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Old May 14, 2012, 09:11 PM   #1
RobertInIowa
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Wide FPS range using Chrony

I recently purchased a chronograph to try and better my reloading tecnique as well as watch for pressure signs etc. At first I put the chrony about 6 feet from the muzzle and that gave me a wide range of FPS so I did some research and found that it should be 12' or better from the muzzle. So now I have the chrony as far as my data cord will allow, which is about 12'-14' from the muzzle.

My problem is that I am getting variances from 500 to 800 FPS. I try to load all the ammo the exact same way but I don't understand why I'm getting such a variance. Any ideas?

Here's some more info. Single stage press's. All use the same dies, primers, sizer/decapper. ll are processes on an RCBS trim mate. I chamfer and debur the necks. I apply no crimp as I'm shooting from a single shot bolt Cooper model 21 in .223 with a 1:12 twist and a 24 inch barrel. I hand weigh on a high precision scale with no drafts or temperature issues and I'm positive the charges are as identical as they can get.

Do you suppose neck tension could be the issue? If so, how do I improve it? What is the normal variance range in FPS for handloaded ammo?

I shot my pistol (.40 s&W Sig) through the chrony and had variations of only about 15 to 20 fps so I don't think it's the chrony.

I'm sure i've forgotten to provide some important info, so ask anything you need. What do you guys think might be the problem?
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Old May 14, 2012, 09:27 PM   #2
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Just to be clear. The variation is 500-800 fps as in the difference between 1500 fps to 2300 fps or 1800 fps to 2300 fps or are your bullets actually clocking at 500 fps and 800 fps?

Neck tension would be my first guess, but primer seating might be the culprit.

What powder and primer are you using? If a hard-to-ignite powder and standard (not magnum) primers, you might get a lot of pressure variation there.

The "high precision scale". Is it electronic or balance beam? Some electronics are sensitive to things like the electronic emanations from flourescent lights or being moved or line voltage fluctuations. The better ones are less sensitive, but still...

I would put a baffle (plywood?) in front of the barrel with a small hole in it about 12" away to catch the muzzle blast and any stray powder granules that might be confusing your sensors. You could move both the Chronograph and the readout unit another few feet away to furthur reduce the chance that muzzle blast is the culprit.

Do you get the same sort of variation with factory ammo in that gun?

Does the powder fill the case pretty well (like 90% of the way to the base of the bullet) or is there a lot of room for the charge to be in different positions? Sometimes a considerable variation in velocity can be produced if the powder is piled up against base of the bullet (far from the primer) or right close to the primer. Though that is unlikely as a source of your puzzle, as the .223 case is not that large.

That's all I can think of off the top of my head.

Good luck, Thanks for asking our advice.

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Old May 14, 2012, 09:32 PM   #3
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Indoors or out ?? , clean the lens & use larger difussers out side, they don`t like direct sunlite or flouresent lites .

Big calibers with big blast I usually set up at 20 ft. with my chrony.

PS: I type too slooooow
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Old May 14, 2012, 10:24 PM   #4
RobertInIowa
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Lost sheep, thanks for your reply.
The variance is like 2800 to 3300.
I'm not sure about neck tension but I think my primer seating is top notch.
Powders are either Varget, IMR4198 or Benchmark. Primers are Rem. BR.
The scale is an electronic Mettler Toledo Lab scale, very precise and reliable and there are no flourescent lights.
I havent fired factory ammo in the rifle, but I'll pick up a box and test it.
The powders fill the case from about 80 - 90%. (.223 Rem)

Thank you for the advice,
RobertInIowa
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Old May 14, 2012, 10:27 PM   #5
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GP100MAN,

I am shooting outdoors using the large difusers. No direct sunlight or light bulbs.

Thank you for your reply

RobertInIowa
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Old May 14, 2012, 10:32 PM   #6
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Three more questions:

Bullet weight. If you are near the maximum for the bullet/powder combination, strange velocities can creep in as the powder burn gets erratic (spikey). This could be a danger sign. Not necessarily, but maybe.

Are the primer flash holes uniform?

Seating depth (as measured from the base of the bullet to the case web). I know, once the cartridge is assembled this cannot be measured directly, so we use the cartridge overall length. But if there is variation in the nose shape you can get some uncontrolled variation.

I love a puzzle.

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Old May 14, 2012, 10:40 PM   #7
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Quote:
Powders are either Varget, IMR4198 or Benchmark.
Different powders have different characteristics and give different velocities.
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Old May 14, 2012, 10:46 PM   #8
RobertInIowa
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Lost Sheep,

Bullet weight is 52 grains. Pretty much top end for the 1:12 I have. It keyholes from 60 grains up.
Primer flashholes are deburred.
My COAL is about 2.260, maximum per SAAMI. I was trying to get as close to the lands as possible.

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Old May 14, 2012, 10:49 PM   #9
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Varget is a relatively slow powder compared to IMR4198 and Benchmark.

You can't shoot a bunch of different powders and expect the same velocities.

If you could, there would be no need for different powders.
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Old May 14, 2012, 10:54 PM   #10
RobertInIowa
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mrawesome22,

The FPS variances are within batches of the same powder. I appologize for not making that clearer.

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Old May 14, 2012, 10:57 PM   #11
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I could be wrong, but I don't read it like he's expecting the same velocity from different powders. I think he's getting velocity variance with the same load of the same powder. He just gets the same wide variance regardless of the powder he used. Is that right, Robert?

Mixed brass, or is it all from the same lot? Full length sizing or neck sizing?

