First shot chronograph differences

yggorf · July 9, 2009, 02:32 PM

I'm seeing a weird pattern developing over several different load development range sessions. Each of the first shots in ten shot strings (different days) seems to chronograph about 200fps lower than the rest of the nine shots. Anyone else experience this? Would this be cold barrel effect? (The barrel never gets that hot even after all ten shots are fired - I can still comfortably hold onto it.) Or could this be a Chrony issue?

**Unclenick** · July 9, 2009, 05:37 PM

Most likely a combination of barrel fouling and chamber heating. The clean barrel is better lubricated and offers less resistance for the powder to build burn pressure against. Faster powders typically are less affected. The chamber heating affects performance especially if you let the cartridge sit in the chamber for a time before firing.

So, the lesson is to foul your rifle to achieve normal performance. If you have to have first second and third shot performance, clean every three shots until you know what that is? Firelapping, hand lapping, or other bore smoothing efforts will tend to even the effect out because fouling then builds up more slowly in the smoothed bore.

July 9, 2009, 02:32 PM	#1
yggorf Senior Member Join Date: April 17, 2009 Posts: 125	First shot chronograph differences I'm seeing a weird pattern developing over several different load development range sessions. Each of the first shots in ten shot strings (different days) seems to chronograph about 200fps lower than the rest of the nine shots. Anyone else experience this? Would this be cold barrel effect? (The barrel never gets that hot even after all ten shots are fired - I can still comfortably hold onto it.) Or could this be a Chrony issue?

July 9, 2009, 05:37 PM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Most likely a combination of barrel fouling and chamber heating. The clean barrel is better lubricated and offers less resistance for the powder to build burn pressure against. Faster powders typically are less affected. The chamber heating affects performance especially if you let the cartridge sit in the chamber for a time before firing. So, the lesson is to foul your rifle to achieve normal performance. If you have to have first second and third shot performance, clean every three shots until you know what that is? Firelapping, hand lapping, or other bore smoothing efforts will tend to even the effect out because fouling then builds up more slowly in the smoothed bore. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle