Chronographing the .243 and 17hmr

declan1980

So I finally got a bit of time to myself after 5 very busy weeks, and I decided I'd chrono my new rifles.
First up was the hmr. The hornady 17gr v-max are doing 2485 fps out of my rifle, which is a bit slower than advertised, but still quite respectable. The only thing I'm not happy with is the fact that hornady are lying about the B.C. Of these bullets. They're quoting .125, but they're actually .120, I know it's not much but when your trying to work out an accurate drop chart it's counting for an extra inch of wind drift at 200 yards.
Next up was the .243, and I have to say I was pleasantly surprised at these rounds. Hornady quote 3925fps for the 58gr superformance and they are doing 3901fps out of my rifle, with an extreme spread of only 41fps. These are going to make a serious foxing round.
I have the rifle zeroed dead on for 240 yards, which makes it 1" high at 100 and only 2.76" low at 300

Cass

That's not a bad spread for factory ammo considering most target shooters look for a max of 25.

A thing a chrono is great for is checking ammo as you have done. Used it a couple of times when trying new ammo from the hunting rifle. In a string of 5 shots i had a 2" flyer (low). Only for the chrono showed 180fps drop from the previous 4 shots i would have assumed i pulled the shot or something of that nature.

The chrono is a very handy tool, but can be contrary. I've used mine and on occasion depending on wind, light, distance form muzzle, etc it can give varying readings. Only the other day i had such a problem when checking my rounds on the range. The sun was coming out, shining brightly then disappearing to be replaced with heavy cloud cover. I tried varying distances, sunshade on, off, etc. Eventually i just ignored the chrono, and went and shot the distance which gave me the truest results.

Another thing i found is when using a ballistic calculator you do not always get the proper results. I used the chrono got my speed, put it into a BC with the ballistic Coefficient of the bullet, wind speed/direction, temp, pressure, HASL, etc and the drops were not the same as my actual drops. I had to play with the BC to get a true reading (assuming the chrono is right) to get the actual drops.

Still and all that's some good results. The Hornady (for the .243) seem to be a good and consistent round for you.

declan1980

Ezridax wrote: »

That's not a bad spread for factory ammo considering most target shooters look for a max of 25.

A thing a chrono is great for is checking ammo as you have done. Used it a couple of times when trying new ammo from the hunting rifle. In a string of 5 shots i had a 2" flyer (low). Only for the chrono showed 180fps drop from the previous 4 shots i would have assumed i pulled the shot or something of that nature.

The chrono is a very handy tool, but can be contrary. I've used mine and on occasion depending on wind, light, distance form muzzle, etc it can give varying readings. Only the other day i had such a problem when checking my rounds on the range. The sun was coming out, shining brightly then disappearing to be replaced with heavy cloud cover. I tried varying distances, sunshade on, off, etc. Eventually i just ignored the chrono, and went and shot the distance which gave me the truest results.

Another thing i found is when using a ballistic calculator you do not always get the proper results. I used the chrono got my speed, put it into a BC with the ballistic Coefficient of the bullet, wind speed/direction, temp, pressure, HASL, etc and the drops were not the same as my actual drops. I had to play with the BC to get a true reading (assuming the chrono is right) to get the actual drops.

Still and all that's some good results. The Hornady (for the .243) seem to be a good and consistent round for you.

I understand what you're saying about having to play with the figures a bit. I had to do the same with my 223 before. But the chrono and BC are still a very good indicator of what to expect from a rifle.
I'm really happy with those rounds for 2 reasons, A: they're ridiculously fast and B: they're grouping under .25moa. This makes me unhappy for one reason though. I can't blame the rifle if I miss.

Cass

declan1980 wrote: »

. But the chrono and BC are still a very good indicator of what to expect from a rifle.

Absolutely.

While the figures may be off they are usually within a minute or so of where you actually need to be so if nothing else it'll get you on target with the first shot, and you can "tweak" it from there.

I'm really happy with those rounds for 2 reasons, A: they're ridiculously fast and B: they're grouping under .25moa.

That's all you want. Are the Hornady the SST? In .308 they were storming out of a 24" barrel. Even faster than the stated speed on the box.

This makes me unhappy for one reason though. I can't blame the rifle if I miss.

There are always other excuses.

declan1980

No, the hornady's are v-max's. I have some 95gr sst superformance that I haven't chrono'd yet, but they were grouping a hair under .5moa without a bag rest when I checked them to see where they were hitting without changing zero from the 58's zero. Luckily they were only a half inch low at 100 compared to the 58's inch high. I'll chrono them and shoot some proper groups soon

ormondprop

Did you try chrono any with mod on and mod off to see does it make any difference

declan1980

ormondprop wrote: »

Did you try chrono any with mod on and mod off to see does it make any difference

I can't shoot without a mod around home because of neighbours and livestock, so I'll have to wait until I can get up to the range before I can see what it's like without a mod