Don Cothran M-Rod Power House Valve

[lloyd-ss]

Here is the .308 cal shot data.   Barrel is 22.6" long.

These are just shots taken to get a feel for this barrel and valve combination.  No real attempt to achieve any shot efficiency or create a string.
To break 200 fpe, I had to use a heavy 135 gn bullet.


You have to click on the chart to make it more readable.
Lloyd

P.S.  Don, take a look at the 3000 psi shots 9, 10, and 11, and i think your 100 fpe question has been answered.

[screwwork]

Lloyd,

I have been sitting on the sidelines and watching the testing of the Don C valve.
Great job on showing real data on how the valve was designed to be used.
I'm will be looking forward to see how the .357 cal preforms on the Mrod.

Thank Randy

[rsterne]

Interesting results.... It would appear that the exhaust port diameter is limiting the FPE to slightly less than I thought it might, although pretty close.... It is clearly just about on a par with my DAQ 308 Exile, at the same pressure, but a whole lot easier to cock.... No question, this valve is going to prove a "Powerhouse" in an MRod....

Bob

[lloyd-ss]

Lloyd,

I have been sitting on the sidelines and watching the testing of the Don C valve.
Great job on showing real data on how the valve was designed to be used.
I'm will be looking forward to see how the .357 cal preforms on the Mrod.

Thank Randy

Thanks Randy.  Being able to share the results is a lot more rewarding  than just doing the testing for myself.  I am anxious to see what the .357 will do also.  That is next on the airgun agenda..... but, the grand kids and I are starting a summer tree house project tomorrow morning and that will be a few hours in the mornings until the sun comes around and it gets too hot.  Will have evenings for the airguns, though, depending on how much energy the grand kids wring out of me, LOL.
Lloyd.

[lloyd-ss]

Bob, I had used this barrel in the past with a special "conventional valve" and was never able to get this much power, despite the fact that I used a .061 wire spring.  Awful to cock.  Felt like I was breaking something each time I cocked it.  Conversely, the Cothran valve cocks like a .177 pea shooter.
What is the barrel length on the Exile?
Thanks,
Lloyd

[MichaelM]

Thanks Randy.  Being able to share the results is a lot more rewarding  than just doing the testing for myself.  I am anxious to see what the .357 will do also.  That is next on the airgun agenda..... but, the grand kids and I are starting a summer tree house project tomorrow morning and that will be a few hours in the mornings until the sun comes around and it gets too hot.  Will have evenings for the airguns, though, depending on how much energy the grand kids wring out of me, LOL.
Lloyd.

Did you say treehouse?  You're like the coolest G-Pa  ever!!!!.... Hrmmm maybe I could come down and camp out after all.... I mean... I could always sleep in the tree house.... bears cant get me there.. right??...?

lol!!!  

[lloyd-ss]

Thanks Randy.  Being able to share the results is a lot more rewarding  than just doing the testing for myself.  I am anxious to see what the .357 will do also.  That is next on the airgun agenda..... but, the grand kids and I are starting a summer tree house project tomorrow morning and that will be a few hours in the mornings until the sun comes around and it gets too hot.  Will have evenings for the airguns, though, depending on how much energy the grand kids wring out of me, LOL.
Lloyd.

Did you say treehouse?  You're like the coolest G-Pa  ever!!!!.... Hrmmm maybe I could come down and camp out after all.... I mean... I could always sleep in the tree house.... bears cant get me there.. right??...?

lol!!!  

This will be a fun summer project with the grand kids.    We cleared the bear thicket out from underneath it. 
Now that i am looking at the sketch I can't figure out if it looks like Gilligan's Island or a deer stand.  Oops!  Honestly, I didn't think of that till just now.
Don said this was a valve for a hunting gun, right? 

[rsterne]

The DAQ used a 24" barrel, but to be honest it was probably 1" shorter than that, measured from the 1/4" diameter barrel port to the muzzle.... The best I ever saw at 3000 psi was 836 fps with 119 gr. bullets, which is 185 FPE.... It was definitely on "the plateau", because the efficiency the way it came was 0.38 FPE/CI (cocking force 28 lbs.).... I got that up to 0.88 FPE/CI by "setting" the hammer spring, and I only lost 3 fps.... The cocking force dropped to "only" 20 lbs.... The hammer weighed 190 grams, and had a travel of 1.62"....

Bob

[lloyd-ss]

Bob,
That is a serious hammer hit.  I had a DQ .357 pistol with a 148 gram hammer, but the hammer stroke was only .84".  It still put the air usage well up on the plateau. 
Lloyd

[Rescue35]

Bob, I had used this barrel in the past with a special "conventional valve" and was never able to get this much power, despite the fact that I used a .061 wire spring.  Awful to cock.  Felt like I was breaking something each time I cocked it.  Conversely, the Cothran valve cocks like a .177 pea shooter.
What is the barrel length on the Exile?
Thanks,
Lloyd

I might revisit a big bore Marauder now. When I made my .308 it's main hindrance was the valve. It looks like Mr. Cothran has resolved that.

