Question for the experts

[rjathon]

Somewhere here I read a post by a knowledgable person that cast bullets don't give greater barrel life of their own accord, it is the lower powder charges and lower pressure that we shoot them at that does it.

That at begs a follow up question. If one uses a full case load of a super slow powder like WC872 to achieve at lower pressure the same velocity that one would get with a smaller charge of 3031 at higher pressure which one is easier on the barrel?

thanks

[Scharfschuetze]

I'm no expert, so I can't really answer your question, but to start things off, Here's what I believe:

I don't think that jacketed bullets wear on the barrel as much as some believe. After wearing out several match and varmint barrels using maximum loads, I believe that the main cause of bore wear is high temperature gas and high volumes of it at high pressure. Looking at worn barrels after they come off my rifles, you can see almost a waffle like surface area where the temperature and pressure has eroded the throat, sometimes for more than a full inch. Some also say that unburned debris from ignition also contributes to this effect. Expansion ratio of the rifle's cartridge will often dictate how fast a throat is shot out.

I currently have three rifles in need of rebarreling (NM rifle in 7.62, NM AR in .223 and a Varmint rifle in .223) after about 4,000 to 5,000 rounds apiece. None of these rifles have had a cast boolit though them. If the jacketed bullets shot through them caused much wear, it should be for the full length of the barrel, but the majority of the wear is at the throats where the gas cutting occurs.

My cast boolit rifles show virtually no detectable wear after who knows how many rounds over the years. My most used powder in cast rifle loads is SR 4759. It is about like IMR 4198 in burning speed so it isn't slow by any means, but it does not seem to contribute to much bore wear.

[44man]

[QUOTE=Scharfschuetze;3574003]I'm no expert, so I can't really answer your question, but to start things off, Here's what I believe:

I don't think that jacketed bullets wear on the barrel as much as some believe. After wearing out several match and varmint barrels using maximum loads, I believe that the main cause of bore wear is high temperature gas and high volumes of it at high pressure. Looking at worn barrels after they come off my rifles, you can see almost a waffle like surface area where the temperature and pressure has eroded the throat, sometimes for more than a full inch. Some also say that unburned debris from ignition also contributes to this effect. Expansion ratio of the rifle's cartridge will often dictate how fast a throat is shot out.

I currently have three rifles in need of rebarreling (NM rifle in 7.62, NM AR in .223 and a Varmint rifle in .223) after about 4,000 to 5,000 rounds apiece. None of these rifles have had a cast boolit though them. If the jacketed bullets shot through them caused much wear, it should be for the full length of the barrel, but the majority of the wear is at the throats where the gas cutting occurs.

My cast boolit rifles show virtually no detectable wear after who knows how many rounds over the years. My most used powder in cast rifle loads is SR 4759. It is about like IMR 4198 in burning speed so it isn't slow by any means, but it does not seem to contribute to much bore wear.[/QU
Good way to say it. Not the bullet/boolit but heat and gas.

[rsrocket1]

Scharfschuetze, most jacketed bullets do not obturate the throat, some not even the grooves. But the hottest and fastest gas blowby is at the throat. Properly fitted lead bullets significantly reduce the blowby. Would that be a reason for longer lasting barrels?
I know that crazy fast calibers like WSSM can toast a barrel in 500-1000 rounds. My M&P 40 has seen less than 300 plated bullets and close to 40,000 lead bullets. Its throat and groove dimensions haven't changed by any measureable amount (maybe less than 0.5 mil).

[shooter93]

Heat is the enemy for sure and it's the throat you burn out long before the rest of the barrel. It's worse with rounds like the 220 swift loaded to the max. I've set barrels back after the throat was toast and they shot fine afterwards. There is also more damage caused by unburnt powder grains slamming into the throat. One of the best advantages to the Ackley steep shoulder angle is it moves that turbulence point into the neck of the case as opposed to in the throat. Merrill Martin once showed how few a number of rounds it actually took before that wear could start to be seen.

[bangerjim]

If you want to REALLY wear out a barrel....shoot Cu FMJ's.

Don't worry about it with Pb.

banger

[M-Tecs]

Pressure and dwell time eroded the throats in rifles. I have about 9,000 rounds on my 223 varmint rifle. It has about the same erosion as my 223 match rifle with 3,000 rounds. 40 grain verse 77 & 80 grain.

Low pressure cartridges like 45 acp show no wear a 50k with lead. With jacketed at 50k the lands are rounded and noticeably worn.

[runfiverun]

think about where that wear and erosion is taking place.
then think about how to fix the problem [cut off the threads and re-chamber]
now correlate that to where the pressure and turbulence is the greatest.
the more pressure /heat/turbulence you have the faster that part of the barrel wears down.

[Tatume]

There's a lot of nonsense out there. I've even seen one highly-regarded gun magazine writer claim that not only will jacketed bullets wear out a revolver barrel faster than cast bullets, but gas-checked cast bullets will wear out a revolver barrel faster than plain based cast bullets. Hooey.

[Don Fischer]

I've never worn out a barrel but then maybe I have but they were still more than accurate enough for my need's. A target competitor goes from .250 and smaller to maybe .500 and claim's the barrel is worn out. The hunter see's the .500 group's and thinks he's found a gem. If I can shoot 1" groups at 100 yds, I'm good to go. I don't compete, I hunt! Barrel wear in a handgun. If it's a defense gun such as Most auto loader's and your shooting seldom goes beyond 21', how would you know? I never met anyone that could hold -1" group's even at 20 yds with an auto loader. I know I don't shoot my auto's any where near as well as my DA revolver's. Scratch that, my High Standard HD military is probably the most accurate handgun I have. So, what do you call worn out in a pistol barrel? Not only have I never had one but I never knew anyone that claimed they had one. I think barrel wear is a pretty flexible term, worn out to a competitor is just broke in to a hunter.

