.357 Gen 1 Mrod based pistol

[mackeral5]

While waiting on parts to put this set of parts in its final form, I assembled it into something semi-useful.  A little long for a pistol, but not much longer than a Prod.  weighs in at a hefty 3.5lb

 

B&A "thirty plus" breech, added bolt handle, converted to 10/32 cocking lug
16" TJ's 1/26 sleeved in 16mm CF
Cothran valve modified to simplified balanced valve format
Prod trigger w/Airgun Lab sear
Gen 1 Brod tube of unknows manufacture
Hogged out and plugged OEM gauge port
Medium weight MDS hammer of unknown manufacture
Home made twin-spring setup

Filled to 2800psi and 81gr pellets, 3 shots
762
787
753
Ends at 1800psi.

130gr slugs peak at 540fps across 3 shots.  158gr peaks at 450fps.

Long term this will have a shorter tube with no gauge block, 350cc bottle, and an AR style collapsible stock.  Just waiting on the tube and stock adapter. 

Until then, I would like to use it as a pistol but do not have a sight/scope.  Can anyone please recommend an economical solution?

[YEMX]

That's purty!

[Tonycalves]

Great job! Good numbers

[FuzzyGrub]

 

[Nvreloader]

Hey Mike

Sharp looking handgun............

I don't know what the recoil flip is, but have you thought of adding a Gill type muzzle break,
It would greatly reduce the bbl flip and felt recoil etc.

https://rossbrakes.com/about

I run a 5 gill on my 284 pistol 18" bbl with a 5 -15 x rifle scope, and don't get scope bit........ now, LOL

Don

[Back_Roads]

 I have not tried these yet but they have good reviews, I see a sale I may have to get one too.
https://www.seeallopensight.com/

[JuryRigger]

Nice looking pistola; some pretty serious power, too! I hope you can find some sights, that's too much gun to have to sit on a shelf because you can't aim it .
Good luck,
Jesse

[mackeral5]

Thanks for the kind words. 

Don--Regarding muzzle flip, it does have a bit.  You had previously shared Ross's info and I bought one of his for another project.  I will be gluing on a 16mm× 1/2-20 muzzle adapter, may as well pick up another one of Ross's brakes.  Thanks for pointing that out. 

I am leaning towards an entry level scope from Simmons, BSA, UTG, etc, but I really hate the concept of trying up $100 in an optic that I may only briefly use. 

[mackeral5]

I decided to bite the bullet and pick up an entry level handgun scope, the BSA 2-7 x 28mm Edge.  Hopefully it will work well..

Today I also had the opportunity break from work and exchange a nitrogen cylinder, so now I can get full fills.  This little hand cannon wakes up a bit with a 3000psi fill.   I had to dial up the hammer spring a bit as the first shot at 3000psi was only 682fps. 

Now 3 shots of 81gr pellets goes 807, 810, 782

the scope should arrive next week and I can demonstrate how poor of a pistol shooter I am.  In carbine form this gun easily shoots under an inch at 50 yards.  I'm betting I will not be able to get under 4" as a pistol, lol....

[mackeral5]

The scope arrived yesterday, I found a set of rings that appear to be close enough so I mounted the scope.



Over recent days I've done some more testing which involved several different configurations which I plan to organize the data and share it later.  The most recent configuration involved converting the valve back to Powerhouse format by reinstalling the rod in the poppet stem.  I also run these valves in Simplified balanced valve format by removing the rod and replacing the seal material with delrin.  Note do not remove the rod of your Cothran Powerhouse valve unless you replace the seal material with something harder such as delrin.  Your OEM seal will be destroyed running without a rod as it is too soft. 

Porting is at .290, valve throat .350.  47gram hammer.  16" barrel. 

In Simplified Balanced Valve format a 2900psi fill produces 5 shots  778, 787, 792, 772, 738 with 81gr pellets, ending at 1700 psi.

In Simplified Balanced Valve format a 2900psi fill produces 3 shots 533, 540, 521 with 130gr slugs, ending at 1600psi.

In Cothran Powerhouse format a 2900psi fill produces 3 shots 827, 797, 742 with 81gr pellets, ending at 1600psi.  Max 123fpe on pellets

Also in Powerhouse format a 2900psi fill produces 3 shots 689, 637, 569fps with 130gr slugs, ending at 1600 psi.  Max 135fpe, not too shabby for a hand cannon.

These results are in alignment with my previous Cothran testing. 

[YEMX]

Whew!  Beauty!

[Sbak]

Super cool, looks like fun

[mackeral5]

So far it has been interesting.  I've never shot a scoped pistol until now.  At least from a rest it isn't quite as difficult as I imagined. 

It is LOUD though.  Loud enough that out of respect for neighbors I won't shoot successive 3 shot strings.  Shoot a string, give it a break for a few minutes, shoot another.  Have a threaded adapter on the slow boat from Poland so I can mount a Ronin. 

While I am glad I am able to get some use out of the gun in its current state, I really am looking forward to it's final form as a sub 7lb lightweight, 350cc, 150fpe BLASTER. 

