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MrWithasee
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Posted: 10/6/2009 5:51:51 PM EST
i was reading the FAQ on Teppo Jutsu site and came across some info on twist rates
it seems that there are two rifle twists available:

1:18 twist - for 250 - 400 grain bullets
1:14 twist - for 500 - 600 grain bullets

according to the FAQ the 1:18 won't properly stabilize the heavier bullets.
my question is how will lighter bullets perform in the 1:14 twist 458 SOCOM barrels?

in the traditional 5.56/.223 platform, super light bullets (like 45 grain and smaller) do not perform well in the faster 1:7 twist barrels. i'm curious if the same is true with the 458 with light(er) bullets and faster twist.
granted, the velocities of the SOCOM are nowhere near that of the 5.56/.223. 1900fps 300 grain SOCOM is much different that of a 5.56 varmint round at 3600fps.

QuicksilverJPR
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Posted: 10/6/2009 5:58:41 PM EST
Originally Posted By MrWithasee:
i was reading the FAQ on Teppo Jutsu site and came across some info on twist rates
it seems that there are two rifle twists available:

1:18 twist - for 250 - 400 grain bullets
1:14 twist - for 500 - 600 grain bullets

according to the FAQ the 1:18 won't properly stabilize the heavier bullets.
my question is how will lighter bullets perform in the 1:14 twist 458 SOCOM barrels?

in the traditional 5.56/.223 platform, super light bullets (like 45 grain and smaller) do not perform well in the faster 1:7 twist barrels. i'm curious if the same is true with the 458 with light(er) bullets and faster twist.
granted, the velocities of the SOCOM are nowhere near that of the 5.56/.223. 1900fps 300 grain SOCOM is much different that of a 5.56 varmint round at 3600fps.



Actually, it's an internet myth that lighter bullets do not perform well in the 1:7' barrels. There's video out there to dispell said rumor/myth...
gearhead721
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Posted: 10/6/2009 6:00:08 PM EST
I didnt think you could over-stabilize a bullet. i thought just the under-stabilizing was a problem. Marty? enlighten us grasshoppers.
MrWithasee
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Posted: 10/6/2009 6:01:47 PM EST
i simply used that reference as an example only - not to debate the fast twist/light bullet combo in the 5.56
QuicksilverJPR
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Posted: 10/6/2009 6:16:51 PM EST
Originally Posted By MrWithasee:
i simply used that reference as an example only - not to debate the fast twist/light bullet combo in the 5.56


Just wanted to make sure

I know that in order to shoot longer/heavier rounds in my muzzleloaders, the barrels definitely need more twist to stabilize said projectiles...so it makes sense to me here in the .458 SOCOM as well...
MrWithasee
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Posted: 10/6/2009 6:24:27 PM EST
i suppose a better way to phrase the question would be;
"will a 1:14 twist 458 SOCOM barrel afford me the flexibility to shoot lighter bullets (250 - 400 grain) as well as heavier bullets (500 - 600 grain) without sacrificing reliability, safety and/or accuracy?
QuicksilverJPR
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Posted: 10/6/2009 6:28:44 PM EST
Originally Posted By MrWithasee:
i suppose a better way to phrase the question would be;
"will a 1:14 twist 458 SOCOM barrel afford me the flexibility to shoot lighter bullets (250 - 400 grain) as well as heavier bullets (500 - 600 grain) without sacrificing reliability, safety and/or accuracy?


I've shot the 100gr Lehigh bullets, and the 255gr with pretty good accuracy as well (the 255gr sub MOA at 100 yds). The Barnes TSX bullets are a good fit in this case with the higher twist weight and the longer bullet per grain weight...
MrWithasee
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Posted: 10/6/2009 6:30:41 PM EST
Originally Posted By QuicksilverJPR:
Originally Posted By MrWithasee:
i suppose a better way to phrase the question would be;
"will a 1:14 twist 458 SOCOM barrel afford me the flexibility to shoot lighter bullets (250 - 400 grain) as well as heavier bullets (500 - 600 grain) without sacrificing reliability, safety and/or accuracy?


