Need advice on proper twist

[TCFAN]

I am thinking about having MGM make me a barrel for the Contender in a 18 inch length.Caliber will be 32-20 Win with a .308 bore. This will be a cast boolit only barrel.The only thing I am not sure about is what twist I need for boolits that will weigh between 80 and 130 gr. The most used boolits will weigh between 110 and 120 grs. Any help or suggestions will be more than welcome.........Terry

[RickinTN]

Terry,
I'll take a stab and say with the weights you want to use probably go for a 1-14". I think Larry Gibson has a 14 in 308 and shoots bullets up to 180. I'm sure others will step in and let you know what they think.
Rick

[Scharfschuetze]

My Savage Model 23 in 32/20 has about (best I can tell with a yardstick and cleaning rod) 1 in 18 1/2" to 1 in 19" twist and my Smith & Wesson Model 1905 Hand Ejector in 32/20 probably has the standard S&W 1 in 18 3/4" twist.

Both shoot a 115 grain boolit well with no sign of tipping or instability on paper and they hit reactive targets well out at extended ranges.

Unless you are planning to use a jacketed spitzer boat tail bullet or a heavier than normal boolit for the 32/20, you should be in pretty good shape and well served with a 1 in 16" twist rate.

[TCFAN]

Thanks for the replies. The reason I ask is that they have to many choices. They offer 1-7,8,9,10,11,12,14,16,18,20,24,28,32,36.I don't want to mess this up for cast boolit shooting. The cost of the barrel is to much to make a mistake.....Terry

[RickinTN]

Terry,
Please excuse my mistake....You typed 32-20 and I read 32-40 somehow. Gettin' old ain't for sissies! My suggestion of 1-14 may work well for you but the suggestions of slower than 1-14 would be very valid as well. Take my suggestion with a large grain of salt!
Rick

[Wayne S]

http://www.mcgowenoutlet.com/twistcalculator.html
BE SURE to send MGM a "dummy round" loaded with the bullet of your choice, or measure on the bullets you plan to use where each one's nose contacts the riflings so you can determine if you want the nose to ingrave into the lands or be .00X off the lands what the action is closed

[TCFAN]

Wayne thanks for that link. After playing with it for a while and just guessing at what velocity I might get out of a 18 inch 32-20 it comes up with a 1-20 inch twist give or take a little bit.I think that is the same twist that the M1 Carbine has.
Unless some one has a better suggestion the 1-20 is probably what I will go with..........Terry

[TCFAN]

Terry,
Please excuse my mistake....You typed 32-20 and I read 32-40 somehow. Gettin' old ain't for sissies! My suggestion of 1-14 may work well for you but the suggestions of slower than 1-14 would be very valid as well. Take my suggestion with a large grain of salt!
Rick

Rick no problem. I know all about that getting old thing. Your suggestion on the 1-14 was my first guess. I just wasn't sure and thats why I asked....terry

[Larry Gibson]

16" at the fastest and 20" twist as the slowest. My choice would be the 16" twist if the 130 gr cast bullets are seriously considered.

Larry Gibson

[TCFAN]

Thanks Larry. Would it hurt if a short light boolit was spun to fast.Like a 311316 HP that might weigh 110grs in a 1-16 twist.....Terry

[Scharfschuetze]

Let me steal a little of Larry's thunder and say that my experience with boolits/bullets rotated faster than necessary (think 56grain FMJ M16A1 ammo in an M16A2) is that it boils down to the quality of the projectile. Poor quality bullets (not concentric weight wise) will wander off in a helix while good quality projectiles shoot pretty well. We could see the lot to lot variation in accuracy of the old A1 ammo when used in the new A2 with its 1 in 7 1/2" twist in the mid 1980s when converting from the A1 to the A2. The difference between good lots and bad lots of the older 56 grain 5.56mm ammo when spun too fast out of the A2s was remarkable.

Long range shooters feel that an over stabilized projectile's orientation may not follow its trajectory (ie. the tip will remain oriented high [initial orientation when it left the muzzle] from gyroscopic stability while the projectile descends on the back side of its trajectory). While that may or may not cost a point in a Palma match, it's of no concern regarding your 32/20. Well selected or well cast boolits will get you by with a faster than required rifling pitch.

I spin the RCBS 30-115-SP 115 grain gas checked cast bullet out of 30/06 Springfield rifles with 1 in 10 twists at upwards of 1800 fps with no obvious loss of accuracy at the shorter ranges (great ballistics for vermin, prairie dogs and jacks out to a hundred yards or so) and if the wind isn't too bad, they hold well enough out past the 200 yard mark on rocks and steel.

Larry's suggestion of rifling pitch rates should stand you in good stead.

[Larry Gibson]

Let me steal a little of Larry's thunder

A "little".....stole it all:-D

No problem, I couldn't have said it any better than Scharfschuetzer said it.....well put:wink:

Larry Gibson