Sporter Profile .223 Question

[Erik_J]

[ar15barrels]

The first 5 rounds should be fine.

It's thermal drift that will get you.
As soon as a skinny barrel warms up, it starts moving around based on which way it is bent.

[Calif Hunter]

I have a CZ 527 American with a thin barrel in .223 and I think it gets hot after about 5 rounds fired pretty quickly. But I don't like to let my barrels heat up too much, so "hot" is probably subjective. I also have a Tikka T-3 Lite in .243 and I think its barrel is a bit thicker than CZ. It is hard to beat the Tikka for a smooth action.

[Khromo]

I have a Rem 700 SPS Stainless in .223 with the sporter barrel. That gun spits out 0.60" five-shot groups very reliably. It will start to creep if I keep it up, but it cools down pretty fast, seems like 10-15 minutes and it will shoot another tight group.

If I alternate five-shot groups with that gun and another, taking my time and shooting as well as I can, that sporter barrel can perform for a few hours. I open the bolt and set it in the rack, muzzle up, and the skinny barrel cools down down almost as quickly as it heats up.

A .30-'06 with the same barrel profile heats up a lot faster! Twice the powder makes a big difference.

[TMB 1]

The first 5 rounds should be fine.

It's thermal drift that will get you.
As soon as a skinny barrel warms up, it starts moving around based on which way it is bent.

What do you mean by bent?

[ar15barrels]

Sporter Profile .223 Question

What do you mean by bent?

All barrels are curved (bent) to some extent.
It might only be 0.010" over the length of the barrel or it might be 1/8" over the length of the barrel.
The outside of the barrel is contoured in relationship to the two ends which are centered in the lathe.
Since the bore is curved to some extent, think of it as being shaped like a jump rope as the outside is machined,
Since the bore is curved, but the outside contour is straight, one side of the barrel wall is always thicker than the other.

Metal expands as it heats up.
In the case of a piece of tubing with equal wall thickness, all sides expand the same amount and the tubing remains straight.
If one side of the tubing is thicker than the other, the thicker side expands more. When one side expands more, the tubing will bend towards the thinner side while it is heated up.

A barrel is just a piece of thick walked tubing with rifling inside.
The straighter the barrel, the less it will drift as it heats up.
The ratio of wall thickness differences to the wall thickness will predicate how much a barrel drifts from differential thermal expansion.
For example, a barrel with a 0.300" wall thickness that has a 0.030" wall thickness differential is about a 10% differential while a barrel with 0.250" wall thickness, but 0.040" thickness differential has about a 16% differential and will drift more with temperature change.

[TMB 1]

All barrels are curved (bent) to some extent.
It might only be 0.010" over the length of the barrel or it might be 1/8" over the length of the barrel.
The outside of the barrel is contoured in relationship to the two ends which are centered in the lathe.
Since the bore is curved to some extent, think of it as being shaped like a jump rope as the outside is machined,
Since the bore is curved, but the outside contour is straight, one side of the barrel wall is always thicker than the other.

Metal expands as it heats up.
In the case of a piece of tubing with equal wall thickness, all sides expand the same amount and the tubing remains straight.
If one side of the tubing is thicker than the other, the thicker side expands more. When one side expands more, the tubing will bend towards the thinner side while it is heated up.

A barrel is just a piece of thick walked tubing with rifling inside.
The straighter the barrel, the less it will drift as it heats up.
The ratio of wall thickness differences to the wall thickness will predicate how much a barrel drifts from differential thermal expansion.
For example, a barrel with a 0.300" wall thickness that has a 0.030" wall thickness differential is about a 10% differential while a barrel with 0.250" wall thickness, but 0.040" thickness differential has about a 16% differential and will drift more with temperature change.

Ok, I was wondering because years ago I read that Savage bend their barrels then hammer them straight. Maybe that has something to do with why they're so accurate if it affects wall thickness?

[ar15barrels]

Sporter Profile .223 Question

years ago I read that Savage bend their barrels then hammer them straight.

What you heard about was savage straightening barrels because they were so crooked.
It was in their video on how they make a rifle.
They do it to finish contoured barrels so it actually does not effect the wall thickness.
Savage barrels are some of the worst at thermal drift.

[TMB 1]

What you heard about was savage straightening barrels because they were so crooked.
It was in their video on how they make a rifle.
They do it to finish contoured barrels so it actually does not effect the wall thickness.
Savage barrels are some of the worst at thermal drift.

I didn't hear it, I read it in a magazine article back in the 80s. There was tons of pics as they toured the factory. They hand bent the barrel then hammered it straight.
These are the only video I could find http://savagearms.com/accuracy/
The one on barrels does talk about consistency and uniform walls.

Do you have link to the video you're talking about?

[ar15barrels]

I don't have a link.
It was embedded in some online magazine article that toured the savage factory.