I'm shooting a 7mag, the load is 168gr berger vld with 69.6gr of H1000. I've had good success grouping this load but didn't know what my fps was. I ran into a guy today at the range with a chrono so I asked if he would let me shoot a few rounds. I shot 3 rounds in this order 2883, 2862, and 2864. I shot all three rounds pretty quick, I would have liked to let the barrel cool down between but didn't want to waste to much of his time. My question is, was 3 shots enough to get an accurate average(2870)? Also will not letting the barrel cool down affect the average any?
Chrono question
- Thread starter RocketDog
- Start date
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FearNoWind
Well-Known Member
As is true of just about every test for consistency, the more data you have the better the analysis will be. Three shots really isn't enough to tell you much. But it does tell you something. There have been times when I took data from three shots as the foundation for a ballistics chart and then took the data to the range and made adjustments based upon target results.
Rich Coyle
Well-Known Member
Three is certainly better than a loading manual. In the real world I am convinced those three are good enough. Often I am the guy with the chronograph. Since a couple guys have actually hit the electric eyes I normally fire the loads for them. I usually ask them if I can fire five. Usually three is good enough to get the idea.
I sure agree with you about keeping the barrel cool. A three shot group takes me about fifteen minutes!
I sure agree with you about keeping the barrel cool. A three shot group takes me about fifteen minutes!
ShtrRdy
Well-Known Member
What happens if you don't let the barrel cool between shots? What do you expect the velocity to be (higher or lower), if you just shoot the shots one after the other?
Darkker
Well-Known Member
I disagree about letting the barrel cool.
I personally use 5-shot groups, but as said; 3-shots is better than guessing.
The reason I say don't let it cool, How are you going to be shooting?? If you are going to be pounding paper, then chrono at the same rate; will effect your loads consistent with your shooting.
If you will be shooting/hunting where you ONLY shoot every 15 minutes, great do it that way.
On another board I shot an 80-something group and shared. Why??
Well that was how many of those loads I had, BUT I fired them at a distance and rate of fire that the local matches run.
So what is more true to how my rifle/loads will respond to that shooting situation:
A - a 3-shot group that took 45 min
B - A group that will show any heating affects on the barrel/ammo, any shooter fatigue
No right or wrong, unless you are doing it differently than you plan on using it.
I personally use 5-shot groups, but as said; 3-shots is better than guessing.
The reason I say don't let it cool, How are you going to be shooting?? If you are going to be pounding paper, then chrono at the same rate; will effect your loads consistent with your shooting.
If you will be shooting/hunting where you ONLY shoot every 15 minutes, great do it that way.
On another board I shot an 80-something group and shared. Why??
Well that was how many of those loads I had, BUT I fired them at a distance and rate of fire that the local matches run.
So what is more true to how my rifle/loads will respond to that shooting situation:
A - a 3-shot group that took 45 min
B - A group that will show any heating affects on the barrel/ammo, any shooter fatigue
No right or wrong, unless you are doing it differently than you plan on using it.
Gunpoor
Well-Known Member
Was the barrel cool when you fired the first round? If it was then you have your bullet speed. Is it enough to figure standard deviation? Probably not. I have run many rounds of the same load over a chronograph and they really don't change much unless something in the equation changed. I had a Remington model 700 Sendero chambered in 338 UltraMag and the load I shot most in it was a 250 grain bullet over 89 grains of H4831SC and every single time I shot it over the chrono it registered 2860 ft/sec with no variance. I probably ran 15-20 rounds of this over the chrono and this is the only rifle, pistol, or load that was that consistent, to the point of being spooky.
This load is going to be my hunting load, so cold bore shots will be common. As far as barrel temp, I shot 6 rounds before the chrono test it was about 30 degrees and it probably sat for 10-15 minutes before testing. Thanks for all the responds, much appreciated!
Rich Coyle
Well-Known Member
I expect the velocities would be the same as if I fired them quickly. I have not seen a pattern. The reason I wait is to preserve the barrel life. I can remember only a couple times when I fired more than one shot at a game animal.
Well said! Once I am happy with my load, I normally do a cold bore shot group ... make the 1st count. However, sometimes the follow-up shot is just as important.
86alaskan
Well-Known Member
I'll chrono my hunting rifle with a quick but smooth session through a full mag. I like the cold bore on its own, but then follow up with the remainder of the loading in a quick controlled fashion. Everybody likes the one and done deal, but in the real world that isn't always the case. I like to know just as much about the last round in the mag as the first one in the chamber. I've seen similar results in the cold as far as the first being a bit ~20fps faster, then the remainder being pretty consistent.
