250Z 250Z tuning, mainly slugs.

[guitarplaya39]

In researching the topic a bit more, it seems that the heavier hammer (with that added weight from the kit) requires more energy to increase the lift of the valve due to the lower velocity of the heavier hammer. The valve/poppet only needs to partially open before the air flow rate maxes out, therefore more momentum is required with a heavier hammer to increase lift, which in turn increases dwell time as the valve travels back and forth.
Theoretically, more hammer spring preload would be needed to compensate for the added weight.
I hope this makes sense... it does in my head

 

[hameditor]

I think what you new pcp guys are doing with your .25 250z's is pretty amazing. You're getting a lot of performance out of a rather limited platform. This is probably going to be the most fun you have in the sport, trying out new stuff (to you) because you don't know not to try. None of of it is a waste of time if you're having fun. And you only remember what you did, not what you thought about, especially if you screw up. Good times.

Agreed! Wise words indeed

 

[Bladefin]

I'm going to try adding a good amount of spring tension and see what happens. I'm hoping the fps will increase and I can drop the pressure some.

 

[Pumacarl]

In researching the topic a bit more, it seems that the heavier hammer (with that added weight from the kit) requires more energy to increase the lift of the valve due to the lower velocity of the heavier hammer. The valve/poppet only needs to partially open before the air flow rate maxes out, therefore more momentum is required with a heavier hammer to increase lift, which in turn increases dwell time as the valve travels back and forth.
Theoretically, more hammer spring preload would be needed to compensate for the added weight.
I hope this makes sense... it does in my head

I went down this road when I started too, just to find out that Bob Stern had already done it all and tested everything and documented it. His archive of knowledge over on the GTA forum is good reading, if you haven't done so yet.

To your point above, yup. I found, through my own testing, but later found out that Stern already came to the same conclusion, is that in the limited airflow enironment of a 30fpe .22 you are better off using a heavier spring, than adding mass. It opens and shuts things faster w/o excess dwell. Now, in a 65fpe .25 things might be different, the porting comes into play too. Everything matters, experimenting is fun anyway.

 

[Pumacarl]

I'm going to try adding a good amount of spring tension and see what happens. I'm hoping the fps will increase and I can drop the pressure some.

I will take a guess. You will overcome the bounce but still be wasting air and you will only get a small gain in speed. If it's accurate doing this is anyones guess.

 

[Pumacarl]

I think that if you want to shoot a lighter slug then you should just drop the reg pressure and balance the hammerspring to that pressure and I wouldn't use the weight on light slugs, but that's just me talking, I don't have a .25, try everything.

 

[Cantona256]

I noticed that when I backed the hammer out the groups got better, out past flush and within fractions of a mm from the stock. I figured the slug kit was just too much spring for the 30gr slugs I'm shooting. So I pulled the kit spring out and put the stock on back it leaving the weight. The hammer is flush and the 1st 3 shots were dead on. Two making a large hole and one within a 1/2".

The thing is this made the gun a lot louder, like too loud. Should I keep turning the spring in and see if it quiets down some and what that does to the groups? The fps is in the same range to slightly higher 954fps to 968. I haven't fired enough to get a solid range of speeds.

Is the loudness due to too much air behind the slug? Should I drop the psi before messing with the spring?

I’m not sure why it’s louder. I had the exact opposite experience. It actually got quieter. My gun was super loud when I had the hammer spring turned in.

 

[Cantona256]

In researching the topic a bit more, it seems that the heavier hammer (with that added weight from the kit) requires more energy to increase the lift of the valve due to the lower velocity of the heavier hammer. The valve/poppet only needs to partially open before the air flow rate maxes out, therefore more momentum is required with a heavier hammer to increase lift, which in turn increases dwell time as the valve travels back and forth.
Theoretically, more hammer spring preload would be needed to compensate for the added weight.
I hope this makes sense... it does in my head

That would make sense if he had turned in the hammer spring but he has it backed out almost as far as it will go.

 

[Pumacarl]

I’m not sure why it’s louder. I had the exact opposite experience. It actually got quieter. My gun was super loud when I had the hammer spring turned in.

Weird huh? I saw a post somewhere, where some University kids in Pakistan were using an oscilloscope to monitor the valve opening and closing with relation to pellet travel down the barrel. I don't know the science but it was very cool how they were tuning real time. Without equipment like that it takes a lot of trial and error. I once stumbled upon a quiet spot when tuning my .30, really spooky. I wish I could find that again.

