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Max Online: 16728 @ 03/25/12 08:51 AM
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#6108580 - 12/29/15 05:45 PM Inconsistent Velocity ( large SD )
syncerus Offline
Pro Tracker

Registered: 12/01/08
Posts: 1992
Loc: Dallas, TX
Hi everyone,

I took a number of my rifles to the range today for a chronograph session, and, as always, it was very informative. One load ran over 200 fps slower than the book indicated (very old data, though) and a number of others ran 50 - 80 fps slow. On the good side, three or four loads had very consistent velocities, including one that was totally unexpected, so that was nice. I also had some good luck with some iron sight shooting, which was also a surprise, as my eyesight is very indifferent.

This brings me to today's reloading conundrum. I had two loads (different rifles) that had very large velocity swings, something in the order of 150 plus fps. I had had reservations about the source of both loads so I backed them down to starter levels. The velocities in both cases were maybe 250 fps below what I would consider "normal" desired velocities. Do you think the reduced loading contributed to the wide swing in velocity and that the velocity range might tighten up as the load level increases? Or do you think it better to just cut bait on these powders?

I intend to bump the load a reasonable amount and re-test to see what happens. I'm really interested in the results.
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#6108591 - 12/29/15 05:52 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
ChadTRG42 Online   happy
THF Trophy Hunter

Registered: 09/16/09
Posts: 9426
Loc: Lewisville, TX
1st- How are you loading your powder? What kind of tolerances are they? (.1 grains, powder dump, etc?)

2nd- What powders are you running, what caliber, and bullet? Mixed head stamp or all same head stamp?

3rd- Can you get higher ES with reduced loads- Yes. The round becomes more efficient/consistent when loaded up near max pressure. When you reduce loads, you have to use the correct powder for the bullet you are running. Too slow of a powder can lead to a much less efficient round causing high ES.

4th- What chrono are you running, and what were the lighting conditions at the time of shooting (light quality and light angle)?
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#6108597 - 12/29/15 05:55 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
ChadTRG42 Online   happy
THF Trophy Hunter

Registered: 09/16/09
Posts: 9426
Loc: Lewisville, TX
Also, what were your spreads?
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#6108643 - 12/29/15 06:27 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
syncerus Offline
Pro Tracker

Registered: 12/01/08
Posts: 1992
Loc: Dallas, TX
I'm currently using the Hornady auto charge scale. FWIW, other loads thrown with the same device were very consistent (TAC in a .350 RM, Benchmark in an '06, etc.)

The first load was 2000-MR in a 8x60S pushing a 200 grain Nosler Partition. The spread was a low of 2157 to a high of 2294.
The second load was RL17 in a .375 ICL (think .375 Weatherby) pushing a 250 grain Barnes TTSX. The spread low was 2677 to a high of 2812.

The 8x60S full power load should run right at 2500 fps.
The .375 ICL full power load should supposedly run at 2950 fps, or at least 2900 fps.

The chronograph is a ProChrono. It seems susceptible to duplicate readings, but otherwise seems reasonably reliable. The lighting conditions this afternoon were reasonably sunny. I had the diffuser hoods up.
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#6108659 - 12/29/15 06:36 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
RiverRider Online   content
THF Trophy Hunter

Registered: 11/11/07
Posts: 6220
Loc: Wise Co.
After seeing some weird stuff happen, I keep my phone away from my electronic scales (not even in the same room) when I'm using them. Yeah, I know---it's a longshot.
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Originally Posted By: Cleric
God I am hating caliber threads more and more

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#6108725 - 12/29/15 07:29 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
Cleric Offline
Veteran Tracker

Registered: 03/11/12
Posts: 2579
I had the same problem with a shooting chrony. Same batch of ammo over a lab radar yeilded lower spread

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#6108756 - 12/29/15 07:54 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
RiverRider Online   content
THF Trophy Hunter

Registered: 11/11/07
Posts: 6220
Loc: Wise Co.
Originally Posted By: syncerus
FWIW, other loads thrown with the same device were very consistent (TAC in a .350 RM, Benchmark in an '06, etc.)


The chronograph is a ProChrono. It seems susceptible to duplicate readings, but otherwise seems reasonably reliable. The lighting conditions this afternoon were reasonably sunny. I had the diffuser hoods up.



I've got to admit I am a bit confused. Were the .350 RM and .30-06 loads fired and chronographed the same day as the other loads?

Another thing...with the cold weather the last few days the air is dry and static electricity (affecting the dispenser's scale, possibly) becomes more of an issue. Maybe the inconsistent loads were loaded in such conditions, and the others were not?
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Originally Posted By: Cleric
God I am hating caliber threads more and more

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#6108906 - 12/29/15 09:03 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
ChadTRG42 Online   happy
THF Trophy Hunter

Registered: 09/16/09
Posts: 9426
Loc: Lewisville, TX
I still need more info to know why, and I'm not sure what all you have loaded. But even with those calibers, I wouldn't know for sure. The main things that cause high ES are- different brands of brass (different head stamps), inconsistent powder charges, inconsistent brass prep, wrong powder (slower burning powder) for a reduced load, bad lighting when using the chrono, and a lower end unit chrono.

The lower end chrono's that are $100 will get you close to the speeds. But they are very finicky on the lighting and the light angle. During the winter time, the sun comes in at an angle, and early in the day or late in the evening it comes in more at an angle. These sharp lighting angles will interfere with the sensors and the accuracy of them.
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#6109015 - 12/29/15 09:52 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
syncerus Offline
Pro Tracker

Registered: 12/01/08
Posts: 1992
Loc: Dallas, TX
The .350 RM and the .30-06 loads were fired and chrono'd during the same shooting session as the .375 ICL and the 8x60S. The 8x60S cases are all from a single vendor and batch. I'm pretty sure the .375 brass is all from the same lot, but I'll check them to be sure. I'm inclined to think that the powders are just too slow for the load levels. In a separate 8x60S load with RL17, I'm getting exceptional consistency, but that load is at full working pressure.

As both loads should be much below max, I'm going to reshoot with loads that should be closer to normal working pressure after checking up on the details, as you've all suggested.

BTW, the 8x60S is basically a lengthened 8x57 or a shortened 8mm-06. The .375 ICL was developed about the same time as the .375 Weatherby and has very similar case capacity, though without the Weatherby shoulder.


Edited by syncerus (12/29/15 09:53 PM)
Edit Reason: spelcheck was too helpful
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#6109876 - 12/30/15 01:08 PM Re: Inconsistent Velocity ( large SD ) [Re: syncerus]
papa45 Online   content
Bird Dog

Registered: 05/14/07
Posts: 473
Loc: Arlington
Lots of good ideas here. Three more to think about:

Book velocities are often higher than real world.

Are any of the loads you tested recently from a new batch/bottle of powder?

Maybe your chrono is wearing out. I had a Shooting Chrony that had served me well for 15? years, then I started getting low velocity and high spread readings. After burning lots of powder chasing the numbers, I bought a new one. Now I'm back to "normal."

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