Did it - extended the polygonal barrel with smooth bore extension

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mubhaur

mubhaur

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Nov 8, 2015
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If I see the older fx smooth twist barrels I find the the longer part of barrel from action to short of a couple of inches from the muzzle is grooved by crimping from outside. 

I see as Yarrah has said in his posts that the effective twist rate of pellets in smooth twist barrel become around 1:60" while the twist rate of front part of crimped barrel is around 1:17".

I understand that the pellet Skids through the last crimped part that reduces the effective twist rate of pellets. 

As against the fx smooth twist barrel I plan to find a polygonal barrel and attach a smooth bore tube on the front end of barrel. 

This may allow the pellets to achieve required twist rate and after that the smooth bore will enhance efficiency and moreover as the smooth bore will reduce the groove marks, the pellets will become more aerodynamic and bc may be improved. 

This experiment may proof to be complete failure as a top expert has advised me that he has done all these experiments without success. 

Still out of my curiosity and will of experimentation I plan to do it.

It will take me time to arrange required tools and machining.

I will update you all either it becomes a success or failure. 

Regards, 

Umair Bhaur 


 
It's an interesting project. Best wishes for a successful result.

Bear in mind the original SmoothTwist produced excellent results with JSB pellets but pretty much nothing else. That isn't necessarily a bad thing but stripping a pellet through rifling once it has gotten up to speed seems carry enough compromises that FX moved away from it. Presumably the soft lead alloy used by JSB tolerated it better than the comparatively harder alloys from H&N, RWS, etc.

 
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It's an interesting project. Best wishes for a successful result.

Bear in mind the original SmoothTwist produced excellent results with JSB pellets but pretty much nothing else. That isn't necessarily a bad thing but stripping a pellet through rifling once it has gotten up to speed seems carry enough compromises that FX moved away from it. Presumably the soft lead alloy used by JSB tolerated it better than the comparatively harder alloys from H&N, RWS, etc.
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I agree. That is why I am keeping the grooved area around 18" all the way from action to the end of rifling so that the pellet get required rpm and then move into smooth bore.

I feel it should work with more than one kind of pellets. 

Bhaur 
 
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Ah okay, thanks for clearing that up. A backward Smooth Twist so to speak. I presume then you were referring to Scott's experiment https://www.gatewaytoairguns.org/GTA/index.php?topic=183960
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Thank you for sharing the post of Scott.

In fact I never read it before. I got the idea from some old firearm barrels which were made in this manner.

I just read the post of Scott. I understand that he was successful upto 70 yards but not at 100 yards. At 100 yards, the pellet couldn't maintain the required spin to remain stabilised.

Scott used 6.5" grooved barrel. I understand that due to this short length of grooved part of barrel he couldn't achieve the required spin that resulted in key hole type paper punches which were without good accuracy. 

My plan is to use 20" .25 polygonal unchoked LW barrel. I understand that in 20" the pellet will attain the required spin to remain stabilised at 100 yards and beyond. Further I plan to add 4 " or 5" smooth bore at the end of polygonal barrel. The smooth bore will be gradually choked.

I understand that after passing though 20" groves, the 4" smooth bore the pellet will not be able to reduce the spin rate materially. 

I hope that this arrangement may provide accuracy and efficiency. 

I thank you for sharing a very relative post.

I have 50% hope of success. 

Let's see when I get time and tools.

Regards, 

Umair Bhaur 
 
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Did he really?
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Lol apparently my phone didnt update with your response before I posted? Idk I've been down 3 days with a stomach flu so could be anything.
 
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Well, I’m kinda disappointed to hear you say that but it’s for my own selfish reasons. Like you expressed in your original post, the idea of passing the pellet through a smooth section at the end to smooth out its periphery sounds like it could be beneficial. However as I expressed to Scott in the other thread, the challenge seems to be how do you achieve a consistent spin rate as it leaves the muzzle. Going through the smooth portion will cause the pellet’s spin rate to decay, and the extent to which it does will be determined by how much friction it experiences on its way through. That suggests sizing may be critical.

At the same time, we know pellets need very little spin so maybe it wouldn’t be all that important after all.

I guess another way of saying it is, we already kinda know what happens when it’s smooth, then rifled. Not so much when it’s rifled, then smooth.

But either way, I’m interested in following along and wish you good luck!
 
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Why not ream the bore of the choke to the groove diameter using a barrel that is long enough for your requirements?
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I am planning to choke the polygonal barrel at the muzzle end and attach the smooth bore at the breach end.

Looks like there are more chances of success in this arrangement as after passing through 5" smooth bore attachment, the pellet will pass through 20" LW barrel which will cover up any imperfections if left in smooth bore. 

Bhaur
 
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Hi mubhaur. Have you had a really good look at a Superior liner at the choke section. I think fx is doing I version what you are trying to achieve. That is the last section is now different to the original liner and is almost round and not polygon. It looks like they turned the liner and pressed the choke section a second time but off set between the original press. I think this was the big difference between original and Superior resulting in a rounder pellet/slug as it exits the barrel with a better BC.


 
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Hi mubhaur. Have you had a really good look at a Superior liner at the choke section. I think fx is doing I version what you are trying to achieve. That is the last section is now different to the original liner and is almost round and not polygon. It looks like they turned the liner and pressed the choke section a second time but off set between the original press. I think this was the big difference between original and Superior resulting in a rounder pellet/slug as it exits the barrel with a better BC.

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Dear Sir,

I have changed my mind after receiving updates on this type of experiment. Specially Scott had done it in the past that I knew latter.

Now I am going to extend the length of the barrel a bit only by adding a smooth bore in the action side.



I hole more chances of success in this arrangement as it is similar to fx smooth twist system.

Regards, 

Bhaur
 
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just make SURE !!! the short section of barrel you add if at breech "DOES NOT" have a tighter bore than barrel it must also seal within and have head support before it hits rifling.



Being a POLY creates a NON ROUND profile out of a Round pellet .... forcing it again to shape shift back to ROUND i have my doubts on being successful ?
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Dear Motorhead,



Thank you for guiding me. 

I just need a bit of elaboration. I understand that the smooth bore at breach should support the pellet but it should be a bit loose than the rest of grooved barrel otherwise the smooth bore will reduce the dia of the pellet and then it will enter the grooves.



I understand that I should give a bit of a taper angle at the joining parts. I shall keep the smooth bore a bit loose than the rest of the rifling while supporting the head of the pellet. 

If executed properly,do you still have doubts of success?

I shall choke the muzzle as well. 

Please advise further.



Regards,



Bhaur 
 
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