250Z Barra 250z Slug Tuning

[Pumacarl]

Because a lot of the time the ports are not exactly doing equal work because they design the whole gun to be several calibers but don't change every dimension equally. The marauder is a good example of this and is easy to swap out the transfer port for more shots at less power. A little can do a lot. It won't always work out, especially going for more power, but this time it kind of balanced out better, and did.

Nice jacks!

 

[Cantona256]

Because a lot of the time the ports are not exactly doing equal work because they design the whole gun to be several calibers but don't change every dimension equally. The marauder is a good example of this and is easy to swap out the transfer port for more shots at less power. A little can do a lot. It won't always work out, especially going for more power, but this time it kind of balanced out better, and did.

Nice jacks!

Ooooh that makes a lot of sense! It’s funny how just that little change in the thimble port made it so much smoother. It even sounds a million times better. At stock power it does that too but my poor attempt at a tune was not helping either. Thanks again for posting that cuz it just made it so much easier for me to figure it out.

 

[CTAirgunner]

I ported my thimble valve from 4-4.4mm and my baby is shooting really nice now. I haven’t pushed it for more power yet. Just went back to where I was (in terms of FPS) and found that I’m at 2600psi instead of 2900psi and between 20-25 shots per fill instead of 10-15…I’m a little surprised it worked out so well. Why do you think opening the thimble port helps so much without opening the block and transfer valve too? I was told to not expect much difference.

Anyways I brained a big ass jackrabbit from about 40 yards last night… the smack from the 40gr Apolo was LOUD haha…View attachment 12339

Nice work!!!

Those are some big bunnies!

 

[Cantona256]

Nice work!!!

Those are some big bunnies!

Haha thank you! It was so much fun to chase them…. I’m mostly sad I called in 2 coyotes but we couldn’t get them to stop long enough for a shot.

 

[CTAirgunner]

Also, while having downtime at work, and being very intrigued by these barra 250s I did a little work on the calculators

Do you guys think these things have enough power to shoot a 49.5 gr slug at 840-890 fps?

Reason I ask is this

The Altaros 49.5 .25 cal slug has a .21 BC (G1) with only an 855 FPS muzzle velocity.

These rifles have a 1:18 twist , so I plugged all the info into the stability factor calculator and this is what I got.

All information is accurate as far as I know, I pulled the ammo specs off Altaros site myself.

This first calculation is at a mere 840 FPS




The second calculation is @ 900 FPS



The next chart is the range table at the medium speed of 870 FPS , look at that retained energy down range, also, I always find the drop in inches funny when using the chart for airgun ballistics lol

 

[Pumacarl]

I will be interested to see people try. Northeastbeast is using a bigger external plenum, so he would be the one to watch. He wants to compete with one so he's trying everything.

 

[Cantona256]

Also, while having downtime at work, and being very intrigued by these barra 250s I did a little work on the calculators

Do you guys think these things have enough power to shoot a 49.5 gr slug at 840-890 fps?

Reason I ask is this

The Altaros 49.5 .25 cal slug has a .21 BC (G1) with only an 855 FPS muzzle velocity.

These rifles have a 1:18 twist , so I plugged all the info into the stability factor calculator and this is what I got.

All information is accurate as far as I know, I pulled the ammo specs off Altaros site myself.

This first calculation is at a mere 840 FPS
View attachment 12433



The second calculation is @ 900 FPS
View attachment 12434


The next chart is the range table at the medium speed of 870 FPS , look at that retained energy down range, also, I always find the drop in inches funny when using the chart for airgun ballistics lol

View attachment 12435

These are really interesting numbers. I got a 40gr doing 800fps with nothing but a slug weight. I’m gonna see what it can do now that I ported the thimble valve to 4.4mm… Northeast beast is also coming out with a new valve so that will help too. But I think it’s possible. You’ll definitely have to open the whole block up to do it but I think it can be done.

 

[CTAirgunner]

These are really interesting numbers. I got a 40gr doing 800fps with nothing but a slug weight. I’m gonna see what it can do now that I ported the thimble valve to 4.4mm… Northeast beast is also coming out with a new valve so that will help too. But I think it’s possible. You’ll definitely have to open the whole block up to do it but I think it can be done.

Once my JTS build is done, I'm moving onto a Barra in .25 so who knows maybe it'll be me who tries

 

[Billm]

I’m not sure 25yds tells me much about accuracy. I’m pretty sure most anything I have will group slugs at 25yds. Probably the only airguns that I have ever owned that couldn’t group anything at 25yds were my Diana mod 2, my trusty “GAT” and my Red Ryder. Img 1467 10 shot group on left JTS .22 21.53 semi-domed - 900fps 1600-1709psi - Group on right 1467 10 shot Rifle 20.52gn slugs same settings. Image 1469 Rifle .22 20.52g slugs, 2200-2300psi 1000fps +-2fps. The black dots on the right were part of the target. As usual 5-10mph crosswind. Stock Barra 250z .22. And if you haven’t shot an English .177 GAT - you haven’t really been airguns challenged lol. Come to think of it I had a German .177 smooth bore pistol made by Record that was really fun to shoot, but probably not at 25yds.