 

[Cantona256]

I have the reg at 2800/2850 and the exact same set up. Factory spring with the slug power hammer weight. Unless the actual mass of the weight is different it shouldn’t be different than mine.

1) You will get more efficient air usage when your ports are matched up. I initially went with 4.4mm exhaust port(thimble valve) then went up to 4.8mm- this is still the best size for caliber but the pellets don’t load right. Needs a double port…. All of those changes gave me some minor gains but it’s about a month ago when I upped the transfer port to 4.4mm and put a new 4.4mm exhaust port that I got the performance I’m seeing now. As I mentioned the other day my 32gr are chrono’ing at around 980… Also I shoot the 30’s and 31’s with the same settings. Not change at all except a zero profile on the scope.

2) my simplest theory is kind of counter intuitive. I tested a with and without the hammer spring weight a couple months ago and the HS is weak. It took me 5-6 turns to get the gun to the same speed (same reg pressure) as with the weight in just flush…. My setup works because I’m running high pressure but very little dwell. When I started running it this way the whole gun got noticeably “snappier.” The metaling ping of the brass weight got quieter and the gun got significantly quieter. My main hunting buddy commented on it the very first time he heard it.

So if you’re getting hammer bounce it could be that you just need to up the reg another 100psi or so. It’s hard to read on the gauge but I’m pretty close to 3k without touching that line. More pressure in front of the poppet will help the valve not get overpowered by the HS weight.

3) the factory lube just sucks. At this point I have re-lubbed the entire gun with reg butter. Especially the valve and hammer spring assemblies. Everything on the gun moves smoother than when I got it…. It could be you’re getting some stickiness somewhere in there. It sounds like your valve is being held open too long for sure. It just might not be from the side you think…

4) if upping the reg doesn’t work the rabbit chase begins…. Is the poppet cracked? Or misaligned?

Is there some debris in an o-ring causing a weak seal?

Check the valve return spring that it’s properly aligned and not compressed when NOT under pressure. That could’ve gotten bumped or pinched when you took the reg out. The way you have to load it back in there is kinda awkward.

Finally make sure the thimble valve is aligned perfectly with the block. It needs to point straight down and if you have touched the valve make sure the transfer port is straight up… if they aren’t aligned the gun does some super weird things. Ask me how I know .

I know you’re frustrated right now but we’ll get it figured out. Doing more troubleshooting sounds like a bummer as does the prospect of taking the gun apart again. But it’s worth it to have the gun perform exactly how you want it to.

Sorry for my late responses but I was up in the mountains getting after some rock chucks… not to brag but I was really proud this weekend because a couple of my powder burner friends were looking at me different when I got the biggest one of the day, the furthest away and the cleanest kill all in one. The other two were shot with .223 and spent a lot of time flopping around and one almost made it back into her whole. I put a Franco right in its trachea at 81y and she dropped a foot or two onto another log and goodnight forever… I’m not some amazing hunter or shot. The gun is just crazy accurate and I had the best ammo for the job because of good penetration with expansion without over-penetrating. My point is just that if you wanna get really fussy over the gun the work will pay off.

 

[Cantona256]

Weird huh? I saw a post somewhere, where some University kids in Pakistan were using an oscilloscope to monitor the valve opening and closing with relation to pellet travel down the barrel. I don't know the science but it was very cool how they were tuning real time. Without equipment like that it takes a lot of trial and error. I once stumbled upon a quiet spot when tuning my .30, really spooky. I wish I could find that again.

That’s fascinating! I can tell you that I had way better luck with tuning after I watched a really old video where the guy talked about “you’ll know it’s right when it sounds right.” That’s basically how I figured out that my cheap chrono was not accurate. The gun sounded way better than what the chrono numbers were saying and the slugs themselves were audibly moving real quick. That lead me to finally figuring out the ballistics app to see if the numbers matched the performance I could now verify by recording my shots… lol it’s been a journey for sure. But I genuinely feel like I could tune most (regulated) guns pretty easily because of this experience.

 

[Bladefin]

I have the reg at 2800/2850 and the exact same set up. Factory spring with the slug power hammer weight. Unless the actual mass of the weight is different it shouldn’t be different than mine.

