Sorry if you've seen this elswhere! First, I've been reloading for over 25 years and believe in safe loading. Second, I'm not a speed freak, but do want to get the most I can within safe pressures. As you may recall I load for a '52 FN commercial Mauser in 7x57. I use RP brass, cci 200 primers and H4350. All are from the same lot #s. The bullets are 150gn Partition seconds. The brass is new, or once fired and fully resized. I use a Chrony. I worked up loads above max to 2660fps using 49.5gns. This is an average of 3 shots one day and 6 shots another. The temperatures averaged in the 70s. It was sunny and we used the shades. Because most have been able to get 2700+fps out of 150s I decided to up the powder by 1/2gn. Using these, same everything except sunny, but high hazy clouds my fps went up 150fps!!! It shot 2830fps!!!!!!! I tried some of the old loads and it was right around 2800fps. To make sure the Chrony was on I shot my '06 and it showed what it should. I had no hard bolt lift and the primers appeared perfect. What are your thoughts? capt david

Something doesn't sound right...from 2660 to 2830 is a 170fps difference, which in terms of pressure is typically a big difference at the top end of the scale. Sounds like your Chrony had a brain fart or two...lol. An additional half grain of powder would account for a 30 fps difference...that makes sense. Got me.

quote:

Originally posted by captdavid:
What are your thoughts? capt david

I've had similar a velocity increase when using ammo that was in my truck cab in direct sun light. They were hot to the touch. In that case I did notice slightly harder bolt handle lift. roger

My guess would be that the barrel was warm, you loaded the chamber and let the cartridge soak up the heat for a minute then shot it. Pressure and velocity will jump 100 fps with the same load in this situation. Try it with one of your other rifles on purpose sometime. The 2800 fps should be a doable load with a 150 grain long-throated 7x57, my 160 NP load goes 2780 fps at 63000 psi with a pressure trace, I'd shot the load for years with a grain more powder but the pressure trace made me back it up a bit.

the chroney is a box that unfolds with sensors at each end and the difference you're talking about is about 5%.

If the chrony wasn't completely unfolded it could give an errant reading and 5% might not be many degrees of angle for the box.

Just a thought!!!!!

vapo may be right too, I had some 2900 fps 270 grain .375's till I made sure the Chrony was flat, It had folded slightly when I was moving it. However if it wasn't touched when you fired the '06 over it that couldn't be the case. I have also seen the speeds pick up over 100 fps in about five shots as compared to a squeaky clean barrel. I have a .220 Ackley that will go 3850 after a barrel cleaning, in five shots it will go to 3990 and stay there till it's cleaned again. I don't think sun, clouds or a malfunctioning Chrony are the problem, at least. Again, 2800 with 150's isn't unreasonable either.

I've seen Chronys do some strange things when the lighting changes. Try it some day moving it from direct sun light to the shade.
Also the un folded theory holds merit as well.

one way to stop the light thingie problem is to use frosted scotch tape over the light sensor thingies. worked for me. it was suggested in handloader magazine buy a writer there. i stopped getting all those weird reading when i started using it.

try it, you'll like it