250Z 250Z tuning, mainly slugs.

[Pumacarl]

I think I've got things back where they should be. Fps consistency is much closer.
Now I need to figure out the dwell and how to dial it down. It sounds, to my untrained ear, that the valve is still open just slightly past the point the slug is out.

I don't know, in these guns I think the only easy way to beat dwelll is to lessen hammer inertia and maintain your force, which means you need to increase it's flight speed by massless power, in other words a stiffer spring. Combine that with increased pressure, and the valve shuts faster. So, if you really wanted to experiment with reducing dwell you could try lightening your hammer and upping your spring rate along with running your reg at 2900psi. You can really go crazy if you want to, if so, please document everything. I did all this for my Gauntlet when they first hit the market. It was very interesting. That was when I realized that unless I was going to run heavy ammo (and I wasn't) that the heavy hammer and it's dwell was a major loser for me trying to get more speed and efficiency and a tighter es. So a lot depends on what weight of ammo you want to run too. Like I've said before, everything matters. Unfortunately, doing all this will usually make your gun a one trick pony, but if it's a good trick, that's a good compromise.

This is why the people who really love tuning and its benefits get Impacts. You can do all this externally and quickly.

 

[Bladefin]

The trick I want for this pony is a 30gr slug shooting as flat as possible out to 70ish yards. At 960fps it's hitting 60fpe.
With the limbs on all the tree's I don't want a heavy arc.

Now I'd just like to quiet it down again little. It's very close to 3000psi and the groups are close. I'll experiment with the hammer springs and with/without the extra weight.

With the second one I have I can make it a multitrick pony. Or send it off to be a test bed for bigger and better things.

 

[Pumacarl]

The trick I want for this pony is a 30gr slug shooting as flat as possible out to 70ish yards. At 960fps it's hitting 60fpe.
With the limbs on all the tree's I don't want a heavy arc.

Now I'd just like to quiet it down again little. It's very close to 3000psi and the groups are close. I'll experiment with the hammer springs and with/without the extra weight.

With the second one I have I can make it a multitrick pony. Or send it off to be a test bed for bigger and better things.

That's really good to know what you want. That is the hardest part for some, they want their gun to be able to do it all, and few can. Those that can, cost a lot, and are complex.

 

[Cantona256]

I think in this case the lightening of the valve return spring makes no sense since the HS pushes the poppet into the plenum. The proposed pressure drop that would necessitate the light valve return spring is all happening downwind from the poppet. I didn’t really think about it until now but the only way a lighter poppet return spring makes any sense here is if you already have a plenum installed and thus have decreases the reg pressure significantly.

lol in fact, if you want less dwell the exact opposite is what makes sense here. Heavier valve return spring so the valve closes faster. Especially considering the limitation in the stock on how far out you can take the hammer spring tension screw out.

 

[Pumacarl]

Even though this gun has a small plenum, it is that air pressing on the valve. Even though the hammer is resting against the valve the force is cumalative. Having a stronger valve spring just makes it so that your hammer has to hit harder. The air pressure is always what closes the valve under pressure, the spring can help, especially if you haver a heavy hammer, but in this case I advocate for a lighter one, hitting harder. I think there is less dwell this way then using a heavy mass hitting a tightly sprung spring. Just the energy needed to crack that poppet and defeat that spring is taking more time and involves more inertia than hitting it fast and light with little resistence. In my gun my hammer does not rest on my valve, I have mine in free flight and use a twin spring system. I don't even need a valve return spring except to hold it in place when I air down.There are different ways to do this stuff. Like we dicussed before, I tested this stuff out before with my Gauntlet just to read later in Bob Stern's articles that he already did all the math and ran the tests with his guns. The only thing that would change this significantly is if you were trying to shoot heavy for caliber projectiles because the system usually isn't balanced for that at all. Try everything, I have tried quite a bit. I don't like heavy hammers, probably because I don't run any heavy for caliber projectiles in anything.

 

[Bladefin]

I'm not going to touch the valve spring, at least not any time soon. I'm hopeful the plenum will be the answer. I'm not an expert on fluid dynamics and have just a basic grasp of physics. The extra volume of air at pressure might be what closes the valve faster due to the lowered momentary drop in pressure when the valve opens.

I'm not shooting out in the middle of nowhere, there are houses all around me. So I need to get the report down a few decibels. Removing the slug kit has helped some and 1.5 turns in has the fps back in the 960's.

