philipbrousseau
Member
222 ,bofers steel barrel. Tight patch test says it's a 15 and 1/2 twist. Shooting 55gr sierra bullets. Could I be on the edge of stability with this combination?
Sako vixen.?
- Thread starter philipbrousseau
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Asa Yam
New member
Which Sierra 55 grainer? Big difference between a softpoint flatbase and a FMJBT.. The FMJBT needs more twist, due to the length of the boattail. Thisis why the US Army changed rifling twist on the M-16 from 1-14" to 1-12" before fielding the rifle. Cold weather tests (Alaskan winter) showed bullets were going sideways through the target when fired in air temperatures of -40* F dense air - (MV of a 5.56mm NATO round out of an M-16 is supposed to be 3200 FPS @ 58*F.)
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philipbrousseau
Member
The 55gr gameking. Spitzer boat tail.
philipbrousseau
Member
Thank you Asa. I found the jbm twist calculator yesterday.
R.G. Robinett
"That'll never work."
Do your self a favor and use this calculator < https://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi >, NOT the Miller model. For any but the shortest .224 bullets, one turn in 15.5" is a very weak spin-rate.
RGP.S. You'll likely achieve best grouping via bullets <0.62" long . . . and FB at that!
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Kevin Gullette
New member
An idea.........
I've never heard of a factory Sako 222 barrel with a twist that slow. Perhaps double checking may help.
As an aside.....I normally use a bronze bore brush(as it won't skip the lands), while pulling the brush back through the bore(as the brush would tend to tighten on the rod).
Hope this helps.
Kevin
I've never heard of a factory Sako 222 barrel with a twist that slow. Perhaps double checking may help.
As an aside.....I normally use a bronze bore brush(as it won't skip the lands), while pulling the brush back through the bore(as the brush would tend to tighten on the rod).
Hope this helps.
Kevin
philipbrousseau
Member
I ran my borescope down the bore and counted 1 and 1/3 revolutions in what I can best tell is 23 inches of rifling. That comes to 15.3 twist approximately. Really slow.
so start a brush or really tight patch. mark the rod and the clocking and push the rod in one rotation and mark the rod again.. withdraw and measure the distance of one full rotation. 15 is just not an industry std
philipbrousseau
Member
Thank you, I will that. I've read they are metric but don't know for sure.
Kevin Gullette
New member
Actually......I've long used an old wooden clothesline pin clipped to the rod, to accurately indicate one complete rod revolution when pulling the brush back from the muzzle.
Old school.......but very accurate, and repeatable.
Kevin
Old school.......but very accurate, and repeatable.
Kevin
bill larson
Member
222
the Speer 50 gr. TNT bullet was designed for 222 use..... I,ve used 1000`s..... good bullets....
the Speer 50 gr. TNT bullet was designed for 222 use..... I,ve used 1000`s..... good bullets....