Hammer Forged Chamber...?

[Naaman]

I've been looking at barrels for a couple of months now, and am trying to find out about different manufacturers.

Specifically, I'm looking for barrels that have the chamber hammer forged along with the rifling. My research has not yielded much info: I read somewhere that Knight's hammer forges the chambers as well as Daniel Defense. Does anyone know if other barrel makers hammer forge the chamber?

Centurion Arms confirmed that their barrels have a cut chamber after the forging process is complete. The ideal barrel for my purposes would be a medium weight or SOCOM profile, mid-length, 14.5 CHF barrel (where the chamber is also hammer forged). As far as I know, such a thing does not exist, but I would like to get as close as possible.

 

[UpSideDown]

Why would this matter? I cannot imagine the grain structure being added to the chamber making any difference?

 

[Naaman]

I have some anecdotal experience that suggests that it may make a difference.

As I understand it, hammer forged barrels, while being "less accurate" are more durable than cut or button rifled barrels.

My understanding is that chamber dimensions are a factor in accuracy/consistency, and that chamber wear is a natural biproduct of shooting a gun.

So my theory is this: a tougher/more resilient chamber should hold it's dimensions over a greater round count or more rigorous firing schedule. But I'm unaware of any testing that would provide me some data points other than my own experiences.

When we switched from button rifled barrels to cold hammer forged barrels at work, we quadrupled the barrel life (many other factors could be at play, but we went from Colt to Daniel Defense barrels; ammo and firing schedule are the same).

After trying to understand this admittedly niche "problem" of wanting a unicorn barrel, I can understand why a lot of folk don't put stock into a particular manufacturing process: not all "hammer forged" barrels are created equal, and the ones of old (Ruger, etc.) were known for being "cheap" and "less accurate" than cut rifled barrels. This lack of consistency across hammer forged samples AND the lack of detailed information on proprietary specs and tolerances leaves a void of information to be filled with speculation and marketing.

I can say that my own shooting will probably never reveal a difference in performance or durability. But I want this barrel because 'Murica!

 

[TonyTheTiger]

My understanding is that chamber dimensions are a factor in accuracy/consistency, and that chamber wear is a natural biproduct of shooting a gun.

So my theory is this: a tougher/more resilient chamber should hold it's dimensions over a greater round count or more rigorous firing schedule. But I'm unaware of any testing that would provide me some data points other than my own experiences.

Chambers may wear, I've never seen it and don't really care enough to attempt measuring it, but long before you notice dimensional chamber changes you'll see the throat disappearing. Kinda like being super worried about your cars clear coat fading while also driving it all winter in a midwestern salt bath without ever washing it.

 

[Naaman]

Chambers may wear, I've never seen it and don't really care enough to attempt measuring it, but long before you notice dimensional chamber changes you'll see the throat disappearing. Kinda like being super worried about your cars clear coat fading while also driving it all winter in a midwestern salt bath without ever washing it.

Your comment uncovers a gap in my understanding:

"Throat erosion" is a term I have read a lot. And based on context, I assumed that the "throat" was part of the "chamber." And that throat erosion happens as a result of "abusive" firing schedules or manufacturing defects, etc.

So, your answer essentially creates new questions in my mind.

Are you saying that regardless of manufacturing process, all throats are equal? Or that the throat is formed during the hammer forging process, while the cut chamber has no bearing on throat life?

 

[LRRPF52]

Chambers may wear, I've never seen it and don't really care enough to attempt measuring it, but long before you notice dimensional chamber changes you'll see the throat disappearing. Kinda like being super worried about your cars clear coat fading while also driving it all winter in a midwestern salt bath without ever washing it.

This. The round count it takes to egg out a chamber is measured in tens of thousands of rounds, unless someone has engineered a bad design with too thin of chamber walls and pushes the chamber pressure.

For 5.56x45 NATO and typical AR-15 chamber walls, this is not an issue under a normal round count.

 

[Naaman]

This. The round count it takes to egg out a chamber is measured in tens of thousands of rounds, unless someone has engineered a bad design with too thin of chamber walls and pushes the chamber pressure.

For 5.56x45 NATO and typical AR-15 chamber walls, this is not an issue under a normal round count.

Thanks, man.

