Sig BDX, Chrono, Reload, and confusion ... (long)

[philcox]

Setup:
RIfle; Tikka 6.5CM Superlite, Mesa Altitude Stock, Leupold VX-3i 4.5-14x40 CDZ/ZL
Zero: 200y
Bullet: 124g Hammer Hunter, Lapua SRP, 40.0 Varget, 2950fps
Range Finder: Sig BDX K1800
Chrono: Caldwell Ballistic Precision

Shooting 1/4-1/2 moa @ 200y ZL set
All ammo using new Lapua Brass
When out shooting at 435y today, RF says the MOA adjust to 5.5 (which is consistent with what vortex LRBC says too). Here is my results:



I then went to a 6.0 moa (which corresponds to ~2850 fps, 100 fps lower) and got the following:



Then I shot 3 "groups" with loads 40.0, 40.2, 40.4 just to see if if there was any better grouping (all of this at 435 yds)



So it seems that the 6.0 moa was the ticket for vertical, THEN I shot my final group using 40.0 Varget and 1x fired Lapua. I did adjust the windage with 1 click to move POI to left, and ended up with:



So this looks more like the 5.5 that the BDX was saying.

Does it make sense that 1X Fired brass would have better velocity than the new brass?

Just trying to get this thing dialed in for the season in a couple weeks. I feel I am almost there, but not quite. Any thoughts/input for a new reloader are appreciated.

Phil

 

[Cahunter805]

IMO the Caldwell chronographs are not very accurate. Also it could be the leupold scope not tracking exactly as dialed.
1X fired brass could result in a slight velocity change.
I would load some more 1x fired brass rounds and retest them for velocity and also run a tracking test with the leupold.

 

[philcox]

IMO the Caldwell chronographs are not very accurate. Also it could be the leupold scope not tracking exactly as dialed.
1X fired brass could result in a slight velocity change.
I would load some more 1x fired brass rounds and retest them for velocity and also run a tracking test with the leupold.

How does one do a tracking test? Basically, center shot at 100, 200, 300, etc and see if it tracks?

 

[Cahunter805]

 

[wind gypsy]

Does it make sense that 1X Fired brass would have better velocity than the new brass?

Yes, it's common for 1x brass to result in higher velocity than virgin brass.

 

[Rifles And More]

Chrono: I used to have a Caldwell and didn't start getting good results from it until I built a box for it to go in. Also, are you accounting for velocity adjustment of how far your chrono is from the muzzle?

Scope: First, I would zero at 100 - just one of my things - everything is up from there. Second, I would definitely do a tracking/return to zero test. I have not had much luck with the big 'L'.

 

[buzzy]

Thanks for sharing. If you have a 250 yard zero is it safe to assume you can conduct this test at 100 yards and all the other calculations are the same. Obviously the initial 3 shot group is about 2 inches high. You would then dial up 30MOA and measure the distance between the 2 groups and do the same calculations to check the tracking?? Or do you have to take the test at 250 yards or rezero at 100 yards?? Thanks

 

[Rifles And More]

Disclaimer: I didn't watch the video.

100 yard zero simplifies everything. Build your own tall target 1MOA=1.047 inches. Put a dot at the bottom and a dot at every interval up.

Shoot at the bottom. Dial-up one MOA, aiming at the bottom shoot again. Dial down to zero, shoot again. Dial-up to 2MOA, aiming at the bottom shoot again. Dial to zero, shoot again. REPEAT all the way you want to.

Keep in mind the accuracy of your rifle and see if the results are accurate (do they fall within the 1MOA accuracy of your rifle).

Also, hang your target with a plumbob. I assume you mounted your scope level using one? That could account for your windage shift.

 

[philcox]

All, thanks for the insight. I also saw some notes on doing the tracking without firing, same principle that your reticle should track appropriately. Advantage of that is that you take shooter and rifle nuances out of the "scope test", but you need to be able to secure the rifle/scope so it does not move at all. I may try both. At some point I am overthinking this, and will get back to "find a load, shoot at distance, if it works, stick with it."

 

[philcox]

Have a pic of the Box? I have the chrono about 1-2' from the muzzle, so should be negligible.

Chrono: I used to have a Caldwell and didn't start getting good results from it until I built a box for it to go in. Also, are you accounting for velocity adjustment of how far your chrono is from the muzzle?

Scope: First, I would zero at 100 - just one of my things - everything is up from there. Second, I would definitely do a tracking/return to zero test. I have not had much luck with the big 'L'.

 

[philcox]

This is the better way to check tracking - static mount and check the scope on a correct target. Looking at your groups, a +/- 0.5 MOA deviation at 6 MOA could leave you thinking you have an 8-9% scope error (which is bad). The reality could be that your scope is completely fine and you, your rifle, your ammo, etc. are the cause for error.

