High Velocity Throat Erosion

[orkan]

I saw that guy post he had over 5000 rounds in his 338 lapua with N570. How does his gun shoot? I guess anything is possible but Hard to believe some one has put that many rounds through a barrel with a hot burning powder like 570 and has "no loss in accuracy" Shawn of defensive edge probably has more experience than most running 338 edges with h-1000 and he will tell you to expect around 1200-2000 rounds from an edge Bbl depending on your load, powder used, and individual Bbl.

I too would like to see some in-person reports of that rifle.

Maybe he's happy with 1-1.5MOA. If so, I can believe it.


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[Philward]

I don't even worry about it, I have a R700 7mmRM from the 60's and it still shoots great. Rifle has been through several owners including my father prior to me getting it, including 2 owners after he had it, and I've had it for 16 years or so. If the rifle shoots it shoots.

There should be a measurement or standard to define what it means when the term "shot out" is used. At what point is the barrel useless? For the competition shooter is it when you cannot hold a group to 0.250"? Or is it when groups enlarge to over 1MOA? Does the rifle go from a 1/2 MOA shooter to a 4MOA shooter?

If you shoot 5000 rounds through a barrel at the rate of 2 rounds every day will the barrel be worn the same as if you shoot 5000 rounds in 10 days time?

 

[baldhunter]

When I first got a borescope the first thing I noticed was all my magnum rifles with several hundred rounds down the barrel all had moderate to severe fire cracking and erosion.When I inspected my 308 Wins and 30-06's with about the same amount of rounds,I saw no sign of fire cracking or erosion.I'm not an advocate for getting my barrels too hot,one reason I only shoot three shots before letting my barrel cool.Magnums get hot a lot quicker due to the amount of powder it burns.I watched the video and the guy brought up a lot of good points.It's a combination of a lot of factors,but I have to say the amount of powder,type of powder and bore size are big factors.The guy in the video discounts heat a lot,but I think it is a big factor.If you have ever used a cutting torch much you get a good idea about high heat and metal.A torch heats the metal to the point of it starting to melt.Then you squeeze the lever that blast more oxygen to blow away the molten metal.The same thing is also happening in the barrel.Those slow burning powders,some burning hotter than others, behind a bullet burn extremely hot with a lot of blasting force behind it trying to push a bullet down the barrel.From what I've seen in my rifles 308 Win,30-06,7mag,7STW,300WSM,300 Win Mag,the higher the powder charge,the more erosion.308 Win and 30-06,charges below 60grs of powder,no erosion on my rifles.On my magnum rifles,the 300WSM showed less erosion.Charge weight is usually around 65grs to 70grs.7mag charge weight about the same,but smaller bore shows a little more erosion.Moving up to the 7STW and 300 Win Mag,charge weights between 72grs to 80grs.Both those had the highest amount of erosion,the 7STW was the worst.I think it's a combination of a lot of factors,but for certain the amount of powder burning behind a bullet is a big factor.

 

[hawlejr]

I wonder if anyone's done a semi-scientific study about barrel life vs. caliber. I remember that the .220 Swift was alleged to have short barrel life. Probably has to do with reaching a certain temperature in the chamber and melting a micro layer of steel per shot. It would be very very interesting to see such data. I'm sure it would have to be stratified by several variables such as barrel steel....for instance stainless vs chromoloy alloys. Developing metrics for the amount of throat erosion would be a study in itself. Like tire wear, there is probably a land/groove depth as well as linear "throat" distance which I'm sure would come into play. It may affect different calibers differently. How about the amount of freebore? Also, cleaning to remove carbon will probably impact the rate of wear. Lots of variables, and the inherent difficulty to measure are the obvious problems. Still it is one of the most important riddles for riflemen to solve, and it's a great one to ponder ( and pontificate!!) about. I wonder if, perhaps folks with lots of $$$ (like the military, maybe) or rifle or barrel manufacturers have done some study. It's a great question. Let's keep this thread going until somebody with some data can help us out!

 

[Pdvdh]

Heat of combustion = primary source of barrel throat fire cracking and erosion. And the higher the pressure, the higher the temperature.

I'd think a heavier bullet can build and maintain higher pressure and temperature at the throat, compared to a lighter bullet.

Therefore shooting a lighter weight bullet faster should result in longer throat life than shooting a heavier weight bullet slower. That is provided both bullets are fired at equal chamber pressures.

 

[epoletna]

No one has mentioned automatic fire with machine guns, but we probably all know that barrel life on a machine gun is a problem. So much so that some are issued with a water jacket and others are issued with multiple barrels and a quick change capability. These should be a case study on the effect of heat (from repeated and rapid firing) on the bore of a barrel.

The issue with machine guns, I believe, is how hot the barrel gets. We have probably all seen video of a machine gun with a red-hot barrel.

Anyone with extensive machine gun experience who can chime in on the wear on the bore of a hot (or super hot) barrel vs. on a barrel that does not get so hot?

 

[Calvin45]

View attachment 382529View attachment 382530

Here is my question. If you look at these two different chamberings both loaded with the same bullet and H 4831 SC which will burn the throat faster? The 7 Rem Mag with 61 grains pushing the bullet at 2959 or the 280 pushing the same bullet at 2888 with 56 grains of powder? There is a big difference in powder charge and velocity. But theoretically the 280 is running at Peak pressure and the 7 rem mag is running a very mild load.

Now ya gotta go making it more complicated haha…but great question. My money is still on the higher powder charge in the same diameter bore being harsher even at lower presure but that's just a guess.