But does manufacturing process affect throat life?

 

[ArTeeKay]

Thanks, man.

But does manufacturing process affect throat life?

I do not believe process measurably affects throat life. Granted, I know just enough about metallurgy to feel like an idiot when talking to actual experts. But I would suspect that you're going to find much larger variations based on what ammunition you feed the rifle, it's firing schedule, and your cleaning regimen than you would ever be able to see from one barrel manufacturers process to another. I think the only significant difference you'll see is in regards to barrel steel, Bartlein's 400MODBB steel for example. @Frank Green would likely be a good resource for this topic.

Edited: Apparently chambers can be formed by hammer forging, but I stand by my earlier statement, in that more variation will be seen from other causes.

 

[rpoL98]

looking for that

 

[Supersubes]

Seems to me when you hammer forge a barrel, its end to end. Cutting the chamber into one end doesn't change the fact that the breech end is still a forging. Any data to suggest that hammer forged barrels are surface hard, as opposed to being homogenous throughout, Ive never heard that specific claim.


I agree with previous posters, barrels die from the throat forward, not in the chamber.

 

[meatpukk]

the one argument I've heard that probably has any merit regarding CHF chambers are that they are cocentric, thery are made with the same mandrel as the rest of the rifling in the same barrel, theres less tool marks that can cause sticky chambers etc.

But an educated guess leads me to believe its mostly a cost reducing measure. its cheaper to hammer it out in one go and get the required quality.
a cheap cut chamber looks like ass, a cheap chf barrel looks ok, while good barrels are good no matter the process.

 

[Naaman]

Thanks for all the replies, everyone. My research has taken me all over the place.

the one argument I've heard that probably has any merit regarding CHF chambers are that they are cocentric, thery are made with the same mandrel as the rest of the rifling in the same barrel, theres less tool marks that can cause sticky chambers etc.

But an educated guess leads me to believe its mostly a cost reducing measure. its cheaper to hammer it out in one go and get the required quality.
a cheap cut chamber looks like ass, a cheap chf barrel looks ok, while good barrels are good no matter the process.

This is the sentiment that I got from reading some threads from around 2011. When I look at rifles that are intended for hard use, I see that there is a trend towards hammer forged barrels in the industry. FN and Knight's, in particular seem to be very well regarded with respect to the products they make. Geissele also up and bought some hammer forging equipment.

So I'm inclined to believe that there is more to it than marketing (as some folks have suggested), but that "modern" techniques may have brought hammer forging to a level that makes it ideal for a duty-use barrel.

In any case, my refined question for anyone who knows is this:

Is the throat machined with the rifling or the chamber? And is its durability affected by the process by which it is made (all other things being equal)?

 

[ArTeeKay]

The "throat" of the barrel is a chamber feature, and is machined as such. And I did answer the second part of your question in my earlier reply, as did many others, however you seem to be a little hung up on specific words and phrases as they relate to your new understanding of what's happening when a barrel is manufactured. Unless you have a reasonable understanding of how steel forms grains and crystals, hardens and toughens, how different alloys, linings, and treatments interact, and how all those things interact with the high pressures, temperatures, and forces involved in firing a bullet (I, for one, do not), you are unlikely to be able to discern any difference at all, let alone a repeatably measurable one, between a cut chamber and a forged chamber.

This is one of those questions that's just picking fly shit out of pepper. Quit asking those questions, buy the thing you want, and go shoot it. If it doesn't perform the way you want, buy a different thing and try again.

 

[clcustom1911]

Thanks, man.

But does manufacturing process affect throat life?

Yes. No. Maybe. Machine gun barrels are usually cold hammer forged (CHF). So if you have a hard on for that process, many companies make CHF barrels. FN makes a good one.

Barrel life is one of those things where if you demand utmost accuracy, your throat erosion standards will be different than a person, like me, whose accuracy standard is like "minute of pump house/brain" (1.5-ishhh MOA) at 500-700 yards is good'nuff for 98.235% of anything I'll likely ever do.

Edit, Tikka cold hammer forges their barrels if you're looking for factory bolt guns with CHF barrel. My T3x Lite in 7mm RemMag has well over 1000 rounds through it and still does ½-¾ moa with my 168 Berger Classic Hunter load.

