Author Topic: Don Cothran M-Rod Power House Valve (Read 56159 times))

dyotat100 · « **Reply #40 on:** May 29, 2016, 06:38:30 AM »

Nick's gun shot in the 970's with 92 gr on 3050 psi. My gun shot 998 with 92 gr on 3000 psi. These numbers are thu lab radar. When shooting mine it was thru chrony also at same time. Chrony said 1004 fps.

I was having a hard time believing the lab radar so we sat Cedric's chrony up so I was shooting thru both at the same time.

The other gun I have has a carbon bottle on it so you can get over 200 fpe with higher fills. It is setup to get 7 shots with around a 15 fps spread with 74 gr on 3400 psi. I know it pushes them in the 1070's with a turn of the PW on 3400 psi.

nielsenammo · « **Reply #41 on:** May 29, 2016, 11:28:43 AM »

Plus if you use heavier bullets like everyone else does to pump up your fpe it will get well over 200 fpe. These guns get the fpe at fps numbers that you want to shoot at for the flattest trajectory. I plan to set my gun for 70 grain slugs around 950 fps.

lloyd-ss · « **Reply #42 on:** May 29, 2016, 11:57:19 PM »

Finally got a chance to make a few new parts for the M-Rod today. The gage block is made form a piece of 6061T6 and the gage adapter is a modified Crosman part.

Because the gage block almost butts tight against the face of the valve, the hole thru the gage block needs to be as large as possible to get max power and not starve the valve for air. The small hole is ok for low and medium power applications, but is bad for a high power setup. The normal hole thru the standard M-Rod gage block is maybe 3/8"? I don't have one handy to get a measurement, but I went up to 5/8" which is 2.8 larger is flow area. I could have made a block with a .20 wall thickness like the P-rod and then used a pipe thread for the adapter, but I have never been too fond of pipe threads (the feeling is mutual) so instead I machined the adapter to a 1/4-28 thread and then added a face groove to capture a size 009 o-ring. The o-ring seal is especially handy if the gun will be taken apart often, like this one will.

The eccentric thru-hole that goes thru the gage block is .625 dia and each end is counter bored to .740 for more air volume. Although it might look like a lot more, the CL of the eccentric hole is only offset .057" from the main CL of the block. I just Scotch taped a few shims together to get the correct offset on the lathe. With the 3 jaw chuck it is trial and error, but it took .098 in shims to get the .057 offset, but it was still a lot easier than changing over to the 4 jaw chuck. You can see in the picture that the air in the main tube now has a wide open straight shot into the mouth of the valve.

More to do!
Lloyd

lloyd-ss · « **Reply #43 on:** May 30, 2016, 12:00:36 AM »

Quote from: dyotat100 on May 29, 2016, 06:38:30 AM

Nick's gun shot in the 970's with 92 gr on 3050 psi. My gun shot 998 with 92 gr on 3000 psi. These numbers are thu lab radar. When shooting mine it was thru chrony also at same time. Chrony said 1004 fps.

I was having a hard time believing the lab radar so we sat Cedric's chrony up so I was shooting thru both at the same time.

The other gun I have has a carbon bottle on it so you can get over 200 fpe with higher fills. It is setup to get 7 shots with around a 15 fps spread with 74 gr on 3400 psi. I know it pushes them in the 1070's with a turn of the PW on 3400 psi.

You guys have set the bar pretty high, and I appreciate the amount of work that went into that.

Lloyd

lloyd-ss · « **Reply #44 on:** May 30, 2016, 12:06:04 AM »

Quote from: Weeb52 on May 29, 2016, 01:07:50 AM

....................................
If the Cothran valve will produce the same numbers with lighter hammer spring load...I'll continue pushing the limits of the Marauder. We're also exploring the Air Force Condor platform too... Why can't we just accept the status quo, I guess because we gotta try to build the impossible...right?
.....................................
Gene

uhhhhhhhhhhh.... grown men who refuse to grow up??

That is fine with me.

dyotat100 · « **Reply #45 on:** May 30, 2016, 12:09:25 AM »

What length barrel are you using?

I have went as high as 4200 psi and made just shy of 250 fpe with 94 gr bullets. I tried 104 gr and lost power. So somewhere between those bullets it starts going backwards.

