.308 winchester

[XHODZAX]

ok i have a problem
i load 47g varget with 155 bergers 24" barrel 1:10 twist
my chrono shows 2840 +- 15fps
1/4" groups @ 100 yard
i sighted in my gun @ 200 and shot it @ 500 and 600 yards
@ 500 yards i need 6.75 moa elevation and @600 yards i need 8.75 moa elevation.
i run these numbers through berger balistic calculator and i get that my bullet travels 3100 fps to get these results.
is my chrono broke or what
.308 win shooting 3100 fps possibe???
any input please

 

[Grumulkin]

Re: .308 winchester

Your chrono is probably accurate. Berger's trajectory calculations are based on ballistic the coefficient which will be different in nonstandard atmospheric conditions.

 

[Fuzzball]

Re: .308 winchester

You really don't have a problem, you've checked the trajectory and KNOW what it is. All any computer model can do is give a rough prediction, they are by no means precise. The people who have a problem are those who check the velocity and than go long range hunting expecting the program is correct. That's rarely so.

(That's why I've been laughing at "scientists" screaming about impending doom since the "man made global warming" farce started! NO computer model can possibly make accurate long term - or long range - projections on such complex things. The weather "scientists" simply choose variables and tweak projections until they get what they want and then use the "computer projections" as proof of their "findings." AKA, "circular logic.")

 

[XHODZAX]

Re: .308 winchester

thanks guys
but i can't believe it was that far off 260 fps !!!!!
or let's say my chrono is right on than bergers bc is off
or their ballistics calculator is junk !!!

 

[bohem]

Re: .308 winchester

What input did you feed the calculator for your scope height?

That's a good way to pick up an extra MOA or more if you didn't get an accurate measurement in there.

 

[TimK]

Re: .308 winchester

It's not scope height, that makes a negligible difference to the calculations.

Something is wrong, I think, though I don't understand what. I checked your numbers with Ballistic FTE and get good agreement. FTE predicts the performance of my .308 almost perfectly, so I have good confidence it should work for yours as well.

It's a puzzle.

Are you sure of the ranges? Scope click values? Did you forget you were shooting on top of Everest?

 

[XHODZAX]

Re: .308 winchester

scope height is right
range is right also because we use it in nra hp long range
scope click values 1/8
top of everest check

well i'm going to the range again on monday and i will sight it in up to 1000 yards
write it down and not wory about stupid calculators

 

[TimK]

Re: .308 winchester

I'm interested to hear the results. Clock you loads again, if it's not too much trouble, with another chrono if possible.

3100 FPS looks about right for that load, maybe 100fps faster than I might have expected. I think your chrony is broken.

 

[USFTR]

Re: .308 winchester

With that short of a barrel, I would think 3100 is too fast. I would believe the chrono. Have you checked your scope clicks? Sight it in at 100 (or 200), move the crosshairs up some known distance (say 5 MOA) and then refire. Did the impact move that amount? Move either right or left the same amount. Idea is to create a box to check the accuracy of your clicks. I remember an article in FCSA magazine that did this for various scopes and some were off by quite a bit. So 1 MOA on your scope may not be exactly 1 MOA. I think I remember Leupold Mark IV fixed power and Nightforce 12-42 were the two best for accuracy with respect to clicks. Just a thought.

 

[Downzero]

Re: .308 winchester

3100 FPS is too fast. My 24" tube with 47 grains of Varget pushes a 155 Scenar 2899 FPS.

 

[deadly0311]

Re: .308 winchester

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Downzero</div><div class="ubbcode-body">3100 FPS is too fast. My 24" tube with 47 grains of Varget pushes a 155 Scenar 2899 FPS. </div></div>

DZ, i have about 6 inches less of barrel and am running right about 50fps slower than you with RL 15...have you given any thought to running that? And 3100 fps is a little high. Let me guess, were you using a Chrony chronograph?

 

[XHODZAX]

Re: .308 winchester

chrony chronograph


i sighted the gun in @ 200 yards and then moved back to 500
@ 500 yards i need 6.75 moa elevation and @600 yards i need 8.75 moa elevation.
i will do the box test on monday and get my moa for 7,8,9 & 1000 yards. i will post them on monday

 

[former naval person]

Re: .308 winchester

Really check your 100 yard zero. A quarter inch of group center impact off will REALLY change the trajectory out there. BC's change with velocity, altitude, humidity...so many things. Do your drop charts and don't worry about the velocities that are predicted. JMHO

 

[Downzero]

Re: .308 winchester

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: deadly0311</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Downzero</div><div class="ubbcode-body">3100 FPS is too fast. My 24" tube with 47 grains of Varget pushes a 155 Scenar 2899 FPS. </div></div>

DZ, i have about 6 inches less of barrel and am running right about 50fps slower than you with RL 15...have you given any thought to running that? And 3100 fps is a little high. Let me guess, were you using a Chrony chronograph? </div></div>

No I haven't given any thought to using Reloder 15.

If you are using RL-15 and getting 2850 out of an 18" barrel, you are shooting dangerous pressures.

A quick search will find my load is well within the norm for my load.