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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/22/2008 at 05:43
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                              Getting ready to have my .25-06 Mauser rebored to 9.3x62. Barrel is now at 26" and will end up at 19"-21". Need to know a proper rate of twist.  8shots,beings your in Africa hopefully this will be right up your alley. Anyones info is APPRECIATED!
 
                                                 til later
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/22/2008 at 14:28
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why so short?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/22/2008 at 14:49
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Great round, 35 whelen on steroids, light kicking, enjoy!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/22/2008 at 15:30
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Shooting Times's Layne Simpson did a nice article for the March issue on this cartridge.  He didn't mention twist rate, but his barrel was 23".  I sent him an email, but not sure he'll respond.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/22/2008 at 16:03
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                               Already have a .25-06 and a .300 with  24" barrels plus a .243 with a 18.5" barrel.  The 9.3 from what I've found out is a cartridge that doesn't lose much velocity in a short bbl.  One example shows a loss of only 60 to 70 fps when going from a 23.6"bbl down to 20".  Plus this isn't a high velocity round anyway.  I  bought this rifle in the late 80s for just such a project. This bbl is a semi-varmint weight bbl so I figure by shortening it to somewhere around 19"-21" and with the amount of metal taken out by the larger bore it will make this rifle handy in the thick woods,brush,and rhododendron thickets we hunt deer and bear in. But I'm still not sure about twist rate although it seems anywhere from 1-10 to 1-14 is being used with good results.  Any new info/suggestions are still APPRECIATED! That's why I'm here!
 
                                              til later
 
THANKS Tip69,I'll have to beat feet to the store and look for that mag!


Edited by 300S&W - March/22/2008 at 16:08
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/26/2008 at 08:59
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                            Anyone needing to know,it seems that 1-14 twist rate is the norm for most factory rifles(LIKE THERE'S THAT MANY!)and for ALOT of custom rifles.
 
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/26/2008 at 10:42
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The 9,3x62 is a great African cartridge! It is mostly used on bigger game.
300S&W, it seems like a 1;14 or 1;16 is the correct rate for your caliber. When in doubt, go for the tighter twist. So 1;14. Barrel lenth will not effect your spin rate, but velocity will.
If you are mathematically inclined, try this:
You can use the Greenhill Formula to determine optimum twist rate for any bullet and caliber you shoot. Mind you, this is a generic formula, subject to change slightly with velocity, but I've found it to be a good rule of thumb when trying new bullets & loads.
You'll need the length of the bullet to start with.
Divide the length of the bullet by the caliber. Divide this number into 150. Now, multiply this new number by the caliber again.
Example:
Hornady #2250 HPBT, 52 grains, .224 caliber, length 0.703":
0.703 divided by .224 = 3.1383
150 divided by 3.1383 = 47.7965
47.7965 multiplied by .224 = 10.706
So, according to the Greenhill formula, the optimum twist rate to stabilize this bullet should be 1 in 10.7 inches


Edited by 8shots - March/26/2008 at 10:45
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/26/2008 at 11:04
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8shots is right on.  I use a factor of 150 up to 1800 fps velocity and 180 if velocity is greater than 1800.  Simplified formula is then: 150xDsquared/L or 180xDsquared/L

1 in 10.7 if 1800 or less
1 in 12.8 if greater than 1800
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/26/2008 at 12:00
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Originally posted by 300S&W 300S&W wrote:

                              Getting ready to have my .25-06 Mauser rebored to 9.3x62. Barrel is now at 26" and will end up at 19"-21". Need to know a proper rate of twist.  8shots,beings your in Africa hopefully this will be right up your alley. Anyones info is APPRECIATED!
 
                                                 til later
.................................You will appreciate that shorter barrel, especially in the thickets and closer quarters. In your case a 19" er will be slightly more handy and lighter than the 21 inch tube!! If it still looks good, I`d even take the barrel down to 18"..You just may be able to do as I do; to sling your rifle on your shoulder with the muzzle below the top of your head!!........Your velocity loss and its effect on any game you`re hunting with this cartridge, will have absolutely no affect! You will still need to place the shot well and use the right bullet even with a 26" tube anyway. In most cases and depending on the cartridge, any velocity loss will be between 15 to 30 fps. for every inch of barrel length lost!................As an example, my little Ruger Frontier 300 WSM with its 16.5" tube, has been chrono`d to come to within 4.5% and even less (or 95.5% and more) of the 24" barreled 300 WSM`s. A 31% shorter tube than the 24" but with only 4.5% loss in velocity!! That falls right in line with a 15 to 30 fps. loss per inch. I can well exceed the ballistics of a 24" barrelled 30-06!!.............My handy little Ruger is a dream to hunt with, very fast to target (using the scout scope option), to carry, store and to pack. I can go from one extreme to another, hunt in the thickets or do some long range plains hunting (with a conventional scope), just like any of the longer barreled 30 cal. magnums and hunt the same big game!!...............A small percentage of velocity loss to gain a lighter, easier to carry, a quicker handling, faster to target rifle and so on, is an excellent trade off!..............Don`t be disuaded by any of the short barreled detractors or critics, with most having no experience either in the fields or behind a chrony.............Your choice to shorten the barrel is a good one and you will definetely appreciate your rifle even more and have alot more fun in the process!!...............I KNOW!!!WinkWinkWinkWinkWink    
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/26/2008 at 12:26
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                          REALLY APPRECIATE ALL the advice and info!!   I'm familiar with the formula which works out to a twist of 16.8" but also wanted some hands on experiences,so I'm going with 1-14 unless whoever does the work has an opinion. I actually found twists from 1-10 to 1-16!  1-14 falls one position short of being half way in the list of bullet OALs and twists for the 9.3(.366)cal at velocities under 2800fps. 
                          As far as barrel length goes,I'm comparing handling to my daughters 18.5"bbl Ruger.  This med-hvy bbl after being cut and rebored is going to lose ALOT of weight and I think any length from 18.5" to 21" will work. Might just split the difference!
                          Again THANKS for the help!!
 
                                                              til later
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