I saw a conversation between Jim Sullivan and Ian from Forgotten Weapons where Jim Sullivan said the AR10 was never as reliable as the AR15 and they couldn't figure out why.

I was having this conversation with another engineer in the industry who said, "Look at the cam pin paths.  They're the same length basically, which creates all sorts of timing problems for unlocking and carrier movement, looking at bore ratios."

So I pulled out my DPMS BCG from my .260 Rem upper, and measured the length of the cam pin path.

.675"

AR15 cam pin path:

.650"

You're getting a lot more gas volume at the port, flowing back through the temporarily closed system, which then starts inertia on the carrier more violently than the AR15 could ever hope to do.

This is why I really like what I've seen from Daniel Defense with their DDV5V1, which has an elongated cam pin path and their approach to retaining the extractor pin due to increased telescoping length of the BCG.

They don't show it in their photos on their site, with only right side views, but they might have cracked the code for reliability on this system with that approach.  I understand they spent 2 years testing the guns, with boat loads of ammunition.

But there are no free lunches either.  By elongating the cam pin path, you create more time for the carrier to get moving without any resistance other than the gas rings and carrier rails, before hitting the cam path angle cut.

Now you have a huge chunk of steel flying rearward against the require spring tension to tame such a beast, and once that spring compresses to the design limit, the bumper pad on the buffer impacts the rear of the RET, and it switches to forward momentum, that energy is more than one with a shorter cam pin path, all things equal.

Now that carrier slams on the bolt catch with every magazine that you run empty, and the bolt catch takes a beating that is hard to overcome, resulting in broken catches.

This is already a known issue in the AR10 world that every serious maker has dealt with, and is even more pronounced when you suppress.  The DDV5V1 has already suffered several broken bolt catches as a result.

You then wonder about reducing the carrier weight and how to tame the inertia with a lighter carrier, without springing too hard.  It's a spiraling set of challenges where for every solution, another problem is magnified.

From an engineering standpoint, the AR10 and AR15 are very different systems looking at the bore space, cam pin paths, carrier inertia, and reciprocating masses.  In some minds, it might as well be an entirely different design.

Without changing pressure, since the gas tube/carrier key diameter is the same between the two (right?), won't the volume be the same, everything else being equal?

I can't find anything I'd consider authoritative, but the one chart I can find shows pressure dropping faster with the .308 than .223 at almost any barrel length, and apparently they tend to start out at about the same pressure.

LR I am always amazed at the quality of the content you post.

I have been studying problems in the AR-10 platform myself, but not near the extent or with the technical expertise you employ.

I have been looking at problems with unlock timing on a customer's 6.5 Creedmoor. His barrel extension was improperly installed (slightly rotated) and I believe it is allowing the bolt to unlock early.

Anyway, all to say that timing is quite important on these high pressure semis. Thanks again for bringing to this to our attention.

You have way more volume from a case that is charged with 44 grains of powder, versus one that is charged with 24 grains, both starting at similar peak pressures.

Even if the pressure is the same at the gas port, the volume is totally different, and the projectile weight is 3x as much with the .308.

If you tried to even move the carrier with 5.56 loaded into an AR10, I wonder if the carrier would even budge.

There is a lot more mass and way more spring rate on the AR10.

Another problem to overcome that does not exist in a bolt gun is that you have pressure against the bolt face while trying to unlock.

That pressure translates to the bolt lugs against the barrel extension, with some shear forces that just aren't there on a bolt gun.

It's one reason why you start to have issues in suppressed self-loaders with rotating bolts, that won't show up unsuppressed.

It isn't me.  I've been racking my brain for years wondering why 2 systems that appear to be the same design, experience noticeably different reliability.

The cam pin path lengths were pointed out to me by one of the most gifted engineers in this industry who has many NRA award-winning, rifle-of-the-year designs under his belt.

I never thought to look at the cam pin path length, even though I have been wanting to elongate it like DD has done on theirs, which brings its own series of problems too like the G36 and SCAR have.

The more I look at it, the more I want to move away from rotating bolts.

Well, sort of.



The solution, and I think the one DD uses, is to reduce angle of the cam helix.

The AR and .308 ARs bolt use a 45 degree cam helix with .070" free travel before the cam pin hits the cam path.  The additional length you measured is due to the larger diameter cam pin and larger diameter carrier.