 

[Naaman]

This is one of those questions that's just picking fly shit out of pepper. Quit asking those questions, buy the thing you want, and go shoot it. If it doesn't perform the way you want, buy a different thing and try again.

That's what I'm working on right now, and is the reason for the thread. I never improved at anything by accepting "good enough." I now have some data points that address a question I couldn't find anyone else asking. Thanks for the info.

 

[UpSideDown]

I think the best way to extend barrel life is to chrome line it. CHF barrels do seem to have good lifespans, but as has been said above, the single element that generally kills a barrel is throat erosion. As each round is fired, even in a slow firing schedule, the high temperature of the just-ignited powder burns some of the throat where the bullet engages into the rifling. That's what kills accuracy.

Chrome lined barrels are the winner here for improved throat erosion and much improved corrosion resistance. Modern chrome lined barrels are pretty accurate as well, my Barrett Rec10 is 1/2-3/4MOA with factory match loads with a chrome lined barrel.

 

[JS8588]

Read the title of this thread & thought "this is gonna be good". I have not been disappointed. As my "Ballistic Hipster" moniker indicates, this is the kind of esoteric shit I find fascinating. Tagging in to read & learn.

Also...

I think the only significant difference you'll see is in regards to barrel steel, Bartlein's 400MODBB steel for example. @Frank Green would likely be a good resource for this topic.

...Bartlein uses different steel? I had no idea. Another research rabbit hole to chase!

 

[UpSideDown]

Read the title of this thread & thought "this is gonna be good". I have not been disappointed. As my "Ballistic Hipster" moniker indicates, this is the kind of esoteric shit I find fascinating. Tagging in to read & learn.

Also...


...Bartlein uses different steel? I had no idea. Another research rabbit hole to chase!

Bartlein is now offering barrels in this new material, there's been at least one thread running on it that you might enjoy.

 

[TonyTheTiger]

Are you saying that regardless of manufacturing process, all throats are equal? Or that the throat is formed during the hammer forging process, while the cut chamber has no bearing on throat life?

No, and yes, at least to the extent that it matters in the real world. A chromed or CHF throat will be tougher than a bare stainless. But regardless of toughness, it's going to be the failure point of any barrel, not the chamber. I've got 3 barrels in my basement right now that have new looking chambers and are missing 1-2" of rifling past the chamber, to the point they keyholed at 50yds.
You may be correct in theory, that a CHF chamber is the pinnacle of barrel toughness, but you'll have bigger problems than the chamber egging out before you'll ever be able to prove it.

 

[LRRPF52]

Thanks, man.

But does manufacturing process affect throat life?

For the type of barrel you’re looking for, none of this matters.

Manufacturing processes that leave tool marks in the throat will provide for failure nodes to begin earlier if they aren’t polished out. It’s fairly normal for reputable barrel makers/finishers to polish out the chamber and throat after they are tooled.

These are things I inspect before I allow a barrel to go into an upper, after I mainly check where known cartridges and ogive profiles sit relative to the lands. The biggest thing I’m looking for with a chamber is if it is short-throated and causes the projectile to jam into the lands. That’s a no-go criteria for me.

For blaster barrels, as long as the round chambers and falls out, I’m generally happy.

For DM and more accuracy-focused barrels, I only buy ones from upper-end sources, so these things are taken care of by companies that care about their reputation. I still check, but they are always squared away.

For a 14.5” CHV chrome-lined pipe, buy it, check that cartridges seat and fall free, measure you gas port diameter, properly assemble the upper, and drive on.

The questions you’re asking would be more appropriate for a manufacturer than the end-user. I have only heard positive things about Centurion, and from what limited I’ve seen of their rifles, they were hassle-free, well-built.

 

[Steel head]

No, and yes, at least to the extent that it matters in the real world. A chromed or CHF throat will be tougher than a bare stainless. But regardless of toughness, it's going to be the failure point of any barrel, not the chamber. I've got 3 barrels in my basement right now that have new looking chambers and are missing 1-2" of rifling past the chamber, to the point they keyholed at 50yds.
You may be correct in theory, that a CHF chamber is the pinnacle of barrel toughness, but you'll have bigger problems than the chamber egging out before you'll ever be able to prove it.

