Baffling Reults, Please Help!

[bobh918]

I was working on a couple of loads yesterday for my 300RUM. I am trying out the 230 Berger Targets and was shooting two loads of 84.2gr & 84.5gr of H1000 loaded .010 off the lands, once fired remington cases all full length sized and shoulders bumped, and cci 250 primers. I ran six shots down a clean barrel of 84.2gr as sighters at 200yds. Move target out to 400yds and proceed to shoot a five shot group with each load of 84.2gr & 84.5gr over the chronograph. I let the barrel cool after the six sighters and these were my results:

84.2gr
shot 1 - 2916 fps
shot 2 - 2889
shot 3 - 2861
shot 4 - 2857
shot 5 - 2858

All shots were fired one after the other. After the first string, I let the barrel cool to fire the 84.5gr group.

84.5gr
shot 1 - 2909 fps
shot 2 - 2875
shot 3 - 2865
shot 4 - 2867
shot 5 - 2873

Temperature was about 50* F at 1600ft elevation. My question is, why would my velocities be dropping? Shouldn't they be increasing, especially firing one after the other? All charges were double checked on weight before dumped into the case. This rifle is a rem 700 trued action with a 30" Kreiger HV taper barrel. If anybody might have some thoughts or theories, please do share. I have not gone out to try these loads again to see if it repeats the same results yet. Thanks!!

 

[woods]

.3 grains in a large capacity case like that will make so little difference in velocity as to be not discernible. If you did the same test 4 or 5 times you would probably begin to see a very minor increase in velocity if you averaged all of the tests.

At over 80 grains I would imagine that it would take almost a full grain of powder to make a noticeable difference unless you were getting close to max, in which case it might make a larger difference

JMHO

 

[bobh918]

Im not so much worried about what the average velocity is for those loads, but as to why the first shot is higher in velocity then the next four shots. My pat experiences have led me to believe that following shots might be slightly faster in velocity due to the warming of the barrel. Am I mistaken on this belief? Just trying to educate myself as I learn more and more about long range shooting.

 

[Browninglover1]

I could be way off my rocker on this one, but as your barrel heats up the bore actually gets bigger. The bore getting just a little bit bigger would reduce the pressure a little bit and could cause the velocities to drop. Someone with more experience than me could probably tell me if that theory is wrong and why. As a matter of fact, please do tell me if I'm wrong.

 

[winmag]

Ok, time for the ol, "Did you check the gas in the lawn mower?" question,
Did you have your first round in each string in your hands, or pocket, or chamber, or even in the pickup exposed to heater, or sunshine, while waiting for the bbl to cool down?

Just a guess, here, but it looks like the first ones in each string were warmed up somehow, temperature wise, while the others sat in the mag or in the box on the bench waiting thier turn thereby keeping them more exposed to ambient temps, & cooler to produce less velocity.
Trying to narrow down all the variables often results in very simple answers to questions that were "over-thunk"

 

[theflyonthewall]

I have another question for ya concerning your strings.

Have you ever done this exact test regimen before? If not, then this is new territory. One guess that I would have, even though I'm not sure of the EXTENT that it would affect velocities, is fouling.

That many shots out of a RUM consecutively would heavily foul a rough bore. If the bore were rough enough, the shots quick enough, and the barrel warm enough, you could have so much fouling that it affected your chrono readings.

That's a lot of things coming together all at once, but it's food for your thought.....

 

[bobh918]

No, all rounds were exposed to the same conditions. They were in the ammo box right next to me exposed to the sun, so if anything, the lasts shots would be a smidge warmer if any cause they were out longer in the sun. I have been thinking over the past few hours and I quite possibly think I have a faulty chrono. It is a Shooting Chrony Beta Master. Yesterday I rezeroed my rifle at 200yds. I have the Shooter app on my android phone and I plugged in 2900fps for an avg. velocity at a 200yd zero. Program gives me a 4.5moa dope for 415yds. I have three shots about 3.5 inches high and two about an 1 inch lower then the previous three, due to the decrease in velocity. But this would lead me to believe that my loads are running faster than what the chrony is telling me, therefore, leading me to believe a faulty chrono. Is there any way that somebody with quickload can give what the estimated velocity should be these loads and gun? I don't have that program so I don't know if this program projects these values. Guess I need to save for a new chronograph.

 

[bobh918]

Most of my testing is done like this and they were necessarily rapid fire. They were all single shots, so I would chamber a round, fire, and then extract the fired case, look at the bottom of the case for any plunger marks and drop it into the ammo box and grap the next round to repeat the procedure. I have close to 200 rounds down the barrel and don't suspect fouling to be a culprit, but again, don't know so that's why I am posting.

 

[gunpower]

lightbulb

I could be way off my rocker on this one, but as your barrel heats up the bore actually gets bigger. The bore getting just a little bit bigger would reduce the pressure a little bit and could cause the velocities to drop. Someone with more experience than me could probably tell me if that theory is wrong and why. As a matter of fact, please do tell me if I'm wrong.

I agree with you on this point, the warmer the barrel, the bigger it increases in size. So you end up loosing velocity. I have done my own testing over the years, fire one shot, let barrel cool, then shoot again.
I have done this over the four seasons and find that I get better velocities when it is cold out- 10 to -30.

