Bullet Selection and Considerations (308)

Get or give advice on equipment, reloading and other technical issues.

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darrward
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Bullet Selection and Considerations (308)

#1 Postby darrward » Wed Jul 25, 2018 4:25 pm

Hi All

As promised another newbie question...

It's mentioned in the other thread on scopes that the velocity of the bullet and how flat a trajectory the ballistics provide can affect the selection of the scope with regards to how much elevation compensation can be required when moving from zeroed at 300yds to go back to the 900yd mound

What I wanted to start discussing now is bullet selection

My understanding is that a heavier grain bullet such as a Hornady ELD Match 155gr is heavier and more 'stable' (windage tolerance?) but drops faster and is slower hence a scope with higher allowance for adjustment is needed versus a lighter bullet Hornady V-Max 110gr

Now of course the powder selection according to the reloading tables will have an effect but using manufacturer spec's theres a significant difference in muzzle fps - such as 2500 vs 2900 for example

Very interested in peoples thoughts and experience to help me in which way i should go...

Cheers
Darren

DannyS
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Re: Bullet Selection and Considerations (308)

#2 Postby DannyS » Wed Jul 25, 2018 4:42 pm

Stick with a 155 grn projectile. There is a reason why we use them.
Last edited by DannyS on Wed Jul 25, 2018 4:46 pm, edited 1 time in total.

DannyS
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Re: Bullet Selection and Considerations (308)

#3 Postby DannyS » Wed Jul 25, 2018 4:45 pm

Stick with a 155 grn projectile. There is a reason why we use them. Bit like comparing tennis balls to cricket balls

darrward
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Re: Bullet Selection and Considerations (308)

#4 Postby darrward » Wed Jul 25, 2018 5:07 pm

DannyS wrote:Stick with a 155 grn projectile. There is a reason why we use them. Bit like comparing tennis balls to cricket balls


Appreciate that but I was hoping for a bit of technical depth on why

I'd prefer to understand the detail behind the recommendation so I can learn more about the ballistics science behind it

For example there are 150gr, 153gr, 155gr, 168gr and even 208gr match grade bullets that I can see just from Hornady - why? :)

macguru
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Re: Bullet Selection and Considerations (308)

#5 Postby macguru » Wed Jul 25, 2018 5:58 pm

Well, light bullets have a lower BC and move around abit more in the wind. 125gr would be fine for smaller game at 100-200 yds - they shoot really flat and less recoil, but at 3-600 yds you will notice the added wind deflection

Heavy bullets move less in the wind but only if they are going at comparable velocities. To get 180-200gr bullets to go at 2800-2900 fps you need a hot load which damages the brass you are reloading and its not fun to shoot unless you have a heavy rifle.

bullets around 150 gr can travel fast with a warm load and hold their velocities out to 800m... OK ? All this applies to a 308win.

BATattack
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Re: Bullet Selection and Considerations (308)

#6 Postby BATattack » Wed Jul 25, 2018 6:42 pm

Basically the lighter the bullet the lowere the ballistic coefficient (BC) ie the lower the BC the more air effects it either by slowing it down or pushing it sideways by the wind. Think of it like a mack truck vs an F1 car. The mack truck has a low BC and a lot of wind resistance and thr F1 car is designed to cut through the air more and would have a higher BC (I WILL slap anyone who mentions downforce!)

Light weight low BC bullets genrally START out going fast and have a flat trajectory in the first few 100m but eventually (4-600m) their poor ability to cut through air means the air slows them down and thry dont retain velocity for long.

Heavy bullets start out slower but becuse they cut through the air better they retain their velocity for longer and will end up being faster at long range than the lighter bullet.

BC is also relative to wind deflection

Mozzie
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Re: Bullet Selection and Considerations (308)

#7 Postby Mozzie » Wed Jul 25, 2018 7:21 pm

Well said, and in a language that everybody can understand
My truck doesn’t run on love, it runs on diesel.
However, I love my rifle and it runs on lead. #-o

Pommy Chris
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Re: Bullet Selection and Considerations (308)

#8 Postby Pommy Chris » Wed Jul 25, 2018 7:59 pm

BATattack wrote:Basically the lighter the bullet the lowere the ballistic coefficient (BC) ie the lower the BC the more air effects it either by slowing it down or pushing it sideways by the wind. Think of it like a mack truck vs an F1 car. The mack truck has a low BC and a lot of wind resistance and thr F1 car is designed to cut through the air more and would have a higher BC (I WILL slap anyone who mentions downforce!)

Light weight low BC bullets genrally START out going fast and have a flat trajectory in the first few 100m but eventually (4-600m) their poor ability to cut through air means the air slows them down and thry dont retain velocity for long.

Heavy bullets start out slower but becuse they cut through the air better they retain their velocity for longer and will end up being faster at long range than the lighter bullet.

BC is also relative to wind deflection

Downforce :D Sorry couldnt resist it :D
Chris

macguru
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Re: Bullet Selection and Considerations (308)

#9 Postby macguru » Wed Jul 25, 2018 10:25 pm

Some of my shots exhibit downforce :(

jasmay
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Re: Bullet Selection and Considerations (308)

#10 Postby jasmay » Mon Jul 30, 2018 7:14 am

Shouldn't the first question be "what discipline are you shooting?

If you are shooting F-Standard you are restricted to 155gr projectiles

If you are shooting F-TR you can shoot what ever weight you want.

Just about no one is using 155's in FTR due to the fact there are heavier bullets with better BC available that will perform better.

Then it comes down to you personally weighing up all the factors.

Wind drift
Velocity & Resulting elevation
How well you can tune the bullet
Recoil management
Will you be shooting majority long or short range
If you already have the rifle, what twist rate it has


Lots to consider if you take an holistic view of what you are trying to achieve.


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