If you use the same .070" free travel but use a shallower cam helix, say 40 degrees, the bolt has the same velocity when it enters the cam path, but takes about .030" longer the rotate the required 22.5 degrees the unlock the bolt, net result: slower unlocking and no additional bolt velocity.

There is a reason the M60 GPMG uses a 5 degrees cam helix (approximately) for the first 1/2 inch of carrier travel...

With an AR you are, however, limited in the cam helix by the distance from the front of the carrier to the gas key and the length of the bolt.

Another problem is trying to use AR-15 parts in a bigger gun.  A different carrier key and gas tube would have allowed for the shallower cam helix.  Similarly a larger receiver extension would have allowed a larger diameter spring and a heavier carrier....

My Armalite has been 100% reliable which is much better than he M1A, FAL, or PTR-91 I owned before.

The original AR10s of course had a larger diameter extension tube, spring, and buffer.

I think it was Saber Defence who had made a modern AR10 with the original extension tube diameter, carrier design, and had Magpul even make a PRS for them.  I handled that rifle in a backroom at SHOT many years ago before the ATF went after them, very interesting gun.

That's what I assumed with the cam pin diameter, that it accounted for the additional length between the DPMS LR-308 BCG and an AR15 BCG, since the cam pins are totally different diameters.

Thanks for the input.

It makes me wonder about the current direction of the market going with lighter carriers in smaller receivers, while chambering in .308 Winchester and 6.5 Creedmoor more and more.

The Colt 901, DPMS GII, Mega SF-MATEN, and now the Savage MSR-10 all use smaller carriers, with either a single fastener on the carrier key like Colt, or shorter towers for the gas key like DPMS and Savage have done, with a pinned tube key in the tower rather than a traditional AR15 carrier key.

Jim Sullivan said something about the AR10 needing a longer carrier key, which would probably help reduce clipping.

Thanks for your input.  I always look forward to your posts.

The "real" AR-10s used a 45° cam helix.  In fact, all the the Armalite/Stoner designs use a 45° cam helix.  They didn't show much imagination in that area.  But, you can see the key is longer. (To be fair, most people use a 45° cam helix - M1/M14s and AKs to name a few)



Some examples of full power designs with a shallower cam angle:



Incidentally, if you make the bolt carrier/operating rod about 10X the weight of the bolt, you get a nice gentle cycle.  The high carrier-to-bolt weight allows the carrier to have a much lower velocity, yet maintain enough momentum to reliably unlock the bolt and complete the operational cycle.  In the AR-type stuff that's the weight of the carrier and buffer.  A lot of .308 ARs would probably benefit from a heavier buffer, especially those with collapsible stock receiver extensions.

In my experience the 308 platform is far less forgiving than the AR15.  It can be tough finding that balance point with gas and recoil mass.

THE Farichild-Armalite AR10 is as reliable or more than any AR15. The ar15 is a bastard, a downsized version of the real AR10 with stolen developments from Artillerie Inrichtingen. Its reliability is due to the low power small bore ammo, the bolt can still pull a pressurized cartridge out of the chamber. What passes for AR10s today are clones of the double bastard sr25 of which the main marketing principle was to use as many off the shelf parts from the ar15 to try to win US military contracts. A novel idea gone bad. Todays guns are over gassed with no regulators, so to compensate double ejectors and o-rings are employed torturing brass, reciprocating weights are crazy heavy slamming a two pound weight back and forth with every shot. What do we know about a compromise, it doesn't do anything well.

What size is the gas tube does the DD 308 use?

I've been wondering how well a fatty or pigtail gastube would work on a 308. Like the ones PRI made awhile back for suppressors and what not.

That coupled with the longer cam path, different gas key, etc etc.

There's alot left to be desired in the AR10. We're getting closer each year. So, maybe by 2055? 100 years should do it right....

I have or have had an Armalite AR10, Bushmaster BAR10, Colt 901, Ruger SR762, and the Windham Weaponry SRC308.  The SR762 and SRC308 had new gun problems that were quickly remedied by the manufacturer.  Once that was done, I can honestly say I have not had any problems from any of my 308 ARs.

Bought my ar10 15+ years ago.

Except for an improperly heat treated bolt release, it has not had any problems.  1000s of rounds through it, including 147gr ball and my 168/175 gr match hand loads.

I still use the m1a mag conversion as well.

Txl

Not the ones I have seen.

