Tuning the Gun 101

[Iraqgunz]

Lately it seems as if there have been a rash threads about "tuning" a particular set up. Whether it's truly needed or it is a perception of the individual, in the end it is for that person to decide. Let's take a look at the various factors that would lead someone to do this and provide considerations that need to be dealt with.

We have a standard in the AR world. It is the Colt M4 carbine or the Colt M16 variant rifle. Quite simply these weapons are proven and we can use them to help guide us if we understand some facts about them.

THE RIFLE

1. Gas System- The rifle uses a rifle gas system with a port size of .093.

2. Buffer Weight- The rifle buffer weighs 5.1-5.3 oz.

3. Spring- The rifle uses a rifle length spring and should measure from 11 3/4 to 13 1/2 inches.

4. Ammo- For optimal function one needs to use full powered MILSPEC ammo. This means M193, M855, MK 262 MOD1 or similar.

5. BCG- The bolt carrier group is a full auto M16 style.

6. Lower Receiver Extension (Buffer Tube)- The rifle uses a full length rifle tube.

7. Suppressor- Are you using or planning to use a suppressor?

THE CARBINE

A carbine is essentially a lightweight more compact version of the rifle. In addition to cosmetic differences it uses a different gas system.

1. Gas System- The carbine uses a carbine gas system with a port size of .063 It may also use a midlength gas system and there is no standard for a midlength port. They are usually anywhere from .076-.080. **THIS IS A GENERAL GUIDELINE**.

2. Buffer Weight- The standard carbine buffer weighs approx. 2.9 oz. However, Colt M4/M4A1 carbines use the H2 buffer and the Colt 6920 carbine uses an H buffer. In addition to the slight difference in barrel length we must realize that M4/1A series is also full auto or busrt which is why the H2 buffer is used.

3. Spring- The carbine uses a carbine length spring and should measure from 10 1/16 to 11 1/4 inches.

4. Ammo- For optimal function one needs to use full powered MILSPEC ammo. This means M193, M855, MK 262 MOD1 or similar.

5. BCG- The bolt carrier group is a full auto M16 style.

6. Lower Receiver Extension (Buffer Tube)- The carbine uses a carbine length tube usually a 4 position or 6 position.

7. Suppressor- Are you using or planning to use a suppressor?

So now that we have that information you need to ask yourself what is the intended goal of your "tuning" effort. Are you simply wanting to slow down the cyclic rate or are you compensating for something?

First and foremost any modification that is made should not affect the operational reliability of the weapon. That means quite simply if you add a heavier or lighter buffer and you encounter malfunctions (when it previously worked) something is wrong and you need to put it back into the original state.

If you have an overgassed weapon (i.e. gas port is too large) then adding a heavier buffer can provide a quick immediate fix to bolt bounce or similar issues. Understand that the underlying problem is the gas port.

If adding a suppressor (which also creates an overgassing effect) then adding a heavier buffer will help to smooth out the operation. In many cases it will solve issues related to the failure of the bolt lock to lock back after the last round was fired.

Ammunition is a major factor here as well. If you are shooting non 5.56 loadings you may not be able to run the heavier buffers. Ultimately whatever you choose, you should be ensuring that your weapon will function with all the ammunition that you have in your stock.

Springs can also affect the operation. This is due to material construction and spring pitch.

So now we can see that if we start to change the pieces of the puzzle we can affect the overall operation of the weapon. All of the above factors need to be considered when you make those changes.

The wild card in all this is the midlength system which due to the fact there is no standard and the variations in port sizes one should attempt to get the port information. Additionally we can also look at some companies such as BCM or Noveske to see what kind of buffers they ship out with their completed carbines. It has been my experience that most properly spec'd carbine and midlength system guns will run with an H buffer and quite frequently an H2. Whenever I have concerns I also check my stuff with the lightest or weakest load in my ammo inventory and go from there.

[Ryno12]

Might as well sticky this right away so we can point the under educated and over thinkers this way.
Oh, and also you should include some info on the ejection chart. That's seems to get some people in a tizzy. I really like point that was made the other day about it being more important where your bullets end up than where the brass does. Some people get too caught up in this.


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[tom12.7]

Yes, thank you! Please sticky this.

[Straight Shooter]

IG-
Most EXCELLENT info ,sir.
Might I ask, that you add...again for the new and uninformed...the LENGHTS of each gas system?

[matemike]

Sticky X 1million

Is it getting too deep into basic tuning to mention different barrel lengths and dwell times with these designated gas systems?

I assume this all for the standard 16" barreled guns; whether rifle or carbine.

[SteveL]

Thanks for the write up IG. This has sticky written all over it.

[Shorts]

Sticky these specs.

[tog]

Good info for us newbies. I have a High Standard 6551 I'm thinking of tinkering on. This info will help.

[Alex V]

Informative as always IG.

I find that some people over think the "tuning" aspect of their guns.

A close friend of mine, one who build and tuned my race cars and many of the fastest cars in that platform in the country built an AR a while back. He spent hours and countless rounds trying to make sure that when the rifle ejected the spent case there was no mark on the brass from the shell deflector. Not like the rifle was leaving huge dents in the brass, they were so minor you would have to run your nail over them to feel them. He went crazy with gas port sizing and buffers... meanwhile it was with only one type of ammo. I guess this is what happens when you build race engines and have access to every kind of CNC machine imaginable lol.

[tog]

Informative as always IG.

I find that some people over think the "tuning" aspect of their guns.

A close friend of mine, one who build and tuned my race cars and many of the fastest cars in that platform in the country built an AR a while back. He spent hours and countless rounds trying to make sure that when the rifle ejected the spent case there was no mark on the brass from the shell deflector. Not like the rifle was leaving huge dents in the brass, they were so minor you would have to run your nail over them to feel them. He went crazy with gas port sizing and buffers... meanwhile it was with only one type of ammo. I guess this is what happens when you build race engines and have access to every kind of CNC machine imaginable lol.

I once got to talk with some engineers from the Mclaren Race Team. We conversed for about 3 hours. I did most of the listening. I can't believe what they go through to get an engine around the track for 500 miles-and believe me, the work is for 500 miles exactly-if that is what the race calls for. Back on topic. IG, since you posted "101" please follow this up with a 102, 103, etc. I (we) appreciate the info.