We should have an answer pretty fast tho!!! I say this becuae of the .277 sig fury. Gets .270 win ballistics out of a smaller case and shorter barrel by running at 80kpsi. We'll see if that higher pressure is harder or barrels, the same, or easier because it uses less powder.

You know what, I change my answer! I'm now guessing that pressure matters more than powder charge given the same bore diameter. Ahhhhh! Now you've done it!

 

[Mark37082]

Logic does not always win the day, but logic does have a higher likelihood of providing the right answer. As Orkan described in his video, logic would point to pressure being a significant factor in the fire cracking of barrels resulting in throat erosion. Heat combined with pressure seems to be the culprit IMHO.

 

[BradyT88]

No one has mentioned automatic fire with machine guns, but we probably all know that barrel life on a machine gun is a problem. So much so that some are issued with a water jacket and others are issued with multiple barrels and a quick change capability. These should be a case study on the effect of heat (from repeated and rapid firing) on the bore of a barrel.

The issue with machine guns, I believe, is how hot the barrel gets. We have probably all seen video of a machine gun with a red-hot barrel.

Anyone with extensive machine gun experience who can chime in on the wear on the bore of a hot (or super hot) barrel vs. on a barrel that does not get so hot?

I think the big difference here is that machine guns are not given time to cool down between shots like most guys on here are doing with their bolt action rifles. So you kind of have an apples to oranges scenario. We were swapping out hot barrels not because of loss of accuracy per se, but because getting the barrel way too hot is not only going to warp the barrel, but at a certain point it will start cooking off rounds and thus firing on its own which is a bad situation. We also weren't very concerned about accuracy because we relied on quantity over quality.

As for the overall title of this thread I don't have much to add, but I recently got some hammer bullets to try in my cheapo Savage 110 with a 22" sporter barrel chambered in 30-06. I shot several loads this weekend. Some factory Winchester Power Point 150gr @ 2900fps , some 190gr ABLR running 55.3gr of H4350 at 2800fps, some 165gr Sierra GameKings running 61.7gr of 6.5 StaBALL, and then some 12 shot ladders of 178gr Absolute Hammers with 55.5gr to 61.8gr of Hybrid 100V at 2860fps to 3068fps; and some 101gr Hammers running 51.8gr to 57.7gr of Varget at 3164fps to 3467 fps.

I cannot speak for barrel wear, but the big thing I noticed is on every shot of the 101gr Hammers the case was uncomfortably hot to the touch, while none of the other ones were. Now there are certainly some variables here because I changed powders and who knows what my pressures are, though I think the 190gr, 165gr and 178gr are at their limits, while I appear to still have some room to run the 101's faster. I meant to check barrel temp on the 101's but I got distracted so I'm not sure if the barrel was significantly hotter as well or not.

 

[orkan]

This thread got me thinking about something.

Look for exciting new content regarding this in the coming weeks.



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[bigngreen]

In 300 round in 338??

In 300 round in 338???????

At some show I am talking with some Norvegian shooter and he uses 338 lapua with lothar walther barrel and 300 grain pills with N570, long story short he was well over 5000 round and no loss accuray.

So to me that 300 round is very questionable.

First LW steel is different than the typical barrel steel used so right out of the gate there is a bonus. Then define no accuracy loss, that can vary from I hit it to it's opened up an inch at 1000+, very subjective. I've seen barrels shoot out standing with inches of rifling toasted out of it, my 308 is a smoothbore for nearly an inch and then tapers in some rifling and it'll shoot very decent groups well under 6 inches at 1000. So there can be a lot of variables there, playing with the throats will lead to shorter life if it gets temperamental due to wear and an aggressive case design.

 

[Carey Farmer]

My experience is that worse fire-cracking in the breech of a barrel is correlated with more rapid retreat of the lands. I don't know for certain that fire-cracking is a result of a chemical reaction, but it sure doesn't look like the burnishing one would expect from friction or from sand-blasting.

It's pretty well established that higher pressure and temperature will increase the rate of any chemical reaction. To the extent that fire-cracking is related to a chemical reaction, one would expect that higher temperature and pressure will result in more rapid retreat of the lands, and opening up of the bore diameter in the grooves.

Higher energy density powders increase the temperature of the burning powder plasma. Higher pressures also increase plasma temperature. Slow powders prolong the high-temperature-and-pressure event duration.

When I run a 28 Nosler with N570 at 60K+ pressures (as back-calculated with Quickload from measured muzzle velocity), the lands retreat 20 to 40 thousandths per hundred shots. Identical barrel with Retumbo at 55K psi, the lands retreat 10 to 20 thousandths per hundred shots. The Retumbo charge loses about 150 fps muzzle velocity compared to the N570 charge.

 

[arch408]

No one has mentioned automatic fire with machine guns, but we probably all know that barrel life on a machine gun is a problem. So much so that some are issued with a water jacket and others are issued with multiple barrels and a quick change capability. These should be a case study on the effect of heat (from repeated and rapid firing) on the bore of a barrel.

The issue with machine guns, I believe, is how hot the barrel gets. We have probably all seen video of a machine gun with a red-hot barrel.

Anyone with extensive machine gun experience who can chime in on the wear on the bore of a hot (or super hot) barrel vs. on a barrel that does not get so hot?

You Tube had a video of torture test on AKs and ARs. Pretty interesting but in no way practical. AR beat the AK.

 

[bigngreen]

Backing off the throttle pedal definitely helps BUT how does that relate to a light fast bullet, in my mind light fast equals more go juice but pressure signs are pressure signs so you can feel like your spicy but still not really pushing with a lighter bullet. Given same pressures does it come down to the temp and time of the powder burn?