Ok so certain rounds are coined barrel burners or over bore. It made sense till i starting thinking about it. Maybe someone can clue me in o what im missing.

220 swift vs 308. One has a bbl life that people say starts going south less than 1k the other ppl say can go over 3k without losing a step.

Here are the pressures of some rounds.

220 swift - 54k CUP
223 rem - 55k psi
308 - 63k psi
270 win - 65k psi

Heat and erosion are functions of pressure. So are the supposed staple "barrel burners" really "barrel burners"???

Erosion is a function of the volume of gas (and therefore the amount of powder burned) in relation to the cross-sectional area of the bore.

In addition to what RR said if you compare the case capacity of the 223 rem vs the 220 swift you get 31 grains vs 47 grains or roughly 50% more powder being burned in the 220 swift. The travel time for the bullet in the barrel is also shorter in the 220 swift - therefore you are expelling 50% more gas (assuming full burn) in less time through a barrel that has the same internal volume. Based on the Laws of Thermodynamics no matter what the initial chamber temperature/pressure is, the pressure and temperature as you proceed down the barrel of the 220 swift will very quickly greatly exceed those in the 223 rem. Shoulder geometry also comes into play as it will affect gas turbulence formation. The more turbulence the more erosion.

^^Answered^^

Thread over.

Basically there are three areas that need to be examined. Thermal, mechanical, and chemical but since someone has declared the thread is over who am I to examine the issue any longer.

Consider the .308, 7-08, .260, and .243 in that relative order. All of them have a .308 parent cartridge and each round has a slightly smaller caliber that the parent case is necked down to. Give or take a little they each have the same basic powder capacity (again +/- to illustrate my point). As the heat and pressure becomes more concentrated moving down to the smaller bore diameter, the greater the throat erosion. So the forces escape through a 7.62mm hole much easier than a 6.00mm hole. The more concentrated the force, the greater the erosion.

I hope that explanation helps.

Yep, i dunno why but i thought i was really on to something driving down to the ranch today. Man, i feel like a total moron now.

I thought this thread was about my 7mm RUM. I bought three extra barrels for it and fully expect to use them all over the next x number of years, Providence willing.

Lol you have a barrel burner for sure. My .300RUM has 600 rounds on it and it's gonna go tits up in the next 100 - 200.

It's like the safety video I saw back in the day, "Speed Kills". Yes it does, barrels.

Barrel life in the "barrel burner" chamberings can be extended dramatically by letting the barrel cool thoroughly between shots. The cooler the barrel is just prior to firing, the less damage there will be.

The only person on the planet who is stupid enough to think that fire cannot weaken and melt steel is 9-11 truther Rosie O'Donnell. - And pre-heated steel is much more susceptible to damage than cold steel is.

Another dodge to prevent barrel damage with an over-bore cartridge is to back off a bit on the load. Starting loads for the .300WSM for example give you velocity in the 30-06 level - and guess what? They also give you 30-06 barrel wear and recoil level too.

Why would one load down a .300WSM to 30-06 level? - Because magnum velocity is not a perfect fit for every hunting situation. If you are just shooting at pigs or whitetails at normal hunting distances, all that magnum velocity does for you is tear up the dead critter a bit more. It's not going to be any deader.

Why have a 300WSM if you are not always going to shoot maximum loads? - Because if you do need magnum velocity the .300WSM can deliver that for you - and the 30-06 cannot.

Having one rifle that delivers either 30-06 or 300 magnum velocity by just changing the loads means that just one rifle covers all of that territory instead of two. Using one rifle for a wide variety of hunting situations means that you are going to be putting in more time with that one rifle - and you will get to be good with it. You can also put more money into that one rifle (optics would be a good example) and have a higher quality firearm than you could wind up with if the same money had to buy two of them.

The reduced loads are great for practice. They recoil less, are less expensive to load, and you can practice a lot more without wearing out your barrel. More practice means that you will be a better shot with that particular gun. You'll be so comfortable with it that bringing it up to your shoulder will be like slipping on an favorite old pair of shoes.

There is no free lunch though... The .300WSM for example can deliver 30-06 performance with starting loads - but it will use a bit more powder to do that than a 30-06 would. Not a lot - but some.

