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5/20/2008 9:28:33 PM EDT
I have a Bushmaster AR in the M4 configuration with a 16 inch 1/9 twist barrel and a fixed stock.  It was short stroking.  I swapped out the buffer and buffer spring from another similar Bushmaster.  The gun ran great after that.  I noticed that the buffer spring that I replaced the original with was shorter.  I have posted a photo of both.  The one on the top is the new buffer assembly that works good.  The lower one is the original one that caused short stroking.  Does anyone know anything about these assemblies?  Why does one have a shorter spring?  What is the purpose of these two types of buffer assemblies?  Which is correct for my gun?  Did I mix up an assembly from a collapsible stock?



5/21/2008 2:51:56 AM EDT
[#1]
What are the dimensions of the two assemblies (length and diameter)?
5/21/2008 7:38:49 AM EDT
[#2]
5/21/2008 9:35:13 AM EDT
[#3]
Both buffers are 5 7/8 inches long.  The long spring is 12 5/8 " and the short one is 10 7/8" long.  From the specs listed above it appears that the short spring is for the carbine.  This is the spring that I am now using in the gun and the gun functions ok now.  Does it make sense that my gun was short stroking because it is a 16" barrel and had a rifle length spring in it?  Am I correct in assuming that a longer barrel has more gas pressure going to the bolt and therefore needs a longer spring to resist the stronger rearward action of the bolt carrier and that this stronger spring was causing my  16" gun to short stroke?  If I switch from a fixed to a collapsible stock do I need to change the buffer or buffer springs?
5/21/2008 10:00:46 AM EDT
[#4]

Quoted:
If I switch from a fixed to a collapsible stock do I need to change the buffer or buffer springs?


Yes. Neither the fixed stock buffer or buffer spring will function in the carbine receiver extension.

A carbine with a full length stock and correct buffer and spring, should function fine. I wonder if you have gas leakage somewhere else in the system, that is causing short stroking with the rifle buffer spring installed.
5/21/2008 3:53:52 PM EDT
[#5]
I am a little confused.  The short versus long spring are a function of barrel length or type of stock (collapsible vs full lenght stock)?  
5/21/2008 3:56:26 PM EDT
[#6]

Quoted:
I am a little confused.  The short versus long spring are a function of barrel length or type of stock (collapsible vs full lenght stock)?  


Type of stock.
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