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Hey guys,
Is there an ideal weight projectile for each particular twist rate in each calibre?
For example, I've been told 165gr is too heavy for my 1:11 308. Ive had reasonable groupings but maybe getting lighter will improve recoil and accuracy.
Also, do boat tails fly better in faster twist rates?
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Don't be too caught up in projectile shapes - it's the length of projectile for the twist that governs stability. Boat tail bullets have slightly less bearing surface than flat base meaning lower barrel friction, but have better ballistic coefficient than their flat based cousins. Some barrels just don't like boat tails though... 1-11 may shoot 165gr fine, it's close to the accepted borderline but I've had a 1-12 twist that handled them fine and another that didn't. Just have to try them to know.
165gr will produce more recoil than 150, but 165 will have less wind drift at slightly more drop for a given range. But, the big but, is the difference between the two different weights may be insignificant when compared to other factors such as stock design and rifle weight.
No. It's not as simplistic as that.
A 1:11 twist 308 will absolutely stabilise 165gr bullets. Going lighter will reduce the recoil a touch. There are recoil calculators you can find via Google.
All bullets (whether they are boat tailed or flat based) require a minimum amount of spin to fully stabilise (based on their length, weight, and shape in that order of importance), and any extra spin above that shouldn't do much/any harm so long as the bullet is of decent quality.
So 165 is on the upper end of 1:11 /308? I shoot both 150 and 165 but figured if i ran hornady 3045 ( lead tip bt, 166gr) my load and impact point would be the same as a 165sst. So i could use each interchangeably without resighting in the rifle.
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Flat based and tangent ogive bullets (aka old style) are more tolerant to twist rates.
The new style, high BC bullets typically require a much faster twist to both stabilize and to achieve the listed BCs.
Berger have a stability calculator that can tell you if your bullet/twist/velocity combination will work or nor.
In regards to 308 and 165gr bullets, I'd say you'd be fine 1:11 is pretty standard for 308 and 165gr I pretty lightweight. If you were talking 175gr+ then you might run into issues but 150-170gr is pretty much the normal range for 308win.
There is a trend towards higher twist rates these days as heavy for caliber bullets, high bc are now the norm.
Cartridges like 243, 260, 284win all used to come in slower twists for the lightweight bullets of the 60s and 70s, but now 1:8 is pretty much the standard twist for almost everything it would seem.
165's go great in my partners 1-11, and in my 1-12 twist. You will only know how they go in your rifle when you actually shoot a few. A lot of rifles will shoot similar bullets to the same POI, a lot wont. Try them both and you may be pleasantly surprised.
I am pretty sure the 178 gr precision hunter would stabilise in a tikka 1 in 11 twist.
Speed is another factor to take in account: the 212 eldx will stabilise in a 300win mag 1 in 11” twist. I m not sure that the same bullet would stabilise in a 308 with a 1 in 11” twist barrel.
Tikka are now coming with an optional 1 in 8” in 243, 1 in 10” in 308 and 300wm and 1 in 9” twist in 7rm instead of 1 in 9.5”.
And the browning hell canyon in 300 win mag has a 1 in 8” twist barrel.
The attached pic from Remington data
Attachment 258527
No I shot 180s for years in my 1-11Quote:
Originally Posted by Rn-85
Correct speed helps marginal twists I can shoot 88gns in my 1-8 .224 but it has speed on its side which seems to help silly that tikka are going 1-9 rather than 1-8 on the 7mmQuote:
Originally Posted by Friwi
I don’t think it is silly, they have to also think about the other end of the spectrum, like 139 gr sp projectiles in the 7 rm. they still have to shoot accurately and not blow up in mid air.
and there might also be what CIP allow them to get away with.
I have been shooting 168's in my 1:10 with good groupings, I'm dropping back to 165's as the 168's are harder to source.
I’d pick that theirs more peopleQuote:
Originally Posted by Friwi
Waiting for an 8 twist 7 prc than their are people wanting to shoot 139sp out of a rem mag
180s will stabile in a 1:12 tube in the real world. .308 velocities of 2600 fps.
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Well, it kinda is - the light-for-length mono copper bullets need a very fast twist for weight to make em fly straight... But yes, there's a little more to it than that although for the most part that's the gist.Quote:
Originally Posted by Pommy
Sako 30 cals (308 and 3006) are 1-11.
Mate has a winchester 70 (for a while I had it in my head it was a remmy) with a 1-13. 300 win mag, bloody waste.
Took a metric shit ton of powder and projectiles trying to get it to group with the heavier projectiles. Measured the twist and found the drama. Went to 155s used in the Palma match and instantly came good.
He has found a 178 that will work just.
He has been talking to the guy that had it built and he has done it again. 300 mag case with a 1-13 twist. Bit dumb really.
That's exactly how I've been shooting lately (Sako factory ammunition). Accurate.Quote:
Originally Posted by Rn-85
I'm not sure what part of what I said you think isn't quite right this time?Quote:
Originally Posted by No.3
This thread jogged my memory of a short-lived cartridge the Spanish tried in the 50's. 7.92x41 CETME with an absurdly long aluminium bullet with a copper band: https://www.youtube.com/watch?v=3Njddshr3n8
And yes, the JBM stability calculator reckons this light-for-length bullet needs about a 1:5.5" twist. Making it heavier increases the stability. Although I don't know whether the unusual mass distribution of the bullet breaks the formula and what the actual twist rates used were.
Don't forget atmospheric density (altitude, temperature, and humidity) affects stability as well. Also a marginally stabilised projectile can shoot well but will have a reduced B.C.
Ha, thats what I was thinking as well...Quote:
Originally Posted by Pommy
