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sig 556R 7.62x39
joshmb1982
Member Posts: 8,929
The sig website lists this rifle as having a 1:9.5 twist barrel. isnt this a very quick twist for this cartridge?
Comments
A 9.5 twist is more than a 123 gr .30 bullet needs but it was convenient and may help accuracy a bit with cheap East-bloc ammunition.
The sig website lists this rifle as having a 1:9.5 twist barrel. isnt this a very quick twist for this cartridge?
Nah.
Whether its the "best" rate of twist for the round is debatable, but as Hawk said, 1:9.5"is the standard rate of twist for military type 7.62x39 guns including the Russian Kalashnikovs and clones.
Technically its one twist per 240 mm, which actually works out to 1 in 9.448" if you do the English/metric conversion, but its close enough for gov't work (particularly Communist gov't work!).
This rate may well be a holdover from the Mosin Nagant days, since that rifle shares the same rate of twist for its 7.62x54R rounds.
My quick internet search also shows that some of the SKS rifles have faster twist rates of 1 in 200mm, which works out to 1 in 7.87". AK-74s use a similar faster rate of twist for the 5.45x39 rounds.
That said, I know of a local guy that done some experimentation, and chambered a 0.308 bore barrel for that round, that he modified slightly in the neck area to hold .308" bullets. He called it the.308x39. He used commercial boxer primed brass. The barrel he used had a 1 in 12 twist, and he used the 125 grain Nosler BT's, and 130 grain Barnes XLC to extremely good accuracy. This was an awesome performer on deer, seeing that it was a TC Encore handgun that he was playing with.
Best