M4 16" gov. cut barrels
Hi Guys!
Is it just me? Or do M4 gov. cut barrels with the cut for the grenade launcher over heat and start opening up your groups astoundingly quick?
Is it just me? Or do M4 gov. cut barrels with the cut for the grenade launcher over heat and start opening up your groups astoundingly quick?
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Maybe. I hate that feature but have several with it. I think it's less about the grenade launcher cut than it is the thin profile under the handguard that's causing the expanding groups.
I prefer the H-bar profile even for 16" barrels BUT it adds a few ounces to the weight.0 -
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Every barrel can react differently to getting hot.
The stresses of manufactoring , variations in the pieces of steel,
and how much care was taken in making the barrel,
will affect it to some degree.
A barrel with large variations in contour I would think would be more susceptible
to variations in point of aim with excessive heat build-up.
I had a barrel like yours that would only hold tight groups when
spacing shots a minute or two apart, when" rapid firing"
a couple of mags at maybe 1 shot a second the group would
open up a lot, even when slowing down afterwards to take precise aim.
I have one now that nothing seems to affect it, cold, warm, hot
or almost to hot to handle it will shoot accurately .
Heavy contour barrels are usually less affected ,
I prefer heavy barrels on any target shooting only rifle now,
but not on one that I would carry all day in the woods.0 -
Some barrels just cant shoot straight... 0 -
Go closer to the target [:D]. 0 -
My first two AR's had HBAR barrels. Super thick up to the gas block, then they abruptly change to .750" and stay that thickness all the way to the muzzle device. They could take all the heat you want "rapid firing" entire 30 round magazines actually aiming in between shots no problem. I recently built an AR with a 16" gov. cut barrel and it over heats after 3 or 4 shots. Pitiful. I can't believe they send America's fines out there with garbage like that. 0 -
quote:Originally posted by 7.62x39Lover
I recently built an AR with a 16" gov. cut barrel and it over heats after 3 or 4 shots. Pitiful. I can't believe they send America's fines out there with garbage like that.
Funny, I have 2 ARs with M4 type barrels, and they don't overheat after 3-4 shots. In fact after 3-4 shots there's barely any heat in them at all.0 -
quote:Originally posted by Horse Plains Drifter
quote:Originally posted by 7.62x39Lover
I recently built an AR with a 16" gov. cut barrel and it over heats after 3 or 4 shots. Pitiful. I can't believe they send America's fines out there with garbage like that.
Funny, I have 2 ARs with M4 type barrels, and they don't overheat after 3-4 shots. In fact after 3-4 shots there's barely any heat in them at all.
Do you know what type of steel they are made of? After my last experience at the range shooting my HBAR side by side with the M4 barrel. The M4 barrel performing very poorly, I have been really looking at barrels online and according to some sources, the type of steel the barrel is made of also contributes to its dissipation (or lack thereof) heat. The M4 barrel I bought was an AR stoner barrel that I did not pay much for. What type of steel? I don't know. But a lot of people, including a couple on this thread have reported that M4 barrels with the very thin area before the gas block are known not to deal well with heat. Now a popular barrel is called the "medium contour M4", which is the same thing as the M4, but with quite a bit more girth between the upper receiver and the gas block. According to Olympic Arms, 416 R stainless dissipates heat very well. You get an HBAR or bull barrel made out of that and watch out!0 -
Could you add some 'number's to your question?
Or at least define what you mean by 'over heat' and 'opening up your groups'.
Simple physics/thermodynamics will allow a thinner barrel to absorb heat faster than a thicker barrel, but the opposite is also true; a thinner barrel will dissipate heat more rapidly than one that is thicker.0 -
quote:Originally posted by iceracerx
Could you add some 'number's to your question?
Or at least define what you mean by 'over heat' and 'opening up your groups'.
Simple physics/thermodynamics will allow a thinner barrel to absorb heat faster than a thicker barrel, but the opposite is also true; a thinner barrel will dissipate heat more rapidly than one that is thicker.
A thicker barrel will dissipate heat faster than a thinner barrel due to the larger surface area that the heat has to escape out of. Heat dissipation is all about surface area. That is why you flute a barrel, to increase the surface area of the barrel so that heat can have an avenue to escape from.
Shoot an old school 16" M4 barrel 3 or 4 times in about as many seconds and it will be hot enough to boil an egg on and there will be no rhyme or reason as to where the subsequent shots fly. Now it is easier to find 16" "medium contour" barrels than it is to find 16" M4 barrels. The "medium contour" barrels are the same general shape as the M4, but with quite a bit more meat on the section between the upper receiver and the gas block. Not quite an HBAR, but significantly thicker than an M4. I have heard that the over heating problem is only with the 16" "gov. cut" (M4) barrels and not the 20" barrels with the same general dimensions.0 -
quote:Originally posted by 7.62x39Lover
quote:Originally posted by iceracerx
Could you add some 'number's to your question?
