This is a deep dive into this subject. If you're of the TL;DR tribe, pass this one by.
Having a bore scope is one of those things that's like a double edged sword. On the one hand it's good for monitoring wear and to determine if that barrel you think is clean, is really clean. On the other hand, that barrel you think is smooth as a baby's butt on the inside probably isn't, as we shall see. Barrels that look absolutely terrible can shoot well, and barrels that look pristine can shoot not so good. One of those "beauty is only skin deep" things. The first time you see inside your barrels, it can be a bit scary.
So for this little treatise, we are going to clean the two AR's I shot in High Power and get them honest to goodness clean so an accurate throat erosion measurement can be made, and to see how what the actual bore condition is. Copper and carbon buildup in the throat will give an erronious reading, so they gotta be clean down to bare metal.
The opinions presented herein will be from the perspective of using the AR for High Power rifle competition, that's what I have experience in, not combat. And we will explore the reasons why.
Also, for comparison, I'll include some bore scope pics of a brand new AR barrel, and an early 80's Colt SP1 that I bought new in my youth, and talk about the pros and cons of the different barrel steel etc. Remember what was said in the bolt steel thread, just because something on the AR is "mil-spec" doesn't mean it's the best for our application. Advancements in technology changes things the mil-spec for the AR dates back to the 60's.
Barrel Steel:
Chrome Moly
Most commercial chrome moly barrels will be 4140, or 4150. Mil-spec calls for 4150, but to an Ordnance Specification, spelled out in MIL-B-11595E, rather than an SAE spec. Usually this means the percentage of the alloying element percentages are held to a tighter spec. Military AR barrels are then chrome lined.
Stainless Steel
Stainless barrels used to be seldom seen because the stainless alloys available in the past just didn't have the properties to make a good barrel. At some point that changed and today stainless is the way to go. Most commercial barrels are 416, but the barrel on my Service Rifle is 17-4, which has much better wear properties. And the bore scope bears this out.
Methods of Rifling:
Cut Rifled
The age old traditional method of rifling a barrel is cut rifling. With this method, the barrel is gun drilled, then reamed to its nominal bore diameter. The hook cutter then cuts each groove, one at a time, a thousandth per pass, until groove depth is met. By todays standards, this is very time consuming and expensive, so only a few match barrel makers offer it. But expertly done, it produces a superior barrel that will out last a button rifled barrel.
The cutter is pulled through the barrel by a machine and the twist rate can be selected, making it the most flexible/versatile method. After each pass, the hook is adjusted for the next cut.
Rifling cutter head.
Broaching
This was the method used for mass production of the M1 rifle barrels. Similar to the hook rifling method, it performs the rifling in a single pass. Not exactly the best for producing an accurate barrel by today's standards.
Button Rifling
This method was pioneered by Remington after WW2 as a method to take the skill out of the rifling operation and require only an operator for the machine. In this method, a reverse image of the rifling is ground onto a carbide "button", which is attached to a rod, which is then pulled hydraulically through the barrel in only a couple of minutes. Twist rate cannot be changed. A different twist rate requires a new button.
Hammer Forging
This is the current favorite method for mass production. A mandrel with the reverse image of the rifling is inserted into the barrel blank and it is literally beaten down and around the mandrel. This produces quality barrels with little variation from one to another. A different twist or caliber requires a new mandrel, so it is not the method of choice for custom barrel makers.
The hammer forging process produces a surface finish that is sometimes retained for esthetic effect.
Alright, so I told you all that background stuff so when we look at some of these photos, you'll know what you're looking at. Sorry if I put some of you to sleep.
The Rifles:
I transitioned (no, not that kind of trans) to the AR from the M14 in 1998. At this point, AR's were out scoring the "wood guns" due to two reasons. They were more accurate due to a floated barrel, and negligible recoil meant you didn't need as tight a position in the rapids.
Prior to about the mid 90's, the AR was at a disadvantage as a High Power platform. The rules allowed its use, but only in "as issued" form. This meant you had to shoot it in bone stock M16A2 configuration to compete in the Service Rifle category. No match sights, no match triggers, no float tube. And those were the 3 things the AR needed to be competitive, together with bullets that could hang with a 30 cal 168 MK for wind drift at 600 yds.
The turning point came when the Army Marksmanship Unit got a new commander. He mandated that they were going to shoot the M16. This built a fire under everyone to pave the way for the M16 to be a Match Service Rifle.
Sierra already had the 69gr. SMK, which is what all the early AR shooters were using. It was fine for the short lines, but it fell short at 600 if the wind was blowing, and the wind always blows at Camp Perry. Then Sierra introduced the 80gr. SMK, and things changed. Peeps started flocking to the AR for High Power.
