11.25 twist

[Zak Smith]

Unless otherwise specified, BC values are G1.

 

[Jim Watson]

Berger now also shows G7 BC which suits BT and VLD bullets without Sierra's kluge of listing a different BC for each velocity range you might see for a given bullet. But that is not likely to catch on for two reasons. First, all the usual charts and programs are figured for G1 and second, G7 gives you a lower number which does not help the advertising.

 

[TonyAngel]

Quote:
My theory is based on my belief that the heavier bullets don't need as much velocity to maintain their higher ballistic coefficient.

This statement doesn't really make sense mathematically.

Ok, that was a brain fart.

 

[sansone]

I also believe you need the heaviest pill that 1x11 twist can stabilize. You're gonna need the best BC rating for that range, usually the heavy pills have the best BC

 

[Zak Smith]

Minimum twist rate is determined by length not mass.

 

[sansone]

heavy pill= longer

 

[Zak Smith]

heavy pill= longer

Not necessarily. The 155 Lapua is longer than a 175 SMK - I believe. It's definitely longer than a 168 SMK

 

[sansone]

there are exceptions to everything, usually your heavy pills are going to be longer and have a better BC.
back on topic for the op: yes I believe your twist is fine, like others have stated try 175gr, if no keyholes try heavier.. again BC, BC

 

[TonyAngel]

Really, we could talk BCs and bullet weight/length until our fingers fall off. The fact of the matter is that your rifle will dicate what it likes best. A friend of mine has a 1:10 twist barrel that shows a real preference for 155s, which kind of disappointed him, since he got the faster twist barrel to shoot the heavier stuff.

Sierra makes very good, affordable target bullets in the Match King line. Many say that if you rifle won't shoot a Match King well, there's something wrong with your rifle. I'd suggest that you try the 155 Palmas and the 175s and see what those get you. The Match Kings don't seem to mind being jumped, whereas some of the "better" bullets (Bergers) like to be jammed to shoot well. Just in my experience.

I wouldn't bother with the 168s, if you want to get out to 1000 yards. I don't have a whole lot of experience (not much at all) shooting out to that distance, but from what I've seen, 600 yards is about the extent of the 168's capability.

Try going over to 6mmbr.com and click on the .308 link. It may shed some light for you.

 

[sansone]

quote: Try going over to 6mmbr.com and click on the .308 link. It may shed some light for you..

this is good advice. Those boys at 6mmBR do nothing but punch holes in paper

 

[franko07]

I'm new and also have the 11.25" twist, what's BC?

 

[pdd614]

BC, is ballistic coefficient. In basic terms it is the numeral value of how a bullet slips through the air. The more slippery the bullet the higher the bc value, which is a good thing for long range shooting.

For anyone who is more interested in ballistic coefficients. They should pick up "applied ballistics for long range shooting" by Bryan Litz. It is a very good read, and is worth the money.

 

[helotaxi]

Yep. Worth the money not only for the text but also for the ballistics software included as well as the tested BCs of a crap load of bullets.

 

[helotaxi]

Using (old) published BC values

_Bullet_           _BC_ _MV_         0     200     400     600     800    1000 | YARDS
175 load          0.51* 2700 >    0.00    2.62   11.18   26.93   51.55   86.72 | wind (inches)
155 Scenar        0.508 2925 >    0.00    2.28    9.69   23.24   44.21   74.16 | wind (inches)
210 VLD           0.617 2450 >    0.00    2.39   10.08   23.97   45.14   74.55 | wind (inches)

175 load          0.51* 2700 >   -0.00    0.51    2.12    4.17    6.72    9.90 | drop (mil)
155 Scenar        0.508 2925 >   -0.00    0.40    1.72    3.42    5.50    8.06 | drop (mil)
210 VLD           0.617 2450 >   -0.00    0.65    2.54    4.84    7.59   10.86 | drop (mil)

Note wind basically identical 155 vs 210, but drop 2.8 mils less at 1000.

The 175 and 155 loads are actuals. The 210 is a guess for MV. If you could shoot the 210gr VLD at 2550, it would look like this (a little more favorable to the 210)

_Bullet_           _BC_ _MV_         0     200     400     600     800    1000 | YARDS
175 load          0.51* 2700 >    0.00    2.62   11.18   26.93   51.55   86.72 | wind (inches)
155 Scenar        0.508 2925 >    0.00    2.28    9.69   23.24   44.21   74.16 | wind (inches)
210 VLD           0.617 2550 >    0.00    2.26    9.51   22.60   42.55   70.39 | wind (inches)

175 load          0.51* 2700 >   -0.00    0.51    2.12    4.17    6.72    9.90 | drop (mil)
155 Scenar        0.508 2925 >   -0.00    0.40    1.72    3.42    5.50    8.06 | drop (mil)
210 VLD           0.617 2550 >   -0.00    0.58    2.31    4.42    6.93    9.91 | drop (mil)

I've written for years that wind is more important than drop. However, once you've sorted with that parameter, the next one to consider is the drop rate (to reduce the effect of ranging error). The drop rate of the 210gr load is 25% more than the drop rate of the 155 load at 1000 yards.

I would recommend recomputing the numbers with actual BCs. The Scenar is significantly lower than what you used. The 155 has a 1.5 mil advantage in drop at 1k but gives up 18" in wind drift compared to the 210 VLD and using your MV numbers.

 

[Zak Smith]

If I run it at sea level

_Bullet_           _BC_ _MV_         0     200     400     600     800    1000 | YARDS
175 load          0.51* 2700 >    0.00    2.82   12.09   29.28   56.42   95.31 | wind (inches)
155 Scenar        0.460 2925 >    0.00    2.73   11.73   28.51   55.09   93.53 | wind (inches)
208 AMAX          0.633 2450 >    0.00    2.50   10.57   25.21   47.60   78.79 | wind (inches)

175 load          0.51* 2700 >   -0.00    0.52    2.16    4.29    6.98   10.40 | drop (mil)
155 Scenar        0.460 2925 >   -0.00    0.41    1.81    3.66    6.03    9.09 | drop (mil)
208 AMAX          0.633 2450 >   -0.00    0.66    2.56    4.91    7.73   11.11 | drop (mil)

175 load          0.51* 2700 >   -0.04    0.07    0.21    0.41    0.69    1.07 | drop per yard (inches)
155 Scenar        0.460 2925 >   -0.04    0.06    0.18    0.36    0.60    0.95 | drop per yard (inches)
208 AMAX          0.633 2450 >   -0.05    0.08    0.25    0.45    0.72    1.07 | drop per yard (inches)

I stand corrected on the AMAX-- my prior statement does not come out based on Litz's numbers. I would still compete with the 155 Lapua based on these numbers in UKD matches, however.