MarauderAirRifle.com

[Do99ie]

You can learn that in order to obtain greater accuracy from a pellet that particular pellet/barrel combinations require a lot of experimentation in various velocities. Having said that, I finally obtained some really good accuracy from the JSB 33.95 grain pellets in .25 cal at velocities at or over 900 fps. I achieved this by drilling the valve port out to 3/16", using the Tim Hill oversized transfer port and drilling the barrel port to 3/16". I'm also using a heavy hammer spring all the way out and a fill psi of 3000. I've gone well over the 3000 psi limit on experiments (not recommended for safety reasons), but as most of us know, the higher the fill pressure becomes, the harder it is for the hammer to open the valve. So there's a balance that has to be found. Also with this same setup in mind, I've taken the JSB 25.39 grain pellets to well over 1000 fps but accuracy goes out the window somewhere around 950 fps and above. I have the green mountain barrel on my M-rod, but I'm considering a Lothar Walther barrel to see if higher velocity accuracy can be achieved with it. Wouldn't I just love to have an accurate pellet at over 1000 fps? You bet! The best groups I've gotten so far are with the 25.39 grain JSB pellets at around 934-940 fps using the Big Bore Regulator to tether with and keeping the pressure around 2600 psi.

[Motorhead]

Much above 925 ish your going see no gains being drag is so high. What is refereed too as the transsonic region just under being supersonic. It is very well documented that the best accuracy most instances and least wind drift happens in the @ 600 - 850 fps range.
While admittedly many of us shoot upper 8's to lower 9's going faster is a waste of time effort and air !!

[alex2865]

Me personally stay away from lw barrels get a tj barrel ale x

[Do99ie]

Alex 2865:

Saw your post of staying away from lw barrels and have to ask, why? It is my understanding, though by no means correct, that lw barrels are the top of the line in accuracy. On the other hand aren't the tj barrels sold by js air rifles? If so this is the place that never answered my emails requesting information on their products. You can read my post on what I had to say about that. I am, however, interested in knowing your opinion on the lw barrels if you don't mind taking the time. Do99ie

[Motorhead]

FYI ... JSAR has stopped doing ANY outside modifying or offering barrels fitting be it TJ or LW etc ...
Bitch as you will about correspondence issues with JSAR, there focus remains on bringing leading edge PCP technology best they can and as many do have experienced hick ups being a newly formed company.

As too the JSB 33.95 being shot at 900 fps + Personally had no luck doing so in an M-rod Green Mountain barrel or a HW barrel fitted to a WAR WarP carbine that shoots give or take 55-65 ft/lbs in .25 caliber.

Tho have read good results from some in FX liners and some other gun barrels ... test test test like the rest of us if you really want a no BS answer to your Q

[Do99ie]

Motorhead:

I'm using no high tech stuff at all... just a stock valve with the port drilled out to 3/16", the reduced tension spring sold by Hill Air Rifles, a 3/16" I.D. transfer port (homemade), and the barrel port drilled to 3/16". In addition to that I'm using the 15 lb. spring, stock hammer and a 3000 psi fill pressure and the metering screw gizmo removed and two of the grub screws locked in its place. That's it. I have an avg. of 905 fps with 62 fpe. Every now and then I get some weird aberration of inaccuracy that I have yet to figure out: I'll be hitting a 3/4" group at 100 yds like 20 times in a row, in a 2.5 mph wind, and then suddenly for no reason I can figure or guess the shots are all over in a 3" group. Can't say it's the wind, I have some pretty kick as- windicators that are dead on at even the slightest change, and I live in a place where the wind blows 24/7 in Wisconsin. I'm starting to think it might be the tp because I really haven't perfected that yet, but I'm working to resolve the issue asap.

[Barnydaddy]

I was going to stay away from this but..
Using a heavy pellet or heavy bullet for caliber requires a faster twist.
Example: The M-16 used by the military when it was first released had a barrel twist of 1-10 or 1-12.
This was fine for the 55gr FMJ bullets used at the time.
However, when the military started using 60gr (and now 69gr) FMJ bullets, the twist was not fast enough to stabilize the bullets.
My .22-250 Ruger rifles confirm that theory.
Both the 77V and Model 1 will stack 50-55 grain bullets at 150-200 yards all day in a calm wind.
They easily hold four inches at 350-400 yards.
But, if I go to a 60-65 grain bullet the groups double and maybe even more.
Slug barrels for air powered arms are running a faster twist then those barrels designed for pellets of a lesser weight.
My own .25 Gen I Marauder absolutely adores the 25.4 grin JSBs and can do very well with the 27 grain Benjamins.
When the heavy JSBs came out I ordered just one tin because I knew the rifling in the Marauder could not properly stabilize them.
Now, each rifle is different and maybe you can stabilize them in your rifle but I suspect not.
42 foot pounds and 16 shots in a .25 caliber air air rifle is fine for me because I will not be shooting that will require more than that.
Good luck with your testing..