MichaelM · « **Reply #46 on:** May 30, 2016, 12:24:01 AM »

love the gauge block!! I will have to remember the shim idea instead of grabbing a 4 jaw... I was trying to figure out how to do something like this without either a rotary table and mill or a 4 jaw.... this is very elegant solution lol

Stikman · « **Reply #47 on:** May 30, 2016, 12:48:57 AM »

Lloyd, you're a clever guy and funny too... I'll never grow up...at my age of 63 it's to late...I love me some BB guns. I could have bought a several of the new Savage A17 HMR's to blast ground squirrels for what I have in these air puffers, but I like catchin whales on a fly rod too.

By the way, I am using a 110gm hammer in the Marauder with that 17lb spring.

Doug, I'm just gettin started with the Condor platform...so far me likey. I have the .25cal 34gr JSB running at 975fps with accuracy at 125yd being super sweet... Don't wanna hijack this thread, just sayin'...

Ok Lloyd, all eyes on you my new friend...we're all in this for fun and giggles...tear it up...

Gene

Monkeydad1969 · « **Reply #48 on:** May 30, 2016, 12:50:42 AM »

Quote from: rsterne on May 29, 2016, 03:20:00 AM

Doug, you didn't mention the pressure to get 200 FPE with the 32".... Is that at 3000?.... My Hayabusa gets over 160 with a 28" barrel at 3000 psi.... Barrel length and pressure are interchangeable, and FPE is pretty much proportional to both, when you are talking about maximums....

Bob

X2 and we are talking about 2 different platforms. Yes the inline valve is a beast, but this is a M-Rod we are talking about...so this is very cool. Don't get me wrong, I like the power you can pull out of a Condor, but the M-rod ( and Disco/22XX) platform is an easier one for novice modders to work with. Plus you Cali guys shoot lil GS and I shoot MONSTER P-DAWGS!!!!! (shut it Nick!)

Monkeydad1969 RULES!!!!!

lloyd-ss · « **Reply #49 on:** May 30, 2016, 01:13:54 AM »

Yup, this is a Marauder rifle platform with the U-Turn that the air has to make. No straight-thru passage like the Airforce guns.
Starting with the 30" .257, 1 in 14 twist, 5/8" O.D. CF sleeve epoxied in place. Later with a .357 barrel of similar length.

Michael, thanks for the comment about the 3 jaw and shims. Works like a charm for this sort of thing.

I am looking forward to the light hammer spring. Tugging on a heavy spring gets old pretty fast.
Lloyd

dyotat100 · « **Reply #50 on:** May 30, 2016, 01:58:16 AM »

Quote

If the Cothran valve will produce the same numbers with lighter hammer spring load...I'll continue pushing the limits of the Marauder. We're also exploring the Air Force Condor platform too... Why can't we just accept the status quo, I guess because we gotta try to build the impossible...right?

The only reason I posted is because of what was said above. Just giving numbers for what can be done.

dyotat100 · « **Reply #51 on:** May 30, 2016, 02:04:56 AM »

Quote

X2 and we are talking about 2 different platforms. Yes the inline valve is a beast, but this is a M-Rod we are talking about...so this is very cool. Don't get me wrong, I like the power you can pull out of a Condor, but the M-rod ( and Disco/22XX) platform is an easier one for novice modders to work with. Plus you Cali guys shoot lil GS and I shoot MONSTER P-DAWGS!!!!! (shut it Nick!)

Monkeydad1969 RULES!!!!!

I think the AF platform is easier to mod. Machining has to be done on both mrod and disco.

AF is bolt on. You can get the gun from R&L with what ever barrel you want or just order a barrel ready to drop in. Then a valve and hammer from me and you have a .257 condor.

You don't see me shooting ground squirrels. If you did it would be at 200 + yds. Not fun unless it's 200-300 yds.

Monkeydad1969 · « **Reply #52 on:** May 30, 2016, 02:13:42 AM »

Well then, Doug, I think it only fair that you send me one of your AF rilfes and I will make sure to give it back to you after the shoot---LOL!

(hush Nick!)

Joe

dyotat100 · « **Reply #53 on:** May 30, 2016, 02:17:14 AM »

Don't worry I will have my .257 and .308. I can only shoot one at a time so you can shoot the other one.

