说说关于缠距的事

maxsterling

好像原来在网上看到过，说overstabilization是个myth，就精确度来说，缠距是越近越好，但是缠距过近会导致枪管的加工问题和寿命，同时也会影响弹头在出枪口前的形变（铜被刮掉太多），所以厂家一般都是找个平衡点。

7seven

MWD 发表于 2016-5-20 05:52
8.96÷11.32=0.7915

多谢纠正，这个我记错了。以前热衷于翻找这些理论性的东西的时候，做了很多不够精确的估算。纯铜的密度是纯铅的78%左右，差别20%。
记得当时研究了SMK的结构，铅芯外面包铜皮，前短还是空心的。就估算了一个密度差别大约10%，然后就只记住了这个数。

7seven

maxsterling 发表于 2016-5-20 20:51
好像原来在网上看到过，说overstabilization是个myth，就精确度来说，缠距是越近越好，但是缠距过近会导致 ...

如果弹头几何形状和密度分布绝对轴心对称的话，我倾向于同意这种说法。

Huntington

解释得太好了，把我的疑惑都解决了！

vt1000

7seven 发表于 2016-5-20 20:05
1:9的应该更合适。我的Ruger m77 223 24" 1:9，200码上77gr Fiocchi 比69gr Fiocchi表现好。说明这个距离 ...

michaelgjw

Miller twist rule

Using Miller's formula we can also calculate the stability factor assuming we already know the twist. Simply solve for .

where:

• m = bullet mass in grains
• s = gyroscopic stability factor (dimensionless)
• d = bullet diameter in inches
• l = bullet length in calibers
• t = twist in calibers per turn
  

Given those definitions we can expand:

where = twist in inches per turn, and

where = bullet length in inches.

Example

If we take the Nosler Spitzer .30-06 Springfield round, which is similar to the one pictured above, we can easily fill in the variables and calculate the estimated twist rate.[2] Starting with the formula

We then fill in:

• m = 180 grains
• s = 2.0 (the safe value noted above)
• d = .308 inches
• l = 1.180" /.308" = 3.83 calibers
  

Which tells us we have 39.2511937 calibers per turn. We calculate using and see that

So our rifling should be roughly 12" per turn. The twist, as listed on Wikipedia's .30-06 article is 10" inches per turn as an average of .30-06 caliber rifles; thus 12" inches per turn is fairly accurate. The discrepancy seen here also helps explain why certain bullets seem to work better in certain rifles when fired under similar conditions.

michaelgjw

michaelgjw 发表于 2016-5-21 16:31
Miller twist rule
Using Miller's formula we can also calculate the stability factor assuming we alre ...

0.224

Sierra

FMJ BT 1355

55

55

0.738

0.157

0.267

0.241

0.231

0.231

0.231

3000

2400

0

0

We then fill in:

• m = 55 grains
• s = 2.0 (the safe value noted above)
• d = .224 inches
• l = 0.738" /.224" = 3.295 calibers
  

result:
T = 9.710525487283371

7seven

michaelgjw 发表于 2016-5-21 16:49
We then fill in:

m = 55 grains

s = 2.0 (the safe value noted above)

coltjedi