I have found that velocity drops with a drecrease in temperature with most powders and cartridges but it does vary with each.The biggest drop that I have seen was about 100fps with my 7mmstw's and imr 7828 when the temperature dropped from 90F to 30F.I have never seen velocity or pressure increase with a drop in temperature.Do not expect published loads to be the same as those obtained with your gun as they often vary by 100fps or more due to variances in barrels,chambers and reloading component lots.

Play with this ballistic calculator and it will give you an idea.
http://www.biggameinfo.com/BalCalc.aspx

I don't understand why any IMR powder would give a higher pressure at a lower temperature. I'm thinking something else must've gone wrong. George Frost in "Ammunition Making" reports some problems decades ago with high pressures in Winchester-Western rifle ammo loaded with double-based Ball powders in extremely cold temperatures, ascribed by the Winchester-Western engineers to the nitroglycerine freezing and fracturing the powder grains. That's not an issue in IMR powders, which are all single-based, and the problem originally occurred at about -40F, not at 0. (They changed the composition of the Ball powder to fix this, BTW.)

I normally shoot through my chronograph, even if I am not specifically testing a load and just shooting or zeroing in. In the past, I noticed big swings in velocity with IMR 4350 and IMR 4831. I don't recall the exact range, but it was in excess of 100 fps.

I now shoot H4831SC Extreme. The mfg claims this to be temperature insensitive. Most loading manuals do not show this powder to produce the best velocity, but it's a tried and true powder so I gave it a shot.

Well, I can say that I was really happy with it. I worked up a load at 85 degrees and my load shot 3084 fps avg. over many shots with a very tight range. Most shots were within 10 fps! That is excellent, IMO.

A few weeks ago the temp was 44 degrees and the load averaged 3079 fps, again with a very low range. Needless to say, I am quite impressed with the H4831SC extreme.

You probably won't the the tip top velocity that other powders can deliver, but the consistency more than makes up for it, IMO.

Jeff, 1st, your reloading book vel. are only a guide. You need a chrono. Every rifle is a rule unto itself. I have seen as much as 100fps frop from an 80deg day to a 35deg day. This seems to be more noticeable w/ magnums/high vel. rounds & slower powders.

Do I remember a warning some time ago about Blue Dot having some pressure excursions when the temperature was 0� or below?