Hello All.  Going to put together a 16" 9mm rifle, want to know the correct Buffer weight for it, cycling strictly 115/124gr Factory ammo.  I'm seeing I need the 4" length and at least 5oz weight, is this info correct?  Thanks for any help.

There is a veritable plethora of potentially cromulent recoil systems that might suffice.  What is your intended use, how sensitive to recoil are you (i.e., what is your physique), and how much money are you willing to spend?

Good luck with whatever you pursue.

Most would consider 5oz to be on the light side.  Mine has a 6.5 oz buffer.  A member has taken buffer weight to the extreme in testing and proven that you can't have too much weight.  Dead blow buffers have become the rage.  They help reduce bolt bounce as I understand.

 https://www.ar15.com/forums/AR-15/Lots-of-9mm-AR-information/15-745598/



 OP....you are new here.

Start by reading the basics, understand the design, and you figure it out pretty quick.

No one can tell you what will work perfectly, you have to do a little work on your end.

Plenty of previous threads discussing the balance of bolt carrier group weight and buffer weight.

Start reading and learning about information for bolts and buffers....click here.




.

Colt who invented the 9mm AR uses a 5.6oz buffer.  I have shot it with this set up on a 6991 Colt full auto.  The rate of fire was about 1050 RPM.  I now run a 6oz hydraulic buffer and the rate of fire is now 800 RPM's.  I have used the 8.5-10oz buffers.  They make the weapon jump around to much on full auto and Simi auto.  I recommendation is stick with 5.6-7oz.

Macon armory 7oz dead blow buffer and standard carbine spring

With a 15.7 oz. BCG and 16 in. bbl., standard carbine buffer tube and spring, same ammo - two-piece, 5.6 oz. mechanical "9mm" buffer: ROF=869;  three different hydraulic buffers, all in the 6.1-6.2 oz. range: ROFs: 930, 765, and 700.

MHO, YMMV, etc.

It’s not just buffer weight but rather the entire system.

In addition to the recoil impulse of the round, you need to consider:
- entire reciprocating mass, (bolt weight plus buffer weight);
- the spring weight;
- buffer length;
- the type of buffer and how it inhibits bolt bounce; and
- whether or not you are running an automatic bolt hold open device.

Your basic starting point in a 9mm AR-15 should be:
- a stock 9mm carbine spring;
- an A5 length (4”) buffer;
- a buffer using internal moving weight(s) that will prevent the bolt from bouncing off the breech face; and
- a minimum combined bolt and buffer weight of around 23-25 oz.

You can go lighter with the total weight to increase the cyclic rate.   But in general lighter weight means higher perceived recoil and a higher cyclic rate.  

If you have a bolt hold open device a higher cyclic rate and commensurately higher bolt velocity increases the hit it takes after the last round is fired.  That’s particularly the case if it is also either under sprung (with the buffer and bolt bouncing off the back of the buffer tube), or over sprung with the spring driving the bolt and buffer forward faster.

You can also go heavier to decrease the cyclic rate, but at some point the reciprocating mass starts to make it harder to control and bring back on target.

Based on my experience, at least 7 oz

I’d follow the advice on Blowback9.com and read up on the gentle recoil system.

NVM