Thread: Is it Pressure or Powder Capacity?

The no 1 cause is case capacity to bore size ratio.

As modern cartridges all run basically the same maximum pressure.

Low loading overbore cartridges will extend life but running a 22-243 at 55000psi wont make it last longer than a 308 running at 60000psi (same case) the 308 will still last probably 5 times as long.

Originally Posted by veitnamcam

The no 1 cause is case capacity to bore size ratio.

As modern cartridges all run basically the same maximum pressure.

Low loading overbore cartridges will extend life but running a 22-243 at 55000psi wont make it last longer than a 308 running at 60000psi (same case) the 308 will still last probably 5 times as long.

Can you supply some studies, written facts to support this? You could be right....just need something to back it up.

Originally Posted by Hermitage

Can you supply some studies, written facts to support this? You could be right....just need something to back it up.

No but search the internet for even one case of a 22-243 barrel lasting 5-10 thousand rounds accurately.

Anecdotally we know that chamberings running the same pressure the smallest bore size will wear first, which makes perfect sense as for the same volume and the same preasure to get threw a smaller hole takes more time.
Another way to look at it is for a same amount of powder/gas to get threw a smaller hole then the surface of that hole is subjected to more contact/abrasion/heat in order to flow the same amount.

Originally Posted by veitnamcam

Anecdotally we know that chamberings running the same pressure the smallest bore size will wear first, which makes perfect sense as for the same volume and the same preasure to get threw a smaller hole takes more time.
Another way to look at it is for a same amount of powder/gas to get threw a smaller hole then the surface of that hole is subjected to more contact/abrasion/heat in order to flow the same amount.

Yes "chamberings running the same pressure the smallest bore size will wear first", but I was meaning your statement of:

Originally Posted by veitnamcam

The no 1 cause is case capacity to bore size ratio.

Low loading overbore cartridges will extend life but running a 22-243 at 55000psi wont make it last longer than a 308 running at 60000psi (same case) the 308 will still last probably 5 times as long.

This is from Guns&Ammo Editorial:
https://www.gunsandammo.com/editoria...ls-life/326755

"The key ingredient here is high pressure, barrels don’t last as the pressure rises. There is no getting around this principle. Pressurized gas in the chamber blasts the throat. The throat, under extreme heat and pressure, rapidly moves between the solid and liquid phase. The bore melts a little bit from the heat and the pressure blasts the metal away.

In addition to SAAMI maximum pressure, the reloader must consider the cartridge’s case capacity. The powder in the case is the fuel that burns when the cartridge fires. More fuel means more heat. Heat is the second great enemy to barrel life and it’s nearly as bad as pressure."

Pressure is #1 with case capacity a close second by this article.

Originally Posted by Hermitage

Yes "chamberings running the same pressure the smallest bore size will wear first", but I was meaning your statement of:



This is from Guns&Ammo Editorial:
https://www.gunsandammo.com/editoria...ls-life/326755

"The key ingredient here is high pressure, barrels don’t last as the pressure rises. There is no getting around this principle. Pressurized gas in the chamber blasts the throat. The throat, under extreme heat and pressure, rapidly moves between the solid and liquid phase. The bore melts a little bit from the heat and the pressure blasts the metal away.

In addition to SAAMI maximum pressure, the reloader must consider the cartridge’s case capacity. The powder in the case is the fuel that burns when the cartridge fires. More fuel means more heat. Heat is the second great enemy to barrel life and it’s nearly as bad as pressure."

Pressure is #1 with case capacity a close second by this article.

You are taking the article out of context, the heading is "extending a barrels life" and yes low loading will extend life, it wont make a under 1000rnd chambering last 20,000rnd.

The key factor is time and flow over area.
Or put more simply case to bore ratio.

You seem to have convinced yourself otherwise tho so you believe what you want to.

Originally Posted by veitnamcam

You seem to have convinced yourself otherwise tho so you believe what you want to.

Well that was easy

Originally Posted by veitnamcam

No but search the internet for even one case of a 22-243 barrel lasting 5-10 thousand rounds accurately.

Anecdotally we know that chamberings running the same pressure the smallest bore size will wear first, which makes perfect sense as for the same volume and the same preasure to get threw a smaller hole takes more time.
Another way to look at it is for a same amount of powder/gas to get threw a smaller hole then the surface of that hole is subjected to more contact/abrasion/heat in order to flow the same amount.

Maybe think of it in terms of total volume of barrel + cartridge case. By the time the bullet is about to exit the muzzle it is at least evenly distributed, probably pressure slightly higher in the case itself. Come the point when the bullet leaves the muzzle, all that pressure now gets vented forwards unhindered, except for barrel resistance. In the case of a magnum size cartridge behind a .22 barrel, that will be quite a rush of fast gases hitting the throat area of the barrel and they will be at a relatively high pressure for longer due to the small diameter (=more resistance to gas flow) of the barrel.

Think of Vietnamcams point in terms of a water pipe 15 and 20mm alkathene both handle the same pressure before bursting. Say you have 100l of water to get through both pipes, the 20 mm pipe is 56% larger in volume than the 15 the water will get through that twice as fast. Not only that but the larger diameter reduces friction so the centre of the water column which moves faster than the edges does more of the heavy lifting.
Now convert that to high pressure gas in your barrel, the smaller bore means it takes longer for the gas to escape and also there is more friction with the barrel walls and that leads to increased erosion. Ask anyone who has had a blown primer what high velocity high pressure does it might as well be a gas axe.

