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I want bore you with the groups sizes although they were a little better. The real odd thing that happened yesterday was my bullet velocities. I shot across a new chony and it was saying I was getting speeds of 2540 fps on average, at 15 feet. Well, I didn't believe it so I shot my .270 across the chrony and they also ran a little higher than normal. I averaged the shots and they were 3% off from what has been normal average velocities for the .270. Even if you apply this 3% error to the .338 MX, it would still be producing right at 2500 fps for the MV. This with only 46.0 grains of LVR. Since these where the last bullets I loaded I went back and checked my powder dispensor, weighed a charge on 2 different scales and came up 46.1 grains. The only other time I have shot 46.0 grains of LVR over a chorny(different one) I got around 2350 fps on average at 15 feet with the ambient temp of 62 degrees F and yesterday it was between 77 and 82 degrees F. All the cases were trimmed to 1.88" and loaded to 2.59" with the 200 grain FTX, then crimped with a Lee Factory Crimp turned in 1/2 turn after touching the shell holder giving it a moderate crimp. I did make sure my bullet was not touching the lands when setted that .005" foreward.

I stumped, but at the same time if they are running 2500 @ the muzzle I would love that. I'm surely hoping 20 degrees F didn't make that kind of difference. I recon time will tell. I recon I have to get the both chronographs together and shoot some more "known" loads across both and see what they read.
 

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I did a LONG write up about chrony accuracy a couple years ago. The 3% difference you saw is perfectly reasonable considering you are talking 2 different chronies and there is a difference in temperature and humidity in the tests (both of which affect the reading even if the bullet travels at the same velocity).
 

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I did a LONG write up about chrony accuracy a couple years ago. The 3% difference you saw is perfectly reasonable considering you are talking 2 different chronies and there is a difference in temperature and humidity in the tests (both of which affect the reading even if the bullet travels at the same velocity).
Quietman, would you mind giving us a thread title or link, I would like to read your chrony info.

James
 

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fwiw; I've observed the same thing over the years. A 3% variation is a nominal variation that can be attributed to atmospheric conditions. I too first thought that the difference in observed data is more likely the temp affect on the chronograph.

Add in additional variables such as different lot#s of primers, powder, and brass can make even more variation.


Several years back I was flying a client to Tampa, FL where he had a contract to service some of the loading equipment used by a contractor making 40mm grenade ammo for the military. While at lunch I got into a conversation where the plant engineer was discussing a batch of practice ammo (their largest money maker) was rejected by the military as it was running about 50-60fps "slow", as in 725fps vs 785fps. On previous trips, I'd found out the the engineer was a reloader, shooter and we shared that interest...
I asked if they had checked the charge weights on powder... check!, powder burn rate, check!!; I asked what primers they were using... Prolonged silence; I stated that I had seen the "ammo" and knew it was a "small, either pistol or rifle primer..." The engineer then admitted it was a Federal small pistol "standard" primer.... I said; "check the primers for brissance and flame duration with ocillograph to check for spec. performance. I got a blank look by the engineer; and a curious look by the plant manager.... After lunch,about mid afternoon, he and plant superviser approached me and asked me "how did you know"???? primers were 10% below spec, but still within industry margins for nominal performance. I just shrugged my shoulders and stated that I had "experienced" it before when checking velocities for "pre- and post- competition checks on ammo velocity with .38spl and 9mm ammo I used in competition.... One year at the NRA NPSC matches, we had a "cold" September morning and a lot of the 9mm ammo was failing to cycle the action and lock the slides open after emptying the magazines. Simply placing the ammo in the "sun" on the dashboard of vehicles, the "warm" ammo worked... It turned out to not be the powder, but the primers..... The plant manager looked at the engineer and said "maybe we ought to hire HIM to do our Q&A"..... My client jumped in and said "he's not available!".... at least not until I finish my pilot training.... We all had a good laugh...

The "factory" had to "recycle" the ammo, and Reloaded the cases with another "lot#" of primers.... $,$$$,$$$ saved !!!
 

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WOW!!! You have a way bigger brain then me Quietman or maybe you did not abuse yours as bad as I did growing up in the 70s! Loved the imfo. Widow
 
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