From .25 to .30 upgrade w/same internals - estimate potential power?

[tefloncoated]

Is there a way or a rule of thumb to estimate potential power when upgrading from a .25 cal set up to a .30 cal?  The only change would be the barrel/bolt, internals would stay the same.

Let's say you're making around 900 fps with 25.4 JSB Kings for ~45 fpe (adjustable to a max of 62 fpe) in your current set up.  What could one expect in terms of speed and power when upgrading to same length barrel in .30 cal with JSB 44.75 gr?  Perhaps someone has made a similar transition and has some numbers to share?

Thanks in advance!

[rsterne]

If you give more information, it is possible to give you a pretty good prediction.... Barrel length, pressure, reservoir volume, shots per fill, and starting and ending pressure are all factors....

With no other information to go on, and assuming you might be starting from an MRod, I would guess about 800 fps with 45 gr. JSBs (64 FPE)....

Bob

[tefloncoated]

Thank you Bob!

It is an M rod, 20 inch barrel, ~285cc (215cc main + 70cc extension - depinger). Modified valve, TP, gauge block, 12.5# spring.  Start pressure 2900 psi, end 1900. Current settings of 0HS, 0HT.  Total of 32 shots with 866-872-828 with JSB Kings.

[Bwalton]

If what you say.....can be adjusted to 64ftlb would be shooting the kings @ 1050ftps, a 34gr pellet would drop around 940fps the .30cal are another 10gr like Bob said it would end up in the low 800fps if indeed you gun can sling a 25.4gr at 1050fps. not enough power gain for me to make that conversion....

[rsterne]

If I understand you correctly, you are getting 32 shots averaging ~840 fps with the 25 gr. Kings?.... That works out to about 40 FPE average, peaking at just under 43 FPE.... Based on that, you are getting a total of 1280 FPE.... The air used to produce that is 285 cc (17.4 CI) x 1000 psi (69 bar) =1200 CI of air, for an efficiency of 1.07 FPE/CI.... Using that, plus the information that with the power maxed you can get 62 FPE, gives me a pretty good idea of what your gun can do with the port sizes it has.... The efficiency required to balance Lloyd's spreadsheet works out to 54%, a bit on the low side, but it is what it is....

Using the settings that produced your 32 shots string above, and using 34 gr. JSBs, I would predict about 720-744-707 over the same pressure range, which is a loss in FPE.... This is because of the relatively mild tune, and increasing the hammer strike to make up for the extra pellet weight would make a big difference.... Interestingly, with the same barrel length, a .30 cal shooting 44.8 gr JSBs should shoot about  763-788-750, averaging about 57 FPE.... This is because the larger bore is making more efficient use of the relatively small amount of air being released by the mild tune....

Now let's look at what could be done by simple tuning of the hammer strike.... If we set the valve dwell so that the valve is closing when the pellet is half way down the barrel (pretty much max. power without wasting a ton of air), we get the following predictions, at 2900 psi.... Note this is for a single shot, not a string....

25.4 gr JSB - 1023 fps (59 FPE)
34 gr. JSB - 935 fps (66 FPE)

That seems reasonable, that tuned up the 34 gr. would give more FPE than the 25 gr.... Whether or not you can get that increase is not proven, however.... Now IF you had ports large enough to provide flow proportional to the increase in bore diameter, we can make a further prediction as follows, for the valve being open to 50% of the barrel length.... The .30 cal 44.8 gr. JSB should be able to reach 966 fps (94 FPE).... However, you specified "no changes", so we have to derate that because your ports would be smaller than ideal.... This is where we get into some guesswork, and my best guess would be about 78 FPE at 2900 psi with the gun maxed out for a single shot.... That works out to 885 fps with the 45 gr. JSBs.... and assumes that you can get enough valve dwell to provide a long enough push to get there....

Back to your original question, what would your gun do with NO changes?.... My prediction is a string from 2900 psi down to 1900 of about 763-788-750, averaging about 57 FPE.... As to the number of shots at that power?.... A WAG would be about 20-22 shots.... Unless you are prepared to do some port work, I wouldn't bother converting to .30 cal.... and a stock MRod valve does not take kindly to hogging out to large enough ports to let a .30 cal breath properly....

Bob

 

[tefloncoated]

Thank you, Baxter and Bob!

Bob, that's a lot of good info. I appreciate the time you took to reply. I looked up some things that you mentioned (like Lloyd's calculator) and will use them in the future.  Could you expand on what you meant by "balancing the Lloyd's spreadsheet"?  I was unable to find that info... or just point me in the right direction to look.

