GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: blackdiesel on September 25, 2015, 11:08:18 AM
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I see that FX sell ST barrel blanks and was wondering have anyone tried fitting them to non-FX guns? It's obvious they shoot JSB pellets very well so I wonder how other guns will fare using the ST barrel.
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Threads pop up on this subject from time and folks have done it and were happy with the results. But the general sentiment taken from what I've read is that the barrels are overpriced compared to other offerings. Many barrels shoot JSB pellets well. Hopefully you'll get some more input here but if it were my money, I would get a TJ barrel instead.
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Oh I wasn't considering buying one. I just wanted to see if others had tried it and how they performed on other guns.
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Oh I wasn't considering buying one. I just wanted to see if others had tried it and how they performed on other guns.
I laughed way too hard when I read this! ;D ;D
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I have only seen it go the other way, and to good effect too...:)
cheers,
Douglas
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Oh okay. You may want to look for Harry's (yrrah) posts on the yellow. He made some interesting observations on longer-range stability and ballistic coefficient compared to a traditionally rifled barrel.
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There is an interesting thread here on the GTA dealing with long range.... At 234 yards, IIRC, the holes in the target, shot with an FX Smooth Twist barrel, are consistently pear shaped, and pellets recovered from the backstop are imbedded nose up.... whereas at 100 yards they are perfect circles.... It has been speculated that the pellets are starting to tumble past 200 yards.... The only way to prove this would be to set up targets every 50 yards, from 100 out to 300 and see what happens.... but I just thought I would pass along what has been observed.... The ST barrels result in an extremely slow spin rate, one test measured it as low as 1 turn in 13 FEET.... Perhaps that is not enough if the range is long enough?....
Bob
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I calculated the angular acceleration required when the pellets hits the pressed-in 16" twist rifling at the end. Assumed it accelerated throughout the 2-3" experience and got a *HUGE* number in radians/s^2. It just skids through and picks up a slow spin.
cheers,
Douglas
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Along that note, I would suggest that the claim for a slightly better BC for the ST barrels may well be the decrease in diameter of the pellet from stripping off / reforming the OD to match the ID of the rifling.... Recovered pellets from ST barrels show no rifling marks.... and having the same weight for a smaller diameter increases the BC.... It is possible that the lack of rifling marks (ie smoother surface) and lower spin rate would also decrease the Magnus Effect which causes the pellet to rise or fall in a crosswind as well.... These are both good things, provided the pellet remains stable at long (~200+ yard) range.... or you never shoot there, which would apply to most....
Bob
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As a semi-technical layperson, the Smooth Twist concept is a fascinating thing. Intuitively, it seems like the typical 1-in-16 twist rate is overkill for a shuttlecock projectile...if we accept that this twist rate is anywhere near optimal for a 22LR bullet.
I've read some of Bob's explanations of stability factor, and perhaps he addressed this and I just don't remember but I assume you can't apply those formulas to a diabolo projectile and evaluate them that way.
Also, Michael Thomas said something about a benchrest shooter running JSB monsters with a 30+ inch twist with excellent results. I thought that was interesting and supportive of the idea that diabolo pellets are overstabilized at the usual twist rates. FX sure seems to get good results with a miniscule effective twist rate.
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Here is a 75 yard 25 shot group in 3-7mph wind with a 1:36 twist Mark Channlyn .22 barrel. I think these were 18.1's.....cant' quite remember, now.
Mike
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If a 30+ inch twist rate works for a JSB Monster pellet (and I feel that likely) then an even slower twist should work for shorter ones.... although the gain might not be enough to worry about.... I would love to try something with a twist half what we currently use for pellets.... I'm betting it would work great, with any possible problem showing up only at extreme range.... It could easily eliminate pellet spiraling, if the reason for that is, as I suspect, too fast a spin as the pellet loses it's forward velocity downrange....
Bob
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Looked back at notes and it was with 16g AA's and the wind was 2-4 mph.....so I was wrong on 2 accounts. Dang this memory thing.
Mike
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Michael, thanks for clarifying the twist rate. Sorry if I botched the pellet, I thought the example you gave was with the 13.4gr Monster in .177.
Bob, when my thoughts align so closely with yours, I don't know whether to be proud or shocked. ;)
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You were right about the one you mentioned......1:36 Lothar Walther Polygon shooting JSB 13.4 monsters. This was a different one. I know of a 1:36 twist Krieger barrel that shoots the 25.4 22 cal monsters quite well out to 75 yards, too. 1:24 Liljas shoot 16g .177 beast pellets just fine.
Mike
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Ah, okay. My brain didn't fail me this time.
By the way, when I see you write something shoots "quite well", I internalize that as "Sweet baby Jesus, it's amazing!".
After all, I'm pretty sure you described your demeanor as "quite pleased" when you showed us your test targets shot in preparation for the recent BR competition.
Quite pleased!? Pfffft. Your poker face must wear all the emotion of a corpse. ;D
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Ya....I guess I'm kind of low key. ;D
I think Dan Brown and Harry Fuller have done a fair amount of testing on the Smooth Twist barrels.....may be able to dig some of that up. I know that we don't see those barrels show up and perform in 25m benchrest....so it makes me wonder how they would group at longer ranges if they aren't that tight at 25m.
