Pressure vs powder/chamber volume and Barrel Life

[Tommie]

Correct me if wrong:
does “ over bore” large case small bore case cause throat erosion and high speed bullets cause barrel wear? but with either one the barrel can be toast

There is no official definition for “overbore”. It’s a term that gets thrown around a bunch. There are plenty of opinions on the subject

 

[Bottom Fodder]

There is no official definition for “overbore”. There are plenty of opinions on the subject

Yep, like a lot of other topic

 

[mikecr]

For every cal and bullet weight there is a best overall capacity. Highest in efficiency.
With that, I see anything under that capacity as underbore, and anything over as overbore.
And I see nothing 'wrong' with any of them. Just advantages & disadvantages.
But it all begins with a bullet.

For example, I see the 260AI as holding peak efficiency in 26cal, 140gr bullets.
A 6.5x47L with same 140gr bullets would be underbore to me.
A 6.5x284 with same 140gr bullets would be overbore to me.
The 260AI as a standard has no advantages nor disadvantages.
The others have advantages and disadvantages w/resp to the 260AI -with 140gr bullets.
Change bullet weight, and it all shifts around.
A very similar comparison could be made with 6Dasher, 6BR, and 243Win for 105-108gr bullets.

Efficiency is also more than just capacity, as it is also affected by cartridge design.
I see this as a sort of relative capacity, and QL allows calibration of it with weighting factor.
I thought this could affect accurate barrel life(ABL), but it turned out that it doesn't. Not directly.
A 260AI will likely get better ABL than a 6.5x284 just because it burns less powder to get the same results.
This, assuming the powders exhibit near same burn temperatures.

PRESSURE AMOUNT and BURN TEMPERATURE does affect ABL, but POWDER AMOUNT to bore size and SHOT RATE are dominant to ABL.
That said, there are always departures from norm. These are still logical though.
A tiny little 6PPC should have fantastic ABL. It's common powder, N133 is pure magic in that it burns so cool for it's speed, and there is little used here. But competitive pressures and fast shot rates hugely override the norms.

 

[Webster]

I have a couple theories I've been formulating, as I slowly but surely burn through barrels on the dog towns. First, powder volume, or degree of overbore, is a much bigger detriment to barrel life than running high pressures. To use an example, you can take a 223AI and run it really hard (high pressures)...let's say 3,700 fps with a 53gn bullet and still get 5,000 rounds before accuracy falls off too much. Or, it seems to me, you can step up to a 22BR and run it at relatively moderate pressures to achieve this same velocities with same bullet, yet you'd be lucky to see 2,500 rounds before accuracy really starts to fall off. I've certainly not done any scientific double-blind studies here, just seems to me, you can run a moderate volume cartridge really hot and still get great barrel life...yet I've not seen overbore cartridges like a 22BR or 22-250 last long, even when pressures were kept low.

Second theory, I also believe there is a threshold you cross, in regards to case volume (relative to bore diameter) where increasing case volume past that threshold increases barrel erosion exponentially. In other words, to get an extra 100-150fps, you might but barrel life in half, or even 1/3rd. Take the mighty 6BR...I've burned out several barrels pushing 55/58 grain bullets HARD, yet I still get about 6,000 rounds of very accurate barrel life typically. But step up into a DASHER and run these same bullets an extra 150fps, and you'll likely get about 1/3d the barrel life. Big price to pay for crossing that 6BR capacity threshold. For the 22 cal, I suspect this threshold is somewhere north of 223AI capacity...go much above that, and watch out!

You only need a barrel burner if you want to shoot very long distances. I have a 6BR with 4200 shots on it. Kelbly bore scoped it for me and said it looked like a 1000 shots on the barrel. Still shoots small groups. It should be good to 600 yards with light bullets. Over 20 reloads on the Lapua cases.

Barrel erosion is directly related to the ratio of powder wt. to bore diameter. How much hot gas at high pressure going down a small hole or a big one.