View Full Version : Benefits of the pencil barrel?
The thread on the HK G36 using pencil barrel as (supposedly) the major issue behind very poor accuracy of the rifle once it gets hot, which is supposedly a known issue of pencil barrels, got me to thinking what the pros of a pencil barrel are. I'm assuming the basic mechanism is, the thin barrel gets hot, which makes it flex, and you get a whipping effect of the barrel and accuracy goes to chit.
The obvious pros are a savings in weight and savings in costs to the manufacturer. As always, there's a trade off to any choices made in a design and a risk/benefit assessment made.
It would seem in a primary mil rifle as the G36, that con far outweighs the pro, unless there's some other benefits of the pencil barrel I'm not aware of. HK is not known for intentionally short changing a design to save a few $$$ (if my assessment of that is correct that it does save on costs some place) and most troops are more than willing to lug the extra weight from the added weight of a barrel that does not give minute of mini van once heated.
What am I missing?
I thought the issue with the G36 was a plastic trunnion, but having never picked one apart I can't say for sure. Weight savings on a pencil barrel is pretty dramatic on longer barrels. Looking back at most military rifles of late 20th century, one can see the trend of lighter barrels. Even new contenders like the SCAR are sporting pencil barrels.
Edit: the trunnion itself is steel, but it sits in a polymer cradle with no other metal support. This is what is likely causing issues.
Depending on what the initial OD of the barrel blanks you're using is, the production costs could actually be a higher. More wasted material and more machine time.....
Advantages really depends on the purpose of the barrel. Precision and sustainable fire and longer service life with consistent use aren't a pencils strong points. A quick handling carbine that's easy to carry and won't be seeing high rates of fire often are. Police and civilians are likely to get the most use out of one. Military with higher rates of fire may not need an Hbar or even a medcon but something between a lw and a medcon is probably minimum at least for them.
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Can't comment on the G36, but my SP1 carbine shot about 1MOA if I was doing my part. That was a really light and handy carbine. I remember the first M4 profile barrel I got I was like WTF?!? because it was so much heavier and out of balance (front heavy).
I always wondered which was more accurate, a SP1 20" barrel rifle or a M4 16" carbine? The rifle in question would be a lot lighter.
Now when it comes to suppressors, I can see where a pencil barrel might not be the best platform.
I cant imagine any downside to pencil barrel when compared to the thin then thick M4 govt profile barrels - particularly now with long FF rails covering the whole BBl like on a 14.5....
BTW I have heard of G36 accuracy issues since at least 2006 from a couple guys I talked with from Fairfax VA county swat team - they were not fans and had recently switched to 416s because of those issues.
Advantages really depends on the purpose of the barrel. Precision and sustainable fire and longer service life with consistent use aren't a pencils strong points. A quick handling carbine that's easy to carry and won't be seeing high rates of fire often are. Police and civilians are likely to get the most use out of one. Military with higher rates of fire may not need an Hbar or even a medcon but something between a lw and a medcon is probably minimum at least for them.
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Which is the intent and design of the G36 no? That was it's primary role I had thought.
Can't comment on the G36, but my SP1 carbine shot about 1MOA if I was doing my part. That was a really light and handy carbine. I remember the first M4 profile barrel I got I was like WTF?!? because it was so much heavier and out of balance (front heavy).
I always wondered which was more accurate, a SP1 20" barrel rifle or a M4 16" carbine? The rifle in question would be a lot lighter.
Now when it comes to suppressors, I can see where a pencil barrel might not be the best platform.
It appears the G36 is too, until it gets hot. How hot, I'm not clear. That appears where the trouble starts.
Business_Casual
04-16-15, 19:04
It appears the G36 is too, until it gets hot. How hot, I'm not clear. That appears where the trouble starts.
Wouldn't crew-served and heavier weapons do most of the killing, while rifle fire is primarily to pin your adversary in place while the aforementioned booms are organized?
Wouldn't crew-served and heavier weapons do most of the killing, while rifle fire is primarily to pin your adversary in place while the aforementioned booms are organized?
A bit above my pay grade. You'd have to direct that at the BTDT mil members here. It would seem me, there's plenty of times where that rifle is the primary weapon troops have and it's spitting bullets and getting damn hot.
Business_Casual
04-16-15, 19:32
Well, my point is kind of more that individual accuracy is hardly the measure if 119 rifles are all shooting at where the green dot is being painted...
Which is the intent and design of the G36 no? That was it's primary role I had thought.
Montrala pointed out in another thread that the German army had some pretty particular weight goals and that the German army version varies from export versions due to this.
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G36 w/ hot barrel & POLYMER chassis doesn't do so well. The whole barrel assembly moves around when it's very hot. Pencil profile barrel heats up faster (less material to disperse the heat soak) and makes this issue more noticeable.
The thread on the HK G36 using pencil barrel as (supposedly) the major issue behind very poor accuracy of the rifle once it gets hot, which is supposedly a known issue of pencil barrels, got me to thinking what the pros of a pencil barrel are. I'm assuming the basic mechanism is, the thin barrel gets hot, which makes it flex, and you get a whipping effect of the barrel and accuracy goes to chit.