 

[Pumacarl]

I’m not sure 25yds tells me much about accuracy. I’m pretty sure most anything I have will group slugs at 25yds. Probably the only airguns that I have ever owned that couldn’t group anything at 25yds were my Diana mod 2, my trusty “GAT” and my Red Ryder. Img 1467 10 shot group on left JTS .22 21.53 semi-domed - 900fps 1600-1709psi - Group on right 1467 10 shot Rifle 20.52gn slugs same settings. Image 1469 Rifle .22 20.52g slugs, 2200-2300psi 1000fps +-2fps. The black dots on the right were part of the target. As usual 5-10mph crosswind. Stock Barra 250z .22. And if you haven’t shot an English .177 GAT - you haven’t really been airguns challenged lol. Come to think of it I had a German .177 smooth bore pistol made by Record that was really fun to shoot, but probably not at 25yds.

Yeah, I don't know how that will pan out either, especially with slugs. Lately I am finding that they shoot a hell of a lot better at distance than I would have thought from shorter groups. I haven't determined yet if that is my fault, because I am much more methodical at distance than at short range, or if the slug is flying so much better than a pellet that it just intrinsically ends up being better. I get my 20.something gr JSB KO's tomorrow, so I'll have a report on those soon too.

I typically only test pellets at 53y because I think at that range I am seeing the accuracy of the pellet more than my accuracy at shooting in the wind or at distance. With slugs I think that I may be able to get by with 75y and I am going to check that next time I shoot. I still haven't figured out the range where accuracy falls off with slugs at all because I really only started playing around with them last year. If it's a linear deal, that would be a lot better than pellets too, and it really should be, but who knows? Just gotta shoot.

 

[Billm]

Yeah, I don't know how that will pan out either, especially with slugs. Lately I am finding that they shoot a hell of a lot better at distance than I would have thought from shorter groups. I haven't determined yet if that is my fault, because I am much more methodical at distance than at short range, or if the slug is flying so much better than a pellet that it just intrinsically ends up being better. I get my 20.something gr JSB KO's tomorrow, so I'll have a report on those soon too.

I typically only test pellets at 53y because I think at that range I am seeing the accuracy of the pellet more than my accuracy at shooting in the wind or at distance. With slugs I think that I may be able to get by with 75y and I am going to check that next time I shoot. I still haven't figured out the range where accuracy falls off with slugs at all because I really only started playing around with them last year. If it's a linear deal, that would be a lot better than pellets too, and it really should be, but who knows? Just gotta shoot.

It’s been storming here for days and there was a break in the rain and so I saw a chance to get a few shots in. Originally I was going to practice for the spring 25yd challenge. Then I decided I would just sling some lead at whatever the Barra was set at. Fifty yards/meters seem to be the ideal range. I don’t keep good records and I tend to rush shots, so my results are iffy lol.

 

[Pumacarl]

It’s been storming here for days and there was a break in the rain and so I saw a chance to get a few shots in. Originally I was going to practice for the spring 25yd challenge. Then I decided I would just sling some lead at whatever the Barra was set at. Fifty yards/meters seem to be the ideal range. I don’t keep good records and I tend to rush shots, so my results are iffy lol.

Me either! I usually will just write about what happened on this forum and if I have to remember I will look at old posts I made. HAM is my cloud storage!

 

[alejandro91]

Agreed, 25 cal is my preferred choice for small to medium sized game hunting as well. Just better stopping power overall especially with the 33.95 grain pellets. Groundhogs drop quickly with this preferred weight of ammo. If i want to punch paper for the afternoon i use the AEA Center Punch 25.39 pellets with great accuracy as my first choice with the JSB pellets as my second

What fps are you pushing does .25cal AEA 25.39

 

[GAJoe]

On my Gen2 .25 I got the main 4.4mm hole in by hand with a tapered hand reamer and a drill bit and then widened it by using a Dremel 9902 in my drill press and the cross slide vise to carefully move the thimble. I didn't trust myself doing it by hand. I think that I left enough brass to keep the O-Rings in place. Is there such thing as too large?

 

[GAJoe]

I had installed Rogue Air's slug power kit but was told by a member that the kit spring was too strong if the valve block hasn't been ported, to put the factory spring back in. I was unable to find my original hammer spring. The shipping from Barra was too high. I found a discussion about using a spring kit from Home Depot.

So I got that and cut the spring length down so that the weight and spring would fit with the adjustment screw thread about half in and just touching and no compression on the spring to give a good range of adjustment. That sound OK?

 

[Pumacarl]

View attachment 23537
View attachment 23538... Is there such thing as too large?

You'll certainly find out! Let us know.

 

[GAJoe]

You'll certainly find out! Let us know.

How about the spring question?

 

[Pumacarl]

I had installed Rogue Air's slug power kit but was told by a member that the kit spring was too strong if the valve block hasn't been ported, to put the factory spring back in. I was unable to find my original hammer spring. The shipping from Barra was too high. I found a discussion about using a spring kit from Home Depot.
View attachment 23539
So I got that and cut the spring length down so that the weight and spring would fit with the adjustment screw thread about half in and just touching and no compression on the spring to give a good range of adjustment. That sound OK?

It "sounds" reasonable. Just back out everything, and incrementally turn it up checking the numbers. You're breaking new ground with that port. I can't wait to hear about your results!

 

[Pumacarl]

How about the spring question?

With springs, don't get hung up on trying one way, there are many ways to do it; SSS, SSG, TSS, are three alternative methods too amongst others, you just have to test them. It's fun if you've got the time to play with it.