Dramatic drop in velocity with exact same components - strange! Ever seen this??

MagnumManiac

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I had a similar instance where 1 grain more powder gave 100+fps increase…..but the Pressure Trace did not show an equivalent rise in pressure. Only explanation was the chronograph, which was my Pact at the time.
I have seen loss in velocity that progressed as a #lot of powder (IMR 4320) aged. It was several years old when I got it, all up was 10 metal cans, none of which had been opened, and as the years progressed, the powder lost intensity, even adding more powder did not regain the initial velocity I was getting with it in my 22-250.
I used it all up and said to myself that was a noteworthy exercise. 300fps over about 7 years was lost if I used the same exact load and components.

I think your chrony may be faulty.

Cheers.
 

BCMAG2

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Did you measure your barometric station pressure on the two different shooting sessions?
 

emp1953

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The original chronograph numbers could have been wrong to begin with. Attribute it to weather, environment, pilot error, equipment error whatever and now the chrony numbers are correct. If you have a buddy with a different chronograph that you can use I'd put a few rounds through the different chrony and then compare numbers. The fact that you still have a 0.5 moa group tells me that the round is still in a node.
 

Dmagna

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So I had a similar issue to this with my first 28 nosler and a few more overbore cartridges. They instantly copper foul when shot with a clean barrel and would create an unsafe amount of pressure and lower speed. I started shooting 3-5 shots of a load that’s 3-4 grains of powder lower than my intended finished load before shooting the higher loads. It has helped maintain a constant on the higher loads.
 

T3ninja

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I haven’t seen ambient temp and or temp of ammo. If your ammo was sitting in the sun or by the heater of the truck shortly before firing the first batch then maybe a dramatic difference cooler with second batch?
 

Muskrat Outdoors

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I have a Browning X-Bolt in 28 Nosler I've been shooting for a couple of years with 143 gr Hammer Hunters. I recently got my hands on some ADG brass and N570 powder. I've been wanting to try some load workup with these new components. Went to the range a week ago to do pressure test and it went like this:

83 grains - 3465 fps with no pressures signs
84 grains - 3575 fps with no pressure signs
85 grains - 3600 fps with no pressure signs
86 grains - 3722 fps with slight ejector mark, no sticky bolt

Decided to focus around the 86 grain level (+/- .3 grains) to test accuracy.

Back at the range yesterday to try those loads and they shot .5 MOA BUT they all ran velocity around 3500 fps instead of around 3700.

I've been loading for 35 years and never seen anything like this. Components were exactly the same each time:

New ADG brass
N570 powder
CCI-250 primer
143 grain Hammer Hunter bullet

using Magnetospeed chrono

Anybody experienced anything like this?? It's driving me crazy trying to figure out why velocity would drop 200 fps with exact same components, seating depth, etc.
Was the temp much different? With my black powder cartridge rifles, I get my best groups in February. Temp and humidity is perfect in February for the bullet lube, and keeping fouling soft. Maybe that powder is temp sensitive? I've never used it.
 

richhymas

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I originally wanted to blame something with the chrony calibration, but it is more likely that your scale was somehow not zeroed. On an electronic scale these things happen. Static etc can effect the zero. With a balance scale I have had a few grains of powder fall in between the tray and the cup part way through reloading effectively lightening up the load. Conversely, one of the weights could get bumped moving the weight somehow. This is more likely given the pressure signs on the first trip and not on the second. If you work up to pressure again, and it’s off by say 2 grains, you will know that something was off by 2 grains on the first trip.
 

Hunterjones

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Similarly, with my first 28 Nosler I switched from Nosler brass which was not lasting anything like I expected to ADG brass and needed a full 3.5 grains more powder in ADG brass to match accuracy and velocity I got in the Brass.
Upon much examination, then case capacity was nearly identical, within 2 grains of water but Nosler brass neck thickness is .003 thicker.
I can very nearly reload the Nosler brass without resizing cases the necks are so tight
 
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