[Scharfschuetze]

Not only have I never had one but I never knew anyone that claimed they had one.

What generally wears in a revolver is the forcing cone. It can get so bad that you can see it with your Mk 1 eyeball. It has a very rough and sometimes almost burnt appearance. I saw many as an FTO on the PD. Generally the 125 grain 357 Magnum rounds were the culprit. Those were/are very high pressure and hot loads.

Not only was the forcing cone eroded, but the top strap above the barrel/cylinder interface was cut from the hot gas.* When buying a magnum revolver on the used gun market, look for that damage before buying. It might get the owner/dealer to drop the price a bit.

I never saw the same level of wear with my PPC revolvers just shooting WCs over Bullseye. At times I was shooting upwards of 500 rounds a week through them between practice and matches.

Once again, it's really the high pressure gas and high temps in large volumes as well as the detritus from combustion that seem to be the suspect.

*Current S&W scandium alloy magnum revolvers have a steel insert here to prevent the gasses cutting the top strap.

[Shiloh]

Heat and pressure are what wears barrels. The other destroyer of barrels is improper cleaning rod use.
I don't think you can wear out a barrel with lead at the pressures involved. I'm not a ballistic expert, so those who can comment please do.

Shiloh

[Le Loup Solitaire]

I will never be an expert, but I have been shooing cast for a very long time and have yet to see any signs of wear in any of my firearms. it is true that barrels can be shot out such as in machine guns or certain high performance calibers such as the 220 swift. It has to be the result of pressure and heat primarily, but for sure it is not lead. LLS

[Bigslug]

Many years ago in Precision Shooting Magazine, there was an article extolling the virtues of the sharp, 40 degree Ackley shoulder and similar case designs as they related to bore erosion.

The theory presented was that the powder column stats burning and generating expanding gasses at the rear, which pushes the yet-to-burn powder at the front of the column forward into the throat where it can have a sandblasting effect on the rifling.

The case that the author presented was that shallow shoulder angles such as seen on the .30-30 will tend to funnel that powder into the throat, magnifying this sandblast effect, while Ackley-style cases tend to cause the powder to bunch up at the neck and burn more completely in the case, reducing your bore wear issues to those of hot gas on steel.

If we hold those theories to be true, a couple other things we could look at:

1. Are extruded powders more or less abrasive than ball powders?

2. Do extruded powders tend to log-jam inside the case better than extruded powders?

[Cap'n Morgan]

No doubt heat & pressure is the main culprit. Heat, combined with pressure is actually used for internal deburring of complicated parts. Google "explosive deburring".

[M-Tecs]

Big slug

I am currently out of town and on my phone so its difficult to post links but research the 6mm Competition Match verse the standard 243. Using a different shoulder angle, H1000 powder and different cleaning methods the claim is almost double the usable barrel life over the 243.

[Scharfschuetze]

The 243 is a world renown throat burner. As you guys surmise, it must be the shallow shoulder angle and the expansion ration of the rather large case to bore diameter ratio. The 6mm Remington on the other hand has a much better reputation, even when burning slightly more powder. Must be something to that shoulder angle theory.

At one time in the early 90s, a few of the civilian NM shooters that I was acquainted with were testing the 243 for NM shooting across the course (200 through 600 yards) using heavy Berger and Match King bullets in short action Remington rifles. They were all very happy with the round till about 2,000 rounds or so and then the accuracy really dropped off at 600 yards. Most rebarreled with the 6.5mm Remington and found that to be much easier on the barrels, yet recoil was still pretty mild.

My Pre-64 Model 70 Featherweight in 243 is now in my son's hands and it is still slaying game. I always loaded below maximum for it to save the original barrel for as long as I could. So far that recipe has paid off.

[Mal Paso]

My cast boolit rifles show virtually no detectable wear after who knows how many rounds over the years. My most used powder in cast rifle loads is SR 4759. It is about like IMR 4198 in burning speed so it isn't slow by any means, but it does not seem to contribute to much bore wear.

SR 4759 was a single base powder, no nitroglycerin. I've noticed powders regarded as hot have a significant amount of nitroglycerin added (double base)

[Scharfschuetze]

SR 4759 was a single base powder, no nitroglycerin. I've noticed powders regarded as hot have a significant amount of nitroglycerin added (double base)

I have found that to be very true using 5744 which is a double base powder. Using it creates barrel temps as fast as shooting full power jacketed loads in my 30/40 Krag and Trapdoors. 4759 on the other hand will warm a barrel up over time, but not nearly as fast or it seems as hot as the afore mentioned 5477.

As a result I use it sparingly and only in slow fire in just one load in the Krag with a cast boolit. That one load is so accurate that I'll continue to use it, at least until the 5477 runs out.

[David2011]

Not sure if this is a general question or a rifle question. Certainly in rifles throat erosion is a big issue and is mitigated by shooting cast at lower velocities than jacketed. The USPSA shooters for the most part shoot cast at the same velocity as they would jacketed. We shoot too many rounds to shoot jacketed all the time. The people at the top of the game shoot around 100K rounds/year and claim to get 200K-300L through a barrel. I'm not at the top of the game and have about 90,000 rounds through my STI Edge over several years. The bore still has crisp rifling. With jacketed a barrel should go 50,000-60,000 rounds before accuracy deteriorates.

David

[OS OK]

Read for yourself what is going on in chamber when whatever you choose to use…is ignited...
'The Wizardry of Propulsion' (http://castboolits.gunloads.com/showthread.php?297867-The-Wizardry-of-Propulsion)