7 PRC Powder burn rate vs velocity? I don't understand.

[ObiWanKannoli]

Thanks for that Jud.
What does the term High energy mean other than it makes the bullets go faster? How can a powder burn slower and make more velocity at lower pressure? To me it seems like this is the perfect powder for the 4 rifles I have used it in. What are the disadvantages to this?

Why would so many people say that N570 is too slow for say 6.5prc with 143's? Are they simply basing this off of burn rate charts and not actual testing?
Thanks Again.

Easy way to put is that the burn rate is the same or slower, but the energy content is great. So much so that even with a slower burn rate you'll see greater velocities.

These are highly simplified numbers...howrver let's say your burn rate is "1" with powder A which has "1" energy content and powder B with "1.3" energy content but burn rate "0.9". B will still be producing more velocity. The reality is both burn rates are still fast enough to complete burn in your barrel, so the burn rate is irrelevant then. Net net, it's more energy. The pressure curve is different between the two. One may spike a lot more quickly to a lower value, while the other may take 10% longer for a 20-30% greater peak pressure. That extra 10% is still within the barrel, and the barrel length is still giving your bullet enough time to make use of the extra pressure and speed up more.

 

[jcoop]

MagnumManiac. This makes sense! Thank you for explaining this so well.

 

[NW NM hunter]

A few additional things, in my 7prc I run the n560 and get about 3050 with the 175eldx, so the n570 may be a little slower than the 560 in your 7prc and possibly your 6.5prc for a similar powder type in different burn rates. Another note since you stated you are moving to n570 over retumbo, when I looked at it similar with n560 over rl23 and h1000 is that above 90+ish degrees the 560 and 570 can have pressure spikes due to the heat which is why they aren't labeled as being temp stable.

 

[john k]

Jud96 is correct. While N570 has a "slower burn rate", it is a double base powder. As has been pointed out, barrel life usually suffers and to the extreme under high rates of fire. It's often claimed to produce 100-200 fps gains over other powders. While I have no personal experience, many claim 40-60% of barrel life compared to othe powders like H1000 and Retumbo.

In my experience, H4831/SC has never been known for exceptional velocity, but often produces exceptional precision.

Your case fill being at maximum, possibly even compressed, while not exceeding pressure, the case fill likely explains your low SD and ES.

Concur with statement in regards to H4831sc. I always have that powder available due to it being accurate in my cartridges. However the noticeable loss of velocity has me selecting other powders in most loads.

 

[jcoop]

A few additional things, in my 7prc I run the n560 and get about 3050 with the 175eldx, so the n570 may be a little slower than the 560 in your 7prc and possibly your 6.5prc for a similar powder type in different burn rates. Another note since you stated you are moving to n570 over retumbo, when I looked at it similar with n560 over rl23 and h1000 is that above 90+ish degrees the 560 and 570 can have pressure spikes due to the heat which is why they aren't labeled as being temp stable.

Good to know.
What is your barrel lenght on your 7 prc?
We don't get to shoot much in temps over 90 degrees here and never while hunting. So far its been relatively temp stable from low 30s to about 80 degrees.

 

[NW NM hunter]

Good to know.
What is your barrel lenght on your 7 prc?
We don't get to shoot much in temps over 90 degrees here and never while hunting. So far its been relatively temp stable from low 30s to about 80 degrees.

24inch. Based on those temps i would think you should be good.

 

[Shane Lindsey]

Barrels torch fast with N570 but speed and accuracy are great. Just shoot slow and clean often.

RUM gone in under 700 rounds shooting a healthy diet of N570.

I have heard Retumbo can spike. Better off trying H1000 if you can get it. It will probably be about 80-100 fps slower than N570.

 

[SheepShapeAK]

Barrels torch fast with N570 but speed and accuracy are great. Just shoot slow and clean often.

Or have a pile of spares chambered and ready to go.

I ran N570 in my 338NM with the Berger 300 OTMS. I shot that barrel for our LR club matches with three strings of unlimited sighters and 20 rounds for record. She's pretty fire cracked at least 1/3 of the way up the barrel. I should bore scope it and get some pictures.

I've got a few powders I'll be trying in my SAAMI 7 PRC and my 7-6.5 PRC. It will be interesting to see if I can find something that works better that isn't already being done. More than likely not, and I'll end up with one of the powders most of the F Class guys are using in their PRCW.

 

[Doom2]

A slower powder reduces the peak pressure at the expense of burning the power longer and further down the barrel (area under the curve). This is why pressure signs tend to be reduced. However, since they burn slower there is a higher likelihood that they will not burn out completely before the bullet exits the muzzle.

Several years ago I tried 2000MR in my 20" 308. The velocities were about 75fps higher than with 4064 but the report and muzzle flash were unreal. Several people thought that I had blown up the rifle!

 

[FEENIX]

This is the part I do not understand about burn rates.

If Retumbo is a faster burn rate than N570, then why are the velocities so much slower with the same charge weight? Especially considering this is in a shorter 22" barrel.

Retumbo 70 gr. = 2742

N570 70gr. = 2925

And why am I able to load more N570 and not find pressure if the velocity is that much higher?

The burn rate is simply a guide, as with anything else, YMMV. I do not have a comparison for the 7 PRC, but here's one from Berger's load recommendations that reflects a much closer comparison, but the "actual" result might be different.

 

[SheepShapeAK]

I've been digging around on VihtaVouri's website looking at their different powder families, and it makes me want to spend more money and see what works for my cartridges.

There are powders listed in there that are recommend for the 6.5prc and 375 H&H.

I just ordered some N170 to try.

 

[jcoop]

Funny you say that SheepShape, When I first started Loading with N570 in my 6.5 prc. the Vv sight did not list it as a recommended powder for the 6.5 prc. They listed most of their other popular powders that you would assume would work better. I had to figure out my own load data. Now they list it and it the fastest powder option they offer for the 6.5prc. I will say, I think their charge recommendations are very conservative.

 

[SheepShapeAK]

Funny you say that SheepShape, When I first started Loading with N570 in my 6.5 prc. the Vv sight did not list it as a recommended powder for the 6.5 prc. They listed most of their other popular powders that you would assume would work better. I had to figure out my own load data. Now they list it and it the fastest powder option they offer for the 6.5prc. I will say, I think their charge recommendations are very conservative.

I'm sure it's for legal reasons with them listing it on the conservative end.