FX slug twist rates

[stoti]

I've been testing .25 caliber slugs for a while now using a 600mm liner. I've gotten some pretty good results but somewhat mediocre and inconsistent. Many of the people shooting the .22 slugs out of the FX liners are getting super accurate results. I was looking at the twist rates that the people at FX shared with us about a week ago and was wondering if someone can explain why the .22 caliber twist rates get faster as the liners get longer and the .25 caliber twist rates get slower as they get longer? 

Thanks, Stoti

 

[JamesD.]

You can punch figures into ANY ballistics calculator all day long, including the Geoffrey/Kolbe twist rate calculator that shows how BC goes up when projectiles go below the sonic barrier (1100 FPS @ sea level 68*F blah blah blah) & the BC skyrockets when you drop from whatever YOUR actual geographic areas sound barrier speed is to down around 900-980 fps. 

Point is FX tests everything in-house, indoors, with and endless combination of barrels, twists, speeds of said slug or pellets. So what is right mathematically on paper/programs doesn’t always look so good on target with slugs/Diabolos. 

http://www.exteriorballistics.com/ebexplained/22rimfire.



What I’m showing you is the variance of BC by speed from what most likely was a 1:16” twist with very similar to air gun slug projectiles.

0.098-0.216 and that’s a huge difference for 20 grain variance & what, a 50-100 FPS reduction?

There’s so much math & testing to get a PCP actually truly optimized. And, that should mean for one projectile at a set speed. I hope I conveyed my point that twist rates and sub sonic get confusing. I have proof of that with my 1:20 .253 Sumatra 500cc standard length barrel. I personally want ANY PCP rifle I own to have a long powerful efficient barrel. The Sumatra is not efficient but it is incredibly accurate with both pellets & correctly sized slugs.

 

[AirSupply]

To understand why the .22 liners get fast as they get longer is logical. With the added power that the longer barrel provides you are able to shoot longer and heavier slugs and they require a quicker twist rate. Why is .25 the opposite I don’t know but it’s a good question. I do think there has been far more R&D for the .22 liners because of Matt Dubbers involvement. 

I threw up as to order a “B” pellet liner or the slug liner in 600mm. Ended up going for the slug liner and glad I did as it is the same twist rate as the B pellet liner. It should shoot the King Heavies as well as a B liner (fingers crossed) Arriving any day now. 

The Utah Airgun guys seem to have the .25 slugs working well judging by there resent video but not sure they mention what slugs there shooting

Hope you find some answers and get the accuracy your after. Michael 

 

[stoti]

Yes, I've talked to Matt and far more research went into the .22 than the .25.

My 600mm .25 slug liner shot the king Heavies better than the STX liner that came with the gun. It is super accurate, you'll love it.

As far as the UA video, I've talked to them and watched the video, I think it's a bit deceiving. 

I have tested quite a few slugs that shot really well but with too many fliers and inconsistencies. Almost everyone I've talked to that has been testing the .25 has said the exact same thing. 

I'm just so curious why the .22 liners would get faster with length and the .25 liners slower with length. Doesn't make sense.

Stoti

 

[edosan]

@stoti as far as I know, you are leading the 0.25 research here in AGN

Been wondering the same for a while too

 

[stoti]

Edosan--- Did you get a .25 liner with your new Impact? Have you tested it yet? Love to hear about it. 

Stoti

 

[edosan]

Not yet, on the waiting list

 

[Julez]

I get pretty ok results with the. 25 slugliner shooting the nsa 34.7grain,and with the 32.8 and 34 grain varmint knockers, but also quite a few flyers. I tought it was just me but apparently not. When I shoot 5 shot groups at 50meters,they group about 20mm,but also get flyers that open the group really bad(to 40-50mm). Glad to read it's not just me experiencing that! 

 

[stoti]

It's not just you and me either I'm afraid. Very common result by quite a few good shooters and people in the know. If I could just pick the best 6-7 shots out of every10 shot group, all of my groups at 50yds would be 1/2-3/4". I know from my testing that there are quite a few different slugs that can perform very, very well. Slugs ranging from 30.4gr all the way up to 39gr. Of course I have to adjust the regulator on my gun, but the groups showed to be absolutely phenomenal... if not for the fliers. It's just so perplexing and there is no rhyme or reason to it at all. I've tried everything and adjusted everything and the consistency just isn't there. Every pellet weight, without exception, throws off some fliers. I've never seen anything like it. It's even more frustrating because it seems that everyone shooting the .22 caliber slug liner justs cleans them and starts shooting and shooting well. They're not finicky, not many fliers and they shoot great from the start. That's what got me wondering about these twist rates. With the .22 caliber, it looks right, faster twist rates with the longer liners. Why FX would completely go the opposite direction with the longer .25 liners absolutely makes no sense at all. I would love to have a 700mm, .25 caliber, 1:18" twist liner to try out and see what happens to the group size and the fliers. 

Stoti