I've seen failure to feed on the last round in the magazine with real AR10s, the Dutch kind, which are superb specimens of manufacturing.

Why would one of the design team drafters from Fairchild ArmaLite say they had reliability problems with the AR10, having more experience with them in volume and sample sizes than anyone else alive outside of the Dutch?

I have owned:

Eagle Arms/ArmaLite AR-10T 24"
DPMS LR-308
DPMS Receivers/BCG/LPK GA Precision-built .308 with Obermeyer
DPMS LR-260
Another GAP-built .260 Rem Bartlein barrel

Have shot and worked on:

SR25s
Home builds of various sorts using high quality components

The Eagle/ArmaLite was reliable, but not shot on a high volume schedule.  ArmaLites I have seen in use and shot overseas seem to have been very reliable, with one exception being broken bolt catches, especially on suppressed guns.

The later SR25E2 ACCs and rifles have been accurate and reliable when fed a strict diet of 175gr SMK or 178gr BTHP.  Some lighter loads will short-stroke them, like 155gr AMAX.

The DPMS LR-308 bent the extractor within the first few rounds, and seemed to use a bolt gun match chamber in tightness.  Needed to be re-reamed, new extractor.

The DPMS LR-260 needed the chamber polished and only fed reduced hand loads.

My GAP LR-260 has been reliable, but has eaten at least 3 firing pin retaining pins.

I have yet to see a home build that is reliable until I worked on it and replaced components, tuned some things.

But these are all anecdotes.  When you look at fleet samples, you get a better idea of what is going on, and one of the biggest fleets is the M110 in the Army, which has had a lot of problems.

ETA- Sorry wrong quote^^^

My experience is a little different. I will give you the last round FTF, that's why the DMPS mags are 19s, a modern spring will fix it or just load 19. The same occurs on the AR15 20s in fact 16 was the magic number to keep from compressing the spring completely when troops carried them loaded for an extended period. I've only fired 4 real ar10s and I own a converted Specialty Arms and when shooting them there weren't any kind of problems. I have a Guatemalan, Portuguese, and Sudanese upper for my rifle all work flawlessly, thousands of rounds, semi, and auto even a match or two. The real BCG is a 100gm lighter than an Arma-Il the buffer is 50. The original buffer spring is larger and heavier, the adaptation just does not work as well with a full mag and a two pound bcg and buffer. There are none of the over gassing problems I had with my Arma-ILs. Even with the low production numbers, ~10k with prototypes and samples, thousands of AI AR10s saw combat in jungles and deserts of colonial Africa. I'd stake my life on mine. It is the rifle the US should have adopted, if only...
Obligatory File Footage

The PSA I built is a hammer, I've shot a couple mid range matches with it, the first version SMK Palma bullets really fly well from it but I've only ever single loaded it.

LRRPF52

interesting thread, you make mention of DD cracking code for reliability in regards to large frame AR's.  what are you thoughts on where the KAC and LMT 308's are in terms of reliability in light of what DD has done.  KAC has always tuned their guns to run on a specific load(M118LR) where as LMT which shares DNA tunes their to run on everything.

I think that the SR25 post 110 are great rifles

I really like DD,  would of liked to see how their 308 would of done in the CSASS

DD increased the time the bolt stays locked, but carrier speed increased.

No matter how I look at it, I keep coming back to the main challenge at the heart of it all:

.308 case size, working pressure, and the amount of propellant volume it has, with the projectile weights it has, combined with a rotating bolt.

It's not as easy at it seems.

well I am not sure of the answer either but what I think most importantly when asking the question about large frame to small frame reliability is that the DoD has been testing the small frame AR since the 60's there is a metric shit tone of test data on the platform. high speed film, NDT, physical test, erosion, dispersion, reliably, ect... the sheer volume data has allowed the industry to turn the m16 into a monster in terms of reliability.

shit in the last 10 years, we had, the original carbine test, M4PiP, the IC, M4a1, 855a1,mk18, m16A4, silencer, and probably about a dozen I am forgetting. after each test, vendors take that data, and make improvements

the large frame AR or SR25 has really never had the wide spread testing that has occurred with the m16/m4 series. Yeah the Navy had some sr25's/mk11's in the late 1980's early 1990's but never really went DoD wide until 9/11 happened and the DoD jumped on the m110. they kind of accepted it, and ran it ragged till the csass came out, ran that for two phase of testing, did the down select and decided after about 3 weeks of testing, fuck it, just go with the HK because "that's what the troops like".