Just a general note: optical chrono's can regularly tell you that your load is slower than reality unless you are exactly square/perpendicular. If you are shooting at any angle through the chrono, the path is going to be a little longer than assumed, so the time of flight through the chrono will spit out a slower velocity because it is assuming a shorter path. Also, when I use an optical chrono, I usually set-up about 10-ft from muzzle - not 1 or 2-ft to reduce blast (movement) to the chrono.

Another note: 435 yards isn't far enough to true-up you MV (but it's a start). You should try to get our to at least 600 - 800 yards to start actually truing MV.

Appreciate the info. I'll be trying 600 tomorrow. Learning a ton on this thread.

 

[wind gypsy]

Thanks for sharing. If you have a 250 yard zero is it safe to assume you can conduct this test at 100 yards and all the other calculations are the same. Obviously the initial 3 shot group is about 2 inches high. You would then dial up 30MOA and measure the distance between the 2 groups and do the same calculations to check the tracking?? Or do you have to take the test at 250 yards or rezero at 100 yards?? Thanks

If you shoot a group centered 3" high of POA at 100 and adjust your scope up 30 MOA to shoot another group, your second group should be centered 30 MOA higher than your first group. It doesn't matter if your first group was 3" high of POA in regards to scope tracking.

 

[Cahunter805]

Have a pic of the Box? I have the chrono about 1-2' from the muzzle, so should be negligible.

Definitely move the Chrono to about 10-12ft from the muzzle. Also I prefer to make sure the bullet is passing through the Chrono in the lower 1/3 of the screens.
Also have you verified your zero is dead on? If slightly low it could easily be .5MOA off that your 435 yard range.

 

[wind gypsy]

Aside from including shooter/ammo/rifle/mount errors, I'm not a big fan of live firing to check tracking because I've seen optics with dead spots, have positive and negative errors and have progressive errors. One in particular had a negative error followed be a positive error. So if you just dialed to 25 MOA (I can't remember the exact value), it was actually 25 MOA. But if you dialed 10 MOA, it was something like 9 MOA in reality.

Live firing just missing a ton of stuff while also adding potential areas for error. I was doing box "tests" a decade ago just like everyone else, because I didn't know any better. But there are better/easier ways to check.

I agree there is lot of room for error, especially with a 1 MOA gun/shooter. That said, its better than nothing if someone isn't set up to static mount a scope and still gives some relevant data.

Edit: to your point, i wouldn't just do 30 MOA and call it good either because good at 30 MOA doesn't mean good at 10, 20, etc.

 

[philcox]

This is the better way to check tracking - static mount and check the scope on a correct target. Looking at your groups, a +/- 0.5 MOA deviation at 6 MOA could leave you thinking you have an 8-9% scope error (which is bad). The reality could be that your scope is completely fine and you, your rifle, your ammo, etc. are the cause for error.

Just a general note: optical chrono's can regularly tell you that your load is slower than reality unless you are exactly square/perpendicular. If you are shooting at any angle through the chrono, the path is going to be a little longer than assumed, so the time of flight through the chrono will spit out a slower velocity because it is assuming a shorter path. Also, when I use an optical chrono, I usually set-up about 10-ft from muzzle - not 1 or 2-ft to reduce blast (movement) to the chrono.

Another note: 435 yards isn't far enough to true-up you MV (but it's a start). You should try to get our to at least 600 - 800 yards to start actually truing MV.

Any recommendations for a static mount? Is there a reason I can't jsut make one with a set of scope rings and some 2x4's. Seems like what I need is:

1. My scope level
2. Scope won't move when dialing
3. Ability to adjust the holder to align the scope
4. Ability to measure from scope front to target (measure at 100y)
5. A target that is horizontally and vertically level, and has marks to show where the reticle is
6. Verify tracking up/down, right/left

That about it?

Phil

 

[philcox]

Also, found out I was doing the Chrono just about as bad as I could:

• Close after sunrise
• In direct sun
• To close to muzzle
• Shadows and Light mixture

Will try to improve that also

 

[Rifles And More]

I do not have pictures of the box I built. It was a plywood box, painted black on the inside with a fluorescent light diffuser on the top. The chrono was bolted to the bottom and the whole contraption fit on a tripod. It made my velocity results more consistent - it was an eyesore and monstrosity to carry around.

I get it about checking the scope independently, without firing. Not something I would do. I shoot ten-shot groups and know what my rifle can do in the realm of accuracy. I feel comfortable running a tracking test up and down live fire.

There are a lot of rabbit holes in this hobby...

 

[Rifles And More]

What if scope error only shows up under recoil?