Bullet Selection

[Chriznak]

At what point does increased time of flight(due to lower velocity) cancel out the advantage of a higher ballistic coefficient? I'd like to run a super heavy .308 bthp out of a bolt gun with a 22" barrel for target shooting.

[anthonyjhallen]

If I understand your question, I would not go over 190gr depending on your twist.

[Tom Freeman]

I use everything from 155-230s in my 308. The longer a bullet the better BC you will have.

The 175 Sierra is a great compromise as is the Berger 185 Juggernaut.

[bigbrowndog]

the easy deciding factor is,... using the heavier bullet what is your trans sonic distance, is it longer or shorter than the lighter bullet. if its longer then you have advantage if its shorter then you don't.

trapr

[bornhunter04]

Best thing would be to plug the numbers into a ballistic calculator like jbm and see at about what distance your bullets will begin to go transonic. Like stated above, if your lighter bullets can stretch further before hitting that mark then you'd be better off.<br /><br />I run 155's and 168's in my .308, it doesn't like 175's. Also, what twist rate does your rifle have? If it's not fast enough it may not stabilize the long heavy bullets enough to get them to distance.

[bruceleroy]

I shoot 210 and 215 grain bergers from my 20 inch barreled 308 and it is awesome.

[Chriznak]

I'm still in the planning phase and it's going to be a frankengun. I hope I can get a pair of actions for a 243 and a 308 build. I'll be starting with the 308 because of the longer barrel life and I figure it will be a good "New York City" standard(if you can make it there{1000 yards with a 30 cal}, you can make it anywhere{with a 243}). The .743 BC of the Berger 230 HPBT seems quite appealing and I'd like to run that if the increased exposure to cross wind doesn't cancel out the advantage of the high BC. The sole purpose of the cartridges and rifles will be target shooting.

[Chriznak]

I figure the most logical purchasing order would be: action, bullet, case, primer, powder, barrel, trigger, chassis, glass. All of which are hard to find at the moment so I have plenty of time to plan out the most competitive build.

[procovert45]

Still gotta keep hp in mind when choosing bullets.a really smart builder who also shoots precision rifle matches chooses the 155 scenar when running 308 alotta times. Hes alot better at calling wind conditions than most though. Id say for your average shooter pick some middle ground and get a little of the best of both worlds.

[broke_again]

Once you go over the 175-185 gr range you need the speed of a 300 win mag to make those heavier bullets effective at LR.

Go for a 6.5 caliber, you will be happier.

[bigbrowndog]

I just pulled some of my 300 win mag data, this comparison shows trans sonic distance comparisons, a 190SMK going 2975fps is just above 1100fps at 1300yds, with wind drift (10mph) being 10.8". I need to push a 155SMK Palma, 3400fps, to be just above 1200fps at 1300yds, wind drift (10mph) is 10.2"

That is using the more common G1 BC data,

Using G7 data, the 190SMK at 2975fps, at 1300yds its just 1129fps, with 10.6" drift, and the G7 155SMK started at 3400fps is 1130fps with 10.9" drift.

So it would seem that you need to push the heavier bullet just over 400fps slower than the light bullet to roughly equal themselves.

This comparison is using both SMK bullets, it also shows the differences in G1 and G7 ballistic profiles, personally I shoot 155's from my 308's and 190+ stuff from my Win Mag.

[AustinT]

Did you miss a decimal on your wind drift, Trapr?

[bigbrowndog]

No I put it in moa not inches

[charms]

155 lapua scenar, .508 bc g1 @2900fps = 315.6" drop and 85.1" drift. velocity @1000yd = 1372

175 sierra mk hpbt .485 bc g1 @2700fps = 386.4" drop and 100.9" drift. velocity @ 1000yd = 1214

210 sierra mk hpbt .530 bc g1 @2400fps = .427.4" drop and 85.5" drift. velocity @ 1000yd = 1249

This is from JBM at 1000 yards with a 10mph wind full value. Just a quick comparison to show the difference between the 3. velocities are approximate. As you can see the drift between the 155 and the 210 is very close but the drop is 100 inches different. This means a lot in a tactical match where range estimation is critical.

[bigbrowndog]

Approximate velocity as in made up? Or rounded to whole numbers from your actual velocities? Or taken from a book?

Thx, Trapr

[charms]

Taken from hodgedons website using their max load data with varget. Just for a comparison. Numbers were rounded but within about 20 fps.

Edited August 3, 2013 by charms