Also, Barra changed the design of the hammer spring tensioner in the latest batches of guns. I thought I took pics when I had it apart but I didn't. Unfortunately it is not something that can easily retrofitable. I haven't tested it yet but with it you will be able to back the tension out further with it for a larger adjustment window. The downside is it will have to be threaded back in to take the stock off.

 

[Cantona256]

Even though this gun has a small plenum, it is that air pressing on the valve. Even though the hammer is resting against the valve the force is cumalative. Having a stronger valve spring just makes it so that your hammer has to hit harder. The air pressure is always what closes the valve under pressure, the spring can help, especially if you haver a heavy hammer, but in this case I advocate for a lighter one, hitting harder. I think there is less dwell this way then using a heavy mass hitting a tightly sprung spring. Just the energy needed to crack that poppet and defeat that spring is taking more time and involves more inertia than hitting it fast and light with little resistence. In my gun my hammer does not rest on my valve, I have mine in free flight and use a twin spring system. I don't even need a valve return spring except to hold it in place when I air down.There are different ways to do this stuff. Like we dicussed before, I tested this stuff out before with my Gauntlet just to read later in Bob Stern's articles that he already did all the math and ran the tests with his guns. The only thing that would change this significantly is if you were trying to shoot heavy for caliber projectiles because the system usually isn't balanced for that at all. Try everything, I have tried quite a bit. I don't like heavy hammers, probably because I don't run any heavy for caliber projectiles in anything.

Yep I completely agree. It’s what I’ve been saying since the beginning. I think this tune works because of high pressure at the reg, a heavier hammer weight with a relatively weak spring, lubed up incredibly well. It hits the valve hard and fast but with very little “torque” aka almost no preload. The valve return spring and high pressure on the opposite side close that valve up super quick. The extra long barrel forces that air to work harder to push out the slug and reach equilibrium.

I’m having the same issue now with the EQ. The hammer spring feels like something that should be on an M1 Abrams suspension … but with a 70cc plenum you need it at high pressures. But the line between perfection and “why does my group look like like cross-eyed shotgun make this?” Is super fine. Haha it’s okay though… it’s not like I’m known for obsessing over tiny little details until I feel like I’m gonna pull my hair out.

 

[Cantona256]

I'm not going to touch the valve spring, at least not any time soon. I'm hopeful the plenum will be the answer. I'm not an expert on fluid dynamics and have just a basic grasp of physics. The extra volume of air at pressure might be what closes the valve faster due to the lowered momentary drop in pressure when the valve opens.

I'm not shooting out in the middle of nowhere, there are houses all around me. So I need to get the report down a few decibels. Removing the slug kit has helped some and 1.5 turns in has the fps back in the 960's.

Also, Barra changed the design of the hammer spring tensioner in the latest batches of guns. I thought I took pics when I had it apart but I didn't. Unfortunately it is not something that can easily retrofitable. I haven't tested it yet but with it you will be able to back the tension of further with it for a larger adjustment window. The downside is it will have to be threaded back in to take the stock off.

Huh that’s interesting. Barra switching it up on me the tricky devils.

 

[Pumacarl]

Huh that’s interesting. Barra switching it up on me the tricky devils.

I really wonder. Usually nobody changes anything unless they have to. I wonder if SPA just did this on their own for some reason that we'll never know?

 

[Cantona256]

I really wonder. Usually nobody changes anything unless they have to. I wonder if SPA just did this on their own for some reason that we'll never know?

Didn’t @Bladefin say you have much more of an adjustment range with the new design? That’s cool but I am really curious what feedback that have gotten to motivate the change.

 

[Bladefin]

Didn’t @Bladefin say you have much more of an adjustment range with the new design? That’s cool but I am really curious what feedback that have gotten to motivate the change.

I was pretty surprised when I saw it initially. I haven't messed with it a whole lot yet. I'll try to in the next few days.
From what I see with it, the spring is the same diameter. The original is a little shorter, could that have come from use? The internal lug should be able to be threaded in further than the original and also backed out further to the point that contact with the spring would be limited when uncocked.

The gritty sear is killing me so I will be pulling that out soon the stone it. When I do I get some better pics for you all.

 

[Cantona256]

I was pretty surprised when I saw it initially. I haven't messed with it a whole lot yet. I'll try to in the next few days.
From what I see with it, the spring is the same diameter. The original is a little shorter, could that have come from use? The internal lug should be able to be threaded in further than the original and also backed out further to the point that contact with the spring would be limited when uncocked.

