I was cleaning one of my AR-15's tonight along with a couple others. This one in particular I've had for some time and have been having trouble getting a load to work. The original load consisting of 24 grains of Varget over a 77gr HPBT just seemed to stop shooting well after years of sub moa performance. I contributed it to mounting up a suppressor and the change in barrel harmonics. After some load development I found a node that seemed accurate. However after loading 10 of two charge weights I got some really wild ES's with one being 100fps. So tonight after cleaning it I got my borescope and was kind of puzzled by what I saw. The edges of the rifling were nearly impossible to see vs another one that I cleaned. This rifle had been a shooter and my go to for coyotes for years. It's a Larue Stealth that I purchased as a complete upper and stripped lower. Last photo is of the second AR, both 223's.
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Rifling Deterioration?
- Thread starter mray190
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dfanonymous
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What's the estimated round count?
(Of the barrel)
(Of the barrel)
I have no idea I didn't track round counts back then. Maybe rough estimate around 5-6k.
dfanonymous
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Yep, that's a burned out barrel. It happens. Seemed like it was a good barrel while it lasted though.
highfinblue
Well-Known Member
I like to say it was good while it lasted, new tube and on to your next adventure
5000 is the average in-spec lifespan of a .223/5.56N milspec barrel. MIL-B-11595E 4150 grade CMV steel with chrome lining. My Colt barrels seem to hold up better than 5,000. I have an old M4 that has 8,000 or so and is still a shooter. Most armorers would plan to replace a barrel by 10K regardless to how it shoots.
Some of the stainless barrels I have seem to have less defined rifling to begin with. In theory stainless barrels should last longer. With heat and friction stainless excels versus cmv. But the stainless has to be properly treated and results vary greatly. Due to the nature of stainless the rifling can also be a weak point if not cut or treated properly.
A forged cryo treated 416R ordinance grade stainless barrel would likely see very high round counts before it starts to fail. Coatings also vary lifespan.
I have some forged dod overruns with the FNH style treatments that are likely to last a very long time. The more cutting edge materials yield a 20,000 round lifespan. An quality grade stainless forged and subjected to a melonite coating, results in up to 20K barrel life.
Lefty7mmstw
Well-Known Member
Rifling looks like crap and she doesn't shoot... toast. Time for a pipe.
Been there, done that, but usually with fire-breathers like a 7rum...
Been there, done that, but usually with fire-breathers like a 7rum...
Rflshootr
Well-Known Member
Can you seat your bullet out .010 further and still work in the magazine?
While the rifling in the photo looks pretty rough, my guess it's likely not that much different then it was before you experienced a loss in accuracy. The section of the barrel that you should be looking with your bore scope is the erosion at the throat, and/or a carbon ring that forms where the free-bore and the rifling begins. It is the heat(fire-cracking), and erosion of the powder burn/bullet entry into the land that causes this wear which migrates with time. Accuracy loss begins with the change in bullet seating depth to the lands. The military has specs for the the amount of rifling erosion permissible at the throat before replacement (ie, .010" throat erosion/1MOA accuracy loss). The other area of barrel wear that can cause an abrupt change in accuracy is at the crown(entry point at the end of the barrel). It can usually be seen with the naked eye. It should be even and square. This damage can be caused by physical contact that damages the crown and/or improper cleaning methods.
What may be cause an accuracy change over time in the main section of the barrel, and observed with a bore-scope, is carbon(carbon slick in the lands), and/or copper build up…..easily seen and can often be removed by cleaning.
When I was competing I would have to monitor barrel wear, replacing barrels as much as 1-2x per season. Barrels were subjected to high heat in the warm summer months and accuracy/precision demands were pretty stringent.
This cutaway is an example of a shot out barrel. First place to bore-scope the barrel. It has much more than .010" of throat erosion/rifling loss which is about when you should start checking accuracy/precision and about a new barrel…..Or perhaps decreasing the seating depth of your bullet to get a little extra accurate barrel life……IMO
What may be cause an accuracy change over time in the main section of the barrel, and observed with a bore-scope, is carbon(carbon slick in the lands), and/or copper build up…..easily seen and can often be removed by cleaning.
When I was competing I would have to monitor barrel wear, replacing barrels as much as 1-2x per season. Barrels were subjected to high heat in the warm summer months and accuracy/precision demands were pretty stringent.
This cutaway is an example of a shot out barrel. First place to bore-scope the barrel. It has much more than .010" of throat erosion/rifling loss which is about when you should start checking accuracy/precision and about a new barrel…..Or perhaps decreasing the seating depth of your bullet to get a little extra accurate barrel life……IMO
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Kendoist4162
Well-Known Member
Ignorant Q - is there necessarily a "This comes first, then …" aspect to the fire cracking and throat wear to a barrel? Or do they tend to happen at about the same round count?
No they are as long as I can get them literally touching end to end.
Tommy T
Well-Known Member
I have a 7 prc and a6.5 prc they both have about 700 hot rounds thru them and they are starting to open up 1/4" to 1-14" groups I think that maybe my problem
Yeah I could not see the lands at all. It just looked like a shiny blur but it wasn't the camera. Ive been pushing this barrel pretty hard, just kinda surprised me when I saw the image. It showed very little fire cracking and there was more definition in the lands and grooves the last time I scoped it after cleaning, wish I had of clicked a couple of pics now. It's been a good barrel and was a quality one for sure. I've shot out a couple in my life now, I hate that it eventually comes to that, but that's the game. Currently I have my old Sendero at Alamo getting a new one spun up for it.