Or at least define what you mean by 'over heat' and 'opening up your groups'.
Simple physics/thermodynamics will allow a thinner barrel to absorb heat faster than a thicker barrel, but the opposite is also true; a thinner barrel will dissipate heat more rapidly than one that is thicker.
A thicker barrel will dissipate heat faster than a thinner barrel due to the larger surface area that the heat has to escape out of. Heat dissipation is all about surface area. That is why you flute a barrel, to increase the surface area of the barrel so that heat can have an avenue to escape from.
Shoot an old school 16" M4 barrel 3 or 4 times in about as many seconds and it will be hot enough to boil an egg on and there will be no rhyme or reason as to where the subsequent shots fly. Now it is easier to find 16" "medium contour" barrels than it is to find 16" M4 barrels. The "medium contour" barrels are the same general shape as the M4, but with quite a bit more meat on the section between the upper receiver and the gas block. Not quite an HBAR, but significantly thicker than an M4. I have heard that the over heating problem is only with the 16" "gov. cut" (M4) barrels and not the 20" barrels with the same general dimensions.
You are mistaken.0 -
quote:Originally posted by yoshmyster
Go closer to the target [:D].
[:D][:D][:D]...0 -
quote:Originally posted by iceracerx
quote:Originally posted by 7.62x39Lover
quote:Originally posted by iceracerx
Could you add some 'number's to your question?
Or at least define what you mean by 'over heat' and 'opening up your groups'.
Simple physics/thermodynamics will allow a thinner barrel to absorb heat faster than a thicker barrel, but the opposite is also true; a thinner barrel will dissipate heat more rapidly than one that is thicker.
A thicker barrel will dissipate heat faster than a thinner barrel due to the larger surface area that the heat has to escape out of. Heat dissipation is all about surface area. That is why you flute a barrel, to increase the surface area of the barrel so that heat can have an avenue to escape from.
Shoot an old school 16" M4 barrel 3 or 4 times in about as many seconds and it will be hot enough to boil an egg on and there will be no rhyme or reason as to where the subsequent shots fly. Now it is easier to find 16" "medium contour" barrels than it is to find 16" M4 barrels. The "medium contour" barrels are the same general shape as the M4, but with quite a bit more meat on the section between the upper receiver and the gas block. Not quite an HBAR, but significantly thicker than an M4. I have heard that the over heating problem is only with the 16" "gov. cut" (M4) barrels and not the 20" barrels with the same general dimensions.
You are mistaken.
Surely we can agree that the thicker barrel dissipates heat from the lands and grooves in the barrel faster than the thinner barrel and that's why the thicker barrel performs optimally for a longer period during sustained fire.0 -
quote:Originally posted by 7.62x39Lover
quote:Originally posted by iceracerx
quote:Originally posted by 7.62x39Lover
quote:Originally posted by iceracerx
Could you add some 'number's to your question?
Or at least define what you mean by 'over heat' and 'opening up your groups'.
Simple physics/thermodynamics will allow a thinner barrel to absorb heat faster than a thicker barrel, but the opposite is also true; a thinner barrel will dissipate heat more rapidly than one that is thicker.
A thicker barrel will dissipate heat faster than a thinner barrel due to the larger surface area that the heat has to escape out of. Heat dissipation is all about surface area. That is why you flute a barrel, to increase the surface area of the barrel so that heat can have an avenue to escape from.
Shoot an old school 16" M4 barrel 3 or 4 times in about as many seconds and it will be hot enough to boil an egg on and there will be no rhyme or reason as to where the subsequent shots fly. Now it is easier to find 16" "medium contour" barrels than it is to find 16" M4 barrels. The "medium contour" barrels are the same general shape as the M4, but with quite a bit more meat on the section between the upper receiver and the gas block. Not quite an HBAR, but significantly thicker than an M4. I have heard that the over heating problem is only with the 16" "gov. cut" (M4) barrels and not the 20" barrels with the same general dimensions.
You are mistaken.
Surely we can agree that the thicker barrel dissipates heat from the lands and grooves in the barrel faster than the thinner barrel and that's why the thicker barrel performs optimally for a longer period during sustained fire.
The 'thicker' barrel 'performs' better than the thinner barrel because it is stiffer due to it's size, in your scenario. (diameter, area, volume).
Since the hear transferred to the barrel is caused by friction between the barrel and the bullet the heat moves from the inside of the barrel to the outside, where by convection, it is transferred to the outside air.
Convection is the least efficient means of cooling.0 -
quote:Originally posted by iceracerx
Convection is the least efficient means of cooling.
