Unfortunately, I succumbed to the “panic” mentality and bought a 16" BCM lightweight middy upper when what I really want is a 14.5" (LW or Govt profile, still debating this…) with a perm flash hider.
I guess what I’m asking is if there is enough meat on the barrel to shorten it to 14.5 (or 14.7) and pin a flash hider? It seems as if the barrel has a small swell right at the FH to give it enough of a shoulder.
Is this possible or should I just sell/trade this upper and wait for a 14.5 inchers to become available?
live with the 16 by the time it’s shot out maybe new barrels will be avaliable:D, serious i was craving a 14 settled for the 16 in lw really happy plus you can collect a box full of comps and flash hiders and change them around without hassle to see what you like(BCM2.0!!!)
I don’t think you can as the 16" BCM LW barrel has a step up in barrel diameter where it meets the threads.
but anyway, I don’t do 14.5 in a LW barrel or midlength gas.
to me, the only advantage of cutting and perming a barrel is the better balance resulting from the reduced weight at the muzzle. there is no practical difference in “compactness” of cutting less than a thumbs length off your barrel.
while there might be a case for cutting a .75" barrel I don’t do this to a LW barrel as I think it is already light enough without affecting handling.
and I don’t do 14.5" midlength.
so if you already have a 16" LW midlength, save yourself the time, money, and trouble and just shoot the best combination out there…
I’m all for shooting the crap out of it, now if I could find some bulk ammo that wouldn’t require me to take out a second mortgage on my house or sell a kidney…
That’s what I recently purchased from BCM. I also purchased a 14.5 middy barrel and am having a 'smith swap barrels and pin a BC for me. Put the barrel up for sale or keep it as a spare. No reason to over think anything.
as far as cheap ammo has’nt been such a thing for a loooooong time (think .10 a rnd for m193 real m193) so my solution is get to know someone with your local pd (depending how friendly they can be) find out when they qual for carbine and go ask for their brass. take along a bucket if it’s a small department 5 or 6 totes for a big qual. your expierience may vary depending on who you deal with. try to get for the cost of a please if that don’t work offer to pay 50.00 for a five gallon bucket full . but that would be the start of cheap ammo cuz then you only have to pay for bullets,powder,primers (when avaliable) and you get to shoot more:happy:
I would think the 16" LW middy would be a highly desirable barrel. I would hate to see it get molested. That was what I was looking for when I finally went with the .750 barrel. I’d do a swap when barrels come back and keep the 16" for a later time or for trade. kwg
a lot of problems crept up in a reliable system when we shortened a 20" barrel with a rifle lower, to 14" with collapsible carbine stock. the gas system was shortened to 7" to keep dwell time app. the same as a 20" rifle.
there is a sweet spot for dwell time. overgassing decreases durability. undergassing decreases reliability as the gun gets dirty or less powerful ammo is used.
midlength is the solution to the problem of overgassing a carbine gas system when .gov arbitrarily required all barrels to be 16" min. cutting a midlength back to 14.5 reduces dwell and sways it over to undergassed.
it’s true, many people have used 14.5 midlength with good reliability but not with all ammo/buffer/spring combinations. there is also variability in gas port sizes among different manufacturers and some vary according to barrel/gas length involved.
the 14.5 midlength was born from the idea of looking for a “soft shooting” gun. that’s nice and if I set up a gun just for competition or paper shooting I might look at that. but that’s not the primary purpose of my guns…
I always thought that the mid length gas system’s purpose was to make a “softer” shooting gun. Plus, frankly, I like the way the middys look with less barrel past the FSB.
Thanks for the education, ra2bach.
To further the technical part of this discussion, can not the barrel length be compensated for by adjusting the gas port’s size?
it can and manufacturers do have different GP sizes for long and short barrels. I don’t know if many or any do vary the size between midlength and carbine though.
but dwell time is the time (in milliseconds) from when the bullet passes the gas port till it exits the muzzle. it has nothing to do with gas port size - that affects the volume of gas, not the time in which that pressure is vented to the carrier. it is important as it relates to where in the pressure cycle extraction occurs.
there is a range that is the best balance between reliability and your gun beating itself to death.
Actually, the gas system length was all about the bayonet. The distance from muzzle to FSB on the M4 was set to match that of the 20" rifle so the issue bayonet could be used. In fact, When the M4 was first introduced, an article came out in one of the gun magazines stating that Colt picked the barrel length by finding what the minimum barrel length would allow the shortened rifle to function reliably while maintaining bayonet use, then added a half inch for insurance. I cannot vouch for the veracity of the statement, but that’s what the author wrote.
When M4 clones became popular on the civilian market, oft repeated criticism was that with the 16" barrel required federal regulation the distance from muzzle to lug was too great to allow the use of a bayonet. In response, Armalite lengthened the gas system to allow bayonet use with a 16" barrel. It was even stated so in their catalogs of the time.
If dwell time is defined by the time it takes the bullet to travel from the gas port to muzzle, then it has little to no affect on the “gassing” of the system, as the actual time it takes a bullet to travel an extra inch and a half is measured in a small fraction of a millisecond. In reality, the bullet has left the barrel before the gases have a chance to charge the carrier to operating pressure. What that extra inch and a half of barrel length has an affect on is how long it takes the gasses to vent. The extra length increases the time needed for the gasses to vent and holds the pressure longer. This in turn fills the gas tube & expansion chamber quicker and the carrier is accelerated quicker. To slow down the rate at which the system pressurizes, a smaller diameter gas port should be used.
This is why the addition of a suppressor causes an AR to be “over-gassed”. The suppressor acts as a pressure reservoir and slows the velocity of the expanding gasses. This prolongs venting, keeping pressure higher longer after the bullet has exited. The gasses that fill the system are at a higher pressure than they’d be without the suppressor
ETA- There are a couple of errors in the linked article-
The gasses do not exit the muzzle at 5x the speed of a high velocity rifle bullet. If I recall correctly, the gasses of modern smokeless powders exit at about 5700 fps when the bullet uncorks the muzzle.
The gasses do not push the bolt forward when they enter the expansion chamber. The pressure of the gas inside the expansion chamber of the carrier cannot exceed the pressure of the gas inside the bore & chamber. In fact, the pressure inside the expansion chamber is much less than it is in the bore when the carrier moves, separating the gas key from the gas tube, cutting off gas flow to the carrier
All hocus pocus aside, do not cut a perfectly good barrel for some perceived notion that you are gaining anything by removing part of the barrel and pinning a muzzle device. The only time it makes any kind of sense is if you live somewhere like NY, CT or other weird state that requires a permed device.