1) You will get more efficient air usage when your ports are matched up. I initially went with 4.4mm exhaust port(thimble valve) then went up to 4.8mm- this is still the best size for caliber but the pellets don’t load right. Needs a double port…. All of those changes gave me some minor gains but it’s about a month ago when I upped the transfer port to 4.4mm and put a new 4.4mm exhaust port that I got the performance I’m seeing now. As I mentioned the other day my 32gr are chrono’ing at around 980… Also I shoot the 30’s and 31’s with the same settings. Not change at all except a zero profile on the scope.

2) my simplest theory is kind of counter intuitive. I tested a with and without the hammer spring weight a couple months ago and the HS is weak. It took me 5-6 turns to get the gun to the same speed (same reg pressure) as with the weight in just flush…. My setup works because I’m running high pressure but very little dwell. When I started running it this way the whole gun got noticeably “snappier.” The metaling ping of the brass weight got quieter and the gun got significantly quieter. My main hunting buddy commented on it the very first time he heard it.

So if you’re getting hammer bounce it could be that you just need to up the reg another 100psi or so. It’s hard to read on the gauge but I’m pretty close to 3k without touching that line. More pressure in front of the poppet will help the valve not get overpowered by the HS weight.

3) the factory lube just sucks. At this point I have re-lubbed the entire gun with reg butter. Especially the valve and hammer spring assemblies. Everything on the gun moves smoother than when I got it…. It could be you’re getting some stickiness somewhere in there. It sounds like your valve is being held open too long for sure. It just might not be from the side you think…

4) if upping the reg doesn’t work the rabbit chase begins…. Is the poppet cracked? Or misaligned?

Is there some debris in an o-ring causing a weak seal?

Check the valve return spring that it’s properly aligned and not compressed when NOT under pressure. That could’ve gotten bumped or pinched when you took the reg out. The way you have to load it back in there is kinda awkward.

Finally make sure the thimble valve is aligned perfectly with the block. It needs to point straight down and if you have touched the valve make sure the transfer port is straight up… if they aren’t aligned the gun does some super weird things. Ask me how I know .

I know you’re frustrated right now but we’ll get it figured out. Doing more troubleshooting sounds like a bummer as does the prospect of taking the gun apart again. But it’s worth it to have the gun perform exactly how you want it to.

Sorry for my late responses but I was up in the mountains getting after some rock chucks… not to brag but I was really proud this weekend because a couple of my powder burner friends were looking at me different when I got the biggest one of the day, the furthest away and the cleanest kill all in one. The other two were shot with .223 and spent a lot of time flopping around and one almost made it back into her whole. I put a Franco right in its trachea at 81y and she dropped a foot or two onto another log and goodnight forever… I’m not some amazing hunter or shot. The gun is just crazy accurate and I had the best ammo for the job because of good penetration with expansion without over-penetrating. My point is just that if you wanna get really fussy over the gun the work will pay off.

That's the weird thing. The groups were getting pretty good with the full slug kit in and the hammer backed almost all the way out. I had just ran out of room to back it off anymore and I didn't want to shoot it with the hammer screw backed all the way into the stock. I didn't touch anything else other than swapping the hammer spring out. The report sounds like it's coming from a different gun, almost to powder level. It'd probably sound like an AR without the moderator on.

I guess I'll try giving the hammer screw a couple full turns in and fire a round to see what effect that has before doing anything else, can't hurt. I'm not to keen up upping the reg any further but if the hammer adjustment doesn't have an effect I'll try that before degasing to drop the reg down.

 

[Bladefin]

Ok, so I ended up taking it all apart again. I left the barrel assembly alone but pulled out the main valve and exhaust valve (or thimble) I removed all the o-rings and bought a couple hand reamers, a tapered set and a 4.5mm that I could put into my tap handle. I used the tapered first to open up the transfer port in the valve and then finished both ports up with the 4.5mm, which has a slight taper to it as well. Once that was done I cleaned everything up, gave it all a light lube and reassembled.

After pressurizing I set the reg to 2100psi, with the slug kit in and the hammer flush fired one of the 29.5 grain AEA pellets. I was shocked at how quiet it was. So I pulled out the crono and fired several more. I was expecting like 600 to 700 fps with it being so quiet. Nope, 902 to 906 fps.
I don't know what was wrong, but this seems to have done something.

The main tank gauge on the gun is also reading 400psi when it is completely degased. If you remember a while back I asked which gauge to trust the pump or the gun... I should have went with the pump as I was probably filling to 4000psi or so. Don't know if that played a part or not.

It was dark when I finished up tonight. So I topped the gun back off to sit over night. Hope to get back to tuning over the weekend.