Correct, I am using 25.4 gr Kings.  I probably should have mentioned that the max power of 62 fpe from my OP comes with the heavy Eun Jins and more HS and HT fiddling (dont recall the exact numbers, but near max).  Not able to get that level of power numbers with the Kings...

The current tune of 0HT/0HS is easily repeatable and is very simple to maintain.  It is also most efficient in terms of shot counts.  With +2HS, i lose a full magazine and my shot count goes down to 24.  The velocities are 903-911-827.  Total FPE 1042.7.  So the efficiency is .87 FPE/CI, with an average of 42 PSI per shot (vs 31 PSI with the 0/0 tune). 

And since i have your guys' attention, any suggestions on where to explore for more efficiency/power for my rifle?  My ideal balance would be in the 32+ shot range while maintaining ~45 FPE or more with 25.4 gr JSB Kings.   Is that doable? What are my options? 

[rsterne]

Lloyd's spreadsheet I referred to is a proprietary one dealing with PCP Internal Ballistics he was nice enough to give me, it's not available publically....

I doubt you could get to 32 shots at 45 FPE, I would think that is just beyond the capability of an MRod, even with an extension....

Bob

[tefloncoated]

Gotcha!

Do you think that's a limitation of the marauder valve design/efficiency? Size of the reservoir?

[rsterne]

Reservoir size compared to power level.... You want to get 45 x 32 = 1440 FPE, so you are going to need about 1400 CI of usable air.... The only way to get that with your reservoir which is 17 CI is to get your usable pressure range up to 82 bar (1200 psi) and still stay within the ES you want.... Possible, maybe, but seems to be more than what I have seen others getting with MRods at 45 FPE....

Bob

[tefloncoated]

Yes, I see.  I'm going to try upping the fill to 3100 psi and adding 1 turn on hammer strike to get a bit closer to my "goal".

and yes, a .30 cal conversion is no longer of interest.

Thank you very much for this discussion!

[Rdsail]

Lloyd's spreadsheet I referred to is a proprietary one dealing with PCP Internal Ballistics he was nice enough to give me, it's not available publically....

I doubt you could get to 32 shots at 45 FPE, I would think that is just beyond the capability of an MRod, even with an extension....

Bob

My best tune on my mrod .25 have me 30 shots at avg 45 fpe. I would find it hard to get more shots than that at that power level unless I added an air extension. You can read about it on the link on my signature

[rsterne]

I stand corrected....

Bob

[tefloncoated]

Hey gents, thank you again for participating in this thread. I appreciate the input.   Even though my original question was answered, if you don't mind, I'll post some more info about the efforts to get to my goal... It's good to hear the feedback and guidance during the process of searching for the "perfect" tune.

I did a bit more tinkering with the ports - enlarged the valve port, TP and barrel port to 5/32 and bumped the fill to 3000 psi. The rest of the settings remained as they were, 0HS/0HT.

Here is the resulting data (xxx shots were fired off the chrony):

Start Fill 3000
end fill 1800

REWORKED gen 1 Valve plus bored port to 5/32, w/Mrod gen2 spring
depinger
Hill gauge port
12.5 # spring
 transfer port bored out to 5/32)
BARREL bored port to 5/32
EXTENDED reservoir ~ 285cc

HT 0
HS 0

JSB Kings


               Statistics/Velocity Report

               String #:     1
          High Velocity:     896
           Low Velocity:     834

       Average Velocity:     ~874
         Extreme Spread:     62
     Standard Deviation:     ?
                 Grains:     25.4


          Velocity #        Velocity         Power Factor         Foot/Lbs
                  1              842               21.387           39.982
                  2              847               21.514           40.458
                  3              859               21.819           41.612

                  4              856               21.742           41.322
                  5              853               21.666           41.033
                  6              860               21.844           41.709
                  7              866               21.996           42.293
                  8              851               21.615           40.841

                  9              857               21.768           41.419
                 10              875               22.225           43.177
                 11              873               22.174           42.980
                 12              877               22.276           43.375
                 13              865               21.971           42.196

                 14              873               22.174           42.980
                 15              872               22.149           42.881
                 16              872               22.149           42.881
                 17              881               22.377           43.771
                 18              888               22.555           44.469

                 19              888               22.555           44.469
                 20              896               22.758           45.274
                 21              891               22.631           44.770
                 22              894               22.708           45.072
                 23              891               22.631           44.770

                 24              892               22.657           44.871
                 25              887               22.530           44.369
                 26              884               22.454           44.070
                 27              885               22.479           44.169
                 28              888               22.555           44.469

                 29              885               22.479           44.169
                 30              885               22.479           44.169
                 31              879               22.327           43.573
                 32              878               22.301           43.473


                 33              xxx               xxx                  xxx
                 34              xxx               xxx                  xxx
                 35              xxx               xxx                  xxx
                 36              xxx               xxx                  xxx
                 37              870               22.098           42.685
                 38              863               21.920           42.001
                 39              859               21.819           41.612

                 40              856               21.742           41.322
                 41              852               21.641           40.937
                 42              847               21.514           40.458
                 43              840               21.336           39.792
                 44              834               21.184           39.225

[rsterne]

Looks like about 30 shots within a 4% ES....

