New Year, new... project

[YEMX]

I WILL get some initial numbers today!! 

[YEMX]

Well that was an underwhelming shooting session today    I did no target work, only shot slugs so I can set the reg and spring tension.  Again- Cothran valve.  So I have it set so the hammer will crack the valve, but not much more.  I noticed no perceivable difference between 2800 psi and 3k psi output on the reg, so I bumped it back down to 2800 psi and kept it there.  I fill to 3.5k psi on the Great White gauge, the gauge on the gun seems to be 500 psi off, since it read 4k psi.  The end pressure figures are corrected to reflect this.  I'm shooting 61.7 grain slugs sized to .243.  I will size to .242 to see if it'll affect speed...  I'll only run a short string of those.  I want to see how accurate the .243's vs .242's will be.  But that'll be a little later.

3.5k psi fill, reg set to 2.8k psi output:
800 fps    87.7 fpe
797         87.0
813         90.5
806         89.0
800         87.7
800         87.7
806         89.0
800         87.7
803         88.3
793 fps (off reg, end fill- 2500 psi)

So, 9 shots...  I did a total of 3 10-shot strings, and all of them were about the same figures.  So I'm only averaging 87 fpe...  Not exactly what I'd hoped to be getting with a 26" barrel, .250 ports and 2.8k psi output on the reg.  I may have to pull a Bob and have a custom tube made, so that I can reverse mount a larger CF tank so I can get a larger plenum...  I think that might be what's holding me back.  I know the 26" barrel will hamper the max potential, but I don't think 2" would hold me back THAT much- Bob's calculations are putting a 28" barrel at 3k output at a whisker under 140 fpe, so I figured I'd be hitting around 120 fpe w/this configuration.  But over 30 fpe less?  I dunno.  Am I doing something wrong?  I can also see that the gauge that reads output pressure dropping from 2800 psi down to 2600 or 2700 psi before slowly going back up to 2800 psi...  The only think I can think of (unless this is normal- though I didn't even notice this with my .357 Brod build) is maybe the plenum is too small?  Thoughts?  I'm grasping at straws trying to figure out why I'm getting such a low FPE with this set up...  Or maybe I'm not.  What say you?

The LDC was nice and quiet though!  So there's that! 

[Rallyshark]

I'm being lazy, and didn't want to go back and look for the info... How large is your plenum? I would think you could make it work with 60cc, but 120cc would be ideal.

[YEMX]

That's what I'm thinking the problem is, but the Brod conversion tube is 11.75" OAL.  I'm not sure how large of a plenum, TBH.  It's either 75cc or 85cc...  I figured it would be large enough for a 6mm.  The same plenum netted me 130 fpe in my .357 build, and that was only seeing 2150 psi or 2200 psi regulated.  Those .357 pellets are also heavier at 81g...  So I'm stumped.

I'm going to take a look at the TP tomorrow- I'm pretty pooped from today.  I'm also kinda dejected w/the results.  But I'll take a look at the TP- I THOUGHT everything is .250" ports- exhaust, TP, barrel.  But maybe I was wrong about the TP?  Easy enough to check.  Tomorrow.  Now, I have 2 plans of attack for this 6mm project:

1:  Pull a Bob and build a longer tube, and use a CF 500cc 4500 psi tank w/a reverse block
2:  Modify the barrel and build an AF gun...  I mean, I have the parts.  So, why not?  Plus, it's a Condor valve w/a huge tank...  It might also be easier/cheaper to do.  I dunno.

[Rallyshark]

That's what I'm thinking the problem is, but the Brod conversion tube is 11.75" OAL.  I'm not sure how large of a plenum, TBH.  It's either 75cc or 85cc...  I figured it would be large enough for a 6mm.  The same plenum netted me 130 fpe in my .357 build, and that was only seeing 2150 psi or 2200 psi regulated.  Those .357 pellets are also heavier at 81g...  So I'm stumped.