So, like everyone else, I switched to the AR. Unlike most peeps at the time, I built my own.
It is common practice in the High Power world to have at least two match uppers, if not two complete rifles.
The "Best" upper/rifle is reserved for major matches like state championships, regional championships, and Camp Perry. The other upper is used for practice and local matches. At some point barrel wear on the second upper rates replacement, and the new barrelled upper now becomes the "Best" and the former "Best" becomes the practice upper. This is exactly what the Army and USMC shooting teams do.
So, the rifle with the SS barrel I built as my "Best".
The other rifle is a BushMaster rifle sold through the CMP back in the early 2000's. It was intended as a rifle for aspiring High Power shooters and was offered at an attractive price, one which you could not duplicate on your own. Myself and several other bought these rifles to serve as our practice rifles. And they shoot very well. It became the rifle I shot the most for local matches. Consequently it suffered the most wear and tear.
When the rules changed to allow optics, I changed the "Best" rifle to a flat top upper and scope.
The Mattel sticker is something one of my shooting buds came up with.
Cleaning:
To do a proper cleaning job, you need proper tools.
In addition to a good cleaning rod and jag, you really need a cleaning rod guide. This one was made by Ray-Vin. Ray recently passed away, but there are others on the market that will work just as well.
I like the foaming bore cleaners because they are not ammonia based and work well. And you can sit back and drink beer while they do their thing.
But, just because the patches stop coming out blue, doesn't necessarily mean you are done cleaning.
Most would consider a barrel that pushes out a white patch as "clean". But is it really? There is still a hint of copper, and obvious carbon.
What clean looks like.
So, the BushMaster had a good bit of copper and carbon fouling which was hiding pitting underneath. It cleaned up fine, but it underscored that a carbon steel barrel isn't the best choice.
The SS barrel cleaned up just fine and exhibits less wear and erosion than the carbon BushMaster barrel. Much less.
Without going back and digging out my data books, I'm thinking this barrel has 3K rounds down the tube. This is the throat.
This is mid barrel. The dark streak is reflection. If I rotate the camera a little, it goes away.
This is the erosion at the gas port.
Compare to a brand new AR barrel.
Same brand new barrel, mid barrel.
So, now let's look at my Colt SP1. Chrome lined barrel.
Gas port.
Here we see not only that the chrome is flaking off, but chatter marks from the rifling process. So it appears at this point, that Colt was still broaching.
Throat reading on the SP1. So chrome is not as erosion resistant as was thought.
Taking photos of the bore is problematic. It's difficult to get a pic that shows what you want to illustrate sometimes.
This is a pic of one of my M1's. This is the rifle that I have shot in Rifleman's Weekend JCG matches for many years. This rifle is the best shooting M1 I own in spite of the wear the bore scope shows.
Here's a pic of the throat. The "alligator skin" heat checking is classic advanced wear. This barrel gages "5" on the throat gage, but it still wins trophys. That beauty is skin deep thing.
The five on the left were won with the same M1.
Throat Gages:
The military uses a gage (correct spelling for a mechanical gage, vs. a analog gauge)
This gage is calibrated for a match Wylde chamber, and reads "0" on a new cut rifled barrel, "1" on a button rifled barrel.
Here's the reading on the BushMaster barrel. Each number is approximately 1K rounds. Assuming BushMaster barrels are button rifled, this shows about 3.5K rounds.
Conversely, the SS barrel, which has at least 3K rounds on it, shows this. Hardly any measurable wear. Keep in mind, this was a premium Black Star Lothar Walther hammer forged barrel that was cryo'd. It also exhibits zero corrosion, even though both this barrel and the BushMaster were cleaned on the same schedule.
This is the reading on the new barrel. The reading indicates this is probably a button rifled barrel.
Now that you've seen the pretty bore pics, here are some to show you that in the past, barrels weren't always this pretty.
This is one of my M1 barrels. While the grooves are nice and smooth, the lands are as rough as a file.
Here's a pic of the muzzle. Note that the groove is not smooth like the last pic. The broach that made this barrel was dull, and the metal has a torn appearance. Also note that cleaning rod wear has rounded the lands right at the crown. While this is minor, wear like this has ruined a lot of M1 barrels. When you see ads for M1's that advertise "counter bored" muzzles, this is to try to half ass make up for cleaning rod wear.
Here's what severe cleaning rod damage looks like. There's 3/8" of rifling worn away by a GI 3 piece cleaning rod and all the enthusiasm a 18 year old GI can muster.
When you get done cleaning your barrel, blow out the gas tube to purge the gunk that collected in the gas port.
Here's a bore pic of the gunk after blowing with canned air.
Here's the patch after the gunk was pushed out.
That's all for this article. If you have questions, feel free to ask.