Bob

[tefloncoated]

While according to my calculations efficiency may have improved a bit, a 4% ES air rifle is far from "great".  But I guess for a .25 cal Mrod 30 shots @ 42-45fpe within a 4% ES is not TOO too bad...

I wonder if a lighter hammer might be a good option here. I am not sure I want to go with the NBH just yet.

I wasn't really expecting to double the shot count with the reservoir extension, perhaps 5-6 more shots, a mag if I'm lucky... instead i was hoping to even and flatten out the string that I had achieved before as much as possible.  Perhaps I won't get there with this particular airgun...

[shorty]

Tefloncoated,
My .22 synrod would do 53 fpe max with 25.39 grain. Your .25 appears to do over 63 fpe max. If I had to guess with your current set up along with a .30 cal barrel, you will hit over 80 fpe (no spreadsheet needed-fact). With a few more items it will hit well over 100 fpe.

I am seeing it with my .22 synrod conversion to .357/9mm already. I hit almost 90 fpe with a 16.5" barrel.

This is tried and proven already. Check out these 2 links...

http://www.airguns.net/classifieds/show_ad.php?adNum=103237&adSort=accessories&StartingAd=0&NumberOfPages=1
and
http://www.gatewaytoairguns.org/GTA/index.php?topic=36435.0

Good luck on your quest. If I had to recommend anything, get a war valve and push that 30 well over 120 fpe.

[rsterne]

Facts?.... I don't see the FPE numbers that you suggest in either link you provide.... let alone with a .25 cal MRod shooting a max. of 62 FPE.... His question was "as is", not modified six ways to Sunday.... Just because you think it can be done doesn't make it "fact", you actually have to do it first.....

Bob

[shorty]

Bob,
Please read carefully.

http://www.gatewaytoairguns.org/GTA/index.php?topic=36435.0

I have read it over 10 times. Simple mods. Increased hammer weight, ports opened, and barrel length.

and (me) my 22 synrod to .357/9mm (89 fpe max-for now).

It's ok. The FACTS are there. Do you want a youtube video of my .22 synrod to .357/9mm over the chrony like Tim Hill posts showing a chrony with numbers ??(come on) I got no reason to BS.Tefloncoated has work to the gun already or he wouldn't get the 63 or 65 fpe out of a stock gun unless he was bs-ing.

He can get the barrel,bolt, and mags and can do stock (without porting mods) achieve over 75 fpe with 60 grain + bullets/pellets. You know it and so do I.

First day back and you still remind of my old engineering manager that I replaced 4 years ago (never work and I don't buy it). Give the guy some solid advice. You have been around a long time and I know you read as much as I do along with "tinkering".

[Rdsail]

Shorty,

You most be great by replacing your manager. Very rude comment by he way show very little  from you. I'm with bob on this one. He has to do it and see the results. Measure and get real data.

I'm going through it myself right now with my high power mrod build. Until I built it I could did not know what I was going to get out it. I ended with a max power of 110fpe with 50g slugs.  I theorized that I was going to get 120. But I was not able to.  Granted with a heavier bullet I might get there.

The point. I did not know until I did it.

[shorty]

Rdsail,
Point well made about being rude. I followed your post on your build from day one. I followed the post of the 30 cal. I read most or all of Bob's posts on this site about big bore's,theory,porting ect....Awesome work and documentation guys.

This site has all the information needed to do what Tefloncoated wants. In one case, he can copy (almost) and achieve his original posting question.

I have been wanting to respond to this post from day one of the post. I just don't know why Bob would sway this guy away from the 30 build with everything that he knows and could have possibly suggested things for the guy to get there.

It would have been another great build.......

It kind of aggravates me hence the possible rudeness. Bob knows about the 30 build and your build along with doing his own. He wrote in those great posts. It is what it is.

Call me what you want. This guy posted only 22 times which means he is a fairly new member. He should get only the best information just like all of us instead of this silly cool guy club.

Bob,
Don't get me wrong, I think very highly of your work and all the work you do for GTA (there is a respect). If I can do half of what you have done, I would be doing great.