Originally Posted by Cordite

Maybe think of it in terms of total volume of barrel + cartridge case. By the time the bullet is about to exit the muzzle it is at least evenly distributed, probably pressure slightly higher in the case itself. Come the point when the bullet leaves the muzzle, all that pressure now gets vented forwards unhindered, except for barrel resistance. In the case of a magnum size cartridge behind a .22 barrel, that will be quite a rush of fast gases hitting the throat area of the barrel and they will be at a relatively high pressure for longer due to the small diameter (=more resistance to gas flow) of the barrel.

But I don't disagree with this @Cordite....in chamberings running the same pressure, it's only natural that the smallest bore size will wear first.

Ok here are the last words I will post up on this 'pressure vs case capacity' thread (hopefully it will help people understand). I just found the below information so am quoting it:

"...after seeing a lot of 6.5x284's go south at 900 and a couple 6.5 WSM's go south at 500-600 I started thinking. Powder Burning does not cause the heat that destroys barrels it's the Pressure. The Pressure causes the extreme heat that's necessary to burn and heat check the barrel.
Anyway the 6.5 Saum case is near perfect because it allows you to throw a 6.5 140gr at 3100 at about 53,000 PSI with H1000. Other cases have too much capacity or not enough. The Saum case was picked not because it's magical, but because it is the perfect fit. In a perfect world, I would take the RCM case and shorten it a tad and give it a longer neck. That would truly be perfect!!!! At any rate, the 6.5 Saum is working as we thought it would.

Here is a thought to those that are still having problems understanding it. Shoot next to a 6mm REM, 243 ETC, any caliber that has a 63,000-68,000 PSI SAMI pressure. As soon as the rifle is fired eject the case into your hands. Those of you that have had a 223 brass land on you or go down your shirt know what will happen, it will burn the crap out of you. The 6.5 Saum with the load I'm talking about comes out only very warm and you can grasp it tightly with your hand without getting burned. Keeping chamber pressures low not only keeps your barrel from puking early it's also easy on your rifle and the components, IE Brass lasts a long time!!

Yes if you hot rod this caliber IE a load of 60.5 grains 4831 SC and the 130VLD at 3400fps you will be pushing 68,000 PSI and toast the barrel in 600-800 rounds.

Initial loadings were based on Quick Load predictions which are not 100% accurate but are ballpark. Bryan Yeung tested these loads with a strain gauge type pressure meter and the predictions were very close to the QL predictions 53 to 56k . Nobody has made a Pizo or CC test Barrel and got actuals yet. But I'm not that worried about it at this point as it's doing what we theorized it would do so it's a moot point. 3k+ with the recommended loads. 61gr H1000 on 140 , 63gr H1000 on 130. You want to add horsepower there is plenty of room but your barrel mileage will suffer.

The 6.5 did its job. I will pull the Barrel with just over 4000 rounds about 4034 or so give or take about 10, I kept a pretty good count. I will keep this barrel for training as it still shoots great, it just lost a lot of velocity. Hopefully, the Nay-Sayers will have the proof they wanted."

velocity is the killer I always thought.....the shear speed thing.... so in THEORY IF that is right if you ran a 22-243 with 55grn projectiles at 3000fps (why the heck would you?) it should last nearly as long as your garden variety 223...conversly if you stoke the crap out of same 223 and push projectile out at say ???3300fps it will wear out faster

sort of the same as wee outboard motors..the 15hp and 18 are the same motor...one is reving its nuts off at maximum capacity ,the other cruising along

or.... run your 308 with 150grns at 3000fps VS doing it with a bigger cartridge ......your 308 will be straining everything to achieve it.....the bigger cartridge can do it with ease...

Originally Posted by Micky Duck

or.... run your 308 with 150grns at 3000fps VS doing it with a bigger cartridge ......your 308 will be straining everything to achieve it.....the bigger cartridge can do it with ease...

Simplification:
Heavy and slower is easier on the barrel, ok short range, and better far downrange.
Light and fast is hard on the barrel, excellent at short range, but loses it far downrange.
So once you have a rangefinder and can cope with rainbow trajectories no need for maximum velocity obsessing.

Originally Posted by Hermitage

Yes if all cases are loaded to equal pressure.
However, I still suggest that if the .243 is loaded to low pressure ie 52,000 PSI and the .308 to 66,000 PSI the .308 barrel will have the shortest barrel life.
I take this idea off my theory that barrel erosion is based on heat (which is increased by pressure) versus time (more case capacity = more burning time) versus pressure build-up. Although yes I could be wrong

Greetings Hermitage,
There is no doubt that reduced pressure will reduce throat erosion but the variable you have missed is projectile diameter. The .308 has 60% more throat area than the .243 ( circumference proportional to the square of diameter) so this may turn the tables on erosion. I suggest you do some comparisons using the barrel life calculator to get a better understanding of the effect of the four main variables. The calculator, while imperfect, is based on science rather than guess work.
Regards Grandpamac.

Greetings All,
There is another factor that can effect barrel life and that is the projectile. About 1980 I was working for the late Tony Loughnan who some will remember as a full bore target shooter. One of the things he told me was that he changed the barrel on his rifles after about 1,000 to 1,200 rounds when accuracy started to decline. At the time the NRA allowed only the NATO 144 grain projectile and most shooters handloaded. To get any sort of accuracy many shooters used Shultz and Larsen 1 in 14 inch twist barrels that had tighter than standard bore and groove dimensions. Tony also sorted his projectiles for weight and exposed lead size at the base which also no doubt helped. Regardless as soon as the first signs of erosion appeared accuracy went south. Tony had two target rifles so he always had one he could use while the other was having the barrel changed.
The barrels were not shot out and still gave excellent accuracy with hunting projectiles. The problem was the projectile and not the barrel. Many of those take out barrels were fitted to hunting rifles and gave long service thereafter. One of Tony's barrels is in my Martini and is more accurate than some new rifles.
Regards Grandpamac.