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rp85
09-28-2013, 02:19 PM
hell;

took a new bersa 380 to shoot with a bunch of reloads at different o.a.l. bullet is a lyman 105 grain cast bullet, sized to .356”.

because of nose design, this bullet cannot have a o.a.l. of .965”, just will work in magazine. started at .960” and went down to .900”. shooting from a rest at 10 yards all groups meassured @3” or a little less. with an o.a.l. of .920” all seven shots formed a single hole. basic question why does o.a.l. make such a difference in accurace?

thanks for any input.

rp

lwknight
09-28-2013, 04:19 PM
The .380 has a tiny powder space to start with so small adjustments make big differences.
The tighter you squeeze the powder, the higher the pressure.
Sometimes the lighter the charge the more radical the pressures can be and
conversely tighter spaces can make pressures either go through the roof or settle down depending on the powder and bullet.

Pb2au
09-28-2013, 09:59 PM
La pretty much hit the nail on the head. In your case, the shift in pressure seemed to have improved the accuracy, but it still comes with a price. It is relalively difficult to even guesstimate to pressure now for that cartridge.

Cmm_3940
09-29-2013, 07:10 AM
+1 for small internal volume, fast powder. Small changes in OAL make big differences in pressure. BE CAREFUL when changing OAL from published data for known bullets. Load too short and you will damage your gun or something even more valuable.