Old barrels effect on bullets?

[Deja vu]

as a barrel gets more warn from shooting what effect does it have on the bullet speed? Do the barrels get faster or slower with use?

 

[stubbicatt]

As the throat wears, if there is a change in velocity, velocity begins to diminish.

 

[g.willikers]

Hmm.
Worn barrels usually make themselves known with a fall off in accuracy.
But it could also make itself known with decreased velocity as the barrel to bullet spec increases.
Might be worth considering as another useful way to determine barrel wear and predicted life span.
??

 

[jmr40]

I've not seen any test data to confirm it, but it is logical that as a barrel wears out a looser fit between bullet and barrel will result in less speed. If anyone has a link to a test I'd be interested to see it. I know that quality match grade barrels with closer tolerances will shoot faster than common factory barrels. Often by a significant margin.

 

[Art Eatman]

Odds are, with some wear in the bore, friction would reduce more than there would be any gas blow-by. So, a tad more velocity, but probably not much.

 

[44 AMP]

it is logical that as a barrel wears out a looser fit between bullet and barrel will result in less speed.

While it may seem illogical, a "worn" barrel can also be "faster", though generally less accurate.

Logic says, "tighter bullet fit, better gas seal, higher velocity..."

But what this is leaving out is FRICTION. Tighter bullet fit means more friction, which can mean LOWER velocity.

It all depends on at what point in the barrel life/bullet fit you are at, when measuring.

When it comes to the gas seal, you have complete sealing, until you don't. When you get gas blow by, then you don't. Until then, you do, and when you do, a tighter fit doesn't get you anything but more resistance to bullet passage (friction) which can mean Lower speeds.

Its not any kind of a hard and fast rule, but it CAN happen, when conditions are just right.

 

[Gunplummer]

Takes a lot to wear out a cut rifled barrel. Frankford Arsenal did do tests on barrels (Older NRA Handloaders Guide). There were tens of thousands of rounds fired through about ten barrels and the accuracy was still improving. These were not fired full auto. I have had older chrome lined barrels and the increase in accuracy was noticeable at the range as the barrels became heated up. I guess it is not any type of set rule and depends on the situation.

 

[handlerer2]

I will quote the Speer manual. " After as few as 500 rounds, the muzzle velocity of 264WM, can deteriorate to 270 velocity" So I would think that MV loss would be more evident due to throat erosion. Loss of pressure due to gas cutting, would,IMO, be a more significant factor than loss of friction.

 

[Shimpy]

I've made many benchrest barrels accurate again by cutting off rear portion of barrel by about an inch or so and re-chambering. This gets rid or the worn throat.