I'm going to take a look at the TP tomorrow- I'm pretty pooped from today.  I'm also kinda dejected w/the results.  But I'll take a look at the TP- I THOUGHT everything is .250" ports- exhaust, TP, barrel.  But maybe I was wrong about the TP?  Easy enough to check.  Tomorrow.  Now, I have 2 plans of attack for this 6mm project:

1:  Pull a Bob and build a longer tube, and use a CF 500cc 4500 psi tank w/a reverse block
2:  Modify the barrel and build an AF gun...  I mean, I have the parts.  So, why not?  Plus, it's a Condor valve w/a huge tank...  It might also be easier/cheaper to do.  I dunno.

I would definitely double check that porting, and make sure you aren't getting any blow by anywhere during the shot cycle.  Of course, it is a heck of a lot easier to make that power with a .357, than a .243.  I do suspect something is going on though.  You'll figure it out after you walk away for a bit and come back to it I'm sure

[YEMX]

I'm pretty sure the TP is either .250" or .243"...  Well, at least I hope it is.  I'm also going to do some measurements for that reverse block tube tomorrow.

I'm also still kinda thinking about making this a AF build though.  I'll do some measurements.  I broke down the .30 Condor because it was too long.  This may be another rifle that's too long.  *sigh*  But- that's a worry for tomorrow.

[dapoun]

Is your bolt retractable? If not that could be a restriction. Also I know Cochran valves don't take much energy to open but have you tried adding hammer tension until there is no gain in velocity at that pressure.     

[FuzzyGrub]

I have been slowly working on getting parts for a Brod and have been reading Bob's "Tale of Three Brods"  allot.  While he didn't do that caliber at that power, all three (25, 30, 357) had much lower reg set-points (1800, 2000, 2200).  It appears your plenum is around the same size, about 80cc.  So, I agree with RS, something seems to be amiss. 

[YEMX]

Is your bolt retractable? If not that could be a restriction. Also I know Cochran valves don't take much energy to open but have you tried adding hammer tension until there is no gain in velocity at that pressure.   

Yessir- hammer tension is set to crack open the valve, and no more.  Bolt isn't retractable, its scalloped. Or what would be considered a "spoon" bolt:


The bolt I have is on top.  Picture courtesy of Lloyd and his .30 Mrod build thread. 

I have been slowly working on getting parts for a Brod and have been reading Bob's "Tale of Three Brods"  allot.  While he didn't do that caliber at that power, all three (25, 30, 357) had much lower reg set-points (1800, 2000, 2200).  It appears your plenum is around the same size, about 80cc.  So, I agree with RS, something seems to be amiss.   

Exactly!  I know my build isn't maxed out for efficiency like Bob's rifles typically are.  But I didn't think I'd see numbers this low...  This is the first time one of my builds hasn't performed close to what I expected...  But we'll figure this out.  Or I'll build something else!!    I WILL have a 6mm!

[YEMX]

A suggestion I got from another airgunner- drop the reg and just let the Cothran valve do it's thing...  I may try that as well...  I just don't like the declining velocity is all...  Thoughts on this path?

Also, just reading through the first few posts on Bob's "Tale of THREE BRods" thread (Thanks for the reminder Fuzzy!), it seems the plenum size of the tube (the ones from Bob's thread look to be the same size as mine) is only around 69cc's.  But when you add the collective volumes from the Cothran valve and the drop block, that'll bring the number up to 80cc+ of plenum.  Which should be large enough for .25 and .30 slugs if compensated with higher set pressure to compensate (it is slightly small for .25 and .30 slugs)...  So said the thread.  So with a 6mm at less than 70gr, this platform should be able to get at least 100-120 fpe.

[YEMX]

Well, I feel dumb...  Some issues have come up 

So I took the upper off to check the TP and such.  To my complete surprise (shock and horror too), none of these ports are .250".  Not even close.  The exhaust port is .170" (as near as I can measure), and the TP (and probably barrel port- I haven't pulled the barrel yet) is .160".  THERE'S my problem.  No wonder I was getting a measly 87 fpe average. 

