Throat erosion question?

[srk]

Just curious as to the erosion issue at the "throat".
Seeing black shoots hotter.
Or has anyone come across this or knows about this.

[Hickory]

Erosion is not only caused by heat, but by pressure.
Black powder, compared to smokless powder doesn't produce "that much" pressure.
In your case, using black powder will corrode the throat also if not cleaned properly.

[Ballistics in Scotland]

I don't believe black powder, grain for grain, does shoot hotter. It may produce more heat because there is more of it, and communicate more of it into the barrel if the bullet's passage up the bore takes longer.

The theory I find most convincing on bore erosion is that it is thermal. Intense heat is conveyed to an extremely thin layer of the bore surface, and it then cools very rapidly as the heat is conducted away into relatively cold steel. This would explain why, although strings of rapid fire are much more erosive than the same number of shots fired slowly and steadily, machine-gun fire is only a bit more erosive. It does just as much heating, but only one lot of cooling at the finish of the burst.

There is no doubt that black powder can give a much longer life to barrels in plain carbon steel, which with smokeless would erode unacceptably quickly. This was the case even when black and smokeless loads would give very similar peak pressure, as was sometimes the case. It may be that the tendency of black powder to maintain its heat and pressure further down the barrel reduced the tendency to thermal cracking. It may also be that when softer steel was used, it reduced the tendency of the thermal stresses to produce cracking.

[Lead pot]

I shot the throat out of my .22-250 with around 1000 rounds fired. I shot over 20,000 in one of my Sharps and it just polished the reamer marks out of the bore and it get so hot at times the screw holding the forearm burns my hand.

[country gent]

Throat erosion is the result of several things, Heat, blast effect of unburned powder, the bullets passage, with fouling, and the way this all enters into the bore throat of the rifle. On modern bottleneck rifle cartridges ( with higher intensities of the issues) a shoulder angle and neck length combination that puts the first hit of these pressures and unburnt powder inside the case neck show much lower errosion rates. A round 243 with short neck and shoulder anngle that allows the first outside of the neck can take a throat in 2500 rds or slightly less. On our cartridges ( straight walled for practical purposes) this shoulder angle neck venturi effect isnt applicable but it shows the blast effect. A black powder can be abrasive and sharp edged. pressures arnt as high as smokless loads and bullets are softer but heavier and sometimes longer bearing surfages. One other over looked effect is the coating of bullet lube in the bore acting as an insulater and lubing the passage of powder and pressure. In the black powder rounds ( fired with holy black loads not substitute or duplication loads) errosion may be at a fairly low rate do to lower pressures, centered pressures and unburnt powder ( no real shoulders to angle this first strike into throat or bore), the powders burn rate helpng ombustion to take place in the case and as mentioned centered more so inthe bore, and last is the lube insulation of the bore from bullet lubes that are soft and oily.

[Red River Rick]

Better check your source of information.............

RRR

[Jim2]

Clean the bore of your BPCR properly and timely and you'll not see any erosion in there in your lifetime.

[srk]

Hi everyone
It was just a question out of curiosity.
Thanks for all the insight.
Always wondered, just wanted some opion's.

[Lead pot]

I don't know what really eats the throat. But I think the high velocity of the jacketed bullet friction has a lot to do with it. The rounds like the .220 and the other rounds that reach over 3800 fps just eat the throat in no time.

[country gent]

Small bores large powder charges are a combination for heavy fast errosion. Had an accuracy smith tell me that a 300 win mag 180-200 grn bullets at full power peak accuracy was going to be around 1200 rds once. My 243 coarse rifle is at 2300 rds and X count at 600 yds started dropping off. I read and researched the shoulder angle neck length theroy ( I think it was refered to divergant angle) several places years ago, It was brought up in varmint hunter magazine and a couple benchrest publications.

[Ballistics in Scotland]

I don't know what really eats the throat. But I think the high velocity of the jacketed bullet friction has a lot to do with it. The rounds like the .220 and the other rounds that reach over 3800 fps just eat the throat in no time.

If bullet metal to bore friction was responsible to more than a very slight degree, it would be greatest where bullet velocity is highest. But that velocity is a very small fraction of 3800 fps where the erosion is greatest. There is also a tendency to erode the muzzle bell-mouthed, where the gas escapes through a narrow gap at higher than bullet velocity. But an inch or so back, a barrel eroded beyond useful accuracy may be of normal diameter.

It is the burning of powder that erodes barrels, and large charges of fast powder seem to do it most. Double based powders, especially early military ones with a higher nitroglycerin content than is used nowadays, are the worst.