I like my middy!

[ColoradoShooter77]

2 weeks ago, I bought a mid-length upper from PSA, 1/7 melonite heavy barrel with magpul handguard. I also mounted a UTG metal rear sight, 25 bucks from Amazon.....I like it.

I mounted it on my S&W lower and shot it today.....compared to my carbines.....its smooth! I really like the softer recoil impulse.

I've got a magpul stock coming for it as well, should be here next week. Gonna be snazzy!

Its running 100% right out of the box.....very pleased.

 

[salt&battery]

that UTG site is very well made at a good price I have two of them. when you shoot it for groups post the results like to see what it does

 

[GunnyUSMC]

It seems like every time I build a Middy a friend comes over and falls in love with it. They twist my arm a little and I end up selling it to them.
The last on I built was on a Bootleg upper with a light weight barrel all dressed up in gray. I didn't let it go easy. It took $1100 to get out of my hands. But I have another Bootleg upper on my shelf waiting for a new lightweight mid length barrel to show up at the house.
There are three advantages to a middy. #1 Softer recoil (Not much sell then a carbine if you ask me) #2 Longer sight radius, and best of all #3 you can mount a bayonet for stabbing Zombies.

 

[ColoradoShooter77]

Also, less pressure in the gas system, which is easier on the bolt.

 

[chicharrones]

. . . and best of all #3 you can mount a bayonet for stabbing Zombies.

LOL.

 

[md7]

Glad you like it, OP. I like mine also. Cannot tell much difference in recoil between it and my carbine, but the longer hand guard and sight radius is nice when shooting irons.

 

[MistWolf]

Also, less pressure in the gas system, which is easier on the bolt.

You do realize that it takes the same amount of pressure to operate the action, whether the rifle has a carbine length system, a rifle length system or something in between...?

 

[ColoradoShooter77]

Pardon my ignorance, dwell time is the primary advantage of mid-length over carbine gas.

http://moaprecision.com/gas_system_length/

Mid Length on a 16" barrel runs the same as carbine gas on a 14.5" barrel, its optimal.

 

[carbine85]

Out of all my rifles I prefer the middy. It's the one I typically take to the range on a regular basis/
I run a H buffer in it. Anything heavier than that and the BHO doesn't always work.

 

[ColoradoMinuteMan]

You do realize that it takes the same amount of pressure to operate the action, whether the rifle has a carbine length system, a rifle length system or something in between...?

Actually, the mid-length gas system has lower pressure than carbine gas length gas systems, although not much lower percentage wise. The rifle length has significantly lower than both.

 

[MistWolf]

The pressure in the bore where the middy and the rifle gas system bleed the gas off is lower. But the pressure required in the expansion chamber to get the BCG moving remains the same. In the middy it's about the same as it has the same reciprocating mass and spring rate. It's probably a little different in the rifle system if it uses the rifle buffer and spring

 

[MistWolf]

Pardon my ignorance, dwell time is the primary advantage of mid-length over carbine gas.

http://moaprecision.com/gas_system_length/

Mid Length on a 16" barrel runs the same as carbine gas on a 14.5" barrel, its optimal.

Dwell time has nothing to do with it. Read the following paragraph, taken from the article. Pay particular attention to the bolded part

The reason the mid-length gas system was developed is dwell time. This is the amount of time the bullet remains in the barrel after the gas port is pressurized. On the original rifle length (20 inch) design, the distance the bullet travels after passing the gas port is only about 7 inches. On the later- developed M-4 carbine (14.5 inch barrel), it is ALSO about 7 inches. The problems started when civilian carbines became popular. Limited by federal law to a minimum 16 inch barrel length, manufacturers retained the standard carbine length gas system for commonality of parts, but increased the barrel length nearly 2 inches. The result is almost 9 inches of bullet travel with gas pressure in the system. By applying the same amount of pressure for a MUCH longer duration, stress on moving parts is greatly increased

It states the dwell time is a "MUCH longer duration" because the bullet travels an extra two inches. Sounds plausible, right?

Now, take a look at this chart-
View attachment 757137
The time it takes the bullet to travel from a carbine gas port to the muzzle of a 16" barrel is .248 milliseconds. Not .248 seconds. Milliseconds.

The time it takes the bullet to travel from the middy gas port to the muzzle of a 16" barrel is .181 milliseconds. That's a difference of .068 milliseconds. That's not much of a difference in time.

If the time the dwell time of the bullet between gas port and muzzle determined carrier speed, the carrier speed would not change if the distance between port and muzzle were changed, particularly of that distance is lengthened. Why? Because the bullet would be the same distance from the gas port when the expansion chamber was charged, moves and disconnects the gas key from the gas tube. The bullet would be in the same place in the barrel regardless if "dwell time" was 7 inches, 9 inches or 9 feet.

What increasing the distance from port to muzzle changes is how long it takes the gas pressure to atmospheric at the gas port. The carrier does not get pressurized until after the bullet leaves the muzzle. The rifle operates on residual pressure, the pressure left in the bore after the bullet uncorks the muzzle

 

[GunnyUSMC]

Ok. We can get all technical and start throwing out numbers, but in the end it will not change the way the OP feels about his new Middy.
You should have heard all the tech talk, on another forum, when I built my Dissipator. I had my buddy cut a 20 inch barrel to 16 inches, without making changes to the gas port. I used a rifle stock and buffer system. You should have read the comments about the troubles that I might encounter. I just took it to the range and it shoots like a dream and has been 100% reliable.
So lets not get all caught up in all the technical mumbo jumbo and talk about why we like Middies.

 

[badkarmamib]

Middy's look better with less barrel sticking out, and have more drop-in handguard. Both subjective, but why I chose midlength.

