A2 GOVT profile or HBAR profile? 20" length?


Thanks

CRC

An AR out of the box with whatever barrel it has is accurate enough as is, a heavy barrel more so but it's...well..heavy.  After playing with one for a while you'd think twice about lugging it around for general use, unless you flute it to shave off some weight.

I stand corrected, as usual [:I]  Should have been more specific.

I've recently got off the HBAR Bandwagon. I still have them but I'm leaning LW myself at the moment.

MM419

Thanks guys.

CRC

I have a light weight barrel in 14.5 inch configuration, it is a cold hammer forged Diemaco C8.  The skinny profile does not to deter accuracy, I shoot paper using Q3131 USA ammo and getting 1MOA easy every time.  Heavy barrel will stay cool longer but will take longer to cool.  The heavy barrel will heat up just as fast if you dump two 30 round mags out of it quick.  

Heat absorption and heat dissapation have been delt with numberouse times on this board and people fail to get it.  Each round expends and transfers a certian amount of energy into the barrel.  The more massive the barrel the more energy it can store without becoming hot.  This is because heat is a function of energy and mass.

Here is an example using made up numbers:

Say one round gives off 10 joules of energy and it takes 1 joule of energy to raise the temperatute of one ounce of barrel steel 1 degree farhernheit.



If you have a 10oz barrel and you fire 10 rounds the temperature of the barrel will raise 10 degrees.

If you have a 20oz barrel and you fire ten rounds (in the same amount of time) the barrel
temperatute will raise 5 degrees.

So SMGLee you are wrong when you say both a heavy and a light barrel will be the same temp after a 30 round mag dump.

Also barrel cooling is a function of its surrface area and a heavey barrel has more surface arrea.  Therefore it will cool faster.

If you have a heavey and a light barrel fired the same number of times the heavey barrel will heat up less and dissapate heat faster.

The only reason it might seem like an HBar cools slower is because if it is heated to the same temperature as a light barrel it has acctualy been shoot more times and has stored more energy.   In this case it will take the heavey barrel longer to cool because it has had more rounds put through it and has more energy to dissapate.

Having said that I do agree that it is hard to imagine a light barrel getting too hot from semiautonatic fire to fail or even loose enough accuarcy to matter in combat.  Even under full auto fire the gas tube of an AR is more apt to fail from heat than the barrel.

I wasn't doing a scientific study on barrel heat build up [:D], but I know one thing, after two or three 30 round full auto dump, I would not want to touch neither barrel.  yes, you are correct in the theologically, but in reality the barrel will heat up sooner or later and it doesn't really take much to get either a heavy or slim line heat up to a point that it will cause failure.  

Right on.  A light barrel will suffice in an AR.  I'd argue my point more if we were talking about susstained FA belt feds or benchrest rifles, but on combat grade AR's it is largely academic.  

"but in reality the barrel will heat up sooner or later and it doesn't really take much to get either a heavy or slim line heat up to a point that it will cause failure."

Just out of curiousity what kind of failures are you talking about happening from excess heat.  I have seen gas tubes melt.  I have heard of bolts breaking (but it is arguable whether they are caused by heat).  I have heared of ruptured barrels though not on AR's. I guess you could call cook offs a failure.  

Just wondered what kind of heat induced failures you have seen.

Wow...what a can of worms...

I've got a 16" Heavy barrel from Bushmaster on the AR I just put together.

Why did I go with a Heavy barrel?

The ONLY reason was because the backorder wait time for a M4 profile barrel was 12 - 15 weeks at the time. The wait time for the Heavy barrel was 7 - 8 weeks.

Patience IS NOT one of my strong suits...[;)]

I'd get the one that you can get the quickest, easiest, and cheapest....

I shot an HBar for over 11 years -- it never bothered me.  But then again I never had to tote it around all day.  

"A standard heavy barrel will be no more accurate than an A2, because the barrel blanks used to make them are identical. A fat barrel does NOT equal more accuracy (and if you believe otherwise, you bought Colt's marketing campaign for the Delta HBAR hook, line, & sinker)."

The 2 identical barrel blanks are no longer identical when half the metal is removed from one and the other is left in its original form.  That is like saying that a piece of 1inch round bar is equal in strength after turning it down to a piece of steel the diameter of pencil lead.

Wrong, the heavier profile barrel has more resistence to flex and thus greater inherint accuracy.

The worst part about the A2 Govt profile is that it gets its thinest just forward of the chamber where the harmonic affects are worst. The heavier part is at the end of the barrel where it has less effect. (WHY? because the gov't wanted to use M203 mounts from A1's on A2's) NOT because this was the best or even a good design.



"The Marines in Iraq agreed universally that they had no one that could outshoot their M16A4s with 4x Trijicon ACOGs installed, and felt that the further-accurized guns were a waste of money for a field/combat rifle. I'd agree."

[b]maybe with the 600m range in combat the rifle is a good compromise between spending $ and getting results[/b]

as far as the true context of their comment...

The Marines should try shooting with David Tubb (David using one of his rifles.) Marines seem to have the IQ of Forrest Gump. My former issue M-16 A2 (basically the same as an A4 without detach handle and RAS) would shoot 3.5-4.5MOA. (why? because the lighter barrel can get damaged by rapid firing without time to cool faster than the HBAR- mine was deffinitely damaged to some degree after being heated to cherry red) What would I need to outshoot it? any Ar I've ever owned/built from Model1Sales to Bushmaster. Quite simply all of them do better than 1.5MOA with iron sights.

[b]If you want the best and don't use a grenade launcher go with the HBAR fluted.[/b]

for the record the highest accuracy to weight ratio barrel design is a heavy tapered toward the muzzle contour.[/b]

and where do I feel the heat? near the chamber where the conture is smallest and those handguards get tosty in as little as 40rds fired in 2 minutes.

GreenO, there are so many things that you say that are true.  Just not to the extent that you think they are.

In reference to the barrel blank, what is meant by that is that the quality of the bore is the same in both blanks.  This has much more to do with accuracy than the mechanical strength provided by a pound of unnessesary steel.  So does free floating.

In reference to why the barrel is turned light under the handguards, remember, the reason the weight was added to the end of the barrel was that the A1 profile [i]supposedly[/i] was damaged to easily.  More weight was not added underneath the handguards because if you think about it, that area is pretty well protected from damage by the handguards.  That is just my take on it.



Yeah, sometimes you have to do with, what you have to do with.  Because not everyone has a watercooled Browning and those that do know that they aren't near as easy to carry around compared to an M16.  [:)]

I am going lightweight!