20" barrel with carbine length buffer tube?

[schambers]

I am building out an SPR for my wife and until yesterday, I was under the impression that I would have to use a rifle length buffer tube, spring, buffer, etc if I wanted the rifle to cycle and operate properly. I have an upper with a 20" barrel and a rifle length gas block (DI).

Yesterday I saw that damage USA made an "H6 buffer kit" that, from what I understand, would allow me to use my 20" upper with a carbine stock. Do kits like this exit and will a rifle length weapon function properly with this kind of kit?

What's the difference between this and a standard carbine kit? More spring tension, a heavier buffer?

Also, are there any other companies that make kits like the one mentioned above? Damage USA is out of stock and there is no projected time to have new kits in stock.

Thanks!

[tpelle]

Isn't the Canadian C7 rifle pretty much just an M16A1 (with the OLD sights) plus a telestock?

Of course you know that you have to use a rifle receiver extension if you use an A1 or A2 rifle buttstock, and a carbine receiver extension with a telestock.

[Creeky73]

It might not have been proper, but my 20" rifle setup worked just fine with a carbine receiver/collapsible stock. And that is with a piston setup. The only thing that wouldn't cycle it was Tula. It had an H buffer. Like I said, might not have been technically correct, but it sent bullets downrange.

[Road-Warrior]

You should be fine using any of the standard carbine collapsible stock kits out there.
Normally the nain differences in kits are either mil-spec or commerical, & weight of buffer. There are other differences, such as price, what the springs are made of, style, storage options, etc. Myself, I like the mil-spec / standard buffer kits, and have never had a problem.

[schambers]

ok, good to know.

Since its a present for my wife, i just wanted to be sure that nothing goes wrong with it. I didn't want to buy carbine parts and end up with a problem with timing.

What difference does buffer weights make? Does it effect the cycling and timing or does the weight only effect the percieved recoil?

[Road-Warrior]

The buffer helps eliminate bolt bounce back. The buffer acts like a dead-blow hammer, when the bolt slams forward; just before it locks into battery; the weights in the buffer slam forward to keep the bolt from bouncing back, giving the locking lugs time to lock into battery.

Cycling / timing problems can be caused by a number of different things, such as weak springs, poor ammunition, dirty weapon, to name a few.

I don't think you would ever notice a difference in recoil from 1 weight to another.

[Stickman]

Does it effect the cycling and timing or does the weight only effect the percieved recoil?

Yes, you can under or over gas the system with the wrong buffer, which results in malfunctions. This is not a problem seen often at all, especially if using standard components. While the buffer weights do have an effect on recoil, it is not noticeable to most people unless they shoot quite a bit. The rifle length gas system itself is a pretty smooth shooter, and will feel better than a 16" carbine to her.

[MistWolf]

I run a 20" upper on a lower with a carbine length (entry style) receiver extension to mount an UBR stock and it runs fine
http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Build/DSC_0196.jpg

[schambers]

just a quick update. I decided to go with the carbine length with a 4.6 oz buffer. I also picked up an extra, standard length buffer, just in case things go wrong. Hope to have a completed project within the next two to three months!

[AKDoug]

You need to make sure that no matter what the weight is, the buffer needs to be a carbine LENGTH buffer and use a carbine length spring.

[Eric]

You need to make sure that no matter what the weight is, the buffer needs to be a carbine LENGTH buffer and use a carbine length spring.
Good call. Occasionally people come up with some bizarre combinations and wonder why it won't run, such as a rifle buffer in a carbine receiver extention.

[schambers]

yup, everything is carbine spec

[CGS]

ok, good to know.

Since its a present for my wife, i just wanted to be sure that nothing goes wrong with it. I didn't want to buy carbine parts and end up with a problem with timing.

What difference does buffer weights make? Does it effect the cycling and timing or does the weight only effect the percieved recoil?