 

[Mikecr]

All NEW QL data has to be validated/calibrated -with good chrono feedback(just like loads from a manual). So QL data would only be a guess without something -with that lot of powder & barrel, actually known.

Just sayin..

 

[bobh918]

Thanks for the info on Quickload. I'm gonna try to track down a decent chrono and verify everything again. On another note, as to the barrel warming and expanding during warming, can a HV taper barrel warm that much for five rounds for that to happen? Enough for a 60fps spread? The barrel barely felt warm to the touch. Thoughts?

 

[CRNA]

Thanks for the info on Quickload. I'm gonna try to track down a decent chrono and verify everything again. On another note, as to the barrel warming and expanding during warming, can a HV taper barrel warm that much for five rounds for that to happen? Enough for a 60fps spread? The barrel barely felt warm to the touch. Thoughts?

Before you throw the chrono out at 200yds and use it as target practice try something.



I had the same problem with numbers all over the place with my chrono. I got so frustrated at that thing I could have blown it to pieces. I couldn't figure out why my ES was all over the place.
After much thought and pondering, I realized I was going to the range at the same time every day I shot. Hence, the sun was in the same position every time I shot. I could recall that every time I shot the sky was clear with a few passing clouds and the sunlight was kind of at an angle if you will in the evening.

I purposely went back to the range on a COMPLETELY overcast day with light drizzle. Guess what? Problem solved.

I have since found that my chrono will give believable numbers if the sun is 1) directly overhead, or 2) completely covered with an overcast sky.

If the sky is partly cloudy, or if the sky is clear and either morning or evening, I don't even get the chrono out of the box.

Try to shoot in CONSISTENT light with the chrono next time either bluebird day at noon, or completely overcast so there is no variation in lighting and see if things don't magically tighten up without changing the loads.

 

[Wile E Coyote]

No, all rounds were exposed to the same conditions. They were in the ammo box right next to me exposed to the sun, so if anything, the lasts shots would be a smidge warmer if any cause they were out longer in the sun. I have been thinking over the past few hours and I quite possibly think I have a faulty chrono. It is a Shooting Chrony Beta Master. Yesterday I rezeroed my rifle at 200yds. I have the Shooter app on my android phone and I plugged in 2900fps for an avg. velocity at a 200yd zero. Program gives me a 4.5moa dope for 415yds. I have three shots about 3.5 inches high and two about an 1 inch lower then the previous three, due to the decrease in velocity. But this would lead me to believe that my loads are running faster than what the chrony is telling me, therefore, leading me to believe a faulty chrono. Is there any way that somebody with quickload can give what the estimated velocity should be these loads and gun? I don't have that program so I don't know if this program projects these values. Guess I need to save for a new chronograph.

I have the same chrono and had similar issues; A Shooting Chrony Beta Master. I also have the LED light kit they sell.

A few months ago I was working up a couple loads for my 7 mag and found I was getting bogus numbers. I had both a sunny afternoon and an overcast day with the same issues. Some shots in the string were apparently good while one or two in a 10 shot string were obviously too low. I just discarded those numbers. The apparent good numbers were in the 3200 + fps range while the bad numbers were half that. As it turns out most those "good" numbers were NG also. They were actually about 3050 or so.

To start, there is probably nothing wrong with the chrono. It's just giving you a number for each shot based on what it sees. To make a long story short, the Numbers that were too high were caused by the muzzle blast upsetting the timing. A portion of the blast apparently either gets to the first eye before the bullet does and/or the blast outruns the bullet to the second eye. either way, the reading is bogus. Secondly the low numbers were caused by one of two things. A) the bullet path was slightly to the side of the eye or B) one day, the shooter ajacent to me was shooting a muzzleloader and the smoke and pressure wave would start and stop the clock and record a number.


After some thought about the problem, I was able to solve ALL of the issues with a simple cardboard box. The box is big enough to house the assembled Chonograph with about 12" in front of the unit. A vertical hole about 1 1/2" wide and 6" tall is cut in the front and rear panels of the box to allow for the line of sight and the bullet path to pass through the chrono at the correct height and alignment. Alignment was checked with a broom handle.

The LED light kit I have is a constant light source that I power with my auto jump pack. When the top of the box is closed, only the LED illuminates the eye. The majority of the muzzle blast is deflected away from the chrono; very little passes through the front hole in the box. The result has been consistant and believable numbers because the chrono is shielded from those things that would upset it including varying daylight conditions.

In the next day or two, I'll take a few pictures of what I did and how I use it and post them. Believe it or not, this whole thing is not as unwieldy a contraption as one might think. In fact, it is actually almost self contained. I store it, transport it and shoot through it without all the setup/breakdown each time. If there is a down side to it is that one must shoot from the prone position only ( if one is bothered by that) Where I shoot, this is not an issue.

This setup had apparently solved my chronograph issues. Now when I see numbers that vary, I have been able to trace them to some other source. Now I just have to get out and shoot at longer ranges to solve for my drop tables - if I could only find the time.

 

[bobh918]

Awesome! Can't wait to see the pics if you get a chance to post them. Always open to new and wild innovations.