Having a bore scope is one of those things that's like a double edged sword. On the one hand it's good for monitoring wear and to determine if that barrel you think is clean, is really clean. On the other hand, that barrel you think is smooth as a baby's butt on the inside probably isn't, as we shall see. Barrels that look absolutely terrible can shoot well, and barrels that look pristine can shoot not so good. One of those "beauty is only skin deep" things. The first time you see inside your barrels, it can be a bit scary.
So for this little treatise, we are going to clean the two AR's I shot in High Power and get them honest to goodness clean so an accurate throat erosion measurement can be made, and to see how what the actual bore condition is. Copper and carbon buildup in the throat will give an erronious reading, so they gotta be clean down to bare metal.
The opinions presented herein will be from the perspective of using the AR for High Power rifle competition, that's what I have experience in, not combat. And we will explore the reasons why.
Also, for comparison, I'll include some bore scope pics of a brand new AR barrel, and an early 80's Colt SP1 that I bought new in my youth, and talk about the pros and cons of the different barrel steel etc. Remember what was said in the bolt steel thread, just because something on the AR is "mil-spec" doesn't mean it's the best for our application. Advancements in technology changes things the mil-spec for the AR dates back to the 60's.
Barrel Steel:
Chrome Moly
Most commercial chrome moly barrels will be 4140, or 4150. Mil-spec calls for 4150, but to an Ordnance Specification, spelled out in MIL-B-11595E, rather than an SAE spec. Usually this means the percentage of the alloying element percentages are held to a tighter spec. Military AR barrels are then chrome lined.
Stainless Steel
Stainless barrels used to be seldom seen because the stainless alloys available in the past just didn't have the properties to make a good barrel. At some point that changed and today stainless is the way to go. Most commercial barrels are 416, but the barrel on my Service Rifle is 17-4, which has much better wear properties. And the bore scope bears this out.
Methods of Rifling:
Cut Rifled
The age old traditional method of rifling a barrel is cut rifling. With this method, the barrel is gun drilled, then reamed to its nominal bore diameter. The hook cutter then cuts each groove, one at a time, a thousandth per pass, until groove depth is met. By todays standards, this is very time consuming and expensive, so only a few match barrel makers offer it. But expertly done, it produces a superior barrel that will out last a button rifled barrel.
The cutter is pulled through the barrel by a machine and the twist rate can be selected, making it the most flexible/versatile method. After each pass, the hook is adjusted for the next cut.
Rifling cutter head.
Broaching
This was the method used for mass production of the M1 rifle barrels. Similar to the hook rifling method, it performs the rifling in a single pass. Not exactly the best for producing an accurate barrel by today's standards.
Button Rifling
This method was pioneered by Remington after WW2 as a method to take the skill out of the rifling operation and require only an operator for the machine. In this method, a reverse image of the rifling is ground onto a carbide "button", which is attached to a rod, which is then pulled hydraulically through the barrel in only a couple of minutes. Twist rate cannot be changed. A different twist rate requires a new button.
Hammer Forging
This is the current favorite method for mass production. A mandrel with the reverse image of the rifling is inserted into the barrel blank and it is literally beaten down and around the mandrel. This produces quality barrels with little variation from one to another. A different twist or caliber requires a new mandrel, so it is not the method of choice for custom barrel makers.
The hammer forging process produces a surface finish that is sometimes retained for esthetic effect.
Alright, so I told you all that background stuff so when we look at some of these photos, you'll know what you're looking at. Sorry if I put some of you to sleep.
The Rifles:
I transitioned (no, not that kind of trans) to the AR from the M14 in 1998. At this point, AR's were out scoring the "wood guns" due to two reasons. They were more accurate due to a floated barrel, and negligible recoil meant you didn't need as tight a position in the rapids.
Prior to about the mid 90's, the AR was at a disadvantage as a High Power platform. The rules allowed its use, but only in "as issued" form. This meant you had to shoot it in bone stock M16A2 configuration to compete in the Service Rifle category. No match sights, no match triggers, no float tube. And those were the 3 things the AR needed to be competitive, together with bullets that could hang with a 30 cal 168 MK for wind drift at 600 yds.
The turning point came when the Army Marksmanship Unit got a new commander. He mandated that they were going to shoot the M16. This built a fire under everyone to pave the way for the M16 to be a Match Service Rifle.
Sierra already had the 69gr. SMK, which is what all the early AR shooters were using. It was fine for the short lines, but it fell short at 600 if the wind was blowing, and the wind always blows at Camp Perry. Then Sierra introduced the 80gr. SMK, and things changed. Peeps started flocking to the AR for High Power.
So, like everyone else, I switched to the AR. Unlike most peeps at the time, I built my own.
