284 bullet drop vs chrony velocity question

[chuckbuster243]

Ok guys,
I have recently been shooting a 284 with 180 Hybrids and 175 smk. My question is with my input velocity and bc in the tables my come ups have been between one and 3 moa high from actual. I cant figure that my velocity readings can be that far off but I will not rule that out. The same chrony when using known loads produces consistent results. Here is my load, Lapua 6.5-284 brass necked up CCI200 51.0 H4350 with both 180 Hybrid and 175 smk. The hybrids are jumping .010 and the SMK jumping .015 shot out of a 9 twist criterion 30" My velocity reading is 2755 average for the hybrids and 2740 for the smk with es between 10-15 fps or less. with a 100 yard zero it took 11.5 minutes with both bullets for a 600 yard zero. The hybrids shot under 3" for 5 and the 175's about 3.5." What should my 1k come up be? What do you think the problem is? Chrony, table or bc? I am all ears. Also what loads and velocity yall are getting. As well as come ups. I still wanna tweak accuracy but need to get my tables right first. Thanks, Matt

 

[6mmcldasher]

Your velocity is about rite for that load , if your come up at 600 was 11.5 your in the ball park, 1000 should be around 27moa

 

[FeMan]

I have the opposite problem in my 284. I am shooting the 180's at what I chronoed to be 2815 fps and I was hitting low from 800 to 1,000. If I use a G1 BC of 0.635 instead of the published 0.674 I get an exact duplication of what I see in the field. Bad chrono data is the suspect but I have several dozen rounds shot over it on different days with low ES.

 

[Keith Glasscock]

Make sure your scope height above bore is correct in the calculation. It makes about 1 MOA difference at 600 plus yards being off ~ 1 inch.

 

[chuckbuster243]

Thanks for the replies. It makes me feel better that my findings are close to what others have had. I am gonna shoot a 1k match this weekend and see how it runs. I think it can do better I just have to figure out what it wants. Matt

 

[chuckbuster243]

Make sure your scope height above bore is correct in the calculation. It makes about 1 MOA difference at 600 plus yards being off ~ 1 inch.

Thanks I will get a better measurement tommorow and recalculate.

 

[dragman]

Two culprits are scope height and actual BC after the bullet is fired. Its normal to adjust speed to make your charts work

 

[Kings X]

I adjust BC to match scope dope.
That is the factor that I cannot measure. Velocity, scope height, etc. I can measure.
How long it takes the bullet to go to sleep out of the gun - I cannot measure.
I then record that as "proven BC", and use it on the rest of my charts.
Works for me.

 

[chuckbuster243]

Well I shot this rifle on the electronic targets in Blakely this weekend. Shot decent considering conditions. Lost most of my points due to stupid things I did like wrong adjustments missing wind switches and such.. I just need to practice more as we all. Of the three loads I shot one was allot better at distance with very low velocity spread at the target. That is another cool feature of the targets. The load was almost spot on to the chart at 1k both elevation and velocity. Thanks for the replies it made me have a little more confidence that my calcs werenot to far off from everybody else. Matt