The gritty sear is killing me so I will be pulling that out soon the stone it. When I do I get some better pics for you all.

Heck yeah bro thanks for the update.

 

[Cantona256]

I was pretty surprised when I saw it initially. I haven't messed with it a whole lot yet. I'll try to in the next few days.
From what I see with it, the spring is the same diameter. The original is a little shorter, could that have come from use? The internal lug should be able to be threaded in further than the original and also backed out further to the point that contact with the spring would be limited when uncocked.

The gritty sear is killing me so I will be pulling that out soon the stone it. When I do I get some better pics for you all.

Any update on the plenums?

 

[Bladefin]

Any update on the plenums?

The fabricator keeps giving him the runaround. The date to get started keeps being tomorrow, tomorrow. He said the company has been great for completion & delivery up until this.

He also said he will be refunding next week if he hasn't heard they are shipped by then. If that ends up being the case he will either have to find a new vendor or wait until this one gets to it.

 

[Cantona256]

The fabricator keeps giving him the runaround. The date to get started keeps being tomorrow, tomorrow. He said the company has been great for completion & delivery up until this.

He also said he will be refunding next week if he hasn't heard they are shipped by then. If that ends up being the case he will either have to find a new vendor or wait until this one gets to it.

Sounds good. Thanks.

 

[guitarplaya39]

In my gun my hammer does not rest on my valve, I have mine in free flight and use a twin spring system.

Any details on how you did this? Can you still adjust the HST with the regular adjustment screw?

 

[Pumacarl]

Any details on how you did this? Can you still adjust the HST with the regular adjustment screw?

I did it by cutting the factory spring so that when the hammer spring adjuster was back and flush to the receiver, it was not touching. Then, I added a second smaller diameter spring inside of the main spring. To adjust using this setup, I keep the smaller spring a little longer and cut it back little by little, and testing. If I go too far I replace the spring with another at the last good length. Sometimes, like on my Marauder, I did the same thing but I also played with the length of the bigger spring too. I must have taken that gun apart 20x! The other thing that I did to the mrod was to back out all of the adjustment screws before doing any of this so that the gun could never go out of adjustment. A couple of years later and the gun always shoots the same. It is a real pain to do, but you only do it once. The trade off is that it is only setup for one projectile. If you are going to do something like this you have to be fairly certain about what you want to shoot out of it. I went for slugs, between 20-23gr, and if I want to do anything else I'd have to start over. I had also settled on a pressure to use first too, can't play with that after the fact either. In both cases I ended up with guns that do exactly what I wanted, and that don't go out of adjustment, even if I take them apart. If you like to play with different types of ammo or change power settings, this is not the way to go though.

 

[guitarplaya39]

@Pumacarl Thanks for the info!
I still like to play with different ammo and power settings, so I'll have to try and find another way to make an HDD. Goal is to find settings/ammo for pesting/plinking @ 30-50yds with pellets with the ability to crank her up for heavy slugs at 100yds occasionally. Slow process so far lol.

 

[Cantona256]

@Pumacarl Thanks for the info!
I still like to play with different ammo and power settings, so I'll have to try and find another way to make an HDD. Goal is to find settings/ammo for pesting/plinking @ 30-50yds with pellets with the ability to crank her up for heavy slugs at 100yds occasionally. Slow process so far lol.

A dual pellet/slug tune is hard… @Northeastbeast is the man to talk to about it. He even made a video about it… my tune lets me shoot 30-32gr Franco slugs with no adjustments out to 100y. But I have a 75y and 50y zero saved on the Zulus so I keep the windows tight and all 3 of those slugs are moving between 970-990fps.

 

[Bladefin]

So, after not having a good time I did a bunch of reading then went back to the basics. On the original 250 I dropped the psi down to 2000 and started shooting slowly with the butt stock off. At that low a pressure every weight slug I tried had a speed drop when I tightened up the hammer. It didn't take much of a reg increase to see some positive results with the hammer, I'm at 2100 and about 3/4 turn in on the hammer. It's not only shooting much quieter but the groups are much tighter. Not same hole yet, but less than moa at 50 yards. I think I have had that ah ha moment for real today.

I'll tinker with the pressure and hammer some, as long as I have one of the two on in the wee hours of the morning when I'm half asleep. The yotes were back last night and I'm ready for their tuchuses now. I'd like to thank @Cantona256 @Pumacarl & @Airgunandy89 for their help.

@Cantona256 the plenums should have shipped or are going out tomorrow to us.