Powder Stability.

Rhovee said:

I use N570 in my 28 Nosler and have tested it from 85-39 degree's. No change in FPS. Shawn Carlock did a really good temp testing on it as well. Came to the same conclusion. Very temp stable. Expensive, but worth it.

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Shawn has recently posted that N570 is cooking the throats in some cartridges prematurely. Less than 1/2 the throat life compared to RL33 - in his own words. He seems convinced. Others still question this, versus the +P throat design as the possible cause for the poor throat life.

The obvious question which I have not seen addressed, is: Are standard throats experiencing short life with N570, or is the N570 shortened throat life tied to the rifles with +P throats?

I have only used N570 in my 28. Most people I have talked to are getting 800/900 rounds using RL33 and the higher node of about 3130-3180. A buddy that runs this set up told me he has .020 throat erosion at 350 rounds. I have .008 with 500 rounds. I read that post from Broz. Pretty sure he was using the +P design with a 30" barrel running a 300 berger out of a 338 edge at something like 3150? I am
Not educated enough on the throat design but being stepped makes it seem like half the throat is already gone from being tapered. Travis at Rbros told me he thinks RL 33 is harder on throats. Doubt anyone could prove either way.

Rhovee said:

Travis at Rbros told me he thinks RL 33 is harder on throats. Doubt anyone could prove either way.

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The conflicting opinions make me shake my head and smile. If one powder or the other is notably reducing throat life, the trend should become clear - "proved" - over time, by the heavy shooters.

If there's really little difference in throat life between the two powders, then the proving could be elusive. Shawn is fully committed to his opinion, based on his Post. Others having contact with, and feedback from, a number of rifle owners have differing opinions. It takes a lot of shooting to determine throat life, but there are guys that shoot enough to get there within a year or two.

I think Shawn's experiences and opinion was associated with his +P throat, but his Post never really spoke clearly on that subject. What was clearly expressed, was his belief that N570 was the cause of severely reduced throat life, compared to RL33. Search for Posts by Shawn. It was within the past 10 days, so should be easy to find. Read for yourself...

There is also the difference between first hand knowledge and second hand. There are tons of people using rl33 and I almost never see people calling it a throat eater but 570 i see posted all the time as being hard on throats.

The reason its hard to make second hand info useful is we have no ixea how fast c9nsecutive rounds are fired. I run 10 rnd in 1 mi vs 10 over 30 mins+ there is quite a difference in its effect on the temps of the throat area.

coyotezapper said:

Heat of Explosion numbers for like powders. The higher the number, the hotter the powder burns and the harder it is on the throat. If the throat is kept polished and shot strings kept low this should not be an issue with N570. Great powder in 7STW.

H1000 - 3630
Retumbo - 3710
RL33 - 3900
N570 - 3950

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Found this in another thread while doing a search on N570. So it is hotter than the other powders but is it to a degree that you would see noticeably shorter throat life? I don't have a clue myself but I've heard the throat erosion issue just enough to make me leery.

The grains of powder used to achieve the same velocity also change it. If it takes less powder with the N570 vs RL33 than it could equal out the same on throat erosion. There is a formula for estimating barrel life with a given load.

N570 is faster burning that RL33. I think the load is about 2-3 grains less using N570.

I have a download to the XL formula here on one of my posts.
http://www.65creedmoor.com/index.php?topic=7772.msg81849#msg81849

Guys want to really depress yourself... Work out the barrel life in actually shooting time. By that I mean the time the bullet is actually in the barrel. The difference between powders would only work out to less than 1/2 seconds LOL

Nice to know your 243 or 6.5x284 only lasts for about 1.5-1.8 seconds!!!!

Nitride them

then you get 4 seconds of barrel life..but you know I am pro nitriding

Honestly the entire idea of ratings powder on temp/fps is flawed. It certainly can help in a comparison but still. Powder voluem bullet weight even barrel length can have an effect.

Consider say the difference in degree to fps gain of say a 6mm but on in 6mm/284 vs 6mmbr even if they were both using the same bullet. One has a ton more powder and the increase is per degree is going to be way higher. The effect is a ratio not a static line. Now throw in different bullet weights. OR same weight but different bearing surface lengths.

Its one of the reasons you we see such wildly varying numbers. At best if we are sure to collect data and ensure its from many different cartridges and bullet weights we can possibly get a rough average but thats best case scenario.

What is really needed is some standard that can then be used as a reference much like we have and use burn rates with powders presently.

Point being with overbore cartridges vs non overbore you are going to see higher fps/temp degree in the prior vs the later for a given caliber (same bullet). As its a ratio of pressure you will likely also see higher vel/degree with a longer vs short barrel in some cases.

mechengr said:

4 year old thread... But he's got RL22 listed in the first post at 1.71 fps/deg. I did some recent testing in my 280 Rem and between 32° and 75° I got 1.68 fps/deg. Might want to check your math, you should end up with units of fps/deg. You have deg/fps listed instead. Flip the units and that gives you about 1.75 fps/deg. Right in line with his data point as well as mine

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That sounds pretty close. I find RL 23 to be more stable.

My RL-33 temperature sensitivity data. Velocity was recorded over triplicate chronographs (Oehler 33 & Pact PC2 & Oehler 35P) run concurrently with each bullet fired.
Cartridge = 338 Rogue (Lapua Improved)
Bullet = 300gr Berger OTM.
Barrel = 28" 5R Bartlein 10-twist.