BDC Scope barrel lenght incidence

[froggy]

Salut ,

I am looking at a scope that has an elevation turret calibrated for a M14 rifle in 308 with a 22 in/56 cm barrel with a 1/10 twist. Like with my russian PU scope if you estimate your target to be at 200 metres you dial the turret on 200, if at 400 meters on 400 etc... etc ...

I am concidering mounting this scope onto a different bolt rifle, also in 308 but with a longer 25.6 in/65 cm barrel and with a 1/12 twist.

Assuming I am using the same Nato ammo, how much do you think I would be out on target with the longer barrel ?

[ovenpaa]

Is this with reloaded ammunition or factory ball and what is the maximum distance you will be shooting at? The 9cm/3.6" difference will add around another 50fps which will change the POI accordingly.

[froggy]

Re-
I think the BDC was calibrated for the 7,62x51 Nato round that has a 145 to 150-gr FMJ bullet.
In practice most of the shooting will be 400 to 600 meters and since I don't re-load I am likely to be using surplus ammo. Do you have a rough idea of the differencial POA/POI at those distances OvenPaa?

[ovenpaa]

I am walking out of the door right now however I can soon work it out when I get back

[pe4king]

Leupold Mk4 fixed 10 power with M3 turrets, I had one a few years ago very nice bomb proof scope, There is one on GT at the moment

[ovenpaa]

Froggy,

Some ball park figures:

147 grain bullet

56cm barrel @829ms

200m 0.6 mils
300m 1.5 mils
400m 2.6 mils
500m 4.0 mils
600m 5.6 mils

65cm barrel @ 855ms

200m 0.5 mils
300m 1.4 mils
400m 2.4 mils
500m 3.7 mils
600m 5.2 mils

So the variance is going to be:

200m 0.1 mils/.344moa
300m 0.1 mils/.344moa
400m 0.2 mils/.688moa
500m 0.3 mils/1.032moa
600m 0.4 mils/1.376moa

[tackb]

Leupold Mk4 fixed 10 power with M3 turrets, I had one a few years ago very nice bomb proof scope, There is one on GT at the moment

I've got two(3.5-10 though) , the 308 turret matches the 168amax/168mk at 2650 FPS nearly spot on. Certainly well enough to kill a roe at 400 and a red at 600.

[froggy]

Ovenpaa...
thanks ever so much for this table - you far exceeded my question
Looks like the son's head will be safe and the proverbial apple will get it with either barrel length.
This leupold Mk4 M3 does look nice indeed - thanks for the tip.