High Velocity Throat Erosion

[mcdil]

Barrel Life Calculator

Barrel Life Calculator

pierrevanderwalt.com

Thank you for this link. I've been keeping up with this thread and find it interesting to see all the theories and test data many of you have witnessed. In the software calculation, playing with the numbers and the moly on or off leads me to what I theorize, but have no test data to support, that reduced barrel friction by the bullet will increase barrel life. The only way to get to the same peak chamber pressure, with a lower friction bullet of the same weight, is to increase its acceleration. Moly and HBN do this as do certain designs that reduce friction by nature. Our bullets do this, as does the OPs. Curious as to how that plays out overall, as barrel erosion isn't a function of just one variable, but rather an interaction between a serious of variables, probably not linear as well, making any test analysis very difficult to wrap a design of experiments around to actually understand all the puts and takes and how they interact.

If I give it my best go, I do think it's a sum of kinetic energy dumped into the barrel and displaced over the surface area of the barrel when the fire cracking phenomenon is an issue. A larger diameter caliber obviously has more surface area, which distributes the load over a much larger area. At some point, whatever that is, the fire cracking phenomenon falls below a critical threshold, hence why we don't see it further down the bore. That's probably a function of a chemical and mechanical reaction, combined. Back to the kinetic energy above; a lower friction bullet has more of that energy physically imparted into it as a function of acceleration rather than the barrel as a function of friction, hence the theorized life improvement due to less energy put in the barrel, especially the first part of the engraving process.

 

[RockyMtnMT]

Thank you for this link. I've been keeping up with this thread and find it interesting to see all the theories and test data many of you have witnessed. In the software calculation, playing with the numbers and the moly on or off leads me to what I theorize, but have no test data to support, that reduced barrel friction by the bullet will increase barrel life. The only way to get to the same peak chamber pressure, with a lower friction bullet of the same weight, is to increase its acceleration. Moly and HBN do this as do certain designs that reduce friction by nature. Our bullets do this, as does the OPs. Curious as to how that plays out overall, as barrel erosion isn't a function of just one variable, but rather an interaction between a serious of variables, probably not linear as well, making any test analysis very difficult to wrap a design of experiments around to actually understand all the puts and takes and how they interact.

If I give it my best go, I do think it's a sum of kinetic energy dumped into the barrel and displaced over the surface area of the barrel when the fire cracking phenomenon is an issue. A larger diameter caliber obviously has more surface area, which distributes the load over a much larger area. At some point, whatever that is, the fire cracking phenomenon falls below a critical threshold, hence why we don't see it further down the bore. That's probably a function of a chemical and mechanical reaction, combined. Back to the kinetic energy above; a lower friction bullet has more of that energy physically imparted into it as a function of acceleration rather than the barrel as a function of friction, hence the theorized life improvement due to less energy put in the barrel, especially the first part of the engraving process.

Where do you fall, in your opinon, on the effects of muzzle vel as it relates to barrel wear? Is added vel of a lighter bullet loaded in the same cartridge to the same pressure as a heavier bullet going to show a relative effect on the barrel life?

 

[Radman]

Firing schedule has a definite impact. The 4th shot does as much damage to the throat as the first 3 combined and the 5th shot does twice as much damage. (talking my 7AM) Three-shot strings and no more if you have an overbore magnum.

Ding, ding, ding.....Give that man a prize! Right or wrong I agree with you.
Down through the years I've noticed (in groups I am familiar with) that the rapid-fire guys are the same ones who seem to have problems keeping barrels. One guy reported fried his .22-250 barrel after only 30 rounds.
I keep my barrels as cool as reasonably possible & so far my factory barrels are still great. (I've never scoped them - I just shoot them) Irregardless of caliber or load I think trying to let a barrel cool (by any means) is a good practice. JMO

 

[mcdil]

Where do you fall, in your opinon, on the effects of muzzle vel as it relates to barrel wear? Is added vel of a lighter bullet loaded in the same cartridge to the same pressure as a heavier bullet going to show a relative effect on the barrel life?

Whew. Hard to say as I haven't spent any real time studying this in depth. This is where the comp guys really have an "exposure" benefit. From the past, I've always felt the opposite, similar to you, that a heavier bullet loaded to the same pressure does more damage, but the barrel wear model provided above would go against that, as does some of the feedback from experienced competitive shooters in this thread alone. My belief probably comes from decades ago where the overbores largely shot heavier bullets to subdue cup and core separation at closer ranges. Nowhere on that software model is bullet weight, but powder charge weight is there. A bit surprising, as I would assume it's a function of energy imparted on the surface area, as mentioned previously. A low friction, lighter bullet will enable a longer tube of surface area versus a heavier, high bearing surface bullet where the bullet takes longer to move with a more sustained pressure curve enabling time to go long with a shorter tube surface during the fire cracking process. At least the moly model would seem to line up with that assumption, so in my head, it's a bit conflicting. It is a model, however, and not necessarily completely representative.