It is common practice in the High Power world to have at least two match uppers, if not two complete rifles.
The "Best" upper/rifle is reserved for major matches like state championships, regional championships, and Camp Perry. The other upper is used for practice and local matches. At some point barrel wear on the second upper rates replacement, and the new barrelled upper now becomes the "Best" and the former "Best" becomes the practice upper. This is exactly what the Army and USMC shooting teams do.
So, the rifle with the SS barrel I built as my "Best".
The other rifle is a BushMaster rifle sold through the CMP back in the early 2000's. It was intended as a rifle for aspiring High Power shooters and was offered at an attractive price, one which you could not duplicate on your own. Myself and several other bought these rifles to serve as our practice rifles. And they shoot very well. It became the rifle I shot the most for local matches. Consequently it suffered the most wear and tear.
When the rules changed to allow optics, I changed the "Best" rifle to a flat top upper and scope.
The Mattel sticker is something one of my shooting buds came up with.
Cleaning:
To do a proper cleaning job, you need proper tools.
In addition to a good cleaning rod and jag, you really need a cleaning rod guide. This one was made by Ray-Vin. Ray recently passed away, but there are others on the market that will work just as well.
I like the foaming bore cleaners because they are not ammonia based and work well. And you can sit back and drink beer while they do their thing.
But, just because the patches stop coming out blue, doesn't necessarily mean you are done cleaning.
Most would consider a barrel that pushes out a white patch as "clean". But is it really? There is still a hint of copper, and obvious carbon.
What clean looks like.
So, the BushMaster had a good bit of copper and carbon fouling which was hiding pitting underneath. It cleaned up fine, but it underscored that a carbon steel barrel isn't the best choice.
The SS barrel cleaned up just fine and exhibits less wear and erosion than the carbon BushMaster barrel. Much less.
Without going back and digging out my data books, I'm thinking this barrel has 3K rounds down the tube. This is the throat.
This is mid barrel. The dark streak is reflection. If I rotate the camera a little, it goes away.
This is the erosion at the gas port.
Compare to a brand new AR barrel.
Same brand new barrel, mid barrel.
So, now let's look at my Colt SP1. Chrome lined barrel.
Gas port.
Here we see not only that the chrome is flaking off, but chatter marks from the rifling process. So it appears at this point, that Colt was still broaching.
Throat reading on the SP1. So chrome is not as erosion resistant as was thought.
Taking photos of the bore is problematic. It's difficult to get a pic that shows what you want to illustrate sometimes.
This is a pic of one of my M1's. This is the rifle that I have shot in Rifleman's Weekend JCG matches for many years. This rifle is the best shooting M1 I own in spite of the wear the bore scope shows.
Here's a pic of the throat. The "alligator skin" heat checking is classic advanced wear. This barrel gages "5" on the throat gage, but it still wins trophys. That beauty is skin deep thing.
The five on the left were won with the same M1.
Throat Gages:
The military uses a gage (correct spelling for a mechanical gage, vs. a analog gauge)
This gage is calibrated for a match Wylde chamber, and reads "0" on a new cut rifled barrel, "1" on a button rifled barrel.
Here's the reading on the BushMaster barrel. Each number is approximately 1K rounds. Assuming BushMaster barrels are button rifled, this shows about 3.5K rounds.
Conversely, the SS barrel, which has at least 3K rounds on it, shows this. Hardly any measurable wear. Keep in mind, this was a premium Black Star Lothar Walther hammer forged barrel that was cryo'd. It also exhibits zero corrosion, even though both this barrel and the BushMaster were cleaned on the same schedule.
Now that you've seen the pretty bore pics, here are some to show you that in the past, barrels weren't always this pretty.
This is one of my M1 barrels. While the grooves are nice and smooth, the lands are as rough as a file.
Here's a pic of the muzzle. Note that the groove is not smooth like the last pic. The broach that made this barrel was dull, and the metal has a torn appearance. Also note that cleaning rod wear has rounded the lands right at the crown. While this is minor, wear like this has ruined a lot of M1 barrels. When you see ads for M1's that advertise "counter bored" muzzles, this is to try to half ass make up for cleaning rod wear.
Here's what severe cleaning rod damage looks like. There's 3/8" of rifling worn away by a GI 3 piece cleaning rod and all the enthusiasm a 18 year old GI can muster.
When you get done cleaning your barrel, blow out the gas tube to purge the gunk that collected in the gas port.
Here's a bore pic of the gunk after blowing with canned air.
Here's the patch after the gunk was pushed out.
That's all for this article. If you have questions, feel free to ask.
Now I want a bore scope. Id love to do some comparisons on different rifles/pistols. Got 120 yrs of S&Ws to eyeball. Lol
Wow.
