180s going slower than 220s with same load?

[MarkK]

I wanting to work up a subsonic load for some 180 SMK that I had. So I thought I would start out with my 220 SMK load and back of from there. 8gr of H110. I last chrono'd some 208 AMAX at 1000fps with this load. I loaded up 10 rounds and chrono'd them. I am shooting from a 16" Noveske barrel with a .092 gas port in the pistol position.

Temp to day was about 90 degrees. The chrono recorded a 5 round average of 865fps!! Then gun cycled just fine. I did not shoot for accuracy. My intent is to use these in a 3 gun match next week, and it will all be CQB.

I am just curious.

Mark K

[Alleycat]

The bearing surface of the bullet has a lot to do with this phenomenon. More surface area = more pressure = more velocity.

[buffetdestroyer]

Also the volume the bullet takes inside the case is more with the longer bullets.
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