A Chrony is your friend...

[bamboomaster]

I hope folks still go to the range with all the news dumps about Bernie, the Corona virus, AOC, Trump, stock market crashes, good prices on survival food at Walmart, etc.

So with a new carbine (the LWRC M6IC – SPR with a 14.7” barrel), a pot-full of old reloads, and a chrony I had sitting around it seemed like a good idea to check the V ( velocities), the SD (standard deviation), and the ES (extreme spread).

Instead of bringing along my time-tested bench rest for such matters (a Caldwell beast), I settled on “banker’s” sand bags which I’ve been tripping over in the garage for years. FWIW, I’m not sure I made the right decision but it still seemed to work out OK.

When you run a chrony, you’re doing it for specific data points related to your rifle and ammo. And those data points have absolutely NOTHING to do with hitting a downstream target. But they have EVERYTHING to avoid at all costs to not shoot the chrony.

Here are a few pics:

Chrony 2.1.jpg

Depending on where the chrony is placed, all you’re doing is avoiding hitting it or shooting it off the nose of your rifle - all good!

Don’t shoot the chrony!!!! And I’m proud to admit that I didn’t shoot the chrony – this time around….

So, about this chrony – it’s a “MagnetoSpeed – V3”. Unlike most chronys’ that measure the velocity in front of the barrel (say, 10 feet away), this one essentially measures at the barrel. While set-up can be a breeze for some, it took me the night before (just to be sure) and then about an additional 45 minutes at the range to finally get the alignment correct.

There are many things to play with regarding the settings – although it is nearly unforgiveable in measuring deeper than ¼” from the projected flight of the projectile. It comes set at a No. 2 setting (which worked best for me on this rifle). You can go up to a #11, but each increment apparently raises the sensitivity up 60 – 70%. And then you get background “noise” which apparently prevents the velocity from reading.


Chrony 1.1.jpg

And you can download the data on to your computer – or write it down on a note pad as each shot occurs…

I was mostly interested in how the rounds I had chronied a decade ago (24” bull barrel) compared to this 14.7” whippet. While I was surprised at how much the velocity decreased (a 14.7” barrel will do that), I also noted that the decrease in velocity is also dependent on the weight of the bullet (55 grains or 77 grains).

So the old saw that you just deduct 40 -50 fps in velocity for each inch of barrel you lose is not entirely correct – the weight of the bullet does matter.

So, here’s some of the data from ten shots for each different load:

23.7 gr. RL15, 77 gr Sierra HPBT

Min velocity: 2,456
Max velocity: 2,479
Average: 2,466 fps
SD: 10.9
ES: 23

Note: the standard deviation of 10.9 and extreme spread on the velocity of 23 fps. mostly explained why my accuracy was so great with these rounds out of a 24” bull barrel. And I was dumb enough at the time to believe it had anything to do with my shooting acumen!

23.6 gr. Ramshot Tac, 77 gr Sierra HPBT

Min Velocity: 2,586 fps
Max Velocity: 2,673 fps
Avg Velocity: 2,629 fps
SD: 26.7
ES: 87

Note: the standard deviation of 26.7 and extreme spread of 87 fps. made me wonder how I was so adept at nailing targets at 600 yds. The average velocity from this at 2,629 fps probably explained my performance and that the round didn’t go sub-sonic at 600 yds. While it could have been just dumb luck, these rounds do find their way to the center of the target.

26.7 gr. BL-(C)2, 55 gr Hornady

Min Velocity: 2,868 fps
Max velocity: 2947 fps
Avg Velocity: 2911 fps
SD: 30.6
ES: 79

Note: these were the lighter 55 gr bullets with a standard deviation of 30.6 and extreme spread of 79 fps. The average velocity of 2,911 fps is clearly higher due to the lighter bullet weight (55 g) and are great rounds to “spray and pray” at 300 yds and under.