Norm_m · « **Reply #54 on:** May 30, 2016, 09:24:58 AM »

Lloyd I machined my factory MRod gauge block very similar to the one you made and airflow was no issue.

If you are going to be using the MRod factory square TP gaskets be careful as I had big issues when I was doing some testing with the Power House valve in my MRod DT AR 25 cal. I could not get very good numbers and after lots of frustration I located the main issue. It was that little O ring as when putting things together that O ring would expand and choke the TP opening enough to reduce air flow. I machined a little step in the end of the transfer port much like the MRod factory TP and that solved the issue. This prevented that square O ring from expanding into the TP air flow path. I know another person that used a regular (round) O ring and that also solved the issue.

I managed to get just shy of 90 FPE and had more things I was going to try before my neighbor shut me down as this gun was no longer neighborhood friendly. I had seen my 93 yr old neighbor lady leave and tried to get a little testing in as I knew it would be loud and did not notice she had returned and things surely went downhill fast from there! NO MORE SHOOTING IN MY YARD WHATSOEVER!!

The high 80s FPE I got was with a factory MRod barrel which is only 20" long and choked both of which reduced the potential of the Power House Valve.

I am sure we will see some real nice numbers with your testing.

Norm

rsterne · « **Reply #55 on:** May 30, 2016, 12:53:35 PM »

Lloyd, I like the oversize, offset gauge block, it certainly shouldn't restrict the airflow at all, judging from the photo.... After all, the air going in has to get out through a 1/4" hole at the back....

Doug, thanks for those numbers.... It's nice to see that my spreadsheet is still working pretty good.... With 3050 psi in a 32" barrel in .257 it predicts 211 FPE as a "lofty goal".... The theoretical maximum, of course, is 422 FPE.... Hitting 50% efficiency with any PCP is excellent (which is why I use that for my predictions)....

Bob

Monkeydad1969 · « **Reply #56 on:** May 30, 2016, 08:34:25 PM »

Quote from: dyotat100 on May 30, 2016, 02:17:14 AM

Don't worry I will have my .257 and .308. I can only shoot one at a time so you can shoot the other one.

I appreciate that.

Joe

Rescue35 · « **Reply #57 on:** May 31, 2016, 10:09:34 AM »

I will be following this as well. Keep up the good work Lloyd!

lloyd-ss · « **Reply #58 on:** May 31, 2016, 11:43:59 PM »

A little more progress to report. Mixing and matching spare parts leads to some unexpected challenges. The exhaust port in the Cothran M-Rod valve that I have is .257, and it is sized to use a .375 dia T-Port, in the standard location. But the Standard M-Rod T-port is only about .261 dia, so the hole in the main air tube and the breech block also needs to opened up to .375. That is not a big deal and certainly necessary to take advantage of the power capabilities of the valve.

But I had another complication in that the barrel port in the .257 barrel I have is .068" forward of the standard location. So it was just another opportunity to do some eccentric turning on the lathe. It looks fairly straightforward, but it is not, LOL. The barrel port was made to accept a .437 dia T-port with an oblong hole.

Here is what the T-port ended up looking like. (Please remember, the complication is because of the non-standard barrel that I am using.)
Valve exhaust port end is .375 dia with a .257 hole. The barrel port end is .437 dia, offset .068 toward the muzzle, with a .187 x .300 oblong port. The round-to-oblong transition within the T-Port is partially machined, and then finish blended with a Dremel and a carbide burr. It looks like it should flow nicely.

Here is how the parts fit together with the offset port. I like the fact that the T-port has an o-ring at both ends.

This is how the gun looks now. The front of the breech block is counterbored to 5/8" dia with a very slight taper so that the CF barrel sleeve gets seated tightly when the barrel is secured into the breech block.

The bolt still needs to be modified and the J-slot needs to be machined into the breech block.

Much closer!
Lloyd

MichaelM · « **Reply #59 on:** May 31, 2016, 11:55:59 PM »

this whole J slot thing has got me so curious....makes me want to machine the B50 I am building into a j slot setup.... and then lop a half inch or so off the breach of the barrel and remake it to seal with an oring but... hrmmm....

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Don Cothran M-Rod Power House Valve

Author Topic: Don Cothran M-Rod Power House Valve (Read 56159 times))