[Motorhead]

Motorhead:

I'm using no high tech stuff at all... just a stock valve with the port drilled out to 3/16", the reduced tension spring sold by Hill Air Rifles, a 3/16" I.D. transfer port (homemade), and the barrel port drilled to 3/16". In addition to that I'm using the 15 lb. spring, stock hammer and a 3000 psi fill pressure and the metering screw gizmo removed and two of the grub screws locked in its place. That's it. I have an avg. of 905 fps with 62 fpe. Every now and then I get some weird aberration of inaccuracy that I have yet to figure out: I'll be hitting a 3/4" group at 100 yds like 20 times in a row, in a 2.5 mph wind, and then suddenly for no reason I can figure or guess the shots are all over in a 3" group. Can't say it's the wind, I have some pretty kick as- windicators that are dead on at even the slightest change, and I live in a place where the wind blows 24/7 in Wisconsin. I'm starting to think it might be the tp because I really haven't perfected that yet, but I'm working to resolve the issue asap.

POI oddities .. likely barrel harmonics if your still fully floated within the front shroud / barrel band. adding a thin o-ring into the gap present, hobby foam etc has done wonders for MANY chasing POI issues with these rifles.

While i see no High Tech stuff ... understand that staying with the factory hammers near 80 gram weight flung by a 15# hammer spring in itself creates some pretty heavy cyclic vibration before the pellet leaves the barrel.

Scott S

[Do99ie]

I like the ideas and subjects you bring up, Motorhead. I suspected you knew your stuff when I first started reading your posts. All the knowledge I have, which ain't much, has been won the hard way. I'm learning, though, and given time I'll know my stuff too. I'm using that heavy spring and hammer because I want the valve to open all the way up. Air ain't an issue for me, having two different 4500 psi compressors and a scuba tank with that Big Bore regulator. I've tried different ideas of opening the valve to a consistent amount different ways, but the only thing that seems to give me a good extreme spread is knocking it all the way open every time. I'm aware of some of the products out there designed to deal with this issue, but I couldn't see spending the money on an iffy idea... especially as the cost of these items is high. Soon I'll be getting a mini-lathe and mini-mill and putting some of those ideas to the test. Until then I got what I got.
I believe what you're saying about the twist rate not being enough to stabilize the pellet. And I have a better accuracy with those 25.4 gr pellets you mentioned, but mostly I shoot or hunt at longer than average ranges and want the fpe the larger pellets offer... plus they're not as effected by the wind as the smaller ones. As for that accuracy issue I mentioned, I finally figured out the problem. I don't clean my pellet rifle barrel as often as some people do, being that it's not a powder burner and doesn't need it too often. But alas it does from time to time, and I've shot a good 10 to 15 thousand rounds since the last cleaning. At any rate, I cleaned it and what do ya know? Yeah, I guess I'm lucky to be getting the accuracy out of the heavy pellets. Have you tried, by any chance, different velocities to see if it matters to your gun? Just a thought. For the best accuracy, I'm shooting them at about 885 fps and slower, depending on the temperature outside.

[Do99ie]

The idea of the twist rate being too slow cannot be the issue in that the Ataman 9mm rifle which gets excellent accuracy has a twist of 1:18... and I suspect that most of the Ataman line does as well. At any rate I did mention that the velocity had much to do with the accuracy and that lower or higher velocities outside the 'sweet spot' tended to cause accuracy to fall off dramatically. Reading stuff is great for general knowledge, but doing is knowledge applied, or learning new knowledge if we're able to connect cause and effect. I only have this one Marauder, which I actually converted over to an Armada because I like the look of it. But having only one allows me to concentrate on making it work great and what needs to be done to care for it well. Another thing I've learned is that the air being pumped into it needs to be cleaned and dried quite well. To that end I run it through an Ingersoll Rand air drier to a storage tank held at 100 psi and then through a series of molecular sieve towers before it goes into the Daystate compressor. This process takes the dew point down to about -100 degree F. I am convinced that absolutely no water condenses in the scuba tank or the pressure tube. Additionally, at the output end of the Daystate, I've installed an activated carbon filter to get out all the oil residue and any smells that may come through. At any rate, this is in preparation for when I finally do buy an expensive air rifle, because I learned the hard way with this Marauder. The first time I took it all the way apart, I was aghast at the degree of corrosion that had occurred inside... both to the tube itself and to the valve end and gauge port assembly. It took a lot of work to restore the tube and I had to replace the valve. There was a good lesson about what high humidity does to the inside of a pressure tube.
I took the gun out today, and although it was fairly windy (3-4 mph) I was able to get about 1 1/2" groups out at 100 yards. It's not the best I've seen this gun do, but I didn't get the 3" group either. Barrel harmonics? Maybe. The one thing I'm really considering is the fact that out here we have real winters, and when it gets cold, say down to 15 or 20 degrees, the air becomes denser and the velocity begins to drop off quite a bit. Knowing that the big 33.95 gr pellets that I like have to maintain a certain velocity gives me the idea that it's dropping off farther that its lower limit. I don't know what the upper limit is because I haven't been able to get them up beyond 925 fps or so. I'll keep working on it, though.