GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: tefloncoated on June 04, 2015, 11:34:22 AM
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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!
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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
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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.
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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....
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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
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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?
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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
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Gotcha!
Do you think that's a limitation of the marauder valve design/efficiency? Size of the reservoir?
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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
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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!
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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
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I stand corrected....
Bob
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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
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Looks like about 30 shots within a 4% ES....
Bob
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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...
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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 (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 (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.
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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
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Bob,
Please read carefully.
http://www.gatewaytoairguns.org/GTA/index.php?topic=36435.0 (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".
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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.
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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.
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Shorty,
I would not consider change my mrod to .30 when it was shooting at 45 even 50 fpe. I think at that power level the pellet moves too slow for my liking. It would not be worth it to me. But if the post was about heavily modifying a mrod that would be a different story. I think at that power level the pellet moves too slow for my liking.
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Can an MRod be made into a good .30 cal?.... probably, maybe even a great one, if you use a custom valve?.... Will you be happy with a 45 FPE one converted to .30 cal without changes, as requested by the OP?.... Not in my opinion.... I suggested what power levels might be available without major changes, you have a different opinion.... However, until you do it, it's just an opinion, so please don't call it a fact, that is misleading....
If you took the time to read my detailed response on what the OP could expect, I gave him 3 different power levels, with 3 different levels of modding, from 57-94 FPE.... If you think that is trying to "discourage" him, then so be it, I was just trying to answer his question as honestly and completely as I could, not just say "go for it, 100 FPE is easy".... cause it ain't.... If it was "easy", your .357 would be there already....
The stock MRod valve is severely limited in what you can do to it by the diameter of the exhaust port, and it's proximity to the back inside wall of the valve.... If you're happy with a 90 FPE .357 cal, then more power to you, but I wouldn't consider it a successful conversion until you doubled that.... Lobbing pellets downrange at 700 fps just isn't my bag, nor would I recommend it to anyone....
Bob
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I completely agree with Bob.
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EXACTLY what BOB said. You will need to get that .30 cal pellet to 880-900 fps for it to be stable and accurate(jsb exact 44.75) and thats no guess thats a fact based on over a year of testing so that means no less than 75fpe but the sweet spot is from 80-90fpe with said .30 cal pellet and if your shooting bullets you better raise that to 100fpe to get the full effect of stability from barrel twist and bullet coef.
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Just buy a FLEX .30 and the job is done! Lol
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I am satisfied that I got 90fpe with an Mrod valve and 16.5" barrel. That's pretty good for a first time around for a big bore attempt "with that platform-and barrel length". Double that, most likely not going to happen without alot of help.
Don't think I am not trying to hit 120+. I just picked up a 21" barrel and increasing the hammer to 120 grams along with porting to .2". I just can't stop running chairgun to see if 800fps is so much different than 700 fps in regards to retained energy and accuracy. It's only a 50 yard gun.
As for the 30 cal Mrod conversion. Here is one of the last posts on strings:
847 2800
841 2600
??? ???
937 2400
928 2300
803 2200
793 2100
780 2000
(Rdsail- this might be an avenue for you to hit 150 fpe at a respectable 850/900 fps) at or below transonic speed for best accuracy.
Since tefloncoated ported already we have no idea what his max fpe/fps is. if I/we had to guess he can push the 25.39 to 70 fpe with the .156" porting on the 25.39-25 cal. With a 41% "or so" increase in cross sectional area from .25 to .30, increases the the "potential" power (fpe) to approximately 98 fpe using a proportional hammer weight/stroke/spring force.
Easy, heck yes. Buy the barrel and bolt, melt some lead and form it to the hammer, replace the HT with a set screw, and get a 12lb spring. If you want more, drill out the valve exit port to .19" or .2", make or get a polymer transfer port at .19" or .2" and drill the barrel port to .19" or .2". Run a 60+ grain bullet/pellet and your over 100 fpe all with a hand drill and your favorite hardware store.
Easier than that, buy a WAR valve, and port the barrel. Done....
Why it's not easy for me, cause I am cheap,I work 10 hrs a day, have 2 kids, a wife that "completely does not understand" the obsession. And Lastly, when I was posting about what I was doing for my .357/9mm Mrod build, the guys that know their stuff pretty much said it was a waste of time and you will not get the numbers up to their expectations. There was absolutely no advice on how to achieve the goal. I do thank QV Tom though for my "safety"manufacturing techniques. Thank you.
I sure had alot of "maybe a 30 would be better or .257"along with Travis saying "give me a call".
For what it's worth, Travis was the only big bore tuner/builder to entertain my build by asking me to give him a call to discuss. Believe me, I still have only one call and I am going to choose it wisely.
Thanks Travis.....
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937 fps with 45 gr. roundball - 88 FPE, and that string only has 3 shots within a 4% ES.... and the gun was significantly modified from what the OP has.... Thanks for making my point....
Bob
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Bob,
Your welcome.
You have no idea what that guy wanted now since you discouraged him not to do it.
From 65 fpe to 88 fpe is an increased fpe of over 35% of his existing gun without the help of us.
How many +70 fpe Mrods do you read about ???? There's not many of us.
I would also like to add that "and you know too" that 30 cal has much heavier than 45 round balls that seal the barrel better and make much more energy than what your trying to point out at greater velocities than 800 fps.
Bob,
It's been a great discussion with you. I think all that is reading the post should have a nay and say. There's no right or wrong but the thinking has been done.
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Love the reading of the MAD modders. So much tallet over here for a bunch of KIDS. ROTFL
THANKS ALL for swaying me over to the DARKSIDE😈😉
FANG
JUNKYARD AIRGUN'S
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oops wrong post.
DT