 

[chicharrones]

2 weeks ago, I bought a mid-length upper from PSA, 1/7 melonite heavy barrel with magpul handguard. I also mounted a UTG metal rear sight, 25 bucks from Amazon.....I like it.

I mounted it on my S&W lower and shot it today.....compared to my carbines.....its smooth! I really like the softer recoil impulse.

I've got a magpul stock coming for it as well, should be here next week. Gonna be snazzy!

Its running 100% right out of the box.....very pleased.

Congrats on the Mid-length upper addition. I too like the layout. Yours will look great when you have the complete Magpul set up in place.

 

[ColoradoMinuteMan]

The pressure in the bore where the middy and the rifle gas system bleed the gas off is lower. But the pressure required in the expansion chamber to get the BCG moving remains the same. In the middy it's about the same as it has the same reciprocating mass and spring rate. It's probably a little different in the rifle system if it uses the rifle buffer and spring

Honestly, it's a little difficult to follow what you have written in both of your responses however, I stand by my assertion that the pressure inside of a mid-length gas system is slightly lower than a carbine gas system with all other things remaining equal. I've made absolutely no claim that it makes much of a practical difference in the end result.

Yes, you are right the pressure "required" to successful cycle the carrier is the same if all other things remain equal such as the buffer weight, spring tension, carrier mass, case/chamber tension, etc. However, the amount required and the potential amount are two different things. Although, the bullet has left the bore when the carrier cycles, the gas enters the gas system while the bore is still pressurized and the bullet is still inside of the bore. The higher the pressure and the longer the dwell time, the more gas that will enter the gas system and the more pressure that will be inside of the expansion chamber when it begins pushing the bolt and the carrier apart.

 

[MistWolf]

The gas does start to fill the gas system while the bullet is in the bore, but the bullet is in the bore only for a very short time. So the system cannot fill with any significant amount of gas before the bullet leaves the barrel.

What matters is the usable pressure curve inside the system after the bullet leaves the barrel. The shorter the distance from port to muzzle, the quicker the usable pressure curve. The longer the distance, the longer the pressure curve. In other words, the longer the distance the more time it takes for the pressure to drop off.

But it diodes not change how much pressure it takes to get the carrier moving. If it takes 2000 psi to get the carrier moving in a carbine AR, it will take 2000 psi to get the carrier in a middy or rifle system moving if using the same buffer and spring

 

[ColoradoMinuteMan]

But it diodes not change how much pressure it takes to get the carrier moving. If it takes 2000 psi to get the carrier moving in a carbine AR, it will take 2000 psi to get the carrier in a middy or rifle system moving if using the same buffer and spring

I hear what you're saying, and maybe we are speaking to too different things. You mentioned a couple of time about the amount of pressure "required" and how much pressure it "takes." That would be a constant amount in all gas systems correct with all things raining equal. However, much like a tire that requires 65 PSI to be inflated properly, the tire may actually have more or less pressure contained in it depending on outside forces. The pressure differential between what is in the air line and what is inside of the tire, the amount of time the tire is being exposed to that pressure, the size of the orifice that will limit the volume of pressurized air going into the tire are factors that will determine how much pressure ends up in the tire. If the size of the of as port is the same and the capacity of the the gas system stays the same, increasing the pressure of the gas entering the gas system as well as the length of time the gas is pressurized will affect the amount of pressure in the gas system as long as the pressure outside of the gas system is greater than the pressure inside the gas system.

 

[MistWolf]

The carrier is nothing more than a pressure relief valve. When the pressure inside reaches the set limit, the carrier moves, separating the gas key from the gas tube and vents the pressure. That pressure won't change regardless of the pressure in the bore or in the gas tube.

What does change, as you point out in your example about filling a tire, is how fast the carrier reaches the pressure limit.

Since the AR has system is open to the atmosphere, the pressure inside the system will never be lower than the pressure outside

 

[ColoradoShooter77]

Interesting technical discussion here, good stuff. Regardless, I like the mid-length uppers, all of my future purchases will be middy's.

 

[ColoradoMinuteMan]

The carrier is nothing more than a pressure relief valve. When the pressure inside reaches the set limit, the carrier moves, separating the gas key from the gas tube and vents the pressure. That pressure won't change regardless of the pressure in the bore or in the gas tube.

What does change, as you point out in your example about filling a tire, is how fast the carrier reaches the pressure limit.

Since the AR has system is open to the atmosphere, the pressure inside the system will never be lower than the pressure outside

Agreed, however, resistance in the of spring tension and mass of buffer and carrier provide a brief delay in pressure release until the gasses are released as the gas rings pass the carrier vents.

 

[az_imuth]

OP, if you like the smooth shooting of the mid-length over the carbine, then you should treat yourself to a rifle length ar at some point. In my opinion, the rifle feels like a whole different animal. I guess the longer gas system combined with the additional weight (20" HBAR) is what makes the difference. Very pleasant rifle to shoot, but not as easy to lug around.

 

[ColoradoShooter77]

Yeah, I've thought about picking up a rifle upper, if PSA runs a black friday sale, it might happen.

 

[md7]

Yeah, I've thought about picking up a rifle upper, if PSA runs a black friday sale, it might happen.

This is why THR is bad for me. Just when I'm content with my carbine and mid.......... I get turned on to a 20" A4 type.

See you guys later. Gotta go perform cpr on my wallet.

 

[ColoradoMinuteMan]

This is why THR is bad for me. Just when I'm content with my carbine and mid.......... I get turned on to a 20" A4 type.

See you guys later. Gotta go perform cpr on my wallet.

Oh man, you are so right. Every time I see some eye candy I start itching to try something new. I've exercised tremendous willpower in not assembling the 3 extra lowers I've had in my safe for the past few months.