I've shot the 100gr Lehigh bullets, and the 255gr with pretty good accuracy as well (the 255gr sub MOA at 100 yds). The Barnes TSX bullets are a good fit in this case with the higher twist weight and the longer bullet per grain weight...


which upper are you running? RRA?
QuicksilverJPR
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Posted: 10/6/2009 6:34:35 PM EST
Originally Posted By MrWithasee:
Originally Posted By QuicksilverJPR:
Originally Posted By MrWithasee:
i suppose a better way to phrase the question would be;
"will a 1:14 twist 458 SOCOM barrel afford me the flexibility to shoot lighter bullets (250 - 400 grain) as well as heavier bullets (500 - 600 grain) without sacrificing reliability, safety and/or accuracy?


I've shot the 100gr Lehigh bullets, and the 255gr with pretty good accuracy as well (the 255gr sub MOA at 100 yds). The Barnes TSX bullets are a good fit in this case with the higher twist weight and the longer bullet per grain weight...


which upper are you running? RRA?


I've got two RRA uppers. Didn't mean to end up two, but somehow I did...

MrWithasee
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Posted: 10/6/2009 6:38:54 PM EST
good deal, thanks
that is what i needed to know
i am on the shop for a SOCOM upper and wanted to be able to shoot a wide range of bullet sizes without sacrificing much
while i would shoot 500+ grain bullets, they would not be exclusive so i do not want a bbl setup that would be too limiting
when i saw that two twist rates were available i wanted to ask those who might be in the know
QuicksilverJPR
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Posted: 10/6/2009 6:43:52 PM EST
Originally Posted By MrWithasee:
good deal, thanks
that is what i needed to know
i am on the shop for a SOCOM upper and wanted to be able to shoot a wide range of bullet sizes without sacrificing much
while i would shoot 500+ grain bullets, they would not be exclusive so i do not want a bbl setup that would be too limiting
when i saw that two twist rates were available i wanted to ask those who might be in the know


Make sure to talk to Marty of Teppo Jutsu as well (here on the board). He has forgotten more than I've yet learned...
MrWithasee
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Posted: 10/6/2009 6:58:31 PM EST
there is much i still want to learn before i pull the trigger on this purchase
the 458 forum is down and from what i can tell from those who are on it, there is a lot of info
that being said, most of those guys are on here also

on the advise of one of those fellas, i'll be posting a question here and there
i'm hoping Marty will jump in on some of them but most likely the guys with rifles in their hands can be counted on as reliable
MrWithasee
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Posted: 10/6/2009 7:18:10 PM EST
hey, look what i ran across

Originally Posted By MartytW:
14 twist is REQUIRED for 500 and 600 gr

14 twist DOES NOT degrade accuracy with any other loads, as low as 86 gr ....

14 twist is the all around best twist to use for this caliber
Brazos_Jack
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Posted: 10/7/2009 3:38:59 AM EST
OK,

The .458 Socom is more or less a rebated rim 45-70.

The original 45-70 had a 1 in 22" twist because that was found to be optimum for the 405 gr lead bullet that was originally standard. The government later decided that it wanted a longer heavier bullet for better long range performance. It selected 500gr because it was the longest heaviest bullet that would still stabize reliably in a 1 in 22" twist. Not optimum for finest accuracy, but reliably stable. Modern BPCR (black powder cartridge rifle) shooters have found that 1 in 18" is more optimum for finest accuracy with 500gr to 550gr lead bullets.

Required spin rate for stability depends more on length to diameter ratio than weight and modern jacketed bullets are longer than a plain lead bullet of the same weight. So for jacketed bullets 1 in 18" is probably optimum for up to about 450gr.

Faster than optimum rifling is slightly less accurate, but rifling slower than the minimum required will cause the bullets to yaw and tumble in flight making any accuracy imposible.

Faster than necessary rifling increases chamber pressure, so loads must be kept milder to avoid pressure problems. Read a bit about the evolution of the 6.8 SPC for some good discussion on this point. Also faster twist rifling picks up jacket fouling faster and also wears faster. However, I doubt that any .458 SOCOM will ever get shot enough for this to matter much.

Marty just finished a barrel for me. I went with 1 in 18" and suggest the same for anyone who sees this as a hunting rifle. The cartridge lacks the capacity to give good hunting performance with bullets over about 400gr. 1 in 18" rifling will allow you to load to higher velocities before encountering pressure signs than 1 in 14".

