Goofy Chronograph Reading-1st shot

[auminer]

Hi Gents: I reload for a couple of different long range rifles and have observed that my loads increase in velocity after the first shot. The varience seems to be a 40-60 fps increase after the first shot is taken. The following shots vary only slightly (5-15 fps) in velocity. I wait a full 1-2 minutes between shots for measurements. Calibers I'm shooting are the 243AI, 7MM and 300WM all shooting in the 3000+ range. I have tried a different chronograph and seem to have the same results. The first shot that is slow is from a clean cold barrel. Should a person throw out the first shot for an average for the long range ballistic tables/ custom turret or leave it in. If you throw it out the first shot what about the cold barrel shot when hunting? Anyway i'd appreciate any thoughts you would have on my problem. Thanks Al

 

[Mikecr]

There is nothing wrong here. It's normal.
If you plan on hitting animals with single shots at distance, you better prepare for just that.

 

[Skyking]

Forget the chron. What does the first shot do at distance? 500-1000 yards? Dont clean your gun so much too.

 

[auminer]

Thanks for the Help. I'll try just cleaning for carbon without trying to remove all the copper and test the cold barrel shots at disstance (750 yds). When I have that down I'll get the turret built for the cold barrel test results as I hunt with these rifles. I can always adjust the turret reading down at the range. Al

 

[Pdvdh]

There is nothing wrong here. It's normal.
If you plan on hitting animals with single shots at distance, you better prepare for just that.

Agreed. I've seen this myself with clean barrels. The reduced velocity with the first shot is because your bore is clean, not because the bore is cold. It's just one of the reasons that many rifles shoot to a slightly different point of impact with the first shot fired down a clean bore, compared to the following shots fired down a fouled bore.

I never take a clean bore rifle out in the field to hunt for long range engagements for this these reasons; 1) the POI is often different than what I've sighted in for (sighted with a fouled bore), and 2) the first round fired out of the clean bore is often slower than what my ballistics program and field charts are based on (developed with a fouled bore).

 

[ArchAngelCD]

Most every shooter knows what their gun will do in groups of 3, 4 or 5 rounds AFTER a fouling round or two and adjust their scope to those groups. No enough shooter know the other 2 shot possibilities will do which are very important. They don't know what a clean barrel cold bore shot will do or a dirty barrel cold bore shot will do. Those 2 circumstances are more important than what warm bore groups will do. When hunting those 2 will come up much more than warm bore shots.