes for easier tuning.
    W.A.R. MDS Hammer
    R.A.W. trigger blade. Had to drill trigger pin out w/a 1/8″ drill bit to work w/Mrod trigger group.
    Clone Ninja reg. I had to go with a clone reg because Ninja doesn’t make a reg that threads into a M18x1.5 tank. I’m going to re-do the belleville stack so the output is where I want it.
    R.A.I. Bottle conversion block
    CF tank from Talon Tunes
    TJ 1-26 .357 barrel liner. 14mm O.D. 28″ OAL. Will have M14x1.5 threads for a LDC.

    That’s pretty much it. Since I’ve been sitting on this project for a while waiting to order the barrel, I’m not going to change it again. The parts listed above, is it for the primary components. Now, here’s what’s left to consider:

    – What size LDC? This gun, by design, will only be 130 fpe. “Only” :rofl: I’d still like it to be as quiet as possible though. Could you imagine a “backyard friendly” .357 with over 100 fpe? :rofl:
    – What AR grip? For now, I have a Tubb 2k rifle grip I picked up years ago. It’s comfy, and I can finally use it.
    – What stock? Some Carbine type? PRS type? So many choices!
    – Do I install a folding hinge? -If I did, it would be a LAW Tactical clone… They’re reasonably priced.

    Other considerations and ancillary projects:

    – How to mount a short rail, so I can install a bipod? Do I mount it to the chassis? Or do I work with a machinist to design a barrel band/picatinny rail that goes around the main tube?
    – Would like a slip-on barrel band, like what Daystate uses on their guns. Simple, 3D printed.
    – What paint scheme or hydro dip pattern to use? What parts to dip/paint?

    That’s where I’m sitting, as of today. I’ll keep y’all updated!


    Barrel is in, and it fits the CF sleeve I have beautifully!! Hopefully soon I can send this barrel and some other parts off to be machined, then I can finally… FINALLY assemble this .357 pellet slinger… I can’t wait!!
    :8: :8:


    Jefferson State Airguns (JSA) is going to be doing all the machine work needed for this build. They JUST got their .357 chamber reamer in, and they emailed me… Which is awesome, considering when I received my barrel! My barrel, breech, bolt and a section of CF was mailed off to JSA today! The end is near!! I can’t wait to get my parts back!

    I had a brain fart… I won’t be using the TSS kit for this build- The Cothran Powerhouse Valve isn’t tuned via spring tension- it’s either open or closed… The Powerhouse is regulated via air pressure. So to change the velocity, you change the pressure the valve sees. I already knew this, but it wasn’t at the front of my mind… Anyhoo, I’ll have to pick up a factory rear plug and hammer spring and such. No worries- I still need to order small odds and ends from Crosman anyway.

    Bottom line: a few more weeks and this build will be assembled, and after I get an LDC, it’ll move on to testing!!! YES!

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