This
I have a few 7 saum and 260 barrels with substantial wear in the throat and a few inches of rifling missing with pristine chambers.

 

[Frank Green]

the one argument I've heard that probably has any merit regarding CHF chambers are that they are cocentric, thery are made with the same mandrel as the rest of the rifling in the same barrel, theres less tool marks that can cause sticky chambers etc.

But an educated guess leads me to believe its mostly a cost reducing measure. its cheaper to hammer it out in one go and get the required quality.
a cheap cut chamber looks like ass, a cheap chf barrel looks ok, while good barrels are good no matter the process.

Some barrels by the hammer forging process gets the chamber done and some hammer forging process from what I understand does not get the chamber done. The chamber work is done at a later time in the barrel making process.

The chamber itself I don't see it making a difference. Your not stopping the wear and tear at the throat which takes the beating from the firing.

It's also been argued that the hammer forging process will also work harden the bore and if so this can work against you in terms of barrel life.

Barrel life has to have a number put with it and an accuracy spec. given as well.

Later, Frank
Bartlein Barrels

 

[Molon]

. . . throat erosion happens as a result of "abusive" firing schedules or manufacturing defects, etc.

No. Throat erosion begins with the first round fired from the barrel and continues throughout the life of the barrel even with a mild firing pace/schedule.

I don't use my Krieger barreled AR-15s for defensive drills, so they haven't seen any "abusive" firing nor do they have "manufacturing defects" in the throat. When I even bothered to measure the throat erosion of one of them, the erosion averaged 0.004" - 0.005" per 100 rounds fired.

...

 

[MarinePMI]

Some barrels by the hammer forging process gets the chamber done and some hammer forging process from what I understand does not get the chamber done. The chamber work is done at a later time in the barrel making process.

The chamber itself I don't see it making a difference. Your not stopping the wear and tear at the throat which takes the beating from the firing.

It's also been argued that the hammer forging process will also work harden the bore and if so this can work against you in terms of barrel life.

Barrel life has to have a number put with it and an accuracy spec. given as well.

Later, Frank
Bartlein Barrels

Frank,

Perhaps you can confirm, but it was my understanding that even if the chamber was part of the hammer forging process, the chamber still needed to be cut, to "clean things up". And as such, that the chamber was hammer forged to be slightly undersize, allowing the chambering to be done quickly, and with reduced wear on the tooling. Finally, that this is also done when the desire was to have a slightly tighter bore dimension (e.g. CZ rimfire barrels) at the muzzle. Essentially a "micro swaged" barrel...

 

[Frank Green]

Frank,

Perhaps you can confirm, but it was my understanding that even if the chamber was part of the hammer forging process, the chamber still needed to be cut, to "clean things up". And as such, that the chamber was hammer forged to be slightly undersize, allowing the chambering to be done quickly, and with reduced wear on the tooling. Finally, that this is also done when the desire was to have a slightly tighter bore dimension (e.g. CZ rimfire barrels) at the muzzle. Essentially a "micro swaged" barrel...

I don't know how every place does the hammer forging process and chamber work. I don't know for example how FN does it vs Steyr or H&K etc....

If you look at the Steyr process and the Ruger process the chamber work is done towards the end of the making of the barrel.

I don't know about CZ but look at the Anschutz match rifles. That larger diameter at the muzzle end of the barrel is intentional so when the button is pulled thru the blank and they turn the o.d. but leaving more meat on the diameter at the muzzle the bore ended up tighter and or resisted opening up/going sour on you.

I getting off topic but button rifling is a cold swaging process. It doesn't remove material it displaces material. If you have any variance in the o.d. of the barrel blank when you pull the button thru it the bore size can change on your. That's why they button rifle the barrel as a blank. No shape, no contour etc...then a good maker will restress relieve the barrel blank prior to contouring the barrel but there is no guarantees on stress and what happens to the bore when they contour the blank.

 

[MarinePMI]

I don't know how every place does the hammer forging process and chamber work. I don't know for example how FN does it vs Steyr or H&K etc....

If you look at the Steyr process and the Ruger process the chamber work is done towards the end of the making of the barrel.

I don't know about CZ but look at the Anschutz match rifles. That larger diameter at the muzzle end of the barrel is intentional so when the button is pulled thru the blank and they turn the o.d. but leaving more meat on the diameter at the muzzle the bore ended up tighter and or resisted opening up/going sour on you.

