6.5x284 drop chart

[pills]

after getting my load right (51.5g H4831sc/ Lapua Brass/ 140g Berger VLD hunting @ 2750fps) in my Cooper 24" 1 in 8 barrel. I am making my drop card, using shooter app. and JBM program. Both gave me the same values . With a 200 yrd zero they give me a 300 yrd drop of 2.4moa (10 clicks) Vortex 4-16 PST on MOA. Problem is when I shoot this I end up 2.5" low at 300. I shot two 3 shot groups then switched to 3 MOA (12 clicks) and was shooting dead center. groups were all very good for me .6 to 1.75" at 300. Any ideas on the difference in the programs and actual results?

 

[BrentM]

basically .5 MOA low. Correction is to go up .5 moa from 2.5 to 3.

My programs show the same result give my basic altitude/barometric pressure and temp.

I would double check the scope is in fact tracking .25MOA per click. My guess is that is not.

 

[kcebcj]

You have to prove the drop chart with real world figures. Shoot at let's say 400, 600 and 800 yards using the come ups you get from shooter or whatever ballistic program you are using. See what the corrections are and adjust the ballistic data to match what you have shot by adjusting velocity and maybe messing with the BC somewhat.

I use Quick Load and QL is by far the most accurate I've ever used especially with its velocity output sometimes making my Ced M2 chronograph data look foolish.

Hope this helps if I understood you right.

 

[BrentM]

Hmmm, if you zero at 200 and use the exact same POA for 300, meaning you make no adjustment, then measure the actual drop that will help you determine FPS. To check against the chrono.

In order for you to be off from 200 yrd zero to 9.9" drop at 300 the FPS is only around 2400. I use 54 gr of 4831sc and get 2900. So I suppose that could be the case.

How did you determine 2750fps?

 

[pills]

I worked up loads using 140g accubonds and got 2700fps at 49.0g of H4831sc. While working up I was gaining approx. 30FPS per .5 grains of powder. Using this math I would be about 2790FPS with 51.5g H4831. assuming the 140 accubond and 140 Berger have the same MV. Also the Berger manual lists 51.0g(max load) to have a mv in the high 2700's. So between these 2 I figured 2750 to be close. I don't think there is anyway it will be as slow as 2400.

I did play with lowering the mv to 2700 in the programs and got no POI change in the solution.

I do understand the need to prove the data and I get what you are saying about playing with the numbers to get them close to the real world results. I guess I'm just wondering why I'm so far off from these two respected ballistic programs?

 

[Greyfox]

Your velocity seems to be in the right range for your load and within 15FPS of what I get with my 24" barrel. Did you re-confirm your 200 yard zero when you shot the 300 yard group? Also, is your scope height entry into shooter correct? It is unlikely that your .5MOA is effected by an incorrect velocity. Even it it were off by 50FPS it would be less than .25MOA of change in POI shooting at 300 yards with a 200 yard zero. Something else may be going on, zero, hold, rest, scope, etc. If everything checks out, I would use your actual drop data and enter it into Shooter.
I have the Berger reloading manual and found that their max loads using H4831sc is understated. Both my 6.5x284's and several other shooters I know have been able to use 53gr with no signs of pressure with the 140's seated at .1" out of the lands or less. Also, the 53 gr load should be used with LR primers, not magnum. This will get you a velocity increase to 2900-3000FPS depending on barrel length. I would still work up to this level in .5 gr increments to be on the safe side.

 

[pills]

200 yard zero was confirmed as I shot at 200 first then went back and forth between 200 and 300 a couple times. All shots were prone , bipod and rear bag. Scope hight is properly set at 1.75"...this load is giving me .25 to .5 MOA right now so I will stick with it for this hunting season. I may experiment more in the off season. I did test the scope at 100 when I got it. Shot a group went up 10MOA shot another group. Measured a 10.5" difference so all should be good....maybe I will run this test again tomorrow.

I guess as long as I shoot all my distances and make my own charts then it wont matter but kinda makes the app useless

 

[Derek M.]

Did you use Brian Litz's corrected BCs? Sounds to me like your chrono may not be 100% and you could be a bit slower than you think, unless another confirmed rifle and distance have been proven.

 

[pills]

Used G7 of .313....also tried the corrected MV function in the shooter program by entering your actual drop and distance. It gave me a mv of 2510....I really dont think its going this slow

 

[BrentM]

It could be that slow. Testing tonight I saw big velocity changes with seating depth etc. I think you will have to shoot 500 and measure actual drop.

 

[pills]

Well that's a good point...I am seating them long .I will shoot and confirm....thanks for everyone's help

 

[kcebcj]

after getting my load right (51.5g H4831sc/ Lapua Brass/ 140g Berger VLD hunting @ 2750fps) in my Cooper 24" 1 in 8 barrel. I am making my drop card, using shooter app. and JBM program. Both gave me the same values . With a 200 yrd zero they give me a 300 yrd drop of 2.4moa (10 clicks) Vortex 4-16 PST on MOA. Problem is when I shoot this I end up 2.5" low at 300. I shot two 3 shot groups then switched to 3 MOA (12 clicks) and was shooting dead center. groups were all very good for me .6 to 1.75" at 300. Any ideas on the difference in the programs and actual results?

At sea level
I just quickly ran the data you provided above in QuickLOAD and it spit out a velocity of 2721. With a 200 yard zero the come up for 300 is 2.39 MOA so your data is close

So if I was getting what you are the first thing I would look at is the zero. It has to be absolutely perfect for the come up data to be correct. In your program run it with a zero of 195 yards and see what you get. In QL that come up would be 3.09 MOA. So if you are zeroed just a tad low at 200 like a 1/4" (a guess) that would account for what you are seeing. Something to check.

 

[Greyfox]

Used G7 of .313....also tried the corrected MV function in the shooter program by entering your actual drop and distance. It gave me a mv of 2510....I really dont think its going this slow

I doubt very much that you are going that slow. The velocity calibration in Shooter doesn't give meaningful information at 300 yards. You need to get out to longer ranges. Using this function at 1000 yards a .5MOA correction is 30FPS. At 300 yards it's 224 FPS. Try entering the same MOA correction in your shooter program at longer distances and check the velocity corrections.