johnnyk
Well-Known Member
I was perusing the Sierra website when I came across these. Anyone seen or tried these? It said they need a 1-8" twist. Now we're getting somewhere!
Sierra .270 175gn Tipped Game King
- Thread starter johnnyk
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Calvin45
Well-Known Member
I was excited by these...at first. But if you look at the picture on sierras site you'll find it's just the 140 TGK with the bearing surface area stretched longer, the boat tail and ogive are exactly the same. Time and again it has been shown that simply making the cylindrical portion/bearing surface/whatever it's called 
longer while leaving all other dimensions/proportions the same gains little bc in comparison to the velocity reduction caused by the extra weight. The 140 tgk has a bc of .500 and the 175 only manages .560. That's a 25 percent increase in weight for a 12 percent increase in bc. It'd take a long long distance and require very fast initial launch speeds to catch up....
longer while leaving all other dimensions/proportions the same gains little bc in comparison to the velocity reduction caused by the extra weight. The 140 tgk has a bc of .500 and the 175 only manages .560. That's a 25 percent increase in weight for a 12 percent increase in bc. It'd take a long long distance and require very fast initial launch speeds to catch up....They are advertising the bc at .616. However, I agree the BC could be higher. If the nose is more aggressive like a berger it would require a longer OAL and not fit in short action/be finicky to reload. Winchester/Browning said wanted the heaviest/highest BC (min .6) could fit in a short action and get good velocity and not be finicky. There are already plenty of super long heavy 7mm bullets can do custom loading for in a long action. I am not advocating just stating what they said as their design parameters. As an example I have a 270 WSM 1-8 twist on Kimber action. With Berger 170 EOL to the lands with the berger is 3.06 (going from memory but it is at least 3.06). With the 175 Matrix it is 2.96 and incidentally the 165 ABLR is also 2.96. If optimize for BC, the ogive could be made longer but would be even longer jump to lands / finicky staying at 2.95" for cartridge.
Calvin45
Well-Known Member
I'm not sure where the .616 bc number you mention comes from but this is straight from Sierra's website regarding the projectile. To be honest if it was running at .61 that'd be a good bit more appreciable benefit but it would seem they've revised their figures or someone other than Sierra is advertising it differently. Not trying to be nit picky just citing where I'm getting my numbers from
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Calvin45
Well-Known Member
Makes sense. Could also be Winchester's "interpretation" haha but more likely the velocity thing.
Calvin45
Well-Known Member
Or a result of the tip being yellow and not green in winchesters load. Yellow is a notoriously efficient ballistic color. . Probably doesn't melt in flight so bad hey?
. Probably doesn't melt in flight so bad hey?
johnnyk
Well-Known Member
Well, I am looking forward to sending some out of my .270 Allen Mag. I wonder if they'll come apart in excess of 3350fps?