I getting off topic but button rifling is a cold swaging process. It doesn't remove material it displaces material. If you have any variance in the o.d. of the barrel blank when you pull the button thru it the bore size can change on your. That's why they button rifle the barrel as a blank. No shape, no contour etc...then a good maker will restress relieve the barrel blank prior to contouring the barrel but there is no guarantees on stress and what happens to the bore when they contour the blank.

Frank,

Thanks (as always) for you comments. It is always interesting hearing your perspectives and experiences.

As to the Anschutz barrels, yes, I'm very familiar with the "Running Boar" barrels. As you said, the extra meat on the muzzle end helps prevent the muzzle bore from opening up on the button rifled barrels (though in the early 1900's they didn't fully understand why, as I recall). An added benefit (and how they got their name) was that the extra weight was believed to aid in swinging a barrel on a moving target. They have largely fallen out of favor since "Running Boar" is no longer an Olympic event (as it originally was intended). I actually have one of the Green Mountain prototype running boar barrels in 17HMR, stuffed in a safe somewhere, that were later available for time, during the early 2000's when there was a resurgence in interest of "running boar" targets with rimfires.

TBH, I had completely forgotten about it, until you mentioned them.

ETA: Not to further derail the thread, but below is a picture of what Frank was talking about (though this one was fluted for aesthetics as a one-off, though actually 5 were made this way). Come to think of it, I'm pretty sure this is one of ONLY 5 ever made with fluting. Production ones were solid, and fluting was never offered.

 

[whatsupdoc]

The HK91/G3 rifles had a hammer forged chamber, this was done allegedly to hammer flutes into
the chamber to assure case extraction.

 

[Macht]

It's certainly possible to forge a chamber, but doing so adds a lot of complexity to the process (which is why almost no one does it). When forging you target a particular % reduction in your blank, including the chamber means you have to contour the blank prior to hammering. Note that a forged chamber also doesn't guarantee a more concentric chamber. It typically involves a mandrel swap, and manufacturing tolerances still exist for the mandrels themselves. By and large, the juice isn't worth the squeeze.

 

[j-dubya]

I had started a thread a couple of years ago with a similar question, only it was based more on gas port erosion. The thread didn’t seem to take off, aside from being at the same time as when Bartlein’s new material was coming out. But the subject is still interesting to me, and may be a bit more relevant than actual chamber wear.

I am unable to actually do the test myself due to the supply and financial shortcomings around all the ammo required, but I wanted to see if we took regular stainless mk12 barrels from the premium manufacturers, and put them up against the hammer forged stainless from Daniel Defense, would there be a significant difference in life? My next replacement one will be a ModBB Bartlein, once my current non ModBB dies, but I still keep my eyes open for a Daniel Defense mk12 barrel in the classifieds.

 

[ArTeeKay]

That's what I'm working on right now, and is the reason for the thread. I never improved at anything by accepting "good enough." I now have some data points that address a question I couldn't find anyone else asking. Thanks for the info.

Don't get me wrong, I'm all for advancing the scope of understanding about what is happening during a firing event. But the law of diminishing returns applies specifically to what you're asking. You're going to gain ground on "chamber durability" much more quickly by approaching it from avenues beyond being selective about what process a manufacturer uses to form the chamber.

Something as simple as complete case obturation in the chamber should minimize "chamber erosion" to nearly nothing, by preventing gas blow back into the space between the case and the chamber. And that has much less to do with the chamber itself than it does the qualities of the brass case being fired in it, the pressure that round is fired at, the way the case is supported in the chamber by the bolt, which relies on bolt lug engagement, the geometry of the cartridge case relative to the chamber, and so on and so forth.

 

[bfoosh006]

Very educational thread... Thanks to all.

 

[Naaman]

No. Throat erosion begins with the first round fired from the barrel and continues throughout the life of the barrel even with a mild firing pace/schedule.

I don't use my Krieger barreled AR-15s for defensive drills, so they haven't seen any "abusive" firing nor do they have "manufacturing defects" in the throat. When I even bothered to measure the throat erosion of one of them, the erosion averaged 0.004" - 0.005" per 100 rounds fired.

