Originally Posted by astroman
Ok so is there a formula or chart available to refer to? I am just beginning to plan my build and don't want to buy wrong components. Thanks.
This is from the AR15 designers guide I wrote...
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.
and while were on gas port sizes...
Gas Port Size is the hole in the barrel which allows gas to bleed off from the barrel, into the gas block, through the gas tube and into the upper receiver and bolt carrier. The size of the gas port is to be specified in conjunction with the gas system length and dwell. The gas port size is one means of tuning the rifle to specific ammunition.
The standard gas port size varies from .059”-.090” and the maximum would be .120” since that is the internal diameter of the standard gas tube. However a larger size gas port diameter can cause the AR15 gas system to become over gassed. The larger size gas ports are not recommended on shorter barrels, and anything over .090 is not usually recommended except with use on an adjustable gas system.
The two trains of thought on the subject; Smaller gas port hole with more dwell OR Larger gas port hole with less dwell.
Common gas port diameters based on barrel length… Please note this chart doesn’t take into account other factors such as barrel diameter at the gas port, bolt carrier weight, buffer weight or buffer spring tension, ammunition or suppressor use. These port sizes will also vary by manufacturer.
11.5” barrel….. .810”-.094”
14” barrel….. .059”-.086”
16” barrel….. .059”-086”
20” barrel….. .086”-.096”
24” barrel….. .089”
Barrels with a larger diameter at the gas port (.750” diameter) tend to lean towards the middle to larger hole size, while barrels with a small diameter (.625” diameter) at the gas port tend to lean towards the low to middle hole size. Gas port size is one thing that should be considered but shouldn’t be over-thought. Most of the quality manufacturers have done the thinking for you, and unless you specifying a custom made barrel it might not be something necessary to consider too much. When in doubt err on the smaller side of port sizes, as the port size may be enlarged later if necessary.