Chrono during testing

[Ryridesmotox]

Let's say you let your buddy borrow your chrono... and he is still on his hunt out 3 states away. Since my magnetospeed is not in the same time zone, I can use my backup caldwell ballistic chrony. But I like to OCW on different dots. How much will the angle change the FPS readings at 10 feet? Enough to matter a ton? Or nah? I never really worried since the magnetospeed measures thr same either way

 

[Rocketvapor]

Try cosine of the angle thru the sensors due to longer path.
I think some of the manufacturers sites show the calculation for you.
5 degrees indicates .4% low, 10 degrees 1.5% low.
(90 degrees and it indicates 100% low )

0.5 degrees won't be noticed.
A 0.5 degree angle will impact 30 MOA (about 30 inches) to the side.
Your target board wider than that?

The ability of a human to align and match angles (without a straight edge) is just slightly better than 1/2 degree anyway

 

[Ryridesmotox]

That makes sense. Thanks. Just have a free day next monday and I'm kinda wanting to get out to the range for more testing.

 

[Rocketvapor]

Now, a question for you
I have been using an optical sensor chrono for years.
A Compitition Plus, and just recently bought a used Magnetospeed Sporter.
Really heavy barrel (28") and the Sporter seems to open up groups?
Ever notice groups and POI shifts?

 

[Ryridesmotox]

POI shift, a tiny bit, but groups for me are the same. I have a 20 inch howa 308, so maybe the shorter barrel helps? Part of me doesnt really care all that much about the difference in velocity since I'm looking at the best ES/SD for a load... so as long as I get a good reading at each Point of Aim I really dont care. But I also like to know what is giving me a better speed node. I'm working up a new load, otherwise I wouldn't care

Edit: make sure the magnetospeed is on tight enough. That might be why the groups are opening?

 

[straightshooter1]

Now, a question for you
I have been using an optical sensor chrono for years.
A Compitition Plus, and just recently bought a used Magnetospeed Sporter.
Really heavy barrel (28") and the Sporter seems to open up groups?
Ever notice groups and POI shifts?

The Magnetospeed on my .308 Krieger 26" barrel produces a vertical POI shift of a little over 2" at 100 yds. Groups with the Magnetospeed are virtually the same as without it.

 

[straightshooter1]

Let's say you let your buddy borrow your chrono... and he is still on his hunt out 3 states away. Since my magnetospeed is not in the same time zone, I can use my backup caldwell ballistic chrony. But I like to OCW on different dots. How much will the angle change the FPS readings at 10 feet? Enough to matter a ton? Or nah? I never really worried since the magnetospeed measures thr same either way

Since you're doing an OCW, the difference shouldn't really matter. In fact, you don't even need a chrono to run an OCW test as configuration of the groups is what tells you what is the best load.

 

[Rocketvapor]

Here's a pic I posted elsewhere a couple days ago.
Not shot in order but all labeled.
The 88-IMR4350 load has about a year history.
It shot high. OK, POI shift.
The 88-SB6.5 with and without Chrono is what I'm talking about.
No time before my next 600 F-Class match to test so I'll go with 2875fps 88's over IMR4350 in case the 2910fps 88-SB6.5 don't group.
There are a couple of flyers that might be me.
I can usually do 3 into .3, 5 into .5, 10 into 1MOA, 60 into 1.5MOA @ 100 yards.

 

[Ryridesmotox]

Since you're doing an OCW, the difference shouldn't really matter. In fact, you don't even need a chrono to run an OCW test as configuration of the groups is what tells you what is the best load.

Yea but I like to collect as much data as possible since the range is an hour away. Making multiple trips is not very convenient. Multiple birds with one stone

 

[Ryridesmotox]

The Magnetospeed on my .308 Krieger 26" barrel produces a vertical POI shift of a little over 2" at 100 yds. Groups with the Magnetospeed are virtually the same as without it.

I wonder why it so different on mine. Does the length difference matter that much. I think my shift is like .5 moa-ish

 

[Rocketvapor]

My barrel is a 28" AR-15.
.980, .936 where a gas block would go , .925 to the recessed target crown.
.5 or so up and to the left.

 

[straightshooter1]

I wonder why it so different on mine. Does the length difference matter that much. I think my shift is like .5 moa-ish

Given the same contours, the length of the barrel alone doesn't make a difference. Just how much of a difference I'm sure depends on other factors like powder burn rates, bullet weights, etc.

 

[straightshooter1]

Yea but I like to collect as much data as possible since the range is an hour away. Making multiple trips is not very convenient. Multiple birds with one stone

Likewise, I like to do the same very often and collect as much data as possible. When I had my 20" barrel on that gun, I didn't mount the chrono on the barrel, but on an extension I fabricated so that I was always using the Matnetospeed at the range.

Obviously, using something like a caldwell ballistic chrony isn't going to give you an actual MV being the distance it's set up from the muzzle. So, one is going to have to do a little math to get a better idea what the MV actually is. And . . . a chrony like that tends not to be as accurate as a Magnetospeed or the likes of a LabRadar set up . . . especially being subject to lighting conditions.