GTA
All Springer/NP/PCP Air Gun Discussion General => European/Asian Air Gun Gates => China/Asian AirGun Gate => Topic started by: darryl on December 28, 2011, 11:18:28 PM
-
I bought this rifle from Mike (to try to keep up with Gary and Jay). I've been trying to calm this rocket down, but I finally heard from Mike that the power adjustment is only for fine-tuning. Well, I've been turning that adjustment screw in as far as I dare, only to see the FPS go up. (Jay and Gary did some work on it for me: replaced the stock valve stem, and cut a slot in the adjustment screw). Anyway, I'm thinking if I just turn that screw in a little more... But here's what I got. I hope you can see it clearly. If not, know this: the lowest recorded of 20 shots is 923FPS. The highest is 998.5 FPS. I'm using JSB Jumbo Heavy 18.13 grain pellets. Start fill is 2700 PSI. end pressure is 1800 PSI. Should I keep it where it's at, and just refill after 20 shots?
darryl
-
What is the intended use? If your goal is power, I would leave it where it is at. 37fpe for 20 shots seems good. Great for hunting. Is it accurate with the 18.13g pellets? If you need a few more shots, you could up the pressure to 2800psi and shoot it down until 1600psi. I'm going to shoot mine for awhile and see if it changes after break-in. I might try a smaller transfer port when I go to fine tune it.
-
Right now there are only 12 shots within 96%. Your going to need to test it near the distance you plan on using it to see if it's throwing accurate pellets at that speed. Some guns will and others won't do it. Like aforementioned, a smaller transfer port might be needed and get you a better shot count too. It may do good with JSB Monsters (Eu Jins can get expensive) and your shot count may go up with heavier pellets like some other fire breathing PCP airguns. Looking forward to the results.
-
I'm thinking the mcmaster-carr spring and a change in the Tport will do the trick, just sent off some 5/16 delrin rod to make some up with different hole sizes, will be interesting to see what you come up with....
-
I'll be sure to keep you all posted. The SW_Ohio Shooting consortium is standing by to assist me. Mike, thanks for the Delrin. It'll be put to good use. I don't think I need almost 39 FPE to be happy. Closer to 30 FPE, and a good shot count (maybe 25-30 within 4%).
thank you all,
darryl
PS if you come up with some other perspectives, let me know. ;)
-
I'm thinking the mcmaster-carr spring and a change in the Tport will do the trick, just sent off some 5/16 delrin rod to make some up with different hole sizes, will be interesting to see what you come up with....
It seems like the lighter spring (mcmaster-carr) would move the sweet spot down to a lower fill pressure and reduce the speed some. Power would be reduced but shot count would stay about the same.
I'm guessing that a smaller transfer port will reduce the power. And should increase the shot count about in proportion to the power reduction. And would leave the sweet spot at approximately the same pressure.
Do I have this right?
-
what can be done to flatten that curve? Doing so would lessen the Sd, and maybe conserve air usage. If I could get a flatter curve, and 30 shots at 30FPE versus the average of 37FPE I have now. So that's my goal ( with 18.1 grain pellets)
A) A flattened shooting curve (with the peak FPS in the middle of the curve)
B) 30 shots per fill (a flatter curve would put more shots within 4% of the highest shot, and may also be reflected in greater accuracy)
C) 30 FPE Just because it's a nice round number.
I didn't see anything in the "book" that points me in that way directly. Can someone break it down? Ya can't fool me 'cause I'm too stoopid! ;D
darryl
-
Funny thing, I've noticed mine experiences some valve lock at 3,000 psi, but works perfectly at 2,700 psi.
-
yep, I ran into that too, but at a bit less than 3k-PSI. I can get by at 2.8K-PSI just fine. Guess i'll have to mod this one to cool it down a little. 998FPS with an 18 grain pellet just don't seem right.
-
It'll probably be a combo between the hammer spring and the smaller transfer port. I'm guessing the hammer spring having less tension will flatten the curve (along with cutting velocity) and then the smaller transfer port will drop some velocity while improving shot count. It'll end up being the bee's knees when you're done. Good luck.
-
... I'm guessing the hammer spring having less tension will flatten the curve (along with cutting velocity) and then the smaller transfer port will drop some velocity while improving shot count. ...
I was thinking that the lighter spring would require a lower fill pressure in order to allow the weaker spring to push the valve open. Valve lock would occur at a lower pressure than it would with the stock spring. So your fill pressure would have to be lower. Less total pressure means less total energy available. That seems counterproductive if you are trying to increase the number of shots. Wouldn't the smaller transfer port be the solution for increased shot count? Same total energy available+less energy per shot = more shots. I have not tried it yet. It just seems logical to me.
-
You may be totally correct. I'm just going off what I did with my Marauder. Decreasing the hammer spring tension lowered the velocity and increased the number of good shots dramatically. The hammer stroke was maxed out, which may be the same on this rifle. Once I had what looked to be good strings of shots, I then opened the transfer port to get the velocity back up (except he'll be putting in a smaller TP to decrease velocity and up the shot count. As far as I know, they all work together as a combo. I'm always willing to learn.
-
So is an 18.1 grain pellet @998fps too wasteful if it results in only 20 shots? I really need to read "the book". Just haven't gotten around to it yet. Been obsessing on the Timberwolf, and waiting on the shroud/riser kit from BigEd. Also, Mike Melick sent me a length of Delrin to paly with making some different TPs. My friend (our friend) Gary has made some customs TPs for me to try as well. I should focus on the end result I want for the B50:at least 30 shots with a low Sd, and 28FPE. Is the McM-Carr spring much softer than the stock spring?
darryl
-
That 998fps is up there in that area where few rifles do their best work. I would try it at some range, at least 40-50 yards and see what it does accuracy wise. You'd then want to test it turned down and see what you're giving up. What kind of shot strings have others got with similar weight pellets turned down to about 30ft/lbs? Most say the 18.1 grain JSB is best between 800-900fps.
-
Good advice from coax. If it shoots accurately at 998fps, you may be ok. As I said before, you could then up your fill pressure and shoot it down to a lower pressure to get your 30 shots. Sure, your SD would get worse. But something to consider: SD (velocity variation) has less affect at higher velocities. So even though the SD is worse, you can possibly hold a tighter group. It becomes more apparent at longer ranges.
PS - I just checked it in Chairgun. A 100fps spread group between 1000-900fps gives a 1.16 inch trajectory variation at 50 yards. But a 900-800fps group gives a 1.63 inch trajectory variation.
-
I'll probably tune it down a bit as you guys suggest. I'm not hunting anything that needs 38FPE for killin.