Another 6.5x284 thread! Help needed.

[backwoods83]

Ok, as I have posted several times before, I shoot a pile of 6.5x284. My current hunting load is 60grns of Retumbo (59.5 in new brass) in neck sized .292 bushing Lapua brass, with Fed215Ms and a 140 berger, base to tip 3.174" +- .003", .052" jump. Chronograph normally reads 3076 avg with an 8-10fps or so spread, yesterday same load averaged 2965, ***? So I figure something is going on, so I did some drop testing at 300yrds today, 6.1" of drop with 3/8" vertical (half of that was likely me!) Anyway I use Shooter and Strelok ballistic apps and put the weather and sight-in conditions in to run it backwards to get my muzzle velocity, both apps are telling me my velocity has to be 3235 +-3fps to equal the drops, once I put it back in this way I ran the apps to 1000yrds, it said 19.4moa up from 100, the last time I shot it at a 1000yrds I was up 19.75moa and was a little over an inch high, so this is about right. I know the thing can't be moving that fast, so what's up with this, anyone else experience something like this? I'm trying to get them to match up, or do you think my chronograph is telling me horrible lies? All responses much appreciated.

 

[coues7]

First of all it sounds like you and rig you are shooting are very capable....that's always good! Secondly, the bullet never lies! Let me put that in CAPS: THE BULLET NEVER LIES!!!!

With that being said, you can either adjust your ballistic coefficient (BC) or your velocity. Clearly the velocity adjustment you've made is working.....it doesn't really matter whether your chronograph is off or not. Likely it's not, which means you should have those two softwares adjust he BC vs. the velocity and see what you come up with. Have you confirmed that you are running the G7 ballistic model using a G7 BC? If not that could be another issue.

Either way, if you've confirmed what the software is telling you, I'd run with it and not worry about it.

 

[Korhil78]

I don't even worry with a chrono anymore. I just use one to get me close to the actual velocity and then just adjust BC and velocity in Shooter until it matches what my actual field drops are.

 

[backwoods83]

I use the .612 G1 bc in Strelok, I use the G1 litz data on Shooter, in you all opinion is it best to ajust the velocity or the bc, Brian usually has his bc numbers pretty spot on. I will put it in in the G7 bc and see what changes. Thanks.

 

[Mikecr]

You didn't mention barrel length, but I'm more inclined to believe the 2965fps in fireformed brass & your load.
The drop and adjustments are a mystery.

Are you SURE the ranges are actually correct?
I've been at a couple ranges where the backers were considerably off from marked ranges.
Maybe your 300yd was actually ~275? and your 1kyd: ~900yds?

 

[backwoods83]

Mike, barrel is 26.5" 1:8.3 twist with Vias brake, chrony started acting weird after the brake was installed, it consistantly crossed the chrony at 3076fps. Range was on my bosses farm, Leica 1200 said 304yrds today, when I had it at a 1000 it was at a match in Fairmont, WV, the range is called Harry Jones, it measures 1002yrds. I have no idea what's going on.

 

[barnesuser28]

Did you check tracking on your scope?

 

[Korhil78]

I have always adjusted my velocity but I have never had to adjust it much.

 

[backwoods83]

I have checked it several times, its a Sightron SIII 8-32x56 in 6 hole weaver tacticals, on a 20moa EGW rail, with a Vortex anti-can't. I have been shooting this round for a while, but this is my first hunting rifle chambered for it. I don't worry about speed as much with the bench guns, I can get good velocity with 4350 and 4831sc in 30 and 31" barrels, but with the speed and accuracy I get outta this thing with a 26.5" barrel, I may switch loads, the throat doesn't eat out as fast with Retumbo or H1000, and the barrel doesn't get near as hot. It has shot 2 groups under 10" at 1k in a Bell and Carlson stock before the brake was installed.

 

[backwoods83]

Ok, I used the G7 litz data on the shooter app and the drops at 300 and 1k match now but I still have a muzzle velocity of 3195fps, that's possible from this case but only at about 65-66k psi, so I guess I will use it this way. Mike if you get a minute run this through QL for me please, Retumbo 60grns, h2o cap 65.6grns, 140 berger (1.414"), 3.174" oal, do it for a jump and a jam with 26.5" barrel, i'd really appreciate it, I would like to get a ballpark of what's actually going on. Its time for a better chronograph or to just use the one I got to check ES and SD.