AR polygonal rifling con't
I question ballistic efficiency of this bullet shape traveling 3.000+fps after distortion by polygonal rifling and would want to see data comparisons over 500 yards between this and conventionally rifled bullets.
Japanese rifles used the British Medford style rifling that had no sharp corners between lands and grooves.
CW rifled Whitworth cannons used preshaped projectiles.
Japanese rifles used the British Medford style rifling that had no sharp corners between lands and grooves.
CW rifled Whitworth cannons used preshaped projectiles.
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As stated before, the 5R rifling is a form of polyagonal rifling. Look and see what 80 % of the top 1K bench rester's are using...that should erase your questions, or at least answer them.
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Why should polygonal rifling deform a bullet any more than conventional spiral cut rifling? If anything, the better fit to the bullet should deform it LESS. 0 -
This is all speculation and begs hard data on performance over useful range.
I'd expect a greater loss in rotational velocity and aerodynamics with instability at long range due to greater drag of a rotating polygon vs an ogive smoothly transitioning to a cylinder.
A better fit of bullet is Medford style.
Compared to gradual engraving of conventional rifling on a perfectly fitting supported cylinder (bullet) the converting of a cylinder to a polygon is a major change in form with the possibility of a lot of blowby in the process.
Again, I'd like to see maximum range data comparison of say a 75 grain pointed boattail.
Also, who wants a signature bullet??0 -
quote:Originally posted by v35
This is all speculation and begs hard data on performance over useful range.
I'd expect a greater loss in rotational velocity and aerodynamics with instability at long range due to greater drag of a rotating polygon vs an ogive smoothly transitioning to a cylinder.
A better fit of bullet is Medford style.
Compared to gradual engraving of conventional rifling on a perfectly fitting supported cylinder (bullet) the converting of a cylinder to a polygon is a major change in form with the possibility of a lot of blowby in the process.
Again, I'd like to see maximum range data comparison of say a 75 grain pointed boattail.
Also, who wants a signature bullet??
That is it...that is what you expect, not the actual results. Like I said before, the benchresters are into the 5-R rifling, which is a form or polygonal rifling. Check the benchrest records.
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Proof of the pudding is in comparative long range data.
My jury is out.
I'd like to see it.0 -
quote:Originally posted by v35
Proof of the pudding is in comparative long range data.
My jury is out.
I'd like to see it.
V35,
Look at is this way, if you can reduce all the backside friction, would that not help? The side that absorbs all the force is squared up with the bullet. Like a normal land. The backside is what is smooth and reduces friction.
As a comparison, last December, one of the guys I shot with, ScottyS, used a .308 shooting 155's to one mile. As you may know, the stability of the bullet is a huge concern.
Anyhow, here's the video:
http://www.youtube.com/watch?v=QRzGuJK8QJI
Scotty shoots to one mile with a .308 His .308 has 5R rifling. He didn't beat the 6.5 Creedmoor (neither did my 7-08), but he got there. I say believe me, the .308 needs every advantage it can get to go one mile accurately.0 -
Impressive shooting.
A proper evaluation would be between two identical rifles, except for barrel, shooting identical ammo: one with and the other without the polygonal rifling.
In 30-06 caliber,the 172gr was the combat bullet. It was proven superior in ranging in Gen Hatcher's time over the 150 gr M-2 that was relegated to practice and training.
I see in Sinclair's catalog there are fancy high ballistic efficiency bullets for sale but I believe the 308 Win may not be the best platform for long range 30 cal shooting with bullets over 150 grains.0 -
quote:Originally posted by v35
Impressive shooting.
A proper evaluation would be between two identical rifles, except for barrel, shooting identical ammo: one with and the other without the polygonal rifling.
In 30-06 caliber,the 172gr was the combat bullet. It was proven superior in ranging in Gen Hatcher's time over the 150 gr M-2 that was relegated to practice and training.
I see in Sinclair's catalog there are fancy high ballistic efficiency bullets for sale but I believe the 308 Win may not be the best platform for long range 30 cal shooting with bullets over 150 grains.
I'll agree with you on that one. At least at that point we could see the effect of each as we stood back and saw what the shooter is actually dialed in to get.
I believe Scotty was using a 1-11.5" twist. Don't quote me on that. It shouldn't have any problem launching the 175 gr. M1 bullets to 2700 fps. I didn't know if you watched the video all the way through but some of Scotty's bullets went subsonic and were unpredictable and those that didn't remained on course. On a cold day in Nevada it was a crapshoot. But, on the hot day we shot in August they were remaining supersonic all the way out.0 -
I know as a fact that Glocks (and other pistols) with polygonal rifling shoot the same bullets faster than similar pistols of similar barrel length with conventional cut rifling. 0 -
v35,
Unfortunately, the assumptions that you've stated are backwards of the real events and how the bullets behave. You need to spend some time studying this type of rifling and maybe even shooting some to gain the necessary experience required to pass judgement on this form of rifling.
Here is an excerpt from an article with a link to the complete article for your reading pleasure:
"The advantages of barrels with polygonal rifling include a smaller gap between bullet and bore, leading to slightly higher bullet velocities, and smoother bores that accumulate less fouling, making them easier to clean. The barrels are also generally more accurate because there is less bullet deformation by the "grooves" (less "bite" into the bullet) and because the bore's surface is formed with more consistency. Because the rifling has no sharp corners to erode, barrels with polygonal bores have a longer, usable life, since they retain their accuracy longer. Finally, the hammer forging process used to create barrels with polygonal rifling is less likely to leave traverse tool marks, another cause of fouling, and a problem more common in conventionally rifled barrels. Accuracy, longevity, and strength may be the greatest practical benefits of barrels with polygonal rifling. A limitation is their inability to be safely used with lead bullets."
http://www.humanevents.com/article.php?id=37197
It is a fact that two barrels manufactured back-to-back will never exhibit the exact same performance let alone two barrels from the same run. So attempting to make a comparison between two disparate types of rifling from separate runs would be a waste of money, time and energy.
It is a waste of our time and hard earned money to attempt to set up a comparative test of two identical rifles with different rifling styles just to satisfy your unfounded doubts and lack of experience. The barrels together would run $600 and then adding in the installations and chambering, we would need around $1,000.00 simply to prove something to you that is already know fact. You need to do the work since you are in the definitive miniscule minority on this knowledge base.
However, proof is in the pudding as you say so here is a relevant historical image featuring the exact information you demanded:
Here is the article which uses this image and the appropriate explanation:
http://firearmshistory.blogspot.com/2010/05/rifling-polygonal-bore-and-whitworth.html
I hope you enjoy the articles.
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