.308 trajectory issues

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yidava25

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Heres my load: 150 Nosler Ballistic Tips
42.2 gr Varget

Rifle is a Rem 700 SPS Varmint (26 inch barrel)

My point of impact is 1.5-2 inches high at 100 (grouping just over an inch) and 2-3 inches low at 200. this isnt even close to conducive with what the books say. according to data i should be dead on at 200. By the way my groups are right around MOA at 200.

please help.
 
It would appear that the data in the books were not derived using your rifle/ammunition combination.
Have you chronographed your load?
It strikes me that 42.2gr Varget with a 150gr bullet is a rather mild load.
 
What is the problem? If your muzzle velocity is about 2500fps that would be fine.
Do you use a scope? Do you know what your muzzle velocity is? What cartridge are you using?
 
According to my expectations (not rocket science). The middle of your group at 100 should be at least 2.1 in. high.
1.5 in. high at 100 could print at least 2 in. low at 200.
 
tiriaq and juster: no i haven't chrony'd my load. according to the books it should be zipping along at around 2700ish. obviously if that is not accurate then the trajectory data for said velocity will not ring true either. yes i use a scope (its a Zeiss conquest 3.5-10x44 with Mil-dots) which brings me to wcats question: I have no idea. its mounted in medium-height talley rings if my memory serves me correctly. why?

Anyway, this isnt a big deal for a couple reasons: 1. ill be switching to 165s as soon as ive blown the rest of my 150s. and b. im primarily concerned with accuracy, not blazing speed (hence, the choice of caliber) so im prepared to deal with large arcs. thanks for the replies.
 
Scope height over bore plays a noticeable role in projected trajecories. Just play around with a ballistics calculator. Just change the scope height variable and see the difference
 
If you don't know the velocity coming out of your barrel then all bets are off.

The books are a very rough guide at best.
 
nosler.PNG

1.5" high Scope, 2350 fps. Doesn't look odd to me.
 
It drops that much, because you are shooting a weak load. I run 48gr Varget with a 150gr BT in my .308's, and 45 gr Varget with 180gr SST's.

44gr is the safe minimum for a 150gr.
 
blargon said:
It drops that much, because you are shooting a weak load. I run 48gr Varget with a 150gr BT in my .308's, and 45 gr Varget with 180gr SST's.

44gr is the safe minimum for a 150gr.
Click to expand...


+1

Lyman 49th lists 42.5gr as the starting load for 150gr bullets. Velocity should be ~2632 out of a 24" barrel.
 
I use 46.5 gr with that bullet/powder. your load is very mild. velocity will be low. Scope height is a major factor. Tables assume 1.5" if it is not an input variable. If your scope is lower, bullet will drop more at 200.
 
OKAY!
I just got off my lazy u-no-wut and went and checked my log and the load is with 44.2 gr of varget, not 42.2. its still lower than my nosler manual says is minimum (44.5) but i was already compressing (my COAL is 2.775 so i could stretch em a bit). So that makes less sense than ever (according to the manual which apparently counts for next to nothing) cuz it should (ooh theres that ugly word again) be doing 2771 at 44.5.
 
The problem with the "books" is they are based on a set of variables. Variables that may be totally different or even slightly different will translate into the differences you are seeing. Even calling 1.8" high good enough will show differences down range. There is never a substitute to going out and verifing your rifle.

Some ballistc calculators are very accurate. I've had the opportunity to shoot out to some pretty decent distances and so long as my variables were accuratly inputed then they were pretty bang on. A slight difference and they were off by as much as MOA or more.
 
I assume you mean .308 Winchester:
QuickLOAD© V.3.2 Interior Ballistics V.3.2 #230031
© Copyright 1987-2006 - H.Broemel, Babenhausen, Germany
-------------------------------------------------------------------------------
Case capacity and propellant properties may vary considerably from lot to lot!

**** Input data: Date: 1-Aug-2010 Time: 20:37:45
Cartridge................. = .308 Win.
Projectile type........... = .308, 150, Speer SP 2023 with flatbase

Max.avg.pressure(Piezo CIP)= 60191 psi Shot start / init pressure = 1600 psi
Projectile weight (gr)= 150 Groove caliber (in)= 0.308
Length of cartridge (in)= 2.774 Length of case (in)= 2.014
Case capacity(Grains Water)= 56.00 Length of projectile (in)= 0.960
Length of barrel (in)= 26.000
**** Values calculated:
Seating depth (in)= 0.200 Volume displaced (gn H2O)= 3.77
Comb.chamber volume(gn H2O)= 52.23 Projectile travel (in)= 24.186
**** Input data:
Propellant type........... = ? Hodgdon VARGET ?
Charge weight..........(gr)= 44.2 Load density......(g/cu.cm)= 0.844
Heat of Explosion (cal/lb)= 438779 Ratio of spec. heats cp/cv = 1.223
Solid density (gr/cu.in)= 404.6 Weighting factor...........= 0.5
Burning rate factor Ba(1/s)= 0.615 Pro-/degressivity factor a = 0.113
Burning limit ......... z1 = 0.4 Combust.Chamber Vb(ft³)= 1.197569E-4
Factor.................. b = 1.367 X-S.Area of Bore A(ft²)= 5.114126E-4
Bulk density (gr/cu.in)= 225.1 Projectile mass mp (lb)= 2.142857E-2
Loading ratio (%)= 94.9 Projectile travel x(ft)= 2.015486E+0

**** Results calculated:
Maximum pressure ........ = 40781 psi Way of projectile at Pmax = 1.65 in
Muzzle velocity ......Ve = 2676 fps Muzzle pressure .......Pe = 6694 psi
Project. energy at muzzle = 2385 ft.lbs Fraction of powder burnt = 95.1 %
Projectile travel time from 10% Pmax to muzzle = 1.32 ms
 
Book values are published for comparison purposes, and as a starting point for field verification. Some folks are concerned about choosing Bullet A over Bullet B because it drops .00x inches less. Some folks choose cartridge a over Cartridge b for the same reason.
Some folks just hunt.
 
ganderite: i had an experience with a different cartridge that showed shorter=tighter groups so i just naturally went as short as i could. also i played with this load for a while already so im a little reluctant to start again. but maybe i will, or maybe ill just hunt.
 
Re OAL. My rule of thumb for rifles not used for extreme accuary applications is 20 thou off the rifling or 20 thou off the magazine, which ever is the shorter.

Your short seating won't do any harm, but looks kinda short. I have 23 rifles in that caliber, and the shortest load called for is 2.795" Some are as long as 2.900" (Remington, chambered by their lawyer.)
 
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