Pressure vs heat

[bigd 7378]

As a rule what would be harder on throats and lands. Running pressures at max say 64-65k or running hotter powder say N570 vs N165. I know N570 is harder on throats than N165. I guess my question would be would N570 at 60k be harder or easier on throats vs N165 at 65k?

 

[Tiny Tim]

Great question. I have no idea, but I want to say flame temp is more destructive than pressure. I'm sure there is some give and take there. Perhaps ql users may be able to shed some light on the subject.

 

[Dean2]

Pressure in and of itself does not wear the barrel, temperature and flame do. Overbore cartridges tend to operate at higher pressure but the real issue is burning that much powder and forcing the flame down a hole that is too small to be optimal. A 7 RUM and a 7 Rem mag run nearly the same pressure 65,000 vs 61,000 PSI but the RUM wears the barrel a whole lot faster, 800 round barrel life vs 2000, because it burns 95 grains rather then 65 grains of powder. If you up the pressure on the 7 Rem mag to 65,000 psi by adding a few grains of powder you will be over SAMMI spec but you will get very close to RUM velocity and still have far longer barrel life.

If you push pressure too far however, catastrophic failure will definitely shorten barrel life before the flame gets it.

 

[blksno]

Pressure in and of itself does not wear the barrel, temperature and flame do. Overbore cartridges tend to operate at higher pressure but the real issue is burning that much powder and forcing the flame down a hole that is too small to be optimal.

If you push pressure too far however, catastrophic failure will definitely shorten barrel life before the flame gets it.

I litterally was in the process of typing almost this exact statement.

Pressure, isn't hard on barrels at all, it's what CAUSES the pressure that is hard on barrels. If you simply plug both ends and increase pressure up, it doesn't harm the barrel at all. It's the combination of heat from the powder, and the heat from the friction that degrades barrels. The hotter you get the steel, the more susceptible it becomes to wear from friction. Heat and friction in conjunction are very bad over time.

 

[bigd 7378]

If N570 is used, would there be a difference in flame temp between 60k and 65k? In other words does 10 grains of said powder burn as hot as 80 grains? Or does pressure have something to do with heat also

 

[bigd 7378]

Then why is N570 so hard on barrels when there are other powders that burn as hot

 

[Tiny Tim]

Then why is N570 so hard on barrels when there are other powders that burn as hot

N570 is double base, and has an extremely large kernel size. It is one of the hottest burning powders and couple that with the abrasive action of these kernels on the throat, and you have increased erosion.

There are other factors like neck length and cartridge design that affect the throat as well.

I'd be interested to know if a powder burns at the same temperature regardless of pressure as you asked in post 5.

 

[bigd 7378]

50BMG burns hotter than N570 according to quickload. 50BMG and N570 are comparable in kernel size. But nobody complains about 50BMG burning out throats as fast as N570. N565 and N560 also double based and have the same flame temp as N570 also. I'm just trying to understand why everybody hates on N570 but not other powders.

 

[blksno]

50BMG burns hotter than N570 according to quickload. 50BMG and N570 are comparable in kernel size. But nobody complains about 50BMG burning out throats as fast as N570. N565 and N560 also double based and have the same flame temp as N570 also. I'm just trying to understand why everybody hates on N570 but not other powders.

That's because pressure curves are different for each powder, for each cartridge and for each bullet.

 

[bigd 7378]

So pressure does have something to do with it?
Well I get back later. I'm taking my wife out for birthday dinner the big 60 today

 

[Greatgrandad]

Heat and abrasion are the main killers of throats along with turbulence point.

I fire form a lot of my wildcats with small but appropriate volumes of pistol powders and cheap bullets (seconds, pulled, hard cast, etc), for case forming is all about "pressure". While the pressures are near or equal, those smaller volumes of pistol powder cause far less heat and throat wear then the larger charges or slower rifle powders.

A great example of this are a few or our varmint rifle loads using Blue Dot or Herc 2400 behind a 35-40 grain .224 bullet in a 222 or 223 for high volume shooting (Hundreds a day). We easily reach and break 3k fps with those loads, and while not as fast as using various rifle powders behind those bullets, our varmint barrels last twice or more as long. Another example is bulk fireforming when hundreds of cases are desired like 223 AI, 243 AI etc, etc.

Recently, I fireformed 50 new cases for my old 6mmRem-AI, and while I did not wish to add any new wear to that older throat, I used 12 grains of Red Dot behind a 70 grain varmint bullet. Those cases formed perfectly, and the barrel never heated overly much. In fact, I have shot 5 rounds of full power loads with slow powders that made the barrel hotter than a 20 round string of those quick fireforming pistol powder loads.

Turbulence point can worsen throat erosion, and a good example of this is the 243 Winchester. They tend to wear throats faster than other 6mm's, but fireforming those to 243 AI reduces throat erosion via changing turbulence point in front of the case mouth.