I have used the .300WSM and the 30-06 as examples here. - But the concept applies to all of the barrel-burner, over-bore cartridges.

270 WSM - 270 Winchester
22-250 - .223
340 Weatherby - 338-06
325 WSM - 8x57
257 Weatherby - 25-06
25-05 - 257 Roberts
etc. etc..

You cant compare bore size vs powder capacity alone.

IF what GAP has been reporting as true, a 6.5 SAUM with 60 grains last almost as long as a 6.5CM with 44grains.

It will take me quite a while to confirm it myself unfortunately as I don't shoot 100 rounds of each caliber every week.

True but if what I have read on the 6.5 GAP SAUM is correct they are running it at 5000+ PSI less than normal pressures of the Creedmoor.

What are your thoughts on case design being a factor? I've heard a lot from the older guys shooting that the 30° and up shoulder designs help force the gasses more down the center of the bore. I know several prs guy's running x47 and saying at 2750 4k rounds but other rounds don't seem to make it as long.

It makes awfully good sense to me. I think you've hit the nail on the head.

Case design does help. 6XC is a good example of an efficient cartridge design that does what your describing.

Powder being used can make difference as well. I have had folks who are quite knowledgable tell me they could shoot longer strings of fire (without getting too hot)while PD shooting by just changing from extruded powders to Ball type. The also noticed longer barrel life as well.

The equation shows that pressure and temperature are directly proportional. So, you don't get one without the other.

I've heard tales of powders that magically are less destructive than others. I suppose it's possible that spherical powders are less destructive due to physical shape of the granules, and there might be other physical properties involved.

I have to wonder what "too hot" means.

I am sure " too Hot" was very subjective no doubt.

That's not totally true, RR. You're ignoring the fact that pressure can also come about by increasing the quantity of gas, which is how powders primarly build up pressure.

The combustion of the powders is exothermic, sure, but a temperature increase of 100x (I'm estimating here) is not enough to account for the 50000+ psi we see in modern long range cartridges.

Now that doesn't really affect throat erosion since it's pretty much a byproduct of unburned powder and hot gases being pushed down the bore, but if you could create a powder that yielded the maximum number of equivalents of gas per amount of powder, while giving off as little heat energy as possible, then you'd have something amazing.

Unfortunately, though, it wouldn't have much application for shooters. Powders must burn slowly out of necessity, because letting too much ready too quickly would push pressures to the extreme. So I imagine that overbore cartridges will always be barrel burners until someone creates a new kind of powder.

PV = nRT

Pressure can increase, but temperature stay constant because of a proportionate increase in the number of miles of gas.

Besides, if there is a 4,000x increase in pressure (14psi to 64000psi), by your logic, there would have to be a 4000x increase in temperature as well.

PV = nRT. It is a law of physics.

There is NO increase in the MOLES of gas. There is a certain amount of matter in the powder charge, and that amount of matter is neither increased nor destroyed. The powder is a solid which transforms rapidly into a gaseous state. It really is that simple.

PV = nRT.

Yes there is, simply because the powder, as it burns, produces gases that build the pressure.
4 C3H5N3O9 --> 12 CO2 + 10 H2O + 6 N2+O2

That's the overall reaction for the decomposition of nitrogrlycerin. Compare the number of moles of nitroglycerin on the left, with the number of moles of gas produced in the right.

For every four moles of nitroglycerin, 19 moles of gas are produced. And considering how the volume that is occupied by that quantity of gas molecules far, far exceeds the volume of nitroglycerin needed, one can expect that the pressure would increase, without necessarily an increase in temperature.

Sure, you're starting with a fixed amount of matter, but keep in mind that moles are more easily thought of as 'equivalents' in chemistry than as a fixed amount of matter.

To prove the point, every mole of gas at STP takes up 22.4L of volume. One mole of nitroglycerin would take up roughly 142mL (calculated using its density of 1.6 g/mL). That gas, of allowed to expand, would occupy 425L of volume. I'll let you calculate the pressure of it wasn't allowed to expand.

Edit: whoops, just realized I forgot to adjust the volume of gas produced based on the 4:19 ratio. Good old phone math. I don't feel like correcting it, because the point is still relevant.

And this is why i went for mechanical instead of chemical lol