the lack of sheer testing data has not allowed the industry to get the large frame AR to where the small frame AR is with reliability,

its the reason its takes about 5 minutes to find MRBF/MRBS data for the m4 but its pretty hard to track that down for a large frame AR.  that's why its somewhat difficult to gauge how exactly where the large frame AR is in terms of reliability compared to its small frame brother.

is the M4 more reliable than the SR25, yup, how much, I have no fucking clue, I personally would love to see a test on large frame AR's


regardless always enjoy reading your post

Hey LRRP...I believe it was you and/or others comment about the Armalite AR10 and their buffer/BCG setup that leads to their relative reliability.  Is that the case that there's actually some difference or just perceived legend?  While I have a pair of B-models that I cannot complain about at all...except weight...I'm not necessarily an Armalite fanboi or such.

I wonder about why some other .308 semiauto platforms are so picky and tempermental...Kel-Tec RFB, other .308 AR's, etc.  Your observations in the 3rd line of your post here have definite credence IMO.  I also wonder if the delay with the MDR bullpup might be related to the .308 platform presenting some challenges...especially since it appears they're trying to go .223 and .308 off of the same basic chassis...which seems like a tough hurdle to me.

Not a semi auto but...
We don't need no stinking pesky gas system

Never mind.

Perhaps the problem companies could get with the ones that don't seem to have problems.

why would you help improve your competition?

----

PS - great thread

You don't.  But there are companies that don't seem to have reliability problems.  That would seem to indicate there isn't an engineering problem.  Only a some companies do it better than others problem.

Awesome thread LRRP!!!  ...and people wonder why we don't recommend home building without a good working knowledge of the platform.

I do love my AR-10s but I am really drifting back to the AR-15 and the Steyr AUG......I've pushed my luck with the .308 platform pretty darn far and I have learned a lot, particularly with the help of several of you guys in here like LRRP and Ranger 556.....

For what ballistic advantages you gain by going to 7.62, there are soooo damn many technical hurdles that the entire concept begins to become effectively hobbled by the law of diminishing returns.

Good read guys, learned something today.

Does this mean the M-1 Garand is the bumblebee of the semi-auto rifle world?

Agree....

I don't think there's really been a whole lot done to improve reliability in the 7.62-sized AR.

I've settled on at least a standard-length M16 gas tube (nominally within a half-inch of the Armalite's) but with a heavy buffer.  I don't like adding weight to an infantryman's weapon or load but it seems to work a happy medium with a 16 to 20-inch barrel.

Dave Tubb dabbled with an SR-25 in 260 Remington (6.5-08) and found he needed two more inches of gas tube length for the happy place to keep the bolt locked, save brass, and keep consistent functioning without excessive movement off target (especially for controlled rapid fire).  Take a look at the 30-06 M1 rifle and compare the distance from bolt face to gas port compared to an early DPMS AP-4 with a 7-inch gas tube.

With an M16-length gas tube the bolt carrier would certainly benefit from a longer cam track to delay unlocking.  With movement to longer fore-end lengths you can certainly place the gas port out further (a la Garand) with the benefit of lower gas port pressure and delayed carrier movement perhaps without the need for a heavier buffer.  The Garand's op rod weight replaces the weight of the AR bolt carrier and buffer -- and is quite a massive body for the gas bleed to move.  The Garand bolt isn't that much bigger or heavier than an AR-10's.

The M1/M14 cam track angle isn't drastically different than an AR's (though it might be smoother without a dogleg angle change):



The beauty of the AR is the low co-axial recoil impulse and the simplicity of the system simply reciprocating back-and-forth in its tubular receiver.  It doesn't suffer some of the technical challenges the M1 and M14 have with op rods.

back during the 1994-2004 AWB, the magazine issue really stifled AR10 development

I remember Bushmaster was working on a fal mag lower and the Armalite conversions from M14 mags were the standard


October 2, 2000

TECHNICAL NOTE 19: MODIFICATION OF M-14 RIFLE MAGAZINES FOR USE IN ARMALITE AR-10B SERIES RIFLES

The AR-10B magazine is based on the proven magazine of the M-14/MlA Rifle.   It is limited to 10 round capacity due to the 1994 Crime Bill.  A good quality metal 20 round M-14/MlA magazine can be modified to function perfectly in the AR-10B.   U.S. G.I. and recently imported Chinese magazines are acceptable. Commercial metal magazines with pressed latch plates and
fiberglass magazines are not usable.  The AR-10B magazine, and modified M-14 magazines, will not work in either AR-10 or AR-10A rifles, or in the SR-25 rifle.   Magazines for those rifles will not work in AR-10B series rifles.

