Benjamin Maximus power Mod?

[Aged]

I regularly shoot pellets at 950fps with other guns and there's no problem.
Anyway the topic is about getting the Max to shoot 13.43gr .177s at 950fps.
I believe it can and that's my quest.

[rsterne]

13.43 gr. pellets at 950 fps is almost 27 FPE.... That will be a challenge in .177 with a Disco based platform at 2000 psi, IMO.... In .22 cal, much easier because of the 54% increase in pellet base area for the air to push on, resulting in 54% more force available to accelerate the pellet....

Transonic starts at about Mach 0.8 (900 fps), and you are correct, that is not an accuracy issue per se, it will depend on the pellet and twist rate at 950 fps.... I use 950-960 a lot myself, with many good round-nose pellets such as the JSB Exact series....

I would suggest you plot velocity vs. preload at 2000 psi and see what you get.... If the velocity is on a plateau, increasing the hammer strike will not give you more velocity, only use more air....

Bob

[Aged]

That would be a problem with the maximus. The spring is within 1/8" of binding when cocked. What I've already tried is adding a spring inside the stock spring (counter wound) with some encouraging results but not enough. I like K.O.'s idea of making an extended rear cap to take a longer heavier spring so I could then use a preload adjuster if I can make one with a hand drill and a hacksaw lol.
Besides a stronger hammer impact I could open up the valve seat. They also sell high flow valve assemblies for the disco but I wonder if it would work in the max.

[Back_Roads]

are their not instability issues when reaching sonic speeds with jets not having the right wing sweep etc , same applies to projectiles.

[rsterne]

You need to be careful opening up the ports in a .177 cal, as going too big in one place without matching the areas can lose performance instead of gaining it.... If you don't make the barrel port oblong, the stock barrel port on a Disco (0.132") is almost as large as possible without causing loading problems with the pellet.... With care, you can go to 0.140", which is the same diameter as a stock Disco transfer port.... Some small gains can be made with careful port work, but nowhere near as much as you can gain in a .22 cal or .25 cal where the stock ports are too small....

Bob

[Underwhelmed]

Just a side note, but doesn't the Maximus come with a different valve than the Disco? I thought I recalled reading that here when they first came out?

[Aged]

I also read the valve was changed for a better shot count. Too bad Crosman hasn't released a schematic parts list yet for the max. I'm new to Benjamin products but when I remove the valve assembly on the max today I can compare it to the parts list diagram for the disco and let you know what I find.

[Doug Wall]

I found that the 0.045 spring on my Maximus to be really hard to cock! I wouldn't even consider making it harder. Opening up the air path would be your best bet if you want more power. The Maximus is really not the best platform for a power gun. The air tube is really too small for high power with a decent shot count. For a hunting gun, where you don't really need a lot of shots, it might be OK, or you could plan on carrying a "Guppy" tank with you.
I actually went slightly the other way with with a 0.042 spring (much easier to cock!) in my .177. I'm going for 900-950 fps, with the best shot count.

[Aged]

You're right Doug the Maximus was a poor platform for a 27fpe gun in .177. Everything I read steered me to believe it was a Discovery economy model
I'm not done yet but I might have to lower my expectations and 900fps is a nice round number.
How did the 0.045" and 0.042" spring affect the power compared to the original? If the porting doesn't achieve my goal I will build an extended rear cap and use a heavier longer spring and adjuster to drive the hammer harder. Being longer should make it a little easier to cock.

[Bicycleman]

I also read the valve was changed for a better shot count. Too bad Crosman hasn't released a schematic parts list yet for the max. I'm new to Benjamin products but when I remove the valve assembly on the max today I can compare it to the parts list diagram for the disco and let you know what I find.

Last word I had from Crosman was that the parts lists/diagrams would be available near the end of this year.  They indicated that the parts lists are usually introduced six months after the product is made available.  Some parts may be available now - but probably not all!??