If you have fantasies of being some kind of hi speed lo drag operator and want to use 600gr sub sonic loads in a suppressed 458, then you need to go 1 in 14".

Brazos Jack
MrWithasee
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Posted: 10/7/2009 5:29:45 AM EST
Jack,
maybe you missed this part where i posted twist advise from Marty

Originally Posted By MartytW:
14 twist is REQUIRED for 500 and 600 gr

14 twist DOES NOT degrade accuracy with any other loads, as low as 86 gr ....

14 twist is the all around best twist to use for this caliber


MartytW
The .458 SOCOM guy
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Posted: 10/7/2009 6:35:34 AM EST
Originally Posted By MrWithasee:
Jack,
maybe you missed this part where i posted twist advise from Marty

Originally Posted By MartytW:
14 twist is REQUIRED for 500 and 600 gr

14 twist DOES NOT degrade accuracy with any other loads, as low as 86 gr ....

14 twist is the all around best twist to use for this caliber




The last line is in reference and in direct agreement with what Jack stated - if you wish to have the broadest flexibility, you need to go with 14 twist. That way, if you run a 9.3" upper, suppressed with 600+ gr loads, your suppressor will not becoming a topic of good-spirited heckling back at the FOB.

If, like Jack, you will never fire a round heavier than 450 gr, the 18 twist will allow you to load a little more powder before seeing pressure signs.

If you will never shoot anything other than 300 gr JHP, we can make you a barrel with 22 twist.

But, the 14 twist is the "jack of all trades" giving good accuracy with the 300 gr loads, decent velocity with the 300 gr loads, good accuracy with the 500-600 gr loads and enough stability to allow short suppressed rigs.

RRA offers ONLY 14 twist, because of its ability to be used with all loads
We offer any odd twist you want as long as we can find it... we had someone as us to use an old 22 twist microgroove blank he had... why not?
“The patriot volunteer, fighting for country and his rights, makes the most reliable soldier on earth”
Bearbait1
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Posted: 10/7/2009 8:47:35 AM EST
I would only add a little actual data. My TJ barrel is a 20" 1:18, and as near as I can tell I am seeing roughly 100 fps more velocity over RRA 16" barrels with 300 grain bullets. This is a very rough approximation, based on where others are holding their top velocities as compared to where I hold mine. And I hold mine just below any brass markings.

Craig
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MrWithasee
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Posted: 10/7/2009 12:05:28 PM EST
i'm glad jack brought it up and that marty has weighed in on this

about pressures.
what sort of CUP are you seeing with the SOCOM?
i realize that each load is different but i am sure Marty was apart of the ballistic testing/development process
since i have been unable to find any sort of ballistic/trajectory table information on any of the SOCOM offerings, if you could point me in the right direction on that i would appreciate it

-marc
Bearbait1
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Posted: 10/7/2009 1:40:18 PM EST
Mr.

There is to date no pressure data that has been made available as far as I know. Marty designed the round to be held at 35K PSI out of deference to the bolt. And what we have are numbers generated from Ballistic software that generates the theoretical pressure for most of the loads that are out there. In reality, when we reload, we try and use conventional brass indicators to help us decide whether we are over the line. Again in reality, these pressures signs, like flattened primers, case head expansion and brass markings are in and of themselves not good. The bottom line to be safe is to use the published numbers that are out there, especially those from Marty as the real world has shown that these are safe, in as much as broken bolts are concerned.

There have been countless thousands of safe 458 rounds sent down range with these numbers, and the only time anyone has had significant problems (two I think, but perhaps just one) was when they went way beyond published. This round is basically still a wildcat, technically speaking from the SAAMI standpoint, but it is very easy to work with.

As to your trajectory query, you can easily do this for yourself with one of the many on-line calculators with the velocity and bullet BC. Or if you have any books, just look to the 45-70 data with the appropriate velocity. For my gun, with a 2.75" scope height and a few of the 300 grain bullets, I am usually (with a 100 zero) right around 5 moa at 200, and 12 at 300.

Craig
Northern born and Southern Bred