ArmaLite will provide a Modified, refinished, and gaged 20 round magazine in exchange for two 20 round G.I. or Chinese magazines, or for one 20 round magazine and a fee of $30.00. Rusty, dented, or pitted magazines are not acceptable for this program. 

New 10 round magazines are available from ArmaLite for $30.00 each. "Post-ban" 20 round magazines are available to government and export purchasers. 

Many M14 magazines, including G.I. magazines, were produced oversize.  Before forwarding magazines for exchange, customers must verify that they will fit the AR-10B magazine well. A $10.00 per magazine charge will be added for unpacking and depreserving magazines coated with greased interiors or exteriors. 

Because of limitations of the 1994 Crime Bill, the AR-10 magazine follower is produced to prevent more than 10 rounds from fitting in the AR-10B magazine.  This results in a tight fit.  Some converted 20 round magazines will accept only 19 shots after conversion. 

Customers who wish to modify and retain their own magazines may do so with the Magazine Conversion Kit available from ArmaLite for $30.00.  We strongly recommend that customers retain their old magazine shells to prove that their magazine is legal.   Doing so makes the conversion reversible, allowing the customer to return their magazine to M14/M1A configuration. 

ArmaLite does not recommend that customers attempt to machine their M-14 magazines to convert them to AR-10 magazines due to the critical nature of the task.

Given the prominence of broken bolt catches, I wonder if there would be any negative repercussions to the lower from using a tool steel material designed to take impact.

Would stop broken catches, but I'd worry about cracked lowers then. That makes me think of suspension components in cars. In the event of am impact, the suspension parts bend/break first before damaging the frame. So, strengthening the suspension makes it stronger, yes, but then you risk damaging more critical components in the event of fatigue/stress/whatever.

I'm not an engineer, and only understand the basics when it comes to physics. But I've thought about that as well, why not use stronger material? I keep thinking is just a cost/return issue keeping them from investing in it.

Interesting read and it does make sense. I have had 4 Armalites over the years since 99 or 2000. My oldest was made around 04 since the older ones had been sold or traded. My 04 T has been shot suppressed about 95% or more and it has close to 5800 rounds on it, the bolt catch has never been changed. I'mean going to pull it and inspect it now because of this thread. I wonder what the approximate round count is when they start to fail? I just order a few has back ups yesterday.

Weird double tap due to signal issues.

M1 Garands have always had reliability issues, despite the mythical status a lot of people associate with them.

Initial test and evaluation reports on the rifle from the USMC reads like a Mini-14 experience with Pro Mags.

Extreme cold conditions in Europe saw all sorts of failures with the Garand, to include seized working parts and broken op rods.  I see it more as an experimental mechanical representation of the late 1920s, early 1930s thinking at best.  It definitely was an achievement that pushed small arms development forward, but is not a highly reliable rifle, especially in real conditions.

The problems we have seen are peening on the bottom bolt lugs when the catch is hardened.  For every fix, there is something that bites you that has to be addressed, and it starts to spiral out of control, like the HK416 with the current A5 model using a basket to protect the disconnector tail from hammer slap.

Why does it have hammer slap?

Because the piston powers up from immediate gas impulse, and instantaneously begins rearward movement of the carrier, which sends the hammer flying down beyond its deigned cocking travel angle, and bashes into the disconnector.

You end up making a think to fix the thing, when the core problem is the operating system.

I hadn't considered bolt lug peening.

I knew about the 416 issue.  My understanding is they also used a lower weight hammer spring in the M27 to meet lowered pull weight requirements compounding the issue.  Should have redesigned to a two stage to meet pull weight IMO.

Very interesting, good information.
LRRPF52, Could you tell me more about the M110s problems that Army are having?

The problems they were having can be seen if you look at the current rifles, the carriers' bearing surfaces were slotted to promote self cleaning, a second ejector was added to the bolt, the evection port length was increased to about the same length at the original AR10.