Mike
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I put a .25 ST FX barrel on my AF Condor and out to 50 yards it is amazingly accurate with any JSB pellet. It does need to be cleaned frequently, say no more than 50 shots between light cleanings. It cleans easily so it's not that bad, one wet patch and 3 or 4 dry patches is sufficient. I haven't shot it that much lately at 50 yards so I can't be precise at the group sizes, but at 25 yards it is easily 1/2 MOA, the group's hole being smaller than 2 pellets wide in any direction. The newish 33.95 gr pellets are clearly superior bucking the wind, less than 10mph has little to no effect out to 25.
I hope this helps.
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I'll take a risk of sounding dumb. From what I've read in Airgun World, the groups tighten up with higher velocities. IIRC, there was a guy over at TAG that had a ST barrel in a condor (TT did the conversion) that was supposed to be a tack driver. Makes sense, with the condors higher velocities as compared to 12 FPE limits in England and 30 +/- FPE with a fac.
My apologies if this is old news
Oh look. His post is right above this. Oops. Guess I should refresh more often
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So far, a good barrel has been a good barrel no mater what I hang it on (so long as it's put on right). If you can manage a uniform blast of gas to the pellet, have it "chambered" so it doesn't maul the pellets at insertion, and have it mounted solidly to the breech, the barrel takes care of spinning the pellets and spitting them out uniformly.
Don't think I'd spring the extra $ for a FX smooth twist at this point....although I'd like to. Certainly good barrels from (almost) all the reviewers, but I'm not so sure how much is the barrel and how much is the uniformity of the guns they are connected to. I'd like to find out. Have hooked up several LW's and one HW barrel to rifles they were not intended for and been pleased, so I suspect an FX would as well...but would it really be enough (if any) better with me at the controls and hung on less than perfect rifl.
Lets hope the Lottery numbers are good to me...win $100M, and I'll spend 5% (5 million) on airguns finding out what I want to find out. Another 10% to the church...gotta take care of that...and the rest blown on booze, drugs, hookers, and gambling.
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What is the benefit of the smooth twist barrel? Does the smooth twist cut down on friction and increase muzzle velocity?
I am just wandering what is the gains over traditional barrel designs?
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What is the benefit of the smooth twist barrel? Does the smooth twist cut down on friction and increase muzzle velocity?
I am just wandering what is the gains over traditional barrel designs?
They are much cheaper to manufacture. A small increase in speed of the pellet. I shot against .30 bobcat on our last 100m br and I was stunned how poorly it shot when compared to my .25 BSA.
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What is the benefit of the smooth twist barrel? Does the smooth twist cut down on friction and increase muzzle velocity?
I am just wandering what is the gains over traditional barrel designs?
They are much cheaper to manufacture. A small increase in speed of the pellet. I shot against .30 bobcat on our last 100m br and I was stunned how poorly it shot when compared to my .25 BSA.
I have thought about lapping the barrel and then using a dry film lubricant like what is used in engines on piston skirt and bearing faces and see how it does. They are designed to greatly reduce friction. I would think if they can hold up inside engines designed for torture races like le mans that it should hold up for a barrel where lead is used. I could buy a cheap crosman barrel and see what happens.
The issues is how to apply evenly and also how would the barrel hold up when heating it since you have to heat it too 300° Fahrenheit.
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I have thought about lapping the barrel and then using a dry film lubricant like what is used in engines on piston skirt and bearing faces and see how it does. They are designed to greatly reduce friction. I would think if they can hold up inside engines designed for torture races like le mans that it should hold up for a barrel where lead is used. I could buy a cheap crosman barrel and see what happens.
The issues is how to apply evenly and also how would the barrel hold up when heating it since you have to heat it too 300° Fahrenheit.
I don't think that the temp will have any negative effect on a steel barrel. I do NOT see how you will get the film to be uniform in the barrel as I would think that there has to be some gravity related migration of the material as it transitions from a dry "film" to a cured product during the heating process. Also, though I may be wrong ( I often am ), the film is used in areas where oil would normally be present between the two metal surfaces of dissimilar materials and therefore different friction coefficients being presented to the oil film which results in shear thereby causing friction at higher levels than normal engine components. The piston skirts and the bearing inserts are softer materials than the cylinder sleeves and the crankshaft bearing surfaces which they face against and will tend to gall up under this stress. This combined with the extreme temperature and linear speed of the moving parts make the use of the dry film lubricants beneficial. The air gun barrel and the pellet don't have the same kind of oil film drag properties to deal with, nor the temperature, nor the constant high speed movement for hours at a time. Lead is quite slick as it is in the environment of traveling through the barrel at high pressure and high speed.
Along these lines however I have experimented with Renaissance Wax on a few pellets after cleaning the barrel of various air guns. It works well on barrels that have a tight bore relative to the pellet. It didn't work on the Smooth Twist barrel; after about 5 pellets the accuracy went bad very fast and never improved until the barrel was cleaned again. Since I was getting such good results from just cleaning the barrel often I didn't pursue it any further.