Busted Chrony or heat sensitive powder

[Doyputasos]

So I decided to rework the load recipe for my 260 Remington because I was starting to get relatively loose primer pockets after my third or fourth reloading. I put together an OCW test starting at 42.2 grains and ending at 43.0 grains in two grain increments. I chrono'd all of the shots and my Lightest load came in at 2908 ft./s. This is about 80 ft./s faster than what I was getting with my 43.1 H4350. The two biggest differences I can think of are that my 43.1 grain load was developed in 60 to 70° weather and yesterday when I loaded up these rounds it was 108°. I thought that I had understood that H4350 was not temperature sensitive like reloader 17 or some of the other ones. The other thing I might used to diagnose the difference is that it has been a while since I've cleaned my bore. My accuracy is still very good shooting 1/3 MOA at 100 yards with several different loads so I don't think it's necessary to clean yet. Finally I wondered if my chronograph is too dusty or has been banged or something else like that. Any clue?

 

[Deadshot2]

First, ALL powders will yield more velocity/pressure as the temp goes up. It's just that some powders don't change AS MUCH as others with temperature variations.

You could be right at the edge where it makes a bigger difference. As for chronographs being "dusty" or "banged up" and giving incorrect readings, not as big a possibility as just plain different lighting conditions. You're measuring speed over an 18" distance for most chrono's. That, in itself, lends itself for wide variations in speed when the environmental (lighting) conditions change. Which part of your bullet is triggering the sensor in the different lighting?

The best way to make sure you're comparing like for like, is to have all the conditions and equipment set up exactly the same. I've started using a chronograph with I/R sensors to kind of level the lighting issue out.

 

[Niles Coyote]

Provided you are using the same powder as before I am inclined to believe it is you crono. I have witnessed large swings from changes in light… that’s the main reason I purchased a magentospeed as the area I do most of my load work is shaded by pines. I have personally not seen any large swings in actual velocity of my 260 loaded with H4350 but my temp range has been limited to 30-95ish.

 

[pawprint2]

The first thing I'd do is to fire some other rounds over through the chronograph, known loads, from another gun, different caliber different load, that'll tell you right fast if your machine is screwed up, or if your 260 loads are in fact giving you the problem. Most of these digital electronics are light light bulbs , they either work or they are broken.

 

[40xs]

I'm seeing more and more match shooters keeping their rounds in a cooler while at the range all day. Now, when I say "cooler" I dont' mean with ice in it. just the cooler to hold off the ambient hot temperatures for a longer duration so as not to affect the burning rate of their powder. I typically have to "crank" down a full moa in the afternoon temps. from my morning setting. If they don't have a cooler some will place towels over their ammo boxes or otherwise place them in the shade, if possible. On another note. I have found that if I have chambered a fresh round but did not send it due to a sudden change in the wind, I will remove that round from my chamber to prevent "cooking" my powder. On times when I did not do this and the round stayed in battery for several seconds my shot always went high. And the longer in battery the higher the shot went. So, real world results show that temps. affect burning rate, and some powders more than others.

 

[6brshooter]

Can u shoot at 6-700 yds, this will tell u whether ur chrono is right or fibbing to u. I have a beta chrony for several years and it is known to lie on sunny days. In fact i try to only use it on overcast days. I use it to get ballpark velocity figures and then confirm those numbers at range. Typically the velocity is a little lower then what the chrony says, but the es&sd is always consistent even if it says the velocity is hotter one day then before.

 

[40xs]

A friend and I were chronographing loads one day and he brought his Chrony (brand name). I had my ohler 33. We set them both up, one in front of the other just to compare results. We found that each shot was exactly 15fps difference between the two chronos. this was consistent throughout the test. I was amazed at the results between the two. both had sky screens over the reader. but still amazing.

 

[FALex]

factory rifle or custom build? Tight neck chamber?

 

[chefcam864]

Can u shoot at 6-700 yds, this will tell u whether ur chrono is right or fibbing to u. I have a beta chrony for several years and it is known to lie on sunny days. In fact i try to only use it on overcast days. I use it to get ballpark velocity figures and then confirm those numbers at range. Typically the velocity is a little lower then what the chrony says, but the es&sd is always consistent even if it says the velocity is hotter one day then before.

+1 My Beta Master barely works on bright, sunny days. In fact, I don't even bother unless it's overcast, in which case it performs flawlessly. A friend just picked up a magnetospeed... What a machine! It works everytime, regardless of light, clouds etc.

 

[40xs]

What is most critical on my Ohler 33 is the narrow reader window. You have to place each shot almost direcrly over the window to record the shot. Sunlight has not shown to be a problem with mine and it's probably 20 yrs old.