I pulled this out of my AR15 Designers guide for you, agree or disagree this is my thought process when specing out parts for a build...
3) The Butt Stock Assembly,
The Butt stock assembly is made up of basically a buffer tube, and a butt stock, which attach to the lower receiver. Within the tube, will reside the buffer and buffer spring. Butt Stock Assemblies come in two basic varieties, fixed and adjustable. Before selecting a butt stock one must familiarize themselves with the laws of their area, as adjustable butt stocks are not allowed in some states, counties or cities.
A fixed butt stock is simple and straight forward, it doesn’t move and does not adjust. Though there are multiple styles available. Fixed butt stocks are available skeletonized or like the traditional A1 or A2 style butt stock you see on M16 service rifles. Weights are even available for bench rest shooters to insert into their stock.
Adjustable butt stocks are increasingly more common because they adjust to the size of the shooter, often times in more ways than one. The most basic M4 Adjustable butt stock adjusts for length of pull. Some more complex butt stocks allow the shooter to adjust for comb height as well.
Before selecting a butt stock, be sure to read on about Military Vs. Commercial Buffer Tubes.

4) The Buffer Assembly is made up of a tube, spring and buffer. There are differences in the tube, but differences in buffers and springs will allow you to tweak or customize the AR15’s perceived recoil.
Selecting a buffer tube is fairly straight forward and often dictated by the butt stock you desire on your AR15. Fixed stocks will typically use an A1 or A2 buffer tube. Adjustable stocks will typically utilize a Commercial or Military style buffer tube.
“Buffer tubes” are also known as receiver extensions, or receiver extension tubes. A Milspec buffer tube is slightly smaller in diameter but it is forged aluminum, not extruded which makes it stronger even though it's slightly smaller. Also there is a difference with how the threads are cut on the milspec versus commercial buffer tubes, making for a better thread lock or thread engagement, with the military size tube and the lower receiver. It is important to note that though the forged buffer tube may be considered stronger and the thread engagement considered better with the military tube, there is not any evidence that this added strength is necessary in a civilian AR15. Under normal use situations, the commercial buffer tubes are more than adequate to do what is asked of them.
(insert picture here of military and commercial buffer tube sizes CAD drawing)
Other differences with the commercial and military buffer tubes include the commercial sized butt stock will have a loose fit on a military sized tube. A military sized butt stock likely will not fit on a commercial tube. A military style buffer tube usually will have less adjustments, only 4 versus the 6 adjustment points on a commercial buffer tube. Some manufacturers have systems that do not use either the milspec or the aftermarket tube size... The early Choate stock is one example of a proprietory tube.

Buffers are essentially engineered weights that help to slow down the cyclic rate of the bolt as it cycles in the upper receiver and the receiver tube. Buffers are available in two basic sizes, Rifle or Carbine. This rifle or carbine size designation refers more to the buffer tube than it does to the barrel length. Pistol sized buffers for the 9mm and the 45 may also vary in size and weight. Non-traditional hydraulic buffers are also available.
Carbine length buffers are available in varying weights. Standard Carbine is a tube with steel weights inside. Two steel weights, plus one tungsten weight is considered a H1, 2 tungsten weights plus 1 steel is H2, and 3 tungsten is H3. Since Tungsten weighs more than Steel, the weights of the buffers will vary. However the weight of the buffer is not the only factor to consider, as the segmentation of the individual weights can prove to provide less bolt bounce. H buffers seem to be the best starting point when in doubt on a carbine sized AR15 buffer, heavier weights may be required for shorter gas systems.
Weights may vary from the chart below, but the chart is provided as a comparison tool to show the differences between the different buffers.
Standard CAR….. 2.9 oz.
H buffer is ….. 3.8 oz.
H2 buffer is….. 4.6 oz.
Rifle buffer is….. 5.17 oz.
9mm buffer is….. 5.5 oz.
H3 buffer is….. 5.6 oz.
Which is right, heavier or lighter buffers and springs. It all comes down to shooter style and preference. Generally speaking a heavier buffer will slow down the cyclic rate more and have less felt recoil on the shooter. Where as a lighter buffer will have a faster cyclic rate allowing for quicker follow up shots. However there is more to it than that, such as gas system length, and pressures from the ammunition so some experimentation may be necessary.
Like buffers, the buffer springs too are available in varying degrees of resistance to the backwards force of the Bolt. The first importance is to ensure your spring is matched to the size of your buffer tube (rifle length or carbine length tube). A rifle length buffer spring is approximately 12” long +- ¾”, and a carbine length spring is approximately 10 ¾” +- ¾”. After determining your proper spring length, you must determine which spring resistance is right for you.
There are springs on the market which have increased or reduced resistance to the bolts rearward movement when compared to a standard military specification spring. Mixing and matching spring tension with buffer weight will have different effects on your AR15. It is generally suggested to start with a standard buffer spring.


Text got condensed in the Copy & Paste, sorry.