250Z Barra 250z Slug Tuning

[GAJoe]

A little background first; I have a 250z, Gen2, 25 cal with RogueAir's trigger and slug power kits, the C-88 Air Plenum, and factory barrel, shooting Franco's 32gr HP's.
I got the gun back together with the ported thimble and Home Depot spring mentioned above. I pressurized it and let it set 12 hours; no leaks. The reg was set at 2500 from my last go-round.
With a couple hours before the afternoon school bus route I wanted to know if my thimble port would load ok and how many shots per fill. My first shot produced 850+ FPS (Trying to get 950.) so I ran the hammer spring adjustment screw from half the threads ran in to all of them ran in (can go deeper in if needed.) The next shot was 952. The next 18 shots stayed in the 950's but was as high as 959 and everywhere in between. After those then it dropped on down into the 940 with the air running low. So at that hammer setting I can shoot two factory magazines per fill.
I'm too new at this to know that good sounding shot that I read about, but I think that I'm way over on the spring setting and wasting a lot of air. I don't want to loose any more shots per fill by increasing the spring tension. I think my next step will be to back the hammer adjustment screw out a half turn and take two shots and repeat until I see the speed drop below the 950's. Then gradually increase with five shot groups on paper until the speed holds steady all five shots and hopefully a tight group. Hopefully I'll pick up a few shots per fill.
How does this sound? Other suggestions are welcome.
But I did learn that the 32gr slugs load fine into the thimble with that porting.

 

[Pumacarl]

952-959 isn't a bad spread at all. That magic sound you are talking about rarely happens when you want to get peak power out of a platform. That's for people going for a balanced tune, which frankly is a boring one. Fine for plinking but probably lacking for hunting. Don't worry about wasting air so much if you are after power, you have to decide what is more important to you. I think, ultimately, accuracy is the most important thing to chase. Run your spring up like you said and leave it where it groups the best. If you're getting two magazines at the power your shooting, that's good enough to me. You're only working with 332cc of air, there is only so much you can do with that and you're just about there now.

 

[Cantona256]

A little background first; I have a 250z, Gen2, 25 cal with RogueAir's trigger and slug power kits, the C-88 Air Plenum, and factory barrel, shooting Franco's 32gr HP's.
I got the gun back together with the ported thimble and Home Depot spring mentioned above. I pressurized it and let it set 12 hours; no leaks. The reg was set at 2500 from my last go-round.
With a couple hours before the afternoon school bus route I wanted to know if my thimble port would load ok and how many shots per fill. My first shot produced 850+ FPS (Trying to get 950.) so I ran the hammer spring adjustment screw from half the threads ran in to all of them ran in (can go deeper in if needed.) The next shot was 952. The next 18 shots stayed in the 950's but was as high as 959 and everywhere in between. After those then it dropped on down into the 940 with the air running low. So at that hammer setting I can shoot two factory magazines per fill.
I'm too new at this to know that good sounding shot that I read about, but I think that I'm way over on the spring setting and wasting a lot of air. I don't want to loose any more shots per fill by increasing the spring tension. I think my next step will be to back the hammer adjustment screw out a half turn and take two shots and repeat until I see the speed drop below the 950's. Then gradually increase with five shot groups on paper until the speed holds steady all five shots and hopefully a tight group. Hopefully I'll pick up a few shots per fill.
How does this sound? Other suggestions are welcome.
But I did learn that the 32gr slugs load fine into the thimble with that porting.

952-959 isn't a bad spread at all. That magic sound you are talking about rarely happens when you want to get peak power out of a platform. That's for people going for a balanced tune, which frankly is a boring one. Fine for plinking but probably lacking for hunting. Don't worry about wasting air so much if you are after power, you have to decide what is more important to you. I think, ultimately, accuracy is the most important thing to chase. Run your spring up like you said and leave it where it groups the best. If you're getting two magazines at the power your shooting, that's good enough to me. You're only working with 332cc of air, there is only so much you can do with that and you're just about there now.

I agree with everything Puma says here with one minor caveat. With the Plenum added you should probably be just a little bit more efficient … 2 mags at 64fpe is exactly what I was getting pre-plenum. The AirgunAndy plenum was 30cc so bigger than the C88 so expect the 4+mags at 64fpe I could get but I do believe with a little more tuning you could get at least 25-30 shots a fill.

I think playing with the hammer spring is the right call.

If that doesn’t work the slightly counter intuitive move is to up the reg slightly… the additional pressure on the poppet can help prevent the hammer spring from overdriving it.

 

[Cantona256]

Also I finally shot some coyotes last night… sadly not with the barra but with the DRS lol