 

[Bladefin]

I'm strongly considering sending my gun out to someone to tune it for me. Once I get a little above the 2400~2500psi range I start getting wild fluctuations in fps. I keep waiting for that Ahh Haa moment where I figure this thing out but it doesn't seem to happen and all I do is blow through rounds chasing my tail.

At 2100psi the gun is nice and quiet with the AEA 29.5 pellets going consistently in the low 900's the 30 grain slugs drop into the 860's. As I easy the pressure up I got them into the 930's but at 2600psi the speeds dropped into the 890's, so I started tweaking the hammer. I got a 940 and the next shot with no changes the report got loud and the speed dropped to 898. I dam near picked it up and chucked it over the retaining wall.

The only thing stopping me from sending it out is I won't learn anything and if I want to change ammo weight what do I do? Send it out again?

 

[Cantona256]

I'm strongly considering sending my gun out to someone to tune it for me. Once I get a little above the 2400~2500psi range I start getting wild fluctuations in fps. I keep waiting for that Ahh Haa moment where I figure this thing out but it doesn't seem to happen and all I do is blow through rounds chasing my tail.

At 2100psi the gun is nice and quiet with the AEA 29.5 pellets going consistently in the low 900's the 30 grain slugs drop into the 860's. As I easy the pressure up I got them into the 930's but at 2600psi the speeds dropped into the 890's, so I started tweaking the hammer. I got a 940 and the next shot with no changes the report got loud and the speed dropped to 898. I dam near picked it up and chucked it over the retaining wall.

The only thing stopping me from sending it out is I won't learn anything and if I want to change ammo weight what do I do? Send it out again?

So if you check back in this thread or the PMs you’ll see I did tell you it would get more quiet with your ports matched up haha.

What combination of spring and slug weight are you using? One quick little test you can do is this… back the hammer all the way out and shoot 3 slugs over the chrono… does the speed start high and go down or does it get faster? High to Low means too much HS and Low to High means not enough. With the slug weight in it becomes really really sensitive… micro adjustments is what I would recommend.

My other recommendation is the same thing I said before but you weren’t keen to try.. put the reg all the way to 2800-2900 psi and with the slug weight in and all the way back. It seems dumb but it won’t drastically affect your air consumption. In my opinion and the experience with my gun (all guns are different though!) is that high pressure but minimal dwell works well. That blast of air has to push the slug through 27.5” of barrel to escape so it really drives those lighter weight slugs. Should tighten your groups up too. Because of that long barrel the slugs get hit with a second wave of turbulent air if the dwell is too high. Your shot count will suck too.

Worse comes to worst just send it to me. Haha I feel like I talked you into this tune so I would be happy to make it work right for you.

 

[Sr.airgunner]

Hi Guys, I'm new here and just getting back into air guns, I just got a 25 cal and this is my 1st PCP.

I'm planning on seeing how she shoots this weekend without changing a thing before I start diving down the rabbit hole. I've got several different grain H&N slugs in .25 (30, 32 & 34) and a sampler pack of .249's, along with a tin of .25 Apollo's in 33. Wish the Sampler in .25 was in stock...
I'd like to see which ones group the best before changing anything. Then I'll back the psi & hammer spring off and try again and see if another weight starts to shine or not as I start moving things up.

The main use will be hunting squirrels and chipmunks. I've also have a coyote problem that arises from time to time, luckily things have been pretty quiet on the yote front the last month or so. But I'm also planning on having fun with friends out back using it as a paper punch. I'm thinking pellets would be best for that.
All of the main shooting will be 25-60yrds. Maybe in the fall, once the leaves are off the trees, I'll be able to stretch it to 75yrds or more.

Here's what I got for the rest of the setup. An Althon Talos 6-24x50 scope. Mloc bipod & red tac light. With an Airgun Capital can to round things out.
It'll probably be a little bit before I get into the real tuning. I'll at least put a trigger kit on it as I see there's already one available, probably stone the sear at the same time I do that.

The current questions I have are:

Should I look into other brands of slugs and do you know of any companies that sell sample packs of their line?

Once I get the slug I want dialed in will I be able to transition to a pellet in the same weight and get similar results without changing much?

Any other pointers y'all may have are most welcome!

Thanks,
Adam

Had a problem with the hammer spring adjust screw on the 250Z in .25. There is no way to back the hammer spring off to a lower setting as it jams against the bolt recess on the stock. Contacted Barra about this and no helpful response. Remove the stock and back the hammer spring adjuster ccw and you cannot replace the stock. Are they all like this or did I get a defective?

