260 ackley calculation help needed

[10X]

I have a 260 ackley with a 28" barrel 1:8 5r
I am using berger 140vld hunting bullets and 46 grains of 4831
My problem is finding a ballistics calculator thats close to realistic. I have tried some online calculators and they are not even on the same planet
here are the real figures I have from shooting at the range in MOA
100=0moa
400= -5.5moa
500= -7moa

my MV is 2850 but I have to put the MV to 3175 on the berger ballistics calculator to get the 400 and 500 figures close to what I am actually getting

 

[260remingtom]

Hi whats the sight height of your scope above the center line of your bore as ballistic calculators ask for this, and what programs are you using ????? besides the Berger
I use the bullet flight app on my android from knight armaments or applied ballistics from Berger and find the bullet flight app to be the easiest to use. or on my PC i use the sierra ballistic program ver 6

 

[10X]

scope is exactly 2" at the rear ring. its on a 20mao base
I have only used the basic online calculators I dont own any programs
tomorrow if its not freezing I will get out the crony and confirm MV

todays info
temp 30f wind 5 to 7 mph full value
100 elevation 0 wind 0 group size .333 for 5 shots
400 elevation 5.5 moa wind 1.75 moa groups under 3"
500 elevation 7 moa wind 2 moa groups under 4"

 

[260remingtom]

I just used the bullet flight program on my android phone and get those same figures using the G7 bullet profile ????? can anybody help out here as to what we are doing wrong ??

 

[10X]

I just signed up and used the LRH calculator and have the same problem. to get close to my actual bullet drop I have to increase the MV to 3000 on the calculator if I have the MV at 2850 its a few MOA out

 

[Farmerbrown]

How did you come up with a MV of 2850? With the actual drop data I'm showing a MV of somewhere around 3100 depending on the conditions. What is the altitude?

 

[10X]

How did you come up with a MV of 2850? With the actual drop data I'm showing a MV of somewhere around 3100 depending on the conditions. What is the altitude?

its a WAG based on hodgdens load data for 6.5x55 and 6.5-284 and using other peoples load data using the same amount of powder in a 6.5 case with the same weight bullet and barrel length and also considering terrys tactical (*) comp load is 48.5grains for a MV of 2950 and I am using 46 grains

(*) I was using his published load data as a starting point for my loads

2850 is really generous for 46 grains. it should be close to 2700 if published data is to be believed

altitude is 1250 ft temp was 30 and flurry's today and 55 and fine last month


correction to my original post: barrel length is 26" not 28"

 

[codyadams]

Are you using the correct barometric pressure when you calculate ballistics? This can make a big difference. With my .308, I have chronoed many times at 2675 fps. If I put in a pressure of 30 (about what my kestrel corrected to sea level, or about what pressure at sea level would be) I have to raise my velocity to around 3000 in my app for it to be correct with my actual ballistics at an ACTUAL pressure of 23 (@7600 ft elevation at time of test) so use a kestrel or look at your absolute pressure at your elevation. I don't trust the 'average pressure at your elevation' setting that some have, because it's just that, an average, not an exact.

 

[10X]

my elevation is 1250 the pressure is 30 shooting due east on a level range
the reason for searching for an accurate ballistics chart is there is no back stop or dust on this range the targets are steel gongs hanging on chain 12" off the ground and the ground is thick green grass so there is no splash or sign if you miss.
I got on at 400 and 500 but its taken nearly 150 rounds to do so. what I have been doing is setting up a cardboard target at 100 checking zero on that and also come back to that to confirm elevations

 

[codyadams]

By 4831 I assume you mean H4831, not IMR4831, IMR4831 would give higher velocities/pressure than the H4831 with the same charge. I don't mean to sound rude or anything...it just wasn't specified and I don't think you said you chronoed yet, and that would be something that would cause it, if you actually were getting 3000fps...

I assume you have a good scope that moves 1 moa when adjusted 1 moa?? Even if it moved 1.25 moa when adjusted 1 moa, that would do it...

on my app, you should be in the 8.75ish moa area @500, if your only getting 5.5 something wacky is up...

How are you ranging your target? Or are you at a verified range?

It will be interesting to see what the chrono says

 

[10X]

H4831
tested the scope 10moa measures 10" at 100
what I did was zero the rifle at 100 then wound up 10moa and shoot a 3 shot group to confirm the scope went straight up and not on an angle or did anything funky the distance between the 2 groups was 10" I have also confirmed that it will come back to zero and that the range settings I have now are repeatable. I have gone from 100 to 500 back to 100 then to 400 wwith no loss of zero
I am at 5.5moa for 400 and 7moa for 500
on the berger balistic calculator site if I change the MV to get 5.5 at 400 gives 8 moa for 500 so I know from that the other settings would be also wrong with only the known 5.5 correct

 

[260remingtom]

I have to do that test of moa at 100m with the MARCH 2.5/25/42 scope I bought about a month back as I heard that there have been a couple of bad ones that don't track correctly but the supplier has supplied replacements that are perfect here in ozzie land, I tested some loads in my 260rem and am getting about 1moa out on my ballistic calculator , but as someone stated earlier maybe height above sea level is whats causing your hassle

 

[10X]

chrony testing results

1) 2760 cold first shot of the day. rifle was not cleaned from yesterday.
2) 2764
3) 2770
4) 2760
5) 2768

ES of 10
average of 2764.4

temp is 15f and clear
elevation 1250ft
chrony was at 12ft from the muzzle
load is
46 grains of H4831
hornady 7-08 case reformed to 260AI
federal 210 primer
barrel length 26" 1:8 twist
berger 140VLD #26504

I only have a cheap scope but it seems to be working as intended. the scope is the AIM XPF 4-16x50
now I might be making a mistake in how I am reading the scope. the turrets have numbers starting at 0 with 8 clicks to the next number so each full number is 1 MOA and thats how I am reading it. I select MOA output in 100 yard increments from 100 to 1000 on the calculator. I have also noticed that there is up to 3moa variation on the 500 yard calculations between the calculators.

 

[260remingtom]

there's some thing that we are missing like is the range really 500 yards and so on , also I would mount another scope on the rifle and test the elevation settings against the one that you are using