Thats simply not true and and a gross misrepresentation of quite a few thingd.  When at a computer, ill respond in full as the phone makes it hard.

"Initial reports"?  As in: before the design was finalized?  As in: testing of prototypes?

I have often heard of all these derogatory reports on the M1 Garand, but nobody has ever provided a link or scanned copy to put there money where their mouth is.

(And, the only "report" I have actually seen was a magazine article that allured to a USMC report that was a comparison of an M1 against the M1903, not surprising which one was judged "more reliable"....)

I do have a few reports that contradict your accretion that the M1 Garand was problematic in cold weather:

You only need to look at the fact that the bolt is exposed almost totally, with easy access of debris to the camming parts, let alone the gas system on the M1 Garand.

It's one of the worst ways to approach gas operation, and problems with the system led them to look at re-designs, eventually leading to the M14, which is also unreliable.

Get beach sand barely on a Garand or M14, and watch what happens.

Cold weather and some dirt?  Malf-o-matic.

But then people will conflate "We won the war with M1 Garands, the greatest battle instrument of all time.  Even Patton said so."

Rifle fire did not win World War II.  That's a simplistic, easy-to-digest view for civilians at home trying to understand and relate to something very complex.

The Garand will run fine on clean rifle ranges, fed a steady diet of loads tuned for the system, but it will fail in field conditions a heck of a lot more than an AR15 ever will.

I'm hardly an expert on the M1 Garand, but I do like history.  On the cold weather performance, especially in some of the Korean battles, the problem appeared to be lubricant related rather than rifle design.  In fact it's pretty well documented from many of the participants that they completely removed as much grease and/or oil in most cases that resulted in the rifles being totally reliable.  That increased wear, but it kind of shows how tough and reliable the weapon could be even without lube.  It appears the grease and lubes of the day and the knowledge of how to use them wasn't as developed as it is today...no real surprise there.  

Mud, crud, and debris in enough quantity may have been another matter in fouling the cycling, but I'm not seeing extremely cold weather being the problem as much as the right lubricant for the conditions.  Back then it was also a 30.06 caliber which may add another layer of difference in comparison.

LR,

I appreciate your post, and have 1 thought to add.
I've always felt that the AR10 would benefit from a pigtail gas tube for several reasons. The dwell time of the gas is longer (and it's losing energy over time and distance), and the impulse imparted to the BCG is longer in duration (with a lower peak pressure) compared to a straight tube.

I'm experimenting with this in a 300 RAUM I'm building with a bi-metalic barrel (aluminum sleeved over steel). Unfortunately I'm in the process of moving to Guam so my project has to be on hold for a few months while I establish a new Bat Cave over there.

I've always wondered why the AR10 didn't have a coiled gas tube (I make them myself with brake tubing from AutoZone).

It's not the cure-all for the AR10, but it makes better sense than a straight tube.

G.

A coiled gas tube fixes a high-pressure problem at the port.  If the port was further out you don't risk damage to an exposed tube.  A longer (thin) tube gives you another potential point of failure.  

Another try to fix the high gas pressure besides a pig-tail was a tube with a relatively large expansion chamber -- but you risk failure where the tube enters and exits the chamber, and you have to tailor it so sufficient gas gets the carrier moving before the bullet uncorks from the muzzle.  The LaFrance twin-tube was yet another stab at a fix.

The pigtail gas tube does more than deal with the pressure of the gas at the barrel port; it changes the travel time (to a meaningful extent) for the impulse of the gas to hit the gas key.
The reason I'm playing with it on the 300 RAUM is to allow chamber pressures to fall off slightly before the bolt unlocks.

As I mentioned, it's not a theoretical change in travel time, it has real-time effects on the forces at play in cycling the action.

I think you'd be better off moving the port further down the barrel.

Especially for a 300 SAUM.

I'm using a rifle length gas system for the 300 RSAUM. No reason to go longer than that.

I've added the pigtail in to allow chamber pressures to fall off prior to bolt opening. Works pretty well.
What I haven't experimented with yet is the bi-metallic barrel. 1 inch outside diameter aluminum sleeve. Steel barrel is 1/16" thick (wall thickness) in front of chamber.

Unlike the carbon fiber sleeved barrels the aluminum carries off the heat quickly, while maintaining stiffness. What I want to see how it works is for strings of 10 or more shots.