View Full Version : Whats the poibt of a standard profile bbl
bowman57_2
09-19-14, 10:37
I was on bcm's websight last night looking at a 14.5 lw and standard bbl. Besides people who shoot full auto or with a can or maybe people that want a little more accuracy since the poi will change faster because of heating up, what would be the benefit of a standard bbl? In the pics it looks like the profile is the same under the handguard, which would mean the rail would get just as hot just as fast either way, then past the fsb the bbl is thick. How would the thicker bbl forward of the fsb help anything?
Thanks
The profile has nothing to do with heat or accuracy. It's just to mount a grenade launcher.
It's retarded, I don't know why anyone even makes that for the civvy market.
bowman57_2
09-19-14, 11:04
What i meant by heat and accuracy was that a thinner bbl will heat up faster than a thick one and everything ive read on here about lw bbls is after they get hot the poi drops about an inch or so. Anyway i wanted to get a standard barrel for the strength but just looking at it i dont really see how it could be any stronger when the profile is the same under the handguards
KalashniKEV
09-19-14, 11:36
You nailed it.
A thicker profile barrel is more rigid and less susceptible to POI shift once things start heating up.
Obviously it also helps if you're going to hang a can on the end of your barrel... especially if it happens to be a heavy one.
The m4 profile is probably the cheapest tooling available.
What i meant by heat and accuracy was that a thinner bbl will heat up faster than a thick one and everything ive read on here about lw bbls is after they get hot the poi drops about an inch or so. Anyway i wanted to get a standard barrel for the strength but just looking at it i dont really see how it could be any stronger when the profile is the same under the handguards
It's not supposed to be stronger. The thicker sections at the end were added to accept the ring on a grenade launcher mount.
You want more heat tolerance and accuracy? SOCOM profile was made for that.
JBecker 72
09-19-14, 16:38
It's not supposed to be stronger. The thicker sections at the end were added to accept the ring on a grenade launcher mount.
You want more heat tolerance and accuracy? SOCOM profile was made for that.
No, an M4 has a cut where it's thinner to accept a grenade launcher. You couldn't mount a M203 to a midlength government profile because it lacks that thin section of barrel the M4 has.
I have personally noticed my BCM lightweight middy to be slightly less accurate when hot than my government or "standard" profile middy. My SOCOM beats them both hot or cold. I still like lightweight profile barrels over government profile however. They are both the same under the handguard and only the gov profile is thicker after the FSB. This is why the SOCOM profile beats government profile during sustained fire, and overall it's just a more rigid barrel.
bowman57_2
09-19-14, 17:55
I forgot to mention that i was referring to a middy not a carbine gas system. I still prefer the standard barrel over the lw i just wondered how the 3 inches of beefier barrel past fsb could affect strength or accuracy once its heated when its such a small portion thats thicker
militant_monkey
09-19-14, 20:03
My question is how much sustained fire will it take for a lw or pencil barrel to lose the poi? I am not looking at rapid fire but a plinking faux spr set up.
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The "Government Profile" barrels are thicker at the gas block, and thinner under the hand-guards because the hand-guards themselves are supposed to add rigidity to the barrel. With a FF tube, a Gov profile is pointless. That is why BCM came out with their new ELW profile, thicker where it needs to be, thinner where it can be to save weight.
I think that the BCM ELW barrel makes a great deal of sense, but some anecdotal data suggests that, all things being equal, the accuracy of the ELW barrel profile is inferior to government profile (government profile = "heavy" profile at gas block and beyond, LW profile under hand guards. Government profile barrel doesn't have anything to do with the M4 cut for M203 G.L.). Ive read several reports of people being a bit underwhelmed w/ the accuracy provided by their ELW barrels. They were comparing the ELW to government profile barrels and expecting the ELW to meet or exceed the accuracy offered by government profile barrels. I could be completely wrong, but it seems that the ELW was designed to maximize the capabilities of the light weight barrel profile, not necessarily to exceed the performance of government profile barrels?? I am aware that the initial move from the light weight m16 a1 barrel profile to the government profile barrel appears to have been caused by a misunderstanding (burr under gas block etc. etc.), but there does seem to be at least a modicum of accuracy/point of impact retention brought about by the government profile as compared to the LW profile?? As rails continue to get lighter, the government profile barrel sounds even more appealing to me. While a heavy/socom profile barrel will obviously provide the biggest performance gains, the weight of that damn thing just makes it out of the question for me.
HighDesert
09-19-14, 23:57
The "Government Profile" barrels are thicker at the gas block, and thinner under the hand-guards because the hand-guards themselves are supposed to add rigidity to the barrel. With a FF tube, a Gov profile is pointless. That is why BCM came out with their new ELW profile, thicker where it needs to be, thinner where it can be to save weight.
I have never heard this logic about the handguard cancelling out any loss of rigidity of the thinner profile under the handguards? It makes sense, but true?
HighDesert
09-19-14, 23:58
No, an M4 has a cut where it's thinner to accept a grenade launcher. You couldn't mount a M203 to a midlength government profile because it lacks that thin section of barrel the M4 has.
I have personally noticed my BCM lightweight middy to be slightly less accurate when hot than my government or "standard" profile middy. My SOCOM beats them both hot or cold. I still like lightweight profile barrels over government profile however. They are both the same under the handguard and only the gov profile is thicker after the FSB. This is why the SOCOM profile beats government profile during sustained fire, and overall it's just a more rigid barrel.
I have both a LW BCM 16" and Standard BCM 16" and have noticed the same.
page 3 of this thread. Look for MarkG's post, and Grumpy's right after it. Although I would suggest that there is never just one reason for anything.
https://www.m4carbine.net/showthread.php?76554-Reason-for-the-government-profile/page3
HighDesert
09-20-14, 01:26
page 3 of this thread. Look for MarkG's post, and Grumpy's right after it. Although I would suggest that there is never just one reason for anything.
https://www.m4carbine.net/showthread.php?76554-Reason-for-the-government-profile/page3
Fantastic - thanks. Still can't believe I've been here so long and never heard this.
They were comparing the ELW to government profile barrels and expecting the ELW to meet or exceed the accuracy offered by government profile barrels.
I don't know that there has been anything definitive either way as far as accuracy. Scientific testing wise. I think Mark came closest and was happy with his accuracy. It will be interesting to see if they do outperform gov. profile or not.
Ran a 14.5 ELW BCM KMR for the Haley D3 Carbine class that I was host for here. Ran mine with a Bushnell Elite Tactical 1-6.5x24 and had zero accuracy loss. The ELW profile cools off very quickly and doesn't heat up nearly as fast as regular LW. This has to do with the Continuous Profile that the ELW barrels have.
Yep, if you're looking for the best accuracy per weight a continuous profile barrel of some sort makes the most sense. In general, the way to get the stiffest object for a given weight if one end is fixed and the other end is free is to have a taper from large at the fixed end to small at the free end. Additionally, having the free end thinner reduces the mass of the free end, which tends to decrease the amplitude of oscillations.
I'm not saying a government profile or M4 profile can't be accurate, but there's a good reason why you don't see match barrels in that profile.
The profile has nothing to do with heat or accuracy. It's just to mount a grenade launcher.
It's retarded, I don't know why anyone even makes that for the civvy market.
Yeah . I don't understand this either .
I would think that making the cutout for the grenade launcher would be more
work then just leaving the barrel without it .
I can see how it could have been cheaper at one time because of availability ,but not anymore .
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