Chronograph issue?

[lrgrendel]

Not sure if I have a problem.

Shot today through the Chrono. Velocity was a little "sketchy". About a 100 FPS higher than usual. I have shot this load a lot without an issue. It was hot today in central Florida. No pressure signs on the brass BUT....
All shots grouped as before at 100, 200 and 300 yds. The scope was still zeroed.


2 questions.
Is AA2520 temperature sensitive? ( change of 15-20 deg F )
Would you notice a POI difference with a change of 100 FPS at those 3 distances.

[motoxxx_ryder]

did you change the distance from the chrono? if you were too close ti could be picking up muzzle blast.

http://snipershide.scout.com/forums/5514-bolt-action-rifles/13858015-temp-sensitivity-data-for-most-common-powders-fps-deg?s=541

according to some independant testing 2520 is about 1 FPS per degree.

did you change anything? Primers, COAL, CBTO, stuff like that?

[lrgrendel]

did you change the distance from the chrono? if you were too close ti could be picking up muzzle blast.

http://snipershide.scout.com/forums/5514-bolt-action-rifles/13858015-temp-sensitivity-data-for-most-common-powders-fps-deg?s=541

according to some independant testing 2520 is about 1 FPS per degree.

did you change anything? Primers, COAL, CBTO, stuff like that?

No the distance to the Chrono is the same.
Also everything else is exactly the same. This is my "long range" load which I have been shooting for quite a while.

That link is very interesting thanks!

[NugginFutz]

lrgrendel -

I would say that it is possible to see a shift in POI with a 100 fps difference in MV, but not a certainty. What type of chronograph are you using? If it is a Shooting Crony (or other folding type) it bears mentioning that you must ensure that it is unfolded completely, and is laying parallel to the muzzle. If not unfolded completely, you can physically shorten the distance between the two sensors, which can give the impression of higher velocities. If not parallel to the muzzle, you can optically "lengthen" the distance between the two sensors, which has the opposite effect.

Hope this helps.

[Savage Shooter]

A few weeks ago I had to move my Pro-Chrono from my standard 12' from Muzzle to only 10' to get the sensors under light shade and avoid a bright sun, which was making my readings go crazy. While the distance between sensors on the Pro-Chrono is fixed, the shortening by 2' the distance of the chrono from the muzzle increased the measured MV by about 100 FPS. If you aren't accurately placing your chrono the same way and distance from the muzzle every time, this could introduce differences.

[lrgrendel]

It was extremely sunny and bright today so my Master Chrony may have been effected.
Also if anything it was maybe a foot or two further away from the muzzle.

As everyone knows, set up is a pain in the a$& as well, especially if you are not shooting by yourself.

I am loosing patience and may go to the Magnetospeed. Just starting to look now at the difference between the standard type at $299 and the Sporty at $179. If anyone knows please chime in....

[Klem]

Agree with both Nuggin and Savage,

Could be a difference in the distance between sensors relative to your bullet path. This can be caused by not folding out the hinged type Chrono's and/or not keeping the Chrony the same level relative to bullet path.

I use a small level-bubble and set it up relative to gravity first.

Have also noticed there is a small window of more exaggerated readings before it shows ERROR. This is when the battery or the ambient light fades.

[LR1955]

It was extremely sunny and bright today so my Master Chrony may have been effected.
Also if anything it was maybe a foot or two further away from the muzzle.

As everyone knows, set up is a pain in the a$& as well, especially if you are not shooting by yourself.

I am loosing patience and may go to the Magnetospeed. Just starting to look now at the difference between the standard type at $299 and the Sporty at $179. If anyone knows please chime in....

LRG:

To go to your original question with your conditions (100, 200, 300 yards). A 100 fps difference in velocity would have shown up very clearly at 300 yards. 2520 is temp sensitive but a 15 degree change in powder temp won't give you a 100 fps change in velocity.

Chronographs, like optics, seem to get better as the cost increases. However, it only matters if the data must be absolutely accurate. We tend to accept variances day to day given light conditions and the precision of set up but generally want good deviation readings since the SD gives us more info on load pressures. 100 fps is way too much for my liking although I accept ten or 15 fps differences day to day using the same load.