Honestly, I'd love to understand what your and my bullets do in comparison to this issue. I would think we would shake out much better than what the acceptable norm is, but it's only my hypothesis.

 

[xsn10s]

IMO given the two 308 win examples you'd have to measure the bearing surfaces of the two bullets. There might be small advantages or disadvantages either way. Probably the biggest factor would be how fast the individual rounds heated up the barrel. And if in fact the pressures were as originally listed. Some of the loads I see on here makes me question the pressures. There are times I wonder if the loads are closer to the 70k psi rather than 61k psi.

 

[cabelasken]

Where do you fall, in your opinon, on the effects of muzzle vel as it relates to barrel wear? Is added vel of a lighter bullet loaded in the same cartridge to the same pressure as a heavier bullet going to show a relative effect on the barrel life?

The lighter bullet will offer less backpressure and won't be in contact with the barrel as long so therefore I think will offer less barrel wear. The longer bullet is not significantly slower enough to make up for the additional contact area and friction build. Also the additional backpressure of the longer and slower bullet will allow the powder to stay at peak pressure in a shorter pressure container making the heat/pressure more severe.

 

[mcdil]

IMO given the two 308 win examples you'd have to measure the bearing surfaces of the two bullets. There might be small advantages or disadvantages either way. Probably the biggest factor would be how fast the individual rounds heated up the barrel. And if in fact the pressures were as originally listed. Some of the loads I see on here makes me question the pressures. There are times I wonder if the loads are closer to the 70k psi rather than 61k psi.

I agree on all fronts. One thing I'll add to the bearing surface that is important but almost never talked about, is HOW the copper bearing surface is manipulated by the rifling, bore. It's not just the volume of it. The key is to get a perfect seal yet eliminate the potential for any galling while minimizing bearing surface and maintaining alignment. That results in an amazingly efficient design that repeats from shot to shot. It imparts the least amount of friction during the engraving process as well.

As far as the internal pressure, I'd agree many are getting up there close to if not over 70 ksi. It's why we purchased a Pressure Trace II in the very beginning to understand what's happening when we fire our bullets compared to factory rounds and other hand loaded competitive designs. While ours is not professionally calibrated, since without a non-SAAMI pressure barrel, that's impossible, but I do believe we have ours within plus or minus 1% in one of our guns based on listed results from test labs that fire similar setups with calibrated values. If I am right, and the fire cracking phenomenon is a combination of chemical and mechanical reactions, then at 70 ksi, it would be a much longer and significantly more accelerated event.

 

[RockyMtnMT]

IMO given the two 308 win examples you'd have to measure the bearing surfaces of the two bullets. There might be small advantages or disadvantages either way. Probably the biggest factor would be how fast the individual rounds heated up the barrel. And if in fact the pressures were as originally listed. Some of the loads I see on here makes me question the pressures. There are times I wonder if the loads are closer to the 70k psi rather than 61k psi.

I looked at Hodgdon data for my 308 example. Max loads for both bullet weights with the stated pressure.

 

[RockyMtnMT]

I agree on all fronts. One thing I'll add to the bearing surface that is important but almost never talked about, is HOW the copper bearing surface is manipulated by the rifling, bore. It's not just the volume of it. The key is to get a perfect seal yet eliminate the potential for any galling while minimizing bearing surface and maintaining alignment. That results in an amazingly efficient design that repeats from shot to shot. It imparts the least amount of friction during the engraving process as well.

As far as the internal pressure, I'd agree many are getting up there close to if not over 70 ksi. It's why we purchased a Pressure Trace II in the very beginning to understand what's happening when we fire our bullets compared to factory rounds and other hand loaded competitive designs. While ours is not professionally calibrated, since without a non-SAAMI pressure barrel, that's impossible, but I do believe we have ours within plus or minus 1% in one of our guns based on listed results from test labs that fire similar setups with calibrated values. If I am right, and the fire cracking phenomenon is a combination of chemical and mechanical reactions, then at 70 ksi, it would be a much longer and significantly more accelerated event.

You said in another thread that running a bullet at high vel would burn out the barrel. It was the reason that I started this thread. Now you seem to be saying something quite different. Figured I would quit beating around the bush. Hopefully I don't get called a bully now.

 

[Creedmoor shooter]

You said in another thread that running a bullet at high vel would burn out the barrel. It was the reason that I started this thread. Now you seem to be saying something quite different. Figured I would quit beating around the bush. Hopefully I don't get called a bully now.

2 different people I believe.

 

[RockyMtnMT]

2 different people I believe.

Really? That becomes awkward! My apologies!

 

[Creedmoor shooter]

Really? That becomes awkward! My apologies!

nralifer was the person in the other thread in question.

 

[mcdil]

Really? That becomes awkward! My apologies!

Yes, definitely not me, lol.

 

[RockyMtnMT]

That's the best thing I did all day!