Help on huge variation on chronied 30-06

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Northman999

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Fellows,

I hit the range yesterday with my M1 garand and a couple of boxes of reloaded ammo; I also had my new chrony (Shooter's F1 Chrony) and I was setting up my adjustable gas system on the rifle, as well as my EER scout scope. I got the gas system set up and the scope sighted in, but I was find ing two things that were problematic regarding the chrony; firstly - about 65% of the shots did no register and I was getting error codes indicating that the sensors were not getting enough light, secondly - on the shots that were registering I was getting huge variations on my speeds - low of 2549 fps up to a high of 2805 fps.

My load is Federal brass, Winchester large rifle primer, 50 gr IMR 4895, 165gr Nosler Accubond's. I check my powder dispenser every 5th round to see that my powder is still bang on and I measure the COL of every round and they are within +/-0.01 inches. All brass full length resized. I've rechecked my scale with known weights and it is on. I just now tested my powder dispenser with about fifteen samples and I've got a slight variation in powder dispensed, most times I'm within +/- 0.1gr, but I've had some samples up to +/-0.3 gr. Now this is some variation, but I don't see this giving me 250 fps difference; my manual suggests I need to go up 2.1gr per 100 fps with this powder, so even if I hit loads with 0.3 gr more or less, that should only be about 30 fps, not 250. BTW, I was shooting pretty tight groups and I question if I could group well with ammo varying by over 250 fps.

So, is my chrony just wacky (or bad light conditions), or is +/- 0.3gr that big a deal or is it something else?

Thanks in advance!
 
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How far from the muzzle was your chrony? If it was too close the gases exiting the barrel can throw it out. I only use the white screens on mine when it is a clear and sunny day. They are not required on cloudy days. 250fps is more than you should see on that powder variant. If the velocity was out that much, I think your groups would open up.

When I first set mine up, I usually run a few 22's across to make sure it is working. Maybe try a new battery?
 
I was using a chorny table that was previously set up in front of the bench, about fifteen feet. The .22 thing would be a good idea if I had one previously chronied - my problem is this is my first chrony and none of the guys I shoot with have one; so I've got no other frame of reference. I do have a Ruger 10/22 - if you know the exact velocity of any specific .22 loads with that rifle, I could buy a box and shoot it through my chrony for reference...
 
If there were light problems, this could explain the velocity numbers. Just try the .22, see if the results are consistent.
 
All high-velocity .22s run about the same, 1150 to 1300 depending on the brand, with maybe 40fps extreme spread or so.

Powder variation is definitely not causing that velocity spread. It is either the lighting, or muzzle blast, or serious ammo issues such as inconsistent start pressure or bullets setting back.
 
Okay, thanks fellows. Next time I hit the range I'll bring my 10/22 and a box of CCI Stingers and see what's what. I am hoping it was just the light; I was pretty disheartened to see my handloads having a spread of over 250 fps on the chrony when I was doing what I thought was a very good job of controlling the variables. There's a huge difference at 400 yards between a bullet with an MV of 2549 and one with an MV of 2805, and the last thing any hunter wants is an animal to get away wounded...
 
Im new to this forums so i dont want to step on any toes but your garand is a 30-06 yes ?? or a 308 or a rebareled to another cal ??

but i checked my IMR book and there was no load data for 165g for 30-06
i checked my older Speer book and no listing for IMR 4859

quote My load is Federal brass, Winchester large rifle primer, 50 gr IMR 4895, 165gr Nosler Accubond's.

my older Speer book has a listing for IMR 4859 for a 150g MAX MAX listing is 49.5 ( the load you have to work up to and use with respect and caution
 
My load is a worked up load and I've used it with my Garand before. I just installed an adjustable gas system as well, which bleeds of excess pressure. IMR 4895 is THE reccomended powder for the M1 Garand and is actually the powder that military ammo is loaded with. Thanks for the advice, but this is a safe load.
 
If the chrony is having a hard time picking up the bullet,felt tip the bullet black. It works for me. But late afternoon light is not Shooting Chrony friendly.
 
If the temperature was below 0 it could be a problem, Chrony's don't like the cold. 15' from the fist screen with a .30/06 shouldn't be a problem, but as suggested if you could shoot the same ammo across the screens with another rifle it should tell you if you have a rifle or chrony problem.

Was there a marked difference in the report or recoil of the loads you fired? If there really was a difference of 250 fps, I'm sure you would be able to tell the difference between subsequent rounds.

There is no way that a half gr or less variation in powder charges will produce that much difference in velocity in that large a cartridge. Even if you allow for volume differences between the heaviest and lightest cartridge cases or between the pressure differences caused by variation in the bullet weight would you come anywhere near that.

The fact that you were getting error warnings from the Chrony leads me to believe it is probably the weak link in this case.
 
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