Tuning a 9mm PCC for factory ammo

[MikieM]

In my view the first thing you need to know, whether it's factory ammo or handloads, is the velocity. When you know the speed you can calculate the power factor. I use JBM Calculations for the conversion. When you know your power factor you can adjust your bolt/buffer, and spring combination to suit your needs.

Generally speaking, the lower the PF the lighter the bolt/buffer can be. Springs require a bit more experimenting but you should find one that falls somewhere between the bolt/buffer slamming hard against the end ot the tube (spring too weak), or the bolt/buffer slamming hard against the barrel breech (spring too strong). This is were it is pretty much up to you as to how the gun feels when shooting. A correct spring choice will also have the bolt stopping within about a quarter inch past the bolt catch.

 

My current setup works like a charm with the following parts. Kaw Valley bolt (14.5 ounces), six ounce buffer (no stop). Sprinco extra power (red) spring. My load is at 128 PF.

 

 

[PigSnowball]

On 3/19/2018 at 6:05 PM, MikieM said:

In my view the first thing you need to know, whether it's factory ammo or handloads, is the velocity. When you know the speed you can calculate the power factor. I use JBM Calculations for the conversion. When you know your power factor you can adjust your bolt/buffer, and spring combination to suit your needs.

Generally speaking, the lower the PF the lighter the bolt/buffer can be. Springs require a bit more experimenting but you should find one that falls somewhere between the bolt/buffer slamming hard against the end ot the tube (spring too weak), or the bolt/buffer slamming hard against the barrel breech (spring too strong). This is were it is pretty much up to you as to how the gun feels when shooting. A correct spring choice will also have the bolt stopping within about a quarter inch past the bolt catch.

 

My current setup works like a charm with the following parts. Kaw Valley bolt (14.5 ounces), six ounce buffer (no stop). Sprinco extra power (red) spring. My load is at 128 PF.

 

 

 

What's the variable that I should be looking out for to see if the buffer is too heavy or too light for the load?