I am a big fan of RL-15/N 203-B. If is relatively temperature insensitive from 20 to 45 degrees Celcius.

I have lit many votive /prayer candles in my catholic church that Bofors/Nexplo would develop some coatings to make RL-22/MRP stable over a wide range of temperatures as well.

A few years ago a fellow shooter and I fired identical cases filled with RR-22 during the course of a desert day that was cool in the morning, hot during mid-day, and almost cold as the sun set. One cartridge wes fired every thirty minutes. The velocity spread was almost 300 fps. The velocity (pressure) was roughly proportional to the ambient temperature.

My question is if MRP has been improved in this regard. I have several cartridges that I would be very happpy to MRP. It is very accurate, and provides pleasing velocity at a reasonable pressure (until it is fired in either hot or cold conditions).

Any new information?

It was disheartening to watch the velocity to head up the mountain, and then down into the valley that day.

Thank you for your input.

LD

Lawndart:

I don't doubt your veracity as to the observation of velocity variations.

However, it seems difficult to believe that the kinetic energy transferred to the bullet, which is only a fraction of the heat energy released from the chemical reaction, could vary so much -- regardless of the ambient temperature. In other words, the kinetic energy increase, which at 300 fps would have to be in the range of 15-20%, seems illogically high to be caused simply by the relatively small teperature variation of the chemical compound prior to the initiation of the chemical reaction.

This variance seems particularly excessive if you accept the (only vaguely accurate) rule of thumb that a 1-unit increase in velocity requires roughly a two-unit increase in pressure. So the (guessing here) 10% increase in velocity equates to something like a 20% increase in pressure. Surely, with loads anywhere near what most people regard as a "working maximum", the 300 fps faster shots should have exhibited significant excessive pressure indications. If they did, you did not mention it.

I would urge you to repeat your test, and do so with several different powders. I suspect that the hype in recent years (mostly promoted by Hodgdon's advertising agency in its introductory advertising of its Australian-made powders) over "temperature insensitive" powders is causing many shooters to find monsters in the closet that didn't exist before.

Let me reiterate: I don't doubt your truthfulness or judgement as you are clearly a guy whose IQ is not in the George Bush league; I just think that the shooting world needs more good data before jumping off of a cliff on the temperature sensitivity issue.

From some old Norma data for 180 gr 30-06 ,no powder info. From -4 F 2624 fps to + 122 F 2770. At 68 F the velocity is 2685.ThePressures go from 39,700 to 50,700 psi. The curves are not linear the rate increases with increasing temperature....Your 300 fps swwms a bit much .

The mid range powders are the most stable. Things fall off more at the slow end of the spectrum.

RL-22/MRP gives me tighter groups.

With H-4831 the groups are slightly larger, but move up and down much less with temperature changes. I've seen that often enough over the last decade.

The application in question is long range shooting from 300 Win Mag and 338 Lapua Magnum. At 1,000 to 1,500 meters all effects are greatly magnified, and any small advantage is worth pursuing. Perhaps I'll do a three way test and include a slower VV powder.

Obviously this is not for a sporting application.

Thanks,

LD