When Do I Replace My Barrel?

[MarcSpaz]

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I am a long-gun noob. I have no idea how to tell if it is time to replace my barrel or not. so, I have a few questions if anyone is willing/able to answer, but first... some specifics.

I have a 2011 Sig 516 Patrol (M4) chambered in 5.56. I bought it new about a year ago. With the exception of the trigger assembly, the internals are original. I have easily put 5,000 rounds through it. It gets cleaned every time it's used (same day/night).

1.) How many rounds are light barrels typically good for in a semi-auto M4?

2.) Is there a known method for using something like a digital gauge to measure bore ID for wear?

3.) If so, are there any recommendations on a.) where to find the gauge b.) what the tolerances are for a light barrel in a 5.56?

I am not seeing any accuracy issues at 100 yards, which is the furthest this gun has ever been fired. I would assume that consistency would be the first thing to go as a barrel wears out. However, I have noticed something that has prompted me to ask these questions.

Specifically, when I first bought the gun, I could hardly push a single 1/4" patch through it for cleaning. It was very tight and took some effort to run the patch through the barrel. Now, when I clean the barrel, there is little resistance to the patch and the wire brush. So there is definitely some wear.

Anyway. Any advise on what to look for and expect would be greatly appreciated.

[jdonovan]

I have a 2011 Sig 516 Patrol (M4) chambered in 5.56. I bought it new about a year ago. With the exception of the trigger assembly, the internals are original. I have easily put 5,000 rounds through it. It gets cleaned every time it's used (same day/night).

1.) How many rounds are light barrels typically good for in a semi-auto M4?

Depending on rate of fire... i.e. how hot the barrel gets,
Mil-spec is just under 10k, A chrome barrel in a semi gun may easily last 20k

I am not seeing any accuracy issues at 100 yards, which is the furthest this gun has ever been fired.

accuracy, and velocity are the 'losses' when a barrel wears out. Keep in mind mil-spec accuracy is only about 1.5-2 MOA... These are battle rifles, not camp perry match guns.

Specifically, when I first bought the gun, I could hardly push a single 1/4" patch through it for cleaning. It was very tight and took some effort to run the patch through the barrel. Now, when I clean the barrel, there is little resistance to the patch and the wire brush. So there is definitely some wear.

[/quote]

Or the high spots from button rifling are finally worn down and you now have a smoothed out bore.

pre-panic...
A M4 barrel is +/- $200, 10k of ammo is $3500.

[MarcSpaz]

That is really good info. I greatly appreciate it.

I am very happy with the performance of the mil-spec. I bought it with defense in mind, not competition. Most of the shots fired have been prone at the 100 yard line and taking my time. Maybe 10-12 seconds between shots and about 10 shot groups. When I was learning CQC, I did have a few hundred shots fired in rapid discharge (30 shots under 15 seconds).

I guess I can assume my barrel is going to be good for another year. I am not too worried about replacing the barrel as far as money goes. My main concerns and reason for the questions are reliability.

I am going to have to see if I can order 1 to have on hand so when it's time, i don't have down time while I look for one.

[jdonovan]

I guess I can assume my barrel is going to be good for another year. I am not too worried about replacing the barrel as far as money goes. My main concerns and reason for the questions are reliability.

I'd guess at that shooting speed, you're more likely to see 20k before wear out.

Buy 2, then you'll have a spare after this replacement.

Also I'd look into spares/replacements for other wear items. All springs, but especially, the trigger and extractor springs, bolt head ( they eventually crack), extractor.

[Reverenddel]

I keep spare parts, but overall, replace the barrel when it ceases to be accurate.

I have bought what someone called a "shot out" gun, cleaned it throughly, and was placing good groups.

[MarcSpaz]

Thanks for the advice. I appreciate it. Can I use any AR 5.56 light barrel or are they brand specific? I see some advertised as being compatible with specific gas block sizes and front sight block sizes, but I don't see any recommendations or compatibility notes about piston vs direct gas.

[jdonovan]

Can I use any AR 5.56 light barrel or are they brand specific? I see some advertised as being compatible with specific gas block sizes and front sight block sizes, but I don't see any recommendations or compatibility notes about piston vs direct gas.

I don't know the specs on your rifle, and what its going to need. All the upper work I've done was matching parts to one specific setup, so I'll defer to the other AR experts around.

[gunderwood]

The LuckyGunner test wore out a barrel in 5-6k rounds shooing the bi-metal jacketed ammo (basically copper washed steel). After 10k of mil-surplus the barrel still had lots of life left and that's under very rapid fire. Normal use should see more like 20k+. Throat and gas port erosion is mostly a function of the powder used, while rifling is mostly a function of bullet jacket. As others have noted, velocity loss is a key indicator for a worn-out barrel. Accuracy is too. Everyone has different standards though. A benchrest shooter might toss a 284 barrel in as little as 1k rounds due to inaccuracy, but people on the other extreme may weight until it starts to keyhole. Personally, I error on the side of caution, especially with suppressors. Replacing a barrel a little early is much cheaper than a baffle strike!

[Jbecker]

When your targets start to look like this.

[MarcSpaz]

hahahahaha that's awesome!