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December 6, 2011
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I have a SRC in .40-70 WCF with a 1:20 twist rate. Been reloading and shooting 320 grain cast bullets. What would be (if any) the lightest weight bullet to shoot with the 1:20 twist rate ?
Thanks in advance,
Buck1898 in Tennessee
April 15, 2005
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Buck,
A 1:20 twist rate will allow you to shoot the lightest .40 caliber bullets that you might find, especially at the velocities you can shoot cast bullets. It will also allow you to shoot bullets somewhat heavier than 320 grains. Just keep in mind that as the bullet weight goes down, the powder charge needs to be increased.
Bert
WACA Historian & Board of Director Member #6571L
September 19, 2014
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Buck, I’ve heard of “over stabilizing” a bullet and having an effect on accuracy, but haven’t directly seen that myself. In my mind, dealing with an old barrel with potential issues, I would posit you may get so short (light) that it doesn’t shoot well as it is affected by bore defects rather than twist rates. With a 1 in 20 twist, its far more likely you could more easily find a too long (heavy) a bullet that would not be sufficiently stabilized by the twist rate. When computing the details on the Berger site for modern bullets, you figure in altitude, temperature, velocity at the muzzle, etc, as well as twist rate. If you wish to go lighter, try it out and see, as I doubt there is any program that deals with a .40-70 to tell if a bullet is too light. My opinions only. Tim
December 6, 2011
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OK !!
I have some 280 grain cast bullets and will give them a try. Will post results when weather un-freezes.
Thanks again !!
October 29, 2011
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Buck–WRA introduced in 1894 330 grain. I assume Carbine and Rifle twist rates are the same.
I got my 330 grain rounds from Buffalo Arms years ago, have owned 4 rifles in this caliber have 2 left–Bill
March 31, 2009
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Like Bert said when the length/weight of a bullet goes down the powder can be increased without causing a pressure issue. If not the lighter bullet will still shoot faster and have a higher point of impact. Over stabilization is not something we need to worry about with the old guns.
November 19, 2006
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Buck1898 said
I have a SRC in .40-70 WCF with a 1:20 twist rate. Been reloading and shooting 320 grain cast bullets. What would be (if any) the lightest weight bullet to shoot with the 1:20 twist rate ?
Thanks in advance,
Buck1898 in Tennessee
You don’t see a .40-70 SRC every day 