Anyways, I hope you found this interesting – and of course, another reason to purchase a new rifle, optics, chrony, more high-tech components, etc. Valentine's day may be over, but your birthday is coming up...

And just remember, the worst day at the range is better than the best day at work!

Chrony 4.1.jpg

Chrony 5.1.jpg

[Delkal]

The only problem I see is with the chrony attached to the barrel it will be impossible to find your accurate loads. The added weight will mess up the barrel harmonics. I guess it would be easy to go to the range and blast away to get your velocities.....But then you have to do some serious shooting later to get the accurate load.

[bamboomaster]

The only problem I see is with the chrony attached to the barrel it will be impossible to find your accurate loads. The added weight will mess up the barrel harmonics. I guess it would be easy to go to the range and blast away to get your velocities.....But then you have to do some serious shooting later to get the accurate load.

Harmonics do matter - which is why I shot for accuracy two weeks prior. See post #1373 here: http://forum.pafoa.org/showthread.php?t=161683&page=138

But I still wanted to know the velocity for different reloads at distance....

[Delkal]

Harmonics do matter - which is why I shot for accuracy two weeks prior. See post #1373 here: http://forum.pafoa.org/showthread.php?t=161683&page=138

But I still wanted to know the velocity for different reloads at distance....

I like that chrony for that. Instead of setting up a regular chrony (with people waiting for you during a ceasefire) you can just load your mag and blast away. You don't even have to wait for a ceasefire. Have your mag loaded with 6 different loads (5 rounds each) when you get to the range and shoot at the backstop. You could be done in 5 min max.


As for the don't shoot your chrony thing.............I still hate to admit it but after 25 years and hundreds of rounds I eventually shot mine. I set it too far away and was shooting a new pistol with a light trigger. I clipped the plastic wing that held the sunscreen on. Luckily no one at the range noticed and I quickly packed it up and put it in my car. A little epoxy and a thin metal shim later and I am now good to go. I just have a reminder every time I use it not to do that again.

[phill]

I like that chrony for that. Instead of setting up a regular chrony (with people waiting for you during a ceasefire) you can just load your mag and blast away. You don't even have to wait for a ceasefire. Have your mag loaded with 6 different loads (5 rounds each) when you get to the range and shoot at the backstop. You could be done in 5 min max.


As for the don't shoot your chrony thing.............I still hate to admit it but after 25 years and hundreds of rounds I eventually shot mine. I set it too far away and was shooting a new pistol with a light trigger. I clipped the plastic wing that held the sunscreen on. Luckily no one at the range noticed and I quickly packed it up and put it in my car. A little epoxy and a thin metal shim later and I am now good to go. I just have a reminder every time I use it not to do that again.

There is two kinds of people and shooting the chrony, those who have and those who will. Got a bunch of mouth from a friend, a couple of months later got to feed it back.

[DukeConnor]

Try the orange one. Problem solved.

[JoshIronshaft]

A friend just loaned me a chronograph and I am very excited to check all my reloads. I might do that today if it warms up a little.

[frankski]

Is that the 1:7 twist barrel, Bamboo? They like the heavier bullets. That might have something to do with the 77s accuracy.

[ExFlyinguy]

You know who impresses the snot out of me- NOT shooting the Chrony? Paul Harrell- That dude can shoot.

Anyway I had a "Pro-chrono" that I shot with a .40S&W LOL

Moved on to the Magneto-speed which I found great for my bolt guns, but since I got the sporter model I have problems mounting it to some ARs and you are SOL if wanting to use it for hand guns.

Now I'm using the Lab-Radar. They're all fickle. I've missed shots with all three. But the Lab Radar is my favorite

[bamboomaster]

Is that the 1:7 twist barrel, Bamboo? They like the heavier bullets. That might have something to do with the 77s accuracy.

This LWRC is indeed a 1:7 twist and really does a great job with the 77 gr Sierra reloads. The 77's also have a BC (ballistic coefficient) of .362 which is notably greater than the 55 gr BC of .237.