[Doug Wall]

You're right Doug the Maximus was a poor platform for a 27fpe gun in .177. Everything I read steered me to believe it was a Discovery economy model
I'm not done yet but I might have to lower my expectations and 900fps is a nice round number.
How did the 0.045" and 0.042" spring affect the power compared to the original? If the porting doesn't achieve my goal I will build an extended rear cap and use a heavier longer spring and adjuster to drive the hammer harder. Being longer should make it a little easier to cock.

The 0.045 spring WAS the original! Cocking was difficult. Velocity started about 1000 fps, and just dropped off for about 20 shots to about 1000 psi (didn't do a lot of velocity recording). With the 0.042 spring, the cocking is much more comfortable. Velocity starts at about 910 fps, goes up to about 950 fps, and back down to 900 fps after about 40 shots. The curve is pretty flat for the middle 20 shots. I'm still tweaking my FFH to get a long, flat shot curve. I'm not sure about a longer end cap. The cocking stroke is only about 3/4", and I don't know that a longer compressed spring will give you any more, or be easier to cock, than a shorter spring. If you go heavier, you might need a crowbar to cock it.

[56S]

Poof that hammer/bolt cavity with Moly bullet lube.  That and pull the bolt back with your index finger while pressing on the endcap with your thumb.  Reduce friction and improve technique worked for me.

[Doug Wall]

Been there and did all that. Still very hard to cock. I prefer the 0.042 spring. Crosman introduced this as an entry level PCP, to attract new shooters to that side of the sport. If they want to include kids as part of the equation, the cocking is too hard!

[56S]

I would love to have another Synco in 177 tuned to shoot 7.9 gr pellets at 950.

[Aged]

I got a new hammer spring today from Traker for the maximus. Heavier guage and longer than the original but less coils per inch so it won't bind before cocking.
It works great but is a bit of an air hog as Bob predicted, so I'm not going to mess with the valve seat. The 2500psi fill is cheating a bit and I do it at my own risk - it was an easy way to get the extra power I wanted. I originally bought the gun to save on scuba tank fills since I don't like filling my Hatsan after the tank is down to 2500psi.
I had a graph showing the string of shots but I can't figure out how to include an image on this site.
Then I tried to Attach it but it came back saying it was too large.
Anyway I'll give you the numbers using Jsb 13.43gr .177 cal. pellets.

1-918fps    6-942     11-932        Average velocity  930fps         Starting pressure 2500psi
2-922        7-946     12-930        High velocity       942fps          Ending pressure  1500psi
3-926        8-936     13-926        Low velocity        901fps          New spring dim.  0.3" OD
4-941        9-933     14-919        Extreme spread   41fps/4%     Wire diameter     0.05"
5-934       10-943    15-901        Muzzle energy        25fp          Length 2"        10 turns/1"

                       

[rsterne]

Please do not assume that the Maximus uses the same quality steel, or even dimensions, as the Disco tube.... nor that it can be overfilled past the recommended pressure.... The valve screws in the Disco should be replaced above ~2000 psi.... AFAIK, nobody has done any testing with the screws in a Maximus.... You are in uncharted territory here.... don't fall victim to your own enthusiasm and/or ignorance....

Bob

[Aged]

I did do it again. I have read so much about the Discovery that I am subconsciously making decisions based on those facts.
Thanks for the heads up.
 

[Aged]

Same gun filled to 2001psi, ending at 1400psi, 13.43gr pellets. Looks like I'm going to have to enlarge and equalize the ports to up the velocity. I'm sure I'll lose more shots per fill but that's what I want. I wonder if I can get a large air bottle attached.

1  850fps    High Velocity 905fps
2  856        Low Velocity  867fps
3  863        Average Vel.  877fps
4  868        ESpread    38fps/4%
5  865        Muzzle Energy   23fp
6  876
7  905
8  903
9  897
10 890
11 884
12 883
13 880
14 869
15 877
16 867