I bought a C.D. Millineum chronograph many years ago with IR sunscreens and have not had an issue due to lighting conditions since. Never had any radical changes in velocity using the same load, no matter what the weather conditions were.

I shoot for group as well as chronograph loads so anything that affixes to the barrel is out for me. Slapping heavy things on to the barrel will change your zero and will probably disrupt the accuracy potential of the rifle.

LR55

[Boostmeister]

As far as setup goes, a simple tip that I was given was to tie a 10 foot piece of string to the first screen for use in spacing the chronograph away from the edge of the bench. Ads consistency to your setup.

[motoxxx_ryder]

the string works but it i doubt that close to the muzzle the even 3-4 feet would reduce the give =/- 10 FPS.

I usually heel to toe ten steps in size 12 so that gets me a little over 10 feet but its consistent.

The magneto speed is great for reading velocities, i wouldn't shoot for groups with it though. It does effect barrel harmonics and can throw accuracy off. If you shoot for best load then shoot a hand ful over the magneto speed for velocity just for notes. Alot of top shooters run it mainly because its convenient, setup is a strap, data can be exported to excel there is no measure this measure that, make sure its level, dont hit the chrono etc.

[Savage Shooter]

The magneto speed is great for reading velocities, i wouldn't shoot for groups with it though. It does effect barrel harmonics and can throw accuracy off. If you shoot for best load then shoot a hand ful over the magneto speed for velocity just for notes. Alot of top shooters run it mainly because its convenient, setup is a strap, data can be exported to excel there is no measure this measure that, make sure its level, dont hit the chrono etc.

On another thread a few of us gave some input on the differences between a Magnetospeed and "standard" chrono. I have found that with the Magnetospeed, group size (Precision) is not that largely affected but accuracy (location of the center of the group relative to your point of aim) certainly is. I have seen POI shifts of as much as 3-4 inches at 100 yards with and without the bayonet hanging off the barrel. If I am doing load development with premium bullets (like Barnes TSX or Hornady GMX), I'll use my old Pro-Chrono unit and nail down velocity and zero at the same time and save my bullets. Also, depending on which range I go to (one is busier than others with range officers and all) I'll use the Magneto speed for convenience of set-up. Or if it's overcast, I'll use the magnetospeed. In other words, most chronos have some unfortunate quirks about them - but it sounds like LR55's had good success with his. However, I just looked up the reviews on Midway for the CED Millenium, and it seems that users either loved it (5 stars) or hated it (1 star) equally, so it too might depend on the exact unit that you get.

[LR1955]

On another thread a few of us gave some input on the differences between a Magnetospeed and "standard" chrono. I have found that with the Magnetospeed, group size (Precision) is not that largely affected but accuracy (location of the center of the group relative to your point of aim) certainly is. I have seen POI shifts of as much as 3-4 inches at 100 yards with and without the bayonet hanging off the barrel. If I am doing load development with premium bullets (like Barnes TSX or Hornady GMX), I'll use my old Pro-Chrono unit and nail down velocity and zero at the same time and save my bullets. Also, depending on which range I go to (one is busier than others with range officers and all) I'll use the Magneto speed for convenience of set-up. Or if it's overcast, I'll use the magnetospeed. In other words, most chronos have some unfortunate quirks about them - but it sounds like LR55's had good success with his. However, I just looked up the reviews on Midway for the CED Millenium, and it seems that users either loved it (5 stars) or hated it (1 star) equally, so it too might depend on the exact unit that you get.

SS:

The key to the CD Chrono was me buying the IR sky screens. And that is where the hassle comes in. You either have to plug them in or use a battery. And the battery pack CD offers is (or was) poor at best. They would last about a year even if you never used them. Since the ranges I belong to have power, I use an extension cord. Takes five more minutes to set up but once you have power to the sky screens, light conditions just didn't matter anymore. The chrono gave the same readings with bright sun or in shade.

I haven't chronographed anything in a couple of years so for guys who are wondering, you won't use them very much. Maybe twice a year after your initial burst of interest fades.

LR55

[lrgrendel]

I shot a match yesterday. The same loaded rounds shot the same as they have done in the past.
So my Chrono was definitely acting a bit "off " the other day.