Do you have enough neck tension that you can't push the bullet into the case any farther by pressing the tip against your workbench withot trying really hard?
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Old May 14, 2012, 11:04 PM   #12
RobertInIowa
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Sport45,

You are correct, I am getting the variances within the same loads, regardless of the powder I use.

Sometimes it's mixed brass, other times it's pure Winchester. And I've been neck sizing.

As far as neck tension, I will have to test that on my next loads, I'm plum out of reloads right now.

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Old May 14, 2012, 11:08 PM   #13
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Thanks for clearing that up.

Were the 40S&W loads factory loads?

If they were factory loads, I can only guess your scale is deviating substantialy.
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Old May 14, 2012, 11:15 PM   #14
RobertInIowa
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the 40 S&W's were handloads 180 gr Hornady FMJFP on either 5.5 Power Pistol or 4.7 Tite Group. My scale is checked everytime I weigh and it's always dead on. I'm pretty sure we can rule the scale out.
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Old May 14, 2012, 11:19 PM   #15
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500 to 800 fps variances and you are weighing each charge? I'm sorry but I think you have a chronograph issue. The pistol bullets are both bigger and moving slower, so using that as a test of the chrono may not be telling you all you need to know. Have you tried shooting factory ammo from the rifle over the chrono?
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Old May 14, 2012, 11:30 PM   #16
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I agree.

Sounds like the chrono is at fault.

Thank you for giving clear, prompt answers.

Sent from MIUI using Tapatalk 2.
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Old May 14, 2012, 11:59 PM   #17
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I also agree. You would have to really work hard at bad reloading practices to get a 500 to 800 fps differential. I honestly don't think you are, reloading incorrectly, that is.

The first thing I would do is eliminate for good the possibility of ultrasonic gases tripping the chrono. Back up to at least 20 ft and try 3 shots. You said you can't get any further than 12' to 14', but unless the wires are tied to your rifle ( ) you should be able to back up as far as you want to. It just means the control box will be a few feet in front of (and to the side of) the muzzle.

If you still get a huge variation in velocity, then you should start looking at the rounds themselves. You mentioned that you are trying to get close to the lands. For a 3 rounds test, back off a bit (shorten the OAL by .010") and see what happens.

Do you have a .22 rifle? If so, see what kind of velocity and variation you are getting from it.
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Old May 15, 2012, 12:25 AM   #18
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I was having the same problem with my chrony and my .223. I found that when I went to full length resizing instead of neck sizing, I got better numbers and groups!

I always set my chrony at 15', and sometimes with hotter loads, I get some variation, but never more than 100 fps.

Try full length resizing. It will make your neck tension more consistant. Just my personal experience.
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Old May 15, 2012, 06:38 AM   #19
RobertInIowa
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AllenJ, I have not tried factory ammo. I'll pick up a box and see what I get.

MrAwesome, I will try all the other suggestions before I consider sending the Chrony in for a checkup, just to be sure.

Mal H, I'll extend out the chrony to 20 feet as you suggest. Good idea on the 22, I have one I'll use to see if I get more consistant results.

Wyoredman, I will try some full length resized loads and see what happens.

Everyone, thanks for the abundance of great ideas, I very much appreciate it.

RobertInIowa
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Old May 15, 2012, 08:12 AM   #20
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Variability in lighting, like under trees on a bright sunlit day, could cause the variations. As the wind moves the tree limbs the light hitting the sensor changes.
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Old May 16, 2012, 05:28 PM   #21
RobertInIowa
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And the winner is..................

Thanks to everyone who so graciously provided input on my chrony problem. I just got back from the range where I applied some of the suggestions I received. First I loaded five 10 packs of rounds with various COAL's. Some had been fireformed and some were new brass which I FL sized. All were otherwise previously established loads. I grabbed my faithful old .22 semi auto rifle and some ammo for it.

At the range I set up my chronograph as far as I could without dragging the display into the dirt in front of the bench. Once I had my target set up I set up and aligned the chrony. I fired 10 shots through it with the .22 to see if it appeared to be functioning properly. It gave me a spread of about 40 FPS on 10 rounds so I figured that was probably o.k. for old ammo in a wore out 22.

Next I anxiously grabbed some of my handloads and hoped for good news. Well, out of the 5 loads I got what I consider to be great news. The bullet seating depth was the issue. In the extreme range catagory I got 2 31's, a 40, a 65 and an 81. This is not great but it is FAR better than I was getting.

So now I have at least (with the help of all you nice people out there) identified an issue I can work on. Now it's time to get back to the bench and do some more loading.

Again, thanks to everyone.

RobertInIowa
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Old May 17, 2012, 09:49 AM   #22
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I'm not sure you found the precise solution to the problem since you changed two factors (distance and OAL) and then fired the reloads.

Did you try some of the rounds at the shorter chrono distance also to see if the problem returned?
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Old May 18, 2012, 12:13 PM   #23
RobertInIowa
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Mal H,

You have a point. The distance wasn't changed by a large margin, but that certainly needs to be checked. My next trip to the range I will check the chrony at the two distances and see what results I get.

Thank you for pointing that out. I will post the results when I return.

Regards

RobertInIowa
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Old May 18, 2012, 06:14 PM   #24
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Far more useful than a chrony for reloading is the use of a bullet comparator, and determining the optimal jump for the bullet...JMO...

Your variations in OAL are inevitable unless you're loading to the ogive for best consistency.

Get yourself two things: Hornady LNL, OAL gauge with modified cases for your calibers (or make your own cases), and the LNL bullet comparator.

http://www.hornady.com/store/Lock-N-...traight-1Each/

http://www.hornady.com/store/Bullet-Comparator-Kits/
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