The obvious pros are a savings in weight and savings in costs to the manufacturer. As always, there's a trade off to any choices made in a design and a risk/benefit assessment made.
It would seem in a primary mil rifle as the G36, that con far outweighs the pro, unless there's some other benefits of the pencil barrel I'm not aware of. HK is not known for intentionally short changing a design to save a few $$$ (if my assessment of that is correct that it does save on costs some place) and most troops are more than willing to lug the extra weight from the added weight of a barrel that does not give minute of mini van once heated.
What am I missing?
Remember that on an M4, the lightweight contour and M4 contour are the same under the handguards. Only the FSB and front portion is smaller on a lightweight, areas that see less heat, pressure and stress than the areas under the handguard.
Now on a Mk-12 barrel or SOCOM barrel, there is much more material under the handguards.
I prefer a barrel with some heft to it for all the reasons stated above. It also builds muscle as well as character.
The Dumb Gun Collector
04-16-15, 21:44
I know my Steyr Scout would open up pretty fast with its super lightweight barrel. More of an academic issue in a bolt gun.
It appears the G36 is too, until it gets hot. How hot, I'm not clear. That appears where the trouble starts.
Seems the G36 has a lot of issues when it gets hot or otherwise is subjected to high rates of fire. Not sure the barrel is to blame for those problems or not.
Moose-Knuckle
04-17-15, 03:22
IIRC the M16A2 got a HB due to the fact that Joes in the field bent barrels using them as pry bars busting steel bands off of ammo pallets, NOT because of accuracy. Urban legend or is there any truth to it?
IIRC the M16A2 got a HB due to the fact that Joes in the field bent barrels using them as pry bars busting steel bands off of ammo pallets, NOT because of accuracy. Urban legend or is there any truth to it?
Probably urban legend. The A2 is only heavy profile forward of the handguards. Only the HBar is a full length heavy barrel. The Colt semi that is a copy of the A2 is called a Government profile barrel.
That said, I'm sure a lot of guys have screwed up rifles using them for stupid things. Pretty sure even if you gave them a full Hbar, they could still screw it up doing stupid things.
My understanding is the change to the A2 was more about mounting a M203 than anything else.
Moose-Knuckle
04-18-15, 00:03
Probably urban legend. The A2 is only heavy profile forward of the handguards. Only the HBar is a full length heavy barrel. The Colt semi that is a copy of the A2 is called a Government profile barrel.
That said, I'm sure a lot of guys have screwed up rifles using them for stupid things. Pretty sure even if you gave them a full Hbar, they could still screw it up doing stupid things.
My understanding is the change to the A2 was more about mounting a M203 than anything else.
Ah hah, I forgot that the A2 didn't have an HB but the Government profile barrel.
BrigandTwoFour
04-18-15, 10:12
IIRC the M16A2 got a HB due to the fact that Joes in the field bent barrels using them as pry bars busting steel bands off of ammo pallets, NOT because of accuracy. Urban legend or is there any truth to it?
FWIW, this was posted on TOS several years ago. Sounds legit, especially given my experiences with military procurement.
Since The M16A2 Product Improvement Program (1980-1983) was my program, this is the down & dirty on the barrel thickness issue.
We (Marines) were replacing a lot of "bent" barrels that were determined to be "bent" because the Armorer's Bore Drop Gauge would not freely pass through some barrels during Ordnance Inspections (LTI's). So the Logisitcs people had "Barrels Bending" on their list of "M16A1" things to "Improve" right after listing "Handguards Breaking."
We "experts" thought this bending was from rough handling like during bayonet drills, etc., as an absence of any mid-barrel handguard damage in these rifles made one assume the fulcrum of such bending was the bayonet lug. So we made that part of the barel thicker because we did not want the excess weight of a full length heavy barrel. In testing using the bayonet lug as a fulcrum, and applying calibrated mechanical pressure to the muzzle, the new barrel was about 9 times more resistant to bend and take a set than an M16A1 profile. So we went with this "improvement."
However, soon after I started using a bore scope with a video recorder and monitor to inspect "bent" barrels. What I found was a mound of bullet jacket material at their gas ports. This build up was caused by a burr left from drilling/reaming the gas port. This was where the Armorer's Drop Gauge was geting stuck. When we removed this "mound", the barrels would all pass the Drop Gauge. We let Colt know what we had deduced, and that is one reason they kept models of "A2's" in their line-up with A1 profile barrels. However, the A2 profile was already down the road for the US Military. So about the only advantage of the A2 profile was to give the rifle a little more muzzle hang. This was noted by most all the Operational Test paticipants, especially when they fired the standing/off-hand leg of our rifle qualification course.
So my advice to mlitary armorers is to never replace a bent barrel until you visually check the gas port, or at least scrub the hell out of the gas port area with a new bore brush and an electric drill. And thank God for chrome bores!
I've heard it directly from at least one credible vet who was there in 1970, so either he saw it or knew people who did.
IIRC the M16A2 got a HB due to the fact that Joes in the field bent barrels using them as pry bars busting steel bands off of ammo pallets, NOT because of accuracy. Urban legend or is there any truth to it?
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