Good luck with the elevated shooting platform... I mean grandkids tree house.

[stalwart]

Watching closely. 

[lloyd-ss]

It is raining today, so no outside work, and i will finally have a chance to get back inside and work on the .357 barrel.  The barrel is a liner from TJs and the effective length will end up being about 27-1/2".  1/2" O.D. and 1 in 16 twist.  That is probably a faster twist than necessary for the short bullets that will be used.
Even though the .257 and .308 and .357 barrels are all 1/2" O.D., and the barrel ports are in the same location, there is a slight complication due to the fact that the 7/16 spot face on the barrels for the T-port o-ring are a slightly different depth for each barrel.  The wall thickness of the barrel dictates the maximum depth of the spot face; the thicker the wall, the deeper the spotface.  The T-port needed to be shortened about .025 going from .257 to .308, and will now need to be shortened another .025 for the .357.   A minor complication, but something to be dealt with.

[mackeral5]

Lloyd-  I'll be paying very close attention to your .357 results.  I'm working a Cothran Double tube qb build using the disco based powerhouse valve.  I am assuming the results should be very similar.  Thank you for your contributions.

[lloyd-ss]

The 357 barrel is now prepped. Muzzle, breech, o-ring seal at the breech, 27.7" long, barrel port .240 wide x .300 long.  The new sleeve for the bolt prob still needs to be made.

Here are a couple of pictures comparing the .257, .308, and .357.   As my 3 year old grand daughter might say, "The daddy, the mommy, and the baby."  The different lengths make it difficult to do apples-to-apples comparisons in performance, but the trends will show.   
All barrels are 1/2" O.D.  It is easy to see what I meant about having to shorten the transfer port progressively for the larger calibers. 
I have at least some 105 and 132 gn .357 bullets, plus some other weights stashed away that I will need to get out and size for the testing.

[rsterne]

I would think you will be pretty close to 230 FPE at 3000 psi with the 27.7" barrel and the 105 gr. bullet in .357 cal, maybe 20 FPE more with the 132 gr.... and adding maybe another 30 FPE at 3500 psi?.... It may be less, because of the 1/4" exhaust port, of course....

Bob

[lloyd-ss]

357 raw data
Finally, some 357 data!  As I keep saying, airguns take a back seat in the summertime as the outdoor projects take precedence.

The following is raw data, just some random shots, taken to get a feel for the Don Cothran Power house valve in a Marauder rifle.
The barrel is a .357 barrel liner, 27.7" long, 1 in 16 twist.  The hammer and spring are totally stock.  For all shots, the striker was turned CCW out all the way to give maximum hammer stroke.  The hammer spring was set from minimum force ( zero turns in CW) to moderate ( 4 turns in CW), but the spring force and cocking effort was still very low (easy to cock).   Unfortunately, the rear stop for the hammer spring adjuster was removed (threaded all the way thru) so the actual number of hammer spring turns might not be exact.

There are two sets of shots. 
The first (set number 12) was the Cothran powerhouse valve with a transfer port that transitioned from the .257 exhaust port to the .240 x .300 barrel port.  After taking several shots, it seemed that there was still more power to be had from the set-up, so I massaged the porting some ( .293 round transitioning to .275x.324 oblong) and did get another increase in power.
No attempt was made to adjust for air efficiency or shoot a string.  This was strictly a snap shot of the power using a variety of bullets and pressure settings.  As Mr. Cothran stated, this is a  valve for a hunting gun.  And it definitely makes effortless power!

Set number 12


Set number 13, with massaged porting.

[match]

those last 3 shots on 13 look like 136gr should give 2 or 3 good shots with some fiddling...

the 167gr shot looks like it might have a bit more and a good followup shot too.

[lloyd-ss]

those last 3 shots on 13 look like 136gr should give 2 or 3 good shots with some fiddling...

the 167gr shot looks like it might have a bit more and a good followup shot too.

Yes, with some fiddling of the hammer adjustments, and possibly an ssg, the air consumption could be reduced quite a bit. 

[rsterne]

Excellent FPE, for sure.... Pretty hard to do an exact comparison to my projections, but it looks like I was optimistic by about 20-30 FPE.... That is likely the exhaust port size of the valve showing up, which at 0.257" is only 72% of the caliber.... or did you actually hog out the exhaust port of the valve itself to 0.293" as well, which is 82% of the bore diameter?.... The 167 gr. bullet, with the larger ports, achieving over 280 FPE, is impressive.... That should drive a 156 gr. bullet at close to 900 fps at 3500 psi....

Just to give guys a feel for how impressive it is to achieve this sort of FPE with such a light valve strike, I got 257 FPE at 3000 psi with a 154 gr. bullet in my Hayabusa, with a 28" barrel and 0.281" ports.... The hammer weighed 147 grams, and had a travel of 1.45", and the hammer spring was 3.5" long, 0.42" OD, made of 0.054" wire.... At coil bind (to get that power) it took over 26 lb.f. to cock it.... 

Bob

[MichaelM]

thats super nice!