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8/29/2007 6:36:20 AM EDT
Its "Capt. Obvious" Material, But Anyway...

Decided to shoot hand rolled ammo for the first time out of my DSA STG58 Para, and I find it interersting the variations of the gas settings.  

Port and SA NATO: 1.5
Wold Gold 150gr PSP: 3
Hornady 150gr BTSP, FMJ, SST: 5 (H4895)

They all run within 50fps of each other, 2640fps out of 18", but such different settings needed.  H4895 is an extruded powder, and Wolf Gold, and of course the NATOs run ball powder.  

Makes me wonder if the changes can be all attributed to powder, or if bearing surfaces of the different bullets comes into play.  

It is nice knowing I'm only using enough gas needed for proper cycling and venting the excess.  

9/1/2007 8:31:21 PM EDT
[#1]
Faster and slower burning powders will result in the gas pressure being higher or lower as the bullet passes the gas port even when the muzzle velocity is otherwise identical.  This differece in port pressure is what requires the different gas settings.  
9/4/2007 1:17:28 AM EDT
[#2]
Somewhat vaguely related to your topic, adjusting the gas regulator can have an affect on the group sizes in FNFALs. My rifles shoot better groups with a couple of clicks more gas than is needed for reliable function. Just something to keep in mind when shooting for groups next time.
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