polygonal rifling, speed increase?

[GrocMax]

What's the consensus experience on polygonal rifling and speeds?

Had a Pac-Nor 6mm 5 groove poly 8 tw 28" in 6XC. Never found any accuracy with it, went in the closet. Recently turned it into a 6TCU, still a scattergun, couldn't find an acceptable varminting load, but oh boy did it have speed compared to 2 other 6TCU's.

Fireforming load for a 58 vmax that hits 3550 and near max hot weather hot barrel in two other tubes was +200 FPS in the 5 groove poly (same reamer), and went up from there considerably.

I was all excited about the speeds and RPM's (The Splat is where its At!), but its a 1.5"-1.75" 10 rd grouper at 100 at best, is an AR mag repeater so my seating depth range is limited.

I never noticed a big speed advantage when it was 6XC, a minor one, but not like this. Is the poly that much faster?

 

[Changeling]

I thought this was a very interesting topic, it's a shame no one knows anything about polygonal rifling.
I did hear that what Pac-Nor does is not polygonal though. There was also a manufacture identified on this forum a while back (forgot name) that did it, I sent them an email and received a BS type answer, so I just let the subject go!

 

[tenring]

Had a Pac-Nor 6mm 5 groove poly 8 tw 28" in 6XC. Never found any accuracy with it, went in the closet.

Exactly my experience with PacNor pre-chambered bbl for Savage.

 

[stansrifles]

Is it my understanding that the round in question is a ar platform an you are shooting 10 shot groups just under 2inches.
Stan

 

[GrocMax]

Had a Pac-Nor 6mm 5 groove poly 8 tw 28" in 6XC. Never found any accuracy with it, went in the closet.

Exactly my experience with PacNor pre-chambered bbl for Savage.

I ordered a 6XC 3 groove 8 twist at the same time, this one had always shot well, it also got turned into a 6TCU and still shoots well.

 

[GrocMax]

Is it my understanding that the round in question is a ar platform an you are shooting 10 shot groups just under 2inches.
Stan

No its a bolt gun, Savage single shot large shank short action I modified to take AR mags, so I was limited to sub 2.280" OAL's to try.

 

[GrocMax]

I thought this was a very interesting topic, it's a shame no one knows anything about polygonal rifling.
I did hear that what Pac-Nor does is not polygonal though. There was also a manufacture identified on this forum a while back (forgot name) that did it, I sent them an email and received a BS type answer, so I just let the subject go!

I don't know what shape they use, but you can't visually see any groove to land lines or corners. I *thought* it was described as a 5 groove but that may not be correct. It was definitely described as polygonal.

 

[Changeling]

Here is a link that will describe polygonal rifling vs ridge (lands) and groove rifling:
http://hkp7.com/Rifiling.html

Another link with better detail:
http://www.firearmsid.com/A_bulletIDrifling.htm