Need Help, tune mv or bc

[Excavator]

so, I just had a 6.5 creed with a 20" tube put together for my little girl. We shot a hand load 130 accubond at 2675. And eld-m 140 at 2620. Mv were through a lab radar. So here is the question. Once I stretch the range out, with both loads. Both shoot low. My thought is to tweek bc to match drop instead of mv. My reason is because I have a shorter tube and am starting slower, then they were probably shot at the factor when bc was recorded. Gun was built by a very reputable smith that has built 10-12 setups for my brother and I. First time I have had this problem. What are y'alls thoughts? Thanks in advance. We have a hunt this weekend, and trying to fix drop tomorrow.

 

[Excavator]

Both loads shoot .2-.35 moa 3 shot groups at 100 yards

 

[Clucknmoan]

I don't know what kind of distance you shot it out to, but You might need a correction factor for your scope if it's doing it with both loads. If it's not the scope, Id shoot it at distance over the lab radar.

If that's not an option, I would reverify my zero, then shoot it at 500. Adjust MV to match drops. Then shoot it 1K and adjust BC to match drops. Shoot is a bit at various distances just to verify.

You may not have that kind of time since the hunt is this weekend. YMMV but it works for me and is pretty simple.

 

[Capt RB]

Tweak velocity at 500 and bc at 800 for jbm or some of the other bc solvers. With the 4dof shoot a group at 500 and adjust form factor to match what is on target.

 

[Excavator]

I zeroed at 200 with the 130 accubonds the shot at 479. Shot a 3.35" group 3" low.
Then zeroed at 200 with the factory eld-m 140 and shot a 3" group 4.2" low. No wind, I can shoot to 633 yards at the house. That is about as far as u can find in central Florida, just to dang flat. Was in a hurry this evening.
What is a exceptable adjustment in mv to match drop, meaning +- 2-3%?
I was thinking that with lab radar my mv should be close. Was thinking bc might be off. Hornady prints 2710fps on the box and I am starting 90fps slower out of the 20" tube. Gun has about 50 rounds down it.

 

[Excavator]

I have StrelokPro, and a g7br2 for calculations. They have both always been spot on in several different setups. That being said all my other guns are running standard length barrels.

 

[Capt RB]

Zero exact on the waterline or up/down a bit it does make a difference. Do a tall target test tape 2 redfield style targets together and make a plumb line through the middle at 100yds. I put a dot at the bottom and dial 1 mil at a time. I should land on the plumb line and it should be 3.6" between each shot. If you using an MOA scope use 5 moa per shot for 25 moa or what ever you max distance will be. If it is not exact most solvers will allow you to adjust the amount of correction per click.

 

[Excavator]

Swarovski z6i 2.5-15x56. Rem 700 action with tally highs. Using 2" as center of bore to center of scope. I will try a tracking test tomorrow. Then try putting a nsx 5-22x56 on it. Thanks for the help guys. I love the gun. Shoots awesome at 200.
Started as my 5r 308 had about 1,500 rounds down it so the action is smooth as glass.
I had it cut down to 11" LOP trued the action screwed a 20" proof carbon fiber on it, and a trigger tec diamon put on it. Painted the stock with dura velvet. Work done by Mc whorters in doe run GA.
Was a very cost effective way to get a custom youth model. Then as the kids grow up just bed in a full length stock.
O yeah I might shoot it some too!

 

[Canhunter35]

I would use the Mach 2 bc for the 140, .320g7 I think,
But my gut is your zero is low and your starting into the curve too early.
Shoot at 500 and 600 and if you"re the same Moa low your zero is off. If not, true your mv, then shoot farther and true your bc.
But I would check the zero, the other possibility is your scope is tracking off

 

[Excavator]

Thx All, will get back with you tomorrow, if I get time to shoot. Work is crazy this time of the year. Hoping to shoot for a hour or two tomorrow. She will only be shooting out to 200 yards this weekend. I was hoping to take one gun for us to share, but if I don't figure it out I will break out the stw for me to carry.

 

[Bstick]

I never understood why anyone would true their MV before their BC.

It is the only known factor once the bullet leaves the barrel other than your initial 100yd zero.

If you can't true BC at 800+, purchase ABM and use a custom drag curve. I am willing to bet that it matches up to your drops.

 

[Clucknmoan]

I never understood why anyone would true their MV before their BC.

It is the only known factor once the bullet leaves the barrel other than your initial 100yd zero.

If you can't true BC at 800+, purchase ABM and use a custom drag curve. I am willing to bet that it matches up to your drops.

Because BC doesn't effect POI nearly as much as MV at closer distances. MV is the course adjustment, BC is the fine.

6.5x284 with 150 Sierras. If I adjust decrease MV by 5% I get 5" more drop @ 500 yards. If I decrease BC by 5% I only get .4" more drop @ 500.

You would have to skew the BC a tremendous amount to get the 3"'s he's talking about. So much that it would be way off at distance when the BC has more effect than the MV.

 

[Bstick]

I don't think you understand what I am saying. Your MV isn't changing at the muzzle unless you have terrible ES. It is a fixed number. Your BC changes as velocity decreases. When you change your MV you change the predicted POI at your zero and farther ranges. Do you think changing your MV from 2620 to 2520 is going to fix all your down range issues? No it isn't. It is telling your computer that your BC is going to bleed faster than what it is. Adjust your BC or purchase a CDM. Your MV shouldn't be changed more than a few FPS. If you are off as much as you say, you need to adjust the BC.

 

[Bstick]

I was using those velocities as an example.