I am a big fan of RL-15/N 203-B. It 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 fill with 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

I ran a load with R22 in my 6.5x55 and had it hooked up to a Pressure trace unit last winter/early summer to check for temp variations in this powder.
I posted the results here.
http://www.24hourcampfire.com/ubbthreads/ubbthreads.php...rch=true#Post1460421

Ol Joe: I suspect that the calibration of your pressure equipment was to blame for the apparent difference in pressures when there was an apparent lack of difference in velocities. The anomolous "hiccup" in the pressure curve of the first set of data would seem to support this theory.

At any rate, it is clear that you didn't experience any significant velocity variation with temperature, at least not in this single test.

This is nit picking to be sure, but just for the record, the air temperature doesn't affect ballistics. It's the temperature of the powder charge that counts. Keep your cartridges at an even temperature and don't allow them to sit in a hot (or cold) chamber for more than a few seconds and there should be uniform ballistics. That's an old Benchrest shooters trick.

Ray

quote:

Originally posted by Cheechako:
This is nit picking to be sure, but just for the record, the air temperature doesn't affect ballistics. It's the temperature of the powder charge that counts. Keep your cartridges at an even temperature and don't allow them to sit in a hot (or cold) chamber for more than a few seconds and there should be uniform ballistics. That's an old Benchrest shooters trick.

Ray

Not gnit-picking at all, Ray. I think everyone assumes that the powder in question has not been exposed to the direct sun or body heat and is therefore approximately the same temperature as the ambient air. But it is a fully valid test to store ammunition in a cooler of ice and fire it immediately upon chambering to check its performance at temperatures approximating freezing.

quote:

Originally posted by Stonecreek:
Ol Joe: I suspect that the calibration of your pressure equipment was to blame for the apparent difference in pressures when there was an apparent lack of difference in velocities. The anomolous "hiccup" in the pressure curve of the first set of data would seem to support this theory.

At any rate, it is clear that you didn't experience any significant velocity variation with temperature, at least not in this single test.

Stonecreek, The unit was checked with a factory load from the same lot before both test, a 140 gr Remington cor-Lok lot # B21LB8017 and showed 39187 ptu for the 2-24-07 test and 43,744 ptu for the June test a difference of 2,457 ptu. This falls with in the extreem spread of this ammo of 39,187 ptu - 46,782 ptu for 5 test runs over a year and a half. The same lot was also shot on 9-4-06 in 75 F temps and averaged 41,359 ptu with a low of 40,272 PTU and a high of 44,086 PTU for 10 rds I believe the unit is measuring fairly consistant.

I don`t know about the secondary spikes but they appear in more then a few of my tests and all have been with slow powders. Some have occured with factory ammo in fact the worst case was with factory.

The secondary spikes usually remain no matter the temp, although I`ve never shot any other load in both hot and cold temps except this one. I am hopeing to redo this load and see if it repetes this winter if time permits. The powder lot will be different though so I don`t know how valid the data will be except to prove the spikes come and go with some uniformity.

The velocities are not unusual. I have seen similar results with other guns.

Example: 270 Win 26 " Walther BBL. M70

5/29/05
130 gr Hornady SST
56gr R22
ammo/rifle temp ambient @ 68 F
Pressure = 42,388 PTU avg.
Velocity = 3101 fps

3/28/05
130gr Hornady SST
56gr R22
ammo/rifle temp ambient @ 55 F
pressure = 44,069 PTU avg
Velocity = 3022 fps avg

A load showing 1,681 ptu less pressure measured 79 fps faster velocities.

Powder was of the same lot and velocity was measured with a Pact M1 @ 10'

Both loads had secondary spikes, the March loads` peak spike was just under 40K ptu or almost as high as the primary peak.

I find more questions then answers when useing this thing most times, but I do believe so far that the pressure of some powders increases with temp, and velocities don`t always reflect the amount of change.