Thread: Is it Pressure or Powder Capacity?

Got a photo of your primers in some spent cases?
I would say perhaps you can fix that little dilemma. Anneal and correctly bump the shoulder and you should still get more than a few cycles.
But your barrel throat sounds like it has given up the ghost. Some of the NRA shooters get 800 to 1000 round count from their barrels so yours is probably on par

Originally Posted by tetawa

When you have a large case and small bore, result is throat erosion, 22-243 or 22-284 are other prime examples.

But you probably only know this based on the 22-243 or 22-284 at the usual 63,000-68,000 PSI SAMI pressure.

If you were to use a slower powder and get 50,000-55,000 PSI SAMI pressure, would the result still be fast throat erosion?

I suggest not.

Originally Posted by Dead is better

Got a photo of your primers in some spent cases?
I would say perhaps you can fix that little dilemma. Anneal and correctly bump the shoulder and you should still get more than a few cycles.
But your barrel throat sounds like it has given up the ghost. Some of the NRA shooters get 800 to 1000 round count from their barrels so yours is probably on par

Yeah my 25-06 barrel is screwed.
I'm going to re-barrel it to 6.5/284 and use 140 grain bullets at a lower pressure using Reloader 25, N170 or H1000.
This should get me a lot longer barrel life at reasonable velocities (not high velocity as a low-pressure load). It will also be easier on the brass and I should be able to get a dozen reloads rather than four.

How did it shoot before you scoped it?

Originally Posted by Hermitage

Yeah my 25-06 barrel is screwed.
I'm going to re-barrel it to 6.5/284 and use 140 grain bullets at a lower pressure using Reloader 25, N170 or H1000.
This should get me a lot longer barrel life at reasonable velocities (not high velocity as a low-pressure load). It will also be easier on the brass and I should be able to get a dozen reloads rather than four.

The angle of the leade and the case shoulder angle are also reputed to effect throat wear.

Your 6.5-.284 won’t give you a great increase in barrel life over a .25-06, especially if you drive it very hard.

Originally Posted by Hermitage

The way I am understanding it from the Speer manual and the Youtube video @Seventy Six above linked (listen from 4:30-6:10 minutes), is that barrel erosion depends on pressure which increases the core temperature of the gases.

Video "It's not necessarily the powder charge,....the bullet weight,....the amount of powder we are using....it's the pressure."

So to answer your questions @grandpamac:

No...more powder does not equal more erosion if pressure is kept low (ie 55,000)
No...a smaller bore does not equal more erosion if pressure is kept low (ie 55,000)
Yes higher pressure equals more erosion (ie 65,000)
Unsure about the answer for the shorter neck question.

Greetings Hermitage,
I had a quick dig on the internet and came up with a couple of barrel life calculators including Mikes Spreadsheet. The input variables for the calculators are:
Projectile diameter.
Powder charge weight.
Powder heat potential.
Pressure.
Projectile coating if any.

The powder charge and heat potential determine the amount of heat available. The pressure determines the way the heat is applied to the throat and the projectile diameter determines how much steel that heat is applied to. So rather than pressure alone driving erosion it is a number of factors. If pressure only was the culprit then the .243 and .308 would have the same life, or .25-06 and .270 for that matter. This is definitely not the case.
Regards Grandpamac.

Its generally powder volume vs bore diameter. The more powder for a given bore dia, the more barrel wear.
eg 243, 7mm-08, 308. All basically the same case / capacity. The 243 will have the shortest barrel life, followed by 7mm, followed by 308 with the longest.

Originally Posted by Marty Henry

.........It's dated 1966 but I'm pretty certain that the infomation is still valid, after all it was worked out by guys with pocket pen protectors, short haircuts and glasses.................

Ahhh, happy days, but you failed to mention the rest of the "uniform."

Originally Posted by Hermitage

But you probably only know this based on the 22-243 or 22-284 at the usual 63,000-68,000 PSI SAMI pressure.

If you were to use a slower powder and get 50,000-55,000 PSI SAMI pressure, would the result still be fast throat erosion?

I suggest not.

Have always understood it's the amount of powder being burnt in comparison to caliber, have owned and used 25-06 and 257 Weatherby mag, throat erosion was there in both after 400 rounds, Weatherby worse. Found the 257 Roberts more to my liking, still did the job with less wear, the powder used was faster burning against what was used in the other two. This was 50 plus years ago and also think those 2 cartridges also accelerated my hearing loss.

Originally Posted by Kiwi Sapper

Ahhh, happy days, but you failed to mention the rest of the "uniform."

Attachment 162532

Stop it Kiwi Sapper,
I must have looked a bit like that, sans the fascial hair when I rocked up to work on 17 Jan 1966. Hopefully my shorts were not two sizes too small like the Gentleman on the left.
Regards Grandpamac.

Originally Posted by grandpamac

Stop it Kiwi Sapper,......................................

Sorry, it was the "pocket protector" that set me off down Mammary Lane.

Originally Posted by charliehorse

How did it shoot before you scoped it?

WARNING: Don't buy or borrow a borescope. If you do you will feel the need to replace the barrel on every rifle you own. Could get kinda expensive.

The 25-06 shot cloverleaves until in the last 3 months when it started tossing errant shots after just 2 rounds. I then have to stop and JB the heck out of the barrel to get rid of the excessive copper-fouling. This probably is because of the heat cracks which are fouling badly.

Originally Posted by Spitfire

The angle of the leade and the case shoulder angle are also reputed to effect throat wear.

Your 6.5-.284 won’t give you a great increase in barrel life over a .25-06, especially if you drive it very hard.

But that's my whole idea....NOT to drive it very hard by using slower powders at less pressure so less erosion.

Originally Posted by grandpamac

Greetings Hermitage,
I had a quick dig on the internet and came up with a couple of barrel life calculators including Mikes Spreadsheet. The input variables for the calculators are:
Projectile diameter.
Powder charge weight.
Powder heat potential.
Pressure.
Projectile coating if any.

The powder charge and heat potential determine the amount of heat available. The pressure determines the way the heat is applied to the throat and the projectile diameter determines how much steel that heat is applied to. So rather than pressure alone driving erosion it is a number of factors. If pressure only was the culprit then the .243 and .308 would have the same life, or .25-06 and .270 for that matter. This is definitely not the case.
Regards Grandpamac.

Oh, I realise pressure is not the 'only' culprit....that it's intuitively expected that there are a number of factors all interconnected. But I still feel it is the #1 cause of barrel erosion if the culprits are to be ranked.
Actually, I suppose if I was to make a simplified list of 'culprits', I would expect erosion to be caused by heat (which is increased by pressure) versus time (more case capacity = more burning time) versus pressure build up. But I can't be 100% sure about my theory.

I also had a quick look on the internet and didn't realise the topic of barrel erosion was so complicated....just look at the below which I read on causes of chemical and thermal barrel erosion:

"Consider the definition of impetus, I, used to gauge the propulsive energy provided by a propellant,
I = RTf = RTf /M, (10)
where R is the specific gas constant, R is the universal (molar) gas constant, Tf is the propellant flame temperature,
and M is the molecular weight of the propellant gas mixture".

Originally Posted by ChrisW

Its generally powder volume vs bore diameter. The more powder for a given bore dia, the more barrel wear.
eg 243, 7mm-08, 308. All basically the same case / capacity. The 243 will have the shortest barrel life, followed by 7mm, followed by 308 with the longest.

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