Prone with a Chrony

[Boom]

First time out with a chrony shooting prone. Besides not shooting the chrony, any words of advice on the best method to set up?

 

[Broz]

A couple bricks and a 2x6 and keep it 18 feet away from the muzzle so the blast does not shake the screens. Turn your scope to the lowest power so you can align your shot between the rods to get adjusted then turn it back up once you see you are not going to shoot the chrony. I had 3 of the shooting chrony's in line on a longer 2x6 once. They all had different readings by about 40 fps.

Jeff

 

[Sully2]

My chrony dont have any "screens"..???

 

[Boom]

Jeff: Thanks, bricks and sticks I can find. Interesting info about variance in your 3 readings. Is that a kind way of telling me to not put too much faith in the results? I downloaded and would like to use the new AB app to figure velocity but 1) I have not figured all that out and 2) I do not have data from as far out as what the instructions indicate I will need. Enojoyed your post about stepping out the back door and testing at 900...that would be nice!

 

[shortpants]

Yes that is exactly why you can't put a lot into the velocity reading from one chrony. I have 2 of the same make and they read around 40fps different. I shot prone a couple weeks ago with the chrony just sitting on top of my rifle case placed 10 feet in front of the muzzle. This worked fine but I like Jeffs idea about moving it back a bit. Lots of little rocks blasting away at it can't be good though mine showed no signs of damage. An EZ-UP shade over the chrony keeps the lighting consistent and another over yourself is nice too!

 

[Broz]

Boom, just use your chrony to get an average MV. Then put that in the AB program. Next check your zero to make sure you are on. Then shoot some 3 shot groups at 500, 700 900 and 1000. Keep a log of fiels conditions like Baro , temp ect. Also log how low or high the groups were and at what distance. Once you have that you can fine tune the AB app with changing the MV to get the dial ups spot on with your rifle and the app.

Jeff

 

[shortpants]

Jeff, at what point in trying to make everything match up on the calculator do you start using more than one bc? Is there a distance you add a second and then at further distance you add another or is it just an option when you can't get things lined up perfectly?

I tested a box of factory ammo the other day at 800yds. First I zeroed at 100 and then did an actual drop test at 800. I had an aiming point 16 feet above the target and aimed for it with the scope still dialed for 100. I then dialed in the correct elevation and shot for the center of the target. It was a min low for some reason so I dialed up and fired 3 more groups. They all were about 10" with 2 flyers. Without the flyers they were more like 4". The winds were not playing nice going from 8 all the way around to 3 at 3mph-8mph. I used a kestrel and entered all the environmental parameters into my Bulletflight app. I entered the heading in and had spin drift and corriollis accounted for. The groups were both left and right but vertically within 4" of center.

My question is in what I did to make the calculator match up perfectly. I used a chrony and have shot these over the chrony before so I have a fair idea on a true velocity. I used the calculate bc feature on the app and was surprised to find the bc reading .347 instead of the advertised .441??? It does match up perfectly however to the actual shooting. I played with velocity a little but it never got exact. Should I worry about not trusting the calculated bc or just run with it? Would using multiple bc's help in this case?

Sorry to the OP for highjacking but thought it might benefit others who read this.

Thanks, Jason

 

[Broz]

Jason, I have never needed multiple BC's until I got past 1200 yards. And not with all rifles or bullets. I have seen some go 1500 plus with one G7 BC. I dont know what was going wrong with your BC from the program but that is huge. I say it is wrong and the factory BC would be closer. I use BC to FINE tune, and velocity to get on path. Most times a velocity adjustment alone will get it done. Also if you had the majority of your hits with in 4" at 800 yards that is probably as good as in obtainable. A rifle, ammo and shooter holding 1/2 moa at 800 yards is a good team. 1/2 moa is 4". My advice for anyone is to use the factory BC or a Litz BC and adjust velocity untill you go past 1000 or 1200.

The more actual dial ups you have from different distances you shot and recorded the better you will be able to fine tune. but always remember the 1/2 moa accuracy of the team (rifle, ammo, shooter skill) 1/2 moa groups are golden, use the center of the group for the reference point to get the needed dial up.

Jef

 

[shortpants]

Thanks Jeff! I've been told in the past to leave bc alone except for fine tuning and adjust velocity. This Bulletflight program is new to me and this calculate bc from drop feature seems pretty slick but if it is not the better way of doing it then I'll go back to adjusting velocity. I just have a hard time believing my velocity is off that far. The average velocity I chose to run with just so happend to match the advertised velocity as well but I didn't realize that until afterwards. Either way something is way off but what really matters is I can get accurate come-ups.

Thanks again!!!

 

[Boom]

Broz - Thanks for the advice. If I understand you, I would run the app, go to callibration, enter yardage and adjustment and then apply to have the app run back at the implied the velocity? Tried and this and it seems to be working.

Shortpants - No problem, defintely a good addition to the discussion.

Thanks

 

[shortpants]

Jeff, I went back and played with the velocity and had to drop it 200fps to match up the real world drop. If that's the case then I just don't know if using a chrony helps at all? I mostly use one to track ES/SD but can I even trust that? Keep in mind this is a box of factory ammo. Fusion 300wsm 165gr. which is actually a Speer deep curl bullet I think. Velocity reads 3135 but have to input 2935 to match drops? Any ideas???

 

[justgoto]

Is that a kind way of telling me to not put too much faith in the results?

It all depends on what you are using it for.

I don't care if my chronograph isn't calibrated to the exact velocity, I care about ES.

 

[Broz]

Jeff, I went back and played with the velocity and had to drop it 200fps to match up the real world drop. If that's the case then I just don't know if using a chrony helps at all? I mostly use one to track ES/SD but can I even trust that? Keep in mind this is a box of factory ammo. Fusion 300wsm 165gr. which is actually a Speer deep curl bullet I think. Velocity reads 3135 but have to input 2935 to match drops? Any ideas???

Well, if you use the factory advertised BC for the bullet, shoot at 300, 500, 750 and 1000 and your drops match up using 2935,,,, then I say your chrony is a lying SOB... Proof is in the pudding!!

Jeff

 

[shortpants]

More testing and I'll bring both chrony's next time. I've compared the 2 chrony's in the past and they read within 40fps. I still have a hard time believing I'm only pushing that bullet at 2935.