This is a pic where I mocked it up a few months ago.  Imagine this gun, but with a tube short enough that the tank block butts right up against the valve.  The 350cc tank will end 1.5" or so rearward of the Ronin.

[FuzzyGrub]

I like the bell curves with the simplified balance valve with delrin seat configuration.       Much better efficiency with the pellets, too.

Did you have the poppet stem hole opened for both configurations?

PS: I hope to get back to my PH valve testing in a couple of weeks.

[mackeral5]

I like the bell curves with the simplified balance valve with delrin seat configuration.       Much better efficiency with the pellets, too.

Did you have the poppet stem hole opened for both configurations?

PS: I hope to get back to my PH valve testing in a couple of weeks.

The stem vent has been slightly enlarged and the same stem used in both valve configurations.  I have a stem with a larger vent that produces lower velocity/greater efficiency, but if you try to over-drive it with HST to get the velocity beyond where it wants to run efficiency falls off.  IIRC the vent is around .025.  I think I'm going to convert the valve back to SBV format.  It was fun to run it WFO for a while, but I would like to tone it down a bit for  target shooting.  It doesn't take much energy/velocity to punch paper at 30 yard....

I look forward to seeing how your testing goes.

[mackeral5]

This particular gun has a bit of modularity designed into it that will support a fairly broad range of configurations.  As pictured above, it is a 60cc tube, 16" barreled large pistol or with a stock mounted it is a short carbine.  By screwing in an Mrod tube extension it becomes a ~130cc tube.  Barrels can be swapped from 16" to a 21".  These changes can be made pretty easily, without having to separate the breech nor trigger assembly from the tube.  There is also another variable in how the valve is setup to run---either as a Powerhouse, in the format Don Cothran designed it to run, or as a Simple Balanced Valve (SBV), a configuration that I have done a lot of testing with.  In the gun's current state, due to having a gauge port, toggling between PH and SBV configurations requires full disassembly. 

What are these 2 valve configurations?   To put it very simply in Powerhouse format it is pretty much a max power effort with efficiency being a bit of a secondary priority and a bit of a challenge to obtain.  In  SBV configuration it becomes a mid power level valve that is easy to open and closes fast, thus is pretty efficient.  Each valve configuration has its own unique tuning nuances.  I sum it up as PH is great for slugs and heavier weight projectiles, SBV is better for pellets and lighter weight projectiles.  These are merely my opinions based on my personal experience and preferences.  YMMV.....

I put together some charts showing PH vs SBV valve configurations, with different length barrels and air tubes.  81gr pellets were used for all testing.  Hammer weight, HST settings, and porting are identical for all configurations.  All strings have a starting pressure of 2900psi.  Porting is .290.  Hammer is an MDS hammer with a total weight of 47grams including striker and cocking bolt.

First up, the gun as pictured. 60cc tube, 16" barrel.  Orange line is Simple Balance Valve configuration, blue is Powerhouse.



Next up, 60cc tube, 21" barrel.  Orange line is Simple Balance Valve configuration, blue is Powerhouse.



Now let's add the  tube extension, effectively increasing air storage to 130ish cc.

Here is the 16" barrel.  Note in this chart you can see a flatter than typical PH string, this is right on the edge of not having enough hammer strike to open the valve properly.  This is due to the larger capacity maintaining a higher average pressure during the shot.  With more hammer energy the first shot would have shown a bit more FPE, likely upwards of 135fpe. 



Here is the 21" barrel.  Again, orange line is Simple Balance Valve configuration, blue is Powerhouse.



Again note the atypical start to the PH string, more hammer strike would have likely pushed this shot up to the 158fpe range. 

In this 21" barrel, 130cc tube configuration, simply switching ammo and lugging it down with 158gr will generate 185fpe. 

[YEMX]

That is some phenomenal work!!

[mackeral5]

That is some phenomenal work!!

Thanks Tom.  I've previously made multiple statements around running the Cothran in this alternative SBV configuration, the intent here was to use real world data to compare the configurations.  This shows with a fairly straight-forward modification the Cothran can be a bit more versatile in higher FPE applications.  The short tube data shows a good job of what could be expected in a B'rod, peak velocities occurred around 2500psi...

[Vee3]

I have not tried these yet but they have good reviews, I see a sale I may have to get one too.
https://www.seeallopensight.com/

I tried their 1st gen sight on a pistol and it was unusable for me. Too hard to line up the reticle/lens. Works okay on a rifle, though.

[mackeral5]

I have not tried these yet but they have good reviews, I see a sale I may have to get one too.
https://www.seeallopensight.com/

I tried their 1st gen sight on a pistol and it was unusable for me. Too hard to line up the reticle/lens. Works okay on a rifle, though.

Thanks for sharing your experience.   

I looked at those and didn't want to roll the dice on something unknown to me.  While I have no previous scoped pistol experience, I was familiar with tubes/lenses/crosshairs so I somewhat knew what to expect when I decided on the entry level BSA piece.     In the end I think it was a good choice for my purposes.