Well that was good for a laugh.[:D][:D]0 -
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
Convection is the least efficient means of cooling.
Well that was good for a laugh.[:D][:D]
Do tell?0 -
quote:Originally posted by iceracerx
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
Convection is the least efficient means of cooling.
Well that was good for a laugh.[:D][:D]
Do tell?
Convection is the MOST efficient mode of heat transfer. Followed by conduction, then by radiation.0 -
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
Convection is the least efficient means of cooling.
Well that was good for a laugh.[:D][:D]
Do tell?
Convection is the MOST efficient mode of heat transfer. Followed by conduction, then by radiation.
Perhaps For a forced air furnace, but you may have noticed 'we' are talking about barrels.0 -
quote:Originally posted by iceracerx
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
Convection is the least efficient means of cooling.
Well that was good for a laugh.[:D][:D]
Do tell?
Convection is the MOST efficient mode of heat transfer. Followed by conduction, then by radiation.
Perhaps For a forced air furnace, but you may have noticed 'we' are talking about barrels.
So, far as I am aware, physics is a universal principle. Now, I am aware that certain physical phenomena are considered to change their behavior when it is being observed. Is that your assertion for this scenario?0 -
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
quote:Originally posted by Mr. Perfect
quote:Originally posted by iceracerx
Convection is the least efficient means of cooling.
Well that was good for a laugh.[:D][:D]
Do tell?
Convection is the MOST efficient mode of heat transfer. Followed by conduction, then by radiation.
Perhaps For a forced air furnace, but you may have noticed 'we' are talking about barrels.
So, far as I am aware, physics is a universal principle. Now, I am aware that certain physical phenomena are considered to change their behavior when it is being observed. Is that your assertion for this scenario?
You win. And heavy barrels cool more rapidly than thin barrels. Guess I need to go read.
Thanks so much for being a gentleman and not rubbing my nose in this.0 -
quote:Originally posted by buschmaster
one way to find out is put on the clamp by itself that holds on the grenade launcher. should act as a heat sink and you have less of a problem. if so that was the problem.
seen a few barrel profiles that have normal dia. outside the handguard but thin under the handguard. stupid. maybe it's for balance.
if you want to go the other direction. that DPMS barrel I had in the XM177 was THICK under the handguard. balances it out because it would have been way too light in front.
You also get the added benefit of a flame thrower! [:p]0 -
Some here may find this helpful:
The heat transfer coefficient due to natural convection, h (rarely purely natural for the bbl cooling scenario being discussed) is greater when the surface area is increased (it is expressed in W*m^-2*K^-1). However, heat transfer due to conduction is thickness dependent, and inversely so than how area relates to convection (k/t; k having units of W*m^-1*K^-1, where k is purely material specific). The overall heat transfer for a bbl (U) is (h*k)/(h*t+K)
The question therefore is, for any two barrel diameters: is the increase in surface area large enough to overcome the increase in thickness. The short answer is yes. Why? Because, for example, a 2x increase in the thickness gives approx. a 3x increase in cylindrical area (assuming constant length).
Doing a little Heat Transfer calc. for this scenario yields:
U1*A1=[(h*k)/(h*t1+K)]*A1 and
U2*3*A1=[(h*k)/((h*2*t1)+K)]*3*A1
...
thus
U1=(h*k)/(h*t1+K)
U2=(h*k/((h*2*t1)+K)
The overall heat transfer coefficient for bbl 1 (the thinner bbl) is going to be greater than for the thicker one, and the amount roughly correlates to the difference in thickness only.
Note that the above assumes the same bbl materials and convective modality (i.e. forced vs. natural).
The overall heat transfer rate (q) depends upon the bbl to air temperature difference:
q1 = U1*(dT1)
q2 = U2*(dT2)
That means the thinner bbl cools faster (it also means it heats up faster). Also, of note is the amount of energy (BTUs or kJ) that needs to be imparted to heat both bbls to the same temperature. Heat capacity Cp relates as follows Q=m*Cp*dT (mass times heat capacity times the temperature difference). This is where the mass of the heavier barrel really helps because it's going to take ~2.5x more input energy to heat the additional mass (note that a 2x thickness increase roughly correlates to 2.66x the mass).
You will also note, perhaps, that nowhere did I assert that the heavy bbl would cool more rapidly than the thinner bbl when I simply noted that convective heat transfer was the most efficient mode of heat transfer.[:)]0 -
After reading Mr. Perfect's excellent post. I think we have been splitting hairs and or talking apples and oranges. I agree that the thinner barrel will heat up and cool off faster in general terms. However, I figure that the thicker barrel will keep the lands and grooves cooler on average throughout the duty cycle of shooting a 30 round magazine relatively fast. Would that be a good meet up point for the three of us? 0
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