...

This is interesting to me. Now that my question has been answered, this segues into another one.

I know nothing about machining other than incidental accumulation of facts from learning about things peripheral to machining. My first introduction to the concept of "thousandths of an inch" came when I started getting into hot rodding.

When you say 0.004" - 0.005", for 100 rounds, that seems like a lot to me. Are you talking about 5.56 in these cases (where a training session can consume 100 rounds in a few minutes), or barrels meant more for long range precision (the "barrel burners" like 6mm or 6.5cm, for example)?

 

[Mj30wilson900]

My theory about why they forged the chamber in the barrel is time savings and to get that chamber in line with the bore. With other processes the chamber reamer will follow the drilled/rifled hole. No deep hole drill will drill perfectly straight. Their is often a arc in the barrel. And the throat will be cooked. By hammer forging them together they stay inline. Wolf precision has a proprietary two piece chamber system called ace that solves this problem. You are not talking about thousands usually you are talking tenths. Go to their website to learn more.

 

[bill alexander]

The HK hammer forging process includes the chamber. The barrel is manufactured complete with chamber in a single operation. To perform this the forging mandrel includes the chamber form behind the rifling mandrel. The bored and honed blank moves over this during the forging process to create the rifling and the mandrel is moved forward in the final stages so the hammers form the steel down onto the chamber form. The process creates a near perfect concentricity and angularity between the chamber and the rifling but this is a side effect not the base intent. At HK we choke the muzzle section of the barrel. When run as heat treated and chrome lined machine gun barrel the manufacturing process creates a grain flow that follows the chamber contour and the dimensioning of the bore extends the barrel life considerably (specifically when firing heavy jacket or AP type projectiles at high rates of fire). The manufacturing process to forge in the chamber does have its own complexity and the reduction of area of the bore required to allow the chamber to be included has advantages but also some disadvantages unless extreme care is taken.

Look to the barrel alloy and the heat treatment in preference to the manufacturing method.

Chamber flutes are not forged in due to the problems with extracting the mandrel from the finished barrel. Originally they were cut on a most wonderous machine that had lots of flailing steel parts and no guards whatsoever. Today they are EDM formed.

I would observe that the new steel barrels from Bartlein are an excellent option.

 

[Frank Green]

The HK hammer forging process includes the chamber. The barrel is manufactured complete with chamber in a single operation. To perform this the forging mandrel includes the chamber form behind the rifling mandrel. The bored and honed blank moves over this during the forging process to create the rifling and the mandrel is moved forward in the final stages so the hammers form the steel down onto the chamber form. The process creates a near perfect concentricity and angularity between the chamber and the rifling but this is a side effect not the base intent. At HK we choke the muzzle section of the barrel. When run as heat treated and chrome lined machine gun barrel the manufacturing process creates a grain flow that follows the chamber contour and the dimensioning of the bore extends the barrel life considerably (specifically when firing heavy jacket or AP type projectiles at high rates of fire). The manufacturing process to forge in the chamber does have its own complexity and the reduction of area of the bore required to allow the chamber to be included has advantages but also some disadvantages unless extreme care is taken.

Look to the barrel alloy and the heat treatment in preference to the manufacturing method.

Chamber flutes are not forged in due to the problems with extracting the mandrel from the finished barrel. Originally they were cut on a most wonderous machine that had lots of flailing steel parts and no guards whatsoever. Today they are EDM formed.

I would observe that the new steel barrels from Bartlein are an excellent option.

Awesome Bill!

Thanks for chiming in!

Later, Frank
Bartlein Barrels

 

[Caflashbob]

Awesome Bill!

Thanks for chiming in!

Later, Frank
Bartlein Barrels

 

[thehun]

Why would this matter? I cannot imagine the grain structure being added to the chamber making any difference?

It matters for concentricity to the bore ... many "cheap" CHF barrels will have a hammer-forged bore but then they cut the chamber after the fact ... DD does hammer forging like HK ...

That said ... a properly made button/cut barrels are great barrels too ...

Cheap QC barrels produced by either method will yield subpar results ...

 

[DeathBeforeDismount]

When you were in school maybe a teacher told you there were no such thing as dumb questions. This thread proves that is a lie.