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250Z 250Z tuning, mainly slugs.
- Thread starter Bladefin
- Start date
- Latest activity Latest activity:
- Replies 317
- Views 22K
- Original poster
- #302
Between the stent being put in last month and some crappy weather I hadn't got much shooting in. When I get home from work I'm lucky to have a half-hour of light outside if it's warm enough. I spent the time polishing the new barrels and getting everything cleaned up ready to go. I was able to spend most of yesterday and a couple hours today tuning them.
I'm happy to report these new barrels are much better. I've got the V2 gun shooting at about 5/8 to 3/4" groups at 50yrds and the V1 ragged hole at 40yrds. I was able to get there pretty quickly compared how this journey started out. But I do have something odd to report that I can't quite figure out. Hopefully one of you can shed some light on it.
I've got both guns set to 2500psi and V1 is shooting a 30gr Zan at 910ish FPS, the V2 is shooting the 33.49gr JSB KO MK II at 935ish FPS. One would think the Zan would be moving much faster. Both guns have plenums although there is one difference beyond the hammer spring tensioner designs. The V1 gun has the main valve & timbal ported to 4.4mm and V2 is stock. I understand that the differences in hammer settings could play a role, but they are both backed out fairly far and I haven't heard any wasted air in the reports. I'm obviously missing something.
I'm happy to report these new barrels are much better. I've got the V2 gun shooting at about 5/8 to 3/4" groups at 50yrds and the V1 ragged hole at 40yrds. I was able to get there pretty quickly compared how this journey started out. But I do have something odd to report that I can't quite figure out. Hopefully one of you can shed some light on it.
I've got both guns set to 2500psi and V1 is shooting a 30gr Zan at 910ish FPS, the V2 is shooting the 33.49gr JSB KO MK II at 935ish FPS. One would think the Zan would be moving much faster. Both guns have plenums although there is one difference beyond the hammer spring tensioner designs. The V1 gun has the main valve & timbal ported to 4.4mm and V2 is stock. I understand that the differences in hammer settings could play a role, but they are both backed out fairly far and I haven't heard any wasted air in the reports. I'm obviously missing something.
Billm
Grand HAMster
That could be just a slight difference in diameter of the slug or barrel creating more friction.
If the V2 thimble is only 4mm it will restrict the airflow, especially the increased airflow from the bigger plenum. I would definately open the stock thimble if you want to make any power at all, plenum or not. Zan and JSB use slightly different lead. There is always a little difference between them but I have found it to be consistent once identified for any particular two choices, so that's kind of good.
- Original poster
- #306
With the speed differences, do you think the skirt on the KO's is playing a big roll? I swear the V2 sooting them is quieter than V1 on the Zan's. Could be the seal is better on the KO and more air is pushing the slugs.
I'll probably open the ports up on V2 at some point. Right now I'm just enjoying shooting accurately the way it should've been all a long and not working on them. It'll also be nice to test the differences between the two. The weather is nice today and should be till Thursday. If I get out of work at a good time I'm going to shoot some KO's out of V1 when I get home. Seeing how the pressures are the same right now it will be interesting to see the results. Hell, if I get 950-960fps that porting may happen sooner rather than than later.
I don't think the difference in drag between your projectiles is the culprit. Air seal, yes, lead chemistry, yes.
Different blends of various alloys can have very different lubricity properties. So of course would create less or more drag depending on chemistry (I worked in steel manufacturing for 37yrs).
What I meant to say was that slugs of same alloy but with slightly different contact patch may not show any velocity difference. See my post from yesterday.
Yes, but not necessarily result in less velocity. Maybe, but maybe not depending on other factors.
Airgunandy89
New member
And as far as porting goes has anyone posted defined speed findings on stock vs thimble port ? Well I have tested a gun today with a couple combinations ..25 caliber
current tune nothing changed over the period of testing .
Thimble…. Stock 914 fps/ ported to 4.5 919 fps .. not enough to warrant this mod alone because you have a through passage in the body itself at 4 mm and a valve that’s at 4 mm
Then I wanted to make a spicey gun and achieved over 100 ft lbs by porting body to 6mm . New valve at 10 mm inlet poppet and 6 mm outlet and a football thimble port at 6x4.5 .. unfortunetly guys your not going to want to do these mods unless you only need a few useable shots . And it’s allready exceeding what the barrel can stabilize with the heavier weights so you will need a new tj barrel with a custom twist rate .
current tune nothing changed over the period of testing .
Thimble…. Stock 914 fps/ ported to 4.5 919 fps .. not enough to warrant this mod alone because you have a through passage in the body itself at 4 mm and a valve that’s at 4 mm
Then I wanted to make a spicey gun and achieved over 100 ft lbs by porting body to 6mm . New valve at 10 mm inlet poppet and 6 mm outlet and a football thimble port at 6x4.5 .. unfortunetly guys your not going to want to do these mods unless you only need a few useable shots . And it’s allready exceeding what the barrel can stabilize with the heavier weights so you will need a new tj barrel with a custom twist rate .
The noise difference could just be from the ports being a different size. That's the thing with these airguns, everything matters, a lot. That's why I'm sure that it is helpful to somebody, to list all of the stuff we do, since we all change this and that and no two guns are the same. Even our own. lol
I did do a comparison, before and after changing my thimble port to 4.3mm and I could drop my reg afterwards by 10b and get the same velocity. Maybe it was because if air was being restricted to 4mm at two spots if one of those spots is made bigger there is slightly less restriction in the system. Either way, my results did improve and I had been running my reg at 170b and I moved it down to 160b afterwards with no loss in velocity. This was in a .22 not a .25, Gen 1 250z. I never pushed my gun over 47fpe either. I don't know what would have happened if I had.
- Original poster
- #316
V1 is ragged hole. Going to change up the distances and see if the groups stay tight. If so I'm going to leave it be.
V2, I'm gonna see if any spring changes hep the groups. If not, I'll degas and start the tuning over. It's the one I want to keep and I'd like to stay at or under 36gr.
V2, I'm gonna see if any spring changes hep the groups. If not, I'll degas and start the tuning over. It's the one I want to keep and I'd like to stay at or under 36gr.
- Original poster
- #317
Been a while since I've posted. The V2 gun has been rock solid and consistent. I tweaked the hammer at the end of February and haven't touched it again. It's shooting dime to nickel at 50yrds.
I've cleared a lot of grey squirrels out and am now going after chipmunks. The KO slugs damn near turn the chippies inside out, complete carnage.
The V1 gun is still a work in progress. Quarter to 1" groups and if I go much more than a half turn in from max out on the hammer it starts wasting air. I'm going to toy with raising the reg and trying different springs. I'm really thinking about selling the V1 gun.
I've cleared a lot of grey squirrels out and am now going after chipmunks. The KO slugs damn near turn the chippies inside out, complete carnage.
The V1 gun is still a work in progress. Quarter to 1" groups and if I go much more than a half turn in from max out on the hammer it starts wasting air. I'm going to toy with raising the reg and trying different springs. I'm really thinking about selling the V1 gun.
Cantona256
HAM Expert
Haha yeah chippers will explode with the right slug… I almost feel bad until I remember their fondness for chewing wires.
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