But this raises another question.  Since ALL Cothrans that I know of have .250 port sizes, Is this even a Cothran valve?  I'll disassemble further once I've de-gassed, and post pics.  I've been told Mr. Cothran made a reducer for his valves, I HOPE that this reducer was mistakenly installed somewhere along the line, and I can simply remove it.  I'll still have to have the tube, breech and barrel modified, along with having a new TP made... But at least then I'll see the max potential given my set up. 

Again, this is if I don't just modify the barrel to have it put into a AF Condor.  Still debating this.  The fully assembled Condor will be 40" OAL w/o the LDC attached.  That's 12.5" shorter than the fully extended Brod conversion.  So it's definitely a consideration. 

[FuzzyGrub]

A suggestion I got from another airgunner- drop the reg and just let the Cothran valve do it's thing...  I may try that as well...  I just don't like the declining velocity is all...  Thoughts on this path?

Also, just reading through the first few posts on Bob's "Tale of THREE BRods" thread (Thanks for the reminder Fuzzy!), it seems the plenum size of the tube (the ones from Bob's thread look to be the same size as mine) is only around 69cc's.  But when you add the collective volumes from the Cothran valve and the drop block, that'll bring the number up to 80cc+ of plenum.  Which should be large enough for .25 and .30 slugs if compensated with higher set pressure to compensate (it is slightly small for .25 and .30 slugs)...  So said the thread.  So with a 6mm at less than 70gr, this platform should be able to get at least 100-120 fpe.

Yea, spent some time on that post because I came up with a lower number and wasn't taking valve and drop block into consideration.   In my case, the 30 cal data is what I was after, and seeing he was getting near 100fpe at 2k reg, was nice to see. 

You will figure it out.  If building was frustration free, everyone would be doing it.   

PS: and it looks like you found it while I was typing! 

[YEMX]

You will figure it out.  If building was frustration free, everyone would be doing it.   

PS: and it looks like you found it while I was typing! 

Yessir!  I found the most likely problem!    Now what to do to fix it?  Hmmmm...

[mackeral5]

Don offered 2 different size Cothran valves.  The one with the smaller transfer port has a proportionately smaller throat as well as balance chamber.  It is a very good valve for .25 and .30 pellet shooters, or perhaps the odd .17 and .22 slug shooter.

whomever recommended to try it unregulated may be onto something----you may find it does what you want it to and rather efficiently due to the smaller transfer.  I would have to try.....

As a sidenote, I like mixing Cothran parts by running the smaller balance chamber in my .250 transfer, Cothran equipped guns.  I find it closes faster and allows for more tune-ability due to lowering the balance ratio....

If your valve has an aluminum body, with a brass core, a steel balance chamber piston, steel balance chamber attached to the poppet, a soft plastic nylon-like poppet seal, and a stepped rod floating loose in the valve stem, you have a Cothran Powerhouse for the Marauder rifle....

[YEMX]

Don offered 2 different size Cothran valves.

whomever recommended to try it unregulated may be onto something----you may find it does what you want it to and rather efficiently due to the smaller transfer.  I would have to try.....

As a sidenote, I like mixing Cothran parts by running the smaller balance chamber in my .250 transfer, Cothran equipped guns.  I find it closes faster and allows for more tune-ability due to lowering the balance ratio....

If your valve has an aluminum body, with a brass core, a steel balance chamber piston, steel balance chamber attached to the poppet, a soft plastic nylon-like poppet seal, and a stepped rod floating loose in the valve stem, you have a Cothran Powerhouse for the Marauder rifle....

Once it's done de-gassing, I'll for sure check it all out.  I didn't know the Powerhouse valves came in 2 configurations!  I thought they only came with .250" exhaust.  I sent you a PM mackeral5...

[YEMX]

Okay... SOME good news- I have a normal Cothran valve, w/.250" exhaust port.  There was just a reducer in the valve.