 

[Bladefin]

Had a problem with the hammer spring adjust screw on the 250Z in .25. There is no way to back the hammer spring off to a lower setting as it jams against the bolt recess on the stock. Contacted Barra about this and no helpful response. Remove the stock and back the hammer spring adjuster ccw and you cannot replace the stock. Are they all like this or did I get a defective?

You can only back the Hammer screw out about 3/4's of a turn past flush before it hits the molding in the stock for the bolt. That is normal. At that point it's add a lighter spring or take the weight out, if you have the slug kit installed.

 

[Cantona256]

You can only back the Hammer screw out about 3/4's of a turn past flush before it hits the molding in the stock for the bolt. That is normal. At that point it's add a lighter spring or take the weight out, if you have the slug kit installed.

This is the answer.

 

[Pumacarl]

You guys have to realize that these guns were not designed to be as flexible as you are all making them. There is a huge difference in shooting a lightweight pellet to a heavyweight slug, and everything in between. Forget about shooting pellets and slugs first and foremost. Nevermind the weight, just the drag differences of a slugs length in the bore changes everything. Pick slug or pellet and pick a small weight range and get one tune right. You can't be changing pressures drastically and then shoot pellets, the timing (dwell ) will be completely off. Sometimes you will get lucky and it works out but most often not. If you're going to try to use both, go for pellets that weigh significantly more than the slugs you are shooting. In .25, if you are going to be shooting 30gr slugs, get some 34gr pellets too. Plus, I think @Cantona256 is right in that you should try your regulator up high, even if you don't think that you want to use it up there, just to see how it does. My brother's Avenger ended up doing it's best at 2900psi, it is just shy of moa with 29.5gr slugs. It's not near as solid as this gun is either. You don't know until you try.

 

[Bladefin]

You guys have to realize that these guns were not designed to be as flexible as you are all making them. There is a huge difference in shooting a lightweight pellet to a heavyweight slug, and everything in between. Forget about shooting pellets and slugs first and foremost. Nevermind the weight, just the drag differences of a slugs length in the bore changes everything. Pick slug or pellet and pick a small weight range and get one tune right. You can't be changing pressures drastically and then shoot pellets, the timing (dwell ) will be completely off. Sometimes you will get lucky and it works out but most often not. If you're going to try to use both, go for pellets that weigh significantly more than the slugs you are shooting. In .25, if you are going to be shooting 30gr slugs, get some 34gr pellets too. Plus, I think @Cantona256 is right in that you should try your regulator up high, even if you don't think that you want to use it up there, just to see how it does. My brother's Avenger ended up doing it's best at 2900psi, it is just shy of moa with 29.5gr slugs. It's not near as solid as this gun is either. You don't know until you try.

I was just using the pellets to get the 1st several rounds out after swapping out the reg and opening the ports. Something cheaper to shoot meaningless shots to get the reg to settle in. Slug's are my priority, and I'm sticking with 30-32 grain.

I had a good text chat with @Airgunandy89 yesterday. His thought's of what I'm seeing are the first things that make sense to me. He told me that when you open up the ports you also need to lighten up the poppet return spring. That's is why I'm seeing the valve floating, resulting in the large variation in fps between shots with no changes. Also why the sound is all over the place. That could also be why @Cantona256 is seeing better results at 2900psi. I will try that, along with a few other pointers. Andy also said that if the aluminum in the receiver wasn't ported to match there is sill a bottleneck right in the middle. That may be another reason why a really high psi is working as it could be enough to overcome the narrower channel in the receiver and the return spring at the same time.

I've decided to make this a project gun for testing. I've got a new 250Z in Veil on the way. I'm going to dial that one in without any port mods so I have something reliable when I need it. Then I'm either going to tinker with the original myself or send it up to @Airgunandy89 to use as a test bed. I just don't have the time to be testing out these changes, learning as I go because I don't have the knowledge set to understand the results I'm seeing. So having something reliable is my priority right now. If Andy doesn't want to use it for testing then as I have time I'll tinker with it and have fun learning at my pace and at the same time, when the yotes are making a racket at 3am I'll have a gun that will do what I want it to and know it will be quiet and the slug will go where I want it to.

I have learned that this is all a balancing act. The stock gun, while not the most efficient in .25, is well balanced. As changes are made in one area you upset the balance in another, and you need to figure out what area(s) of the gun need to be tweaked to right the balance... as you continue down the rabbit hole.