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Posted: 9/28/2014 9:37:21 PM EDT
| How do I know what length upper I should get? I have a fully built Aero Precision lower and I'm now in the market for an upper. Not sure where to start. |
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THIS thread is always a good place to start. Here is one of the quotes from that thread:
What's the difference between a carbine, rifle, and midlength gas system?
There are four types of AR15 gas systems, Pistol, Carbine, Mid length/Intermediate, and Rifle. Pistol gas systems are dependent on the barrel length. The AR15 .223/5.56 was designed with a 12" gas system for a 20" barrel, therefore a 20" barrel with 12" (rifle) gas system performs optimally, & gives an approximate 7.5" of bullet travel from the gas hole to the end of the Flash hider, around 0.200 ms referred to as Dwell Time. Increased Dwell time will allow for more gas to be forced back through the gas tube into the gas key. Target rifles will usually have adjustable gas blocks. Carbine length or 7" gas system is the gas system used in the M4 Carbine with a 14.5" barrel & yield 7.5" of travel dwell time. Measured from gas hole to end of flash hider. Uses a gas tube that is approximately 9.75" total length. The carbine length 7" gas system is also used on 16" barrels and have 9.5" of travel dwell time. Mid length or 9" gas system is a commercial solution designed to be used on 16" barrels with an approximate 7.5" of travel dwell time. It is visually different from the Carbine having the front sight base 2" further down the barrel. Uses a gas tube that is approximately 11.75" total length. Intermediate gas systems are also available by two manufactures, one(noveske) is 1.5" shorter than rifle length approximately 13.6 " in length. The other(knights armament company) is approximately 13.2" in length the same gas tube on all SR models. Rifle length or 12" gas system is the gas system used in the M16 series of rifles with 20" barrels, and can be found on barrels of 18" to 24" in length. Uses a gas tube that is approximately 15" total length Carbine buffers: the H stamped buffer is issued with the M4 14.5" barrel and is optimal for the 16" barrel with either the 7" carbine or 9" mid length gas systems, however some will use the H2 buffer. Most lowers with a collapsible stock come with the standard carbine buffer (no stamp). Examples of buffer weight in ounces No Mark 3.0 / H 3.8 / H2 4.6 / H3 5.4 (actual weight will vary by manufacture) Increasing the buffer weight will slow the auto cyclic rate and increase time for the bolt to unlock, the brass has more time to shrink away from the walls of the chamber and slightly reduces the felt recoil, but puts more mass in motion, which may or may not affect the follow up shots depending on the shooter. Increasing the buffer weight too much will result in a short stroke or fail to function. A lighter buffer has less mass in motion, which lessens the chance the sight picture will be disrupted between shots. |
| What do you want to do with it? To paraphrase a military planning dictum, let the mission drive the gear. Range fun? Defense? Hunting? Competition? Match shoots? Start there, then start whittling the choices. Rifle vs mid-length vs carbine, 20" barrel (or longer) vs 18" vs 14.7"/16". |
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Quoted:
How do I know what length upper I should get? I have a fully built Aero Precision lower and I'm now in the market for an upper. Not sure where to start. |
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Quoted:
ITGuy: IMO the 5.56 round needs 20" to get up to speed, say 3000+ fps with 55 grain bullet. For a shorter, lighter rifle, I prefer the 6.8 SPC, which reaches optimum velocity with a 16" barrel. If you assembled your own lower from detail parts, there is no good reason why you can't do the same for your upper. Only a few extra tools are required, primarily the action block. Check out AR Performance, Wilson Combat and Rainier Arms for 6.8 barrel choices. Check Green Mountain for outstanding 5.56 barrels at very reasonable cost. good luck - CW Quoted:
Quoted:
How do I know what length upper I should get? I have a fully built Aero Precision lower and I'm now in the market for an upper. Not sure where to start. You trying to confuse the shit out of the guy? 
14.5/14.7" P/A or 16" barrel upper in mid length would be a nicely rounded multi role upper with the right optic. |
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Quoted:
What do you want to do with it? To paraphrase a military planning dictum, let the mission drive the gear. Range fun? Defense? Hunting? Competition? Match shoots? Start there, then start whittling the choices. Rifle vs mid-length vs carbine, 20" barrel (or longer) vs 18" vs 14.7"/16". Quoted:
What do you want to do with it? To paraphrase a military planning dictum, let the mission drive the gear. Range fun? Defense? Hunting? Competition? Match shoots? Start there, then start whittling the choices. Rifle vs mid-length vs carbine, 20" barrel (or longer) vs 18" vs 14.7"/16". You have hit the nail on the head. These are the questions that need to be decided before any recommendations are given. Other wise, you are shooting into the darkness with no idea of where your target is. What's the difference between a carbine, rifle, and midlength gas system?
There are four types of AR15 gas systems, Pistol, Carbine, Mid length/Intermediate, and Rifle. Pistol gas systems are dependent on the barrel length. The AR15 .223/5.56 was designed with a 12" gas system for a 20" barrel, therefore a 20" barrel with 12" (rifle) gas system performs optimally, & gives an approximate 7.5" of bullet travel from the gas hole to the end of the Flash hider, around 0.200 ms referred to as Dwell Time. Increased Dwell time will allow for more gas to be forced back through the gas tube into the gas key. Target rifles will usually have adjustable gas blocks. Carbine length or 7" gas system is the gas system used in the M4 Carbine with a 14.5" barrel & yield 7.5" of travel dwell time. Measured from gas hole to end of flash hider. Uses a gas tube that is approximately 9.75" total length. The carbine length 7" gas system is also used on 16" barrels and have 9.5" of travel dwell time. Mid length or 9" gas system is a commercial solution designed to be used on 16" barrels with an approximate 7.5" of travel dwell time. It is visually different from the Carbine having the front sight base 2" further down the barrel. Uses a gas tube that is approximately 11.75" total length. Intermediate gas systems are also available by two manufactures, one(noveske) is 1.5" shorter than rifle length approximately 13.6 " in length. The other(knights armament company) is approximately 13.2" in length the same gas tube on all SR models. Rifle length or 12" gas system is the gas system used in the M16 series of rifles with 20" barrels, and can be found on barrels of 18" to 24" in length. Uses a gas tube that is approximately 15" total length Carbine buffers: the H stamped buffer is issued with the M4 14.5" barrel and is optimal for the 16" barrel with either the 7" carbine or 9" mid length gas systems, however some will use the H2 buffer. Most lowers with a collapsible stock come with the standard carbine buffer (no stamp). Examples of buffer weight in ounces No Mark 3.0 / H 3.8 / H2 4.6 / H3 5.4 (actual weight will vary by manufacture) Increasing the buffer weight will slow the auto cyclic rate and increase time for the bolt to unlock, the brass has more time to shrink away from the walls of the chamber and slightly reduces the felt recoil, but puts more mass in motion, which may or may not affect the follow up shots depending on the shooter. Increasing the buffer weight too much will result in a short stroke or fail to function. A lighter buffer has less mass in motion, which lessens the chance the sight picture will be disrupted between shots. This is very pertinent information that the OP should read. First and foremost, the OP needs to get educated on what his options are based on his wants and/or needs. Once he has determined a purpose/need for the AR, then we can direct him on which route to take. Until he does this, it is wise to refrain from posting recommendations. Patience is needed here. No need to start a diatribe that goes on for pages without any direction from the OP. |
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