But the decision still stands:  Do I modify the tube, breech, barrel and have a new TP made all in .250", or do I just re-purpose the barrel and slap it in a AF gun?  I'm really going to have to think on this.

Brod

Pros:  All the parts are on-hand, is regulated
Cons:  Heavy as it's currently configured, LONG, parts need to be modified/made

Condor

Pros:  Slightly shorter, lighter, 99% of parts are on-hand
Cons:  Have to have barrel made, it's only slightly shorter than Brod, unregulated hammer. 

*facepalm*  Decisions, decisions.

[Rallyshark]

Now that you've found the problem, I say stick to this build myself.  High power/regulation tip this one in your favor, imo. 

[YEMX]

*sigh* You're probably right... I should probably just stick to this build for now...

I'll have to:

-  Open up the Barrel port
-  Open up the Breech for larger TP
-  Open up the tube for larger TP
-  Have new TP made

All the ports will be .250", just to make sure I have max flow.  I may have to re-do the bolt as well, and go back to a probe design...  Again, for better flow.  I could also take the time to have the bore in the breech for the sleeve deepened (it's not as deep as I'd like).  Basically, I'm starting all over again.  See, this is why I was debating in the first place! 

Okay- that's the game plan.  Quick thought on making this set up lighter:

-  Armada main chassis
-  Same stock/folding adapter as the Aluminium chassis
-  Saber Tactical tank bi-pod mount because Armada chassis won't have a place to mount a bipod.

It won't be as pretty, but it should be lighter.

[YEMX]

After sleeping on it, I do feel better about going forward w/the Brod build, as opposed to converting the barrel for AF use.  Even though I have already removed some of the CF sleeve, I have more than enough to re-do the sleeving that I removed.  There's a short section of barrel that was machined to .50" that needed to stay the original O.D. and that little section was one of the area's of Loctite that didn't cure- too big of a gap I suppose.  JB Weld will definitely fill it, in addition to filling the seam between the 2 sections of CF.  Now, it could be argued that because I'm using 2 different adhesives that it'll change the harmonics.  Well, that's probably true- to an extent.  But will it really make that much of a difference in our case?  I guess we'll find out, when I get this back together and start shooting groups.  Not like anyone else would ever be in a situation like this- 2 different adhesives whilst sleeving a barrel.  But I suppose it may be useful information to squirrel away.   

Re-doing the project (I mean, that's basically what I'm doing  ) also allows me to fix some nagging issues I have:

-  Barrel sleeve depth (I want the sleeve to seat deeper into the breech)
-  The weight of rifle (It's a little too heavy for my liking)
-  The trigger blade (both location and type- I want to use my RAW trigger blade!) 
-  Bipod location (I want it further out) 

The good news is, I have a good TP I can copy- from my .357 build!  I didn't even think about it before...  Since I'm having a new tube made for the .357, I'll use the .357 tube on this build...  One less thing to machine.  So really, all that has to be done is modify the breech and open up the barrel port.  I'd use the TP from the .357, but I need it for assembling the .357 Brod in the future, so I'll just copy the TP, and use the original for the .357 when the time comes.   

I'm leaning towards making a new bolt as well- I'd like to use my Daystate bolt handle.  Also, isn't a probe better for flow than a spoon bolt, over a certain caliber and/or power level?  Regardless.  I'm considering it.  Might as well do it now, since the gun is apart.  Do it right the first time, right?   

[YEMX]

Breech TP hole is done.  The breech TP is laughable, but will be serviceable.  The new TP will be made to fit the breech better anyway, so I'm not worried about it.  I just used the TP I have on hand to get close.  The barrel port has been drilled out to .250", and the area smoothed. 

Could someone please tell me the o-ring size for the barrel o-ring for a Gen2 Mrod?  TIA!!

Still a lot of work ahead, but at least some forward motion has occurred. 

I'll also order the Armada chassis today.