First shot highest FPS?

[CA_Shooter]

Was about 60 degrees tonight and I was doing some group testing. Weird results - my first shot of each group 0had the highest FPS. Anyone have any ideas? Saw another thread that mentioned if you leave the round in the chamber longer it could cause a higher velocity.

Thoughts?

40.7, 2.2080, 90 PSI

2699

2674

2688

2678

2675

40.7,2.2080,82 PSI
2709
2672
2689
2692
2689
2681
2683

41.2,2.2050
2716
2687
2704
2710
2701
2691
2706
2703
2714

41.2,2.2080,82psi

2711

2689

2702

2688

2693

41.2, 2.2080, 90 PSI

2718

2701

2703

2708

2707

2707

 

[CA_Shooter]

These shots were all taken in a 40 minute time frame

 

[Longtrain]

I’ve never seen that phenomenon from my crony’s.

If you’re shooting a heat sensitive powder and let one cook in the chamber for a minute or so, I would think it could/should be higher. All my match rounds are either Norma 203B or RE-15 (about the same powder), in a match I will unload if I get a slow pull or a major wind change prevents me from firing in my normal cadence. They will shoot higher if they sit for a bit.

 

[CA_Shooter]

These were shot with H4350 so its pretty temperature tolerant.

I think I did end up loading and then starting moving into position which took some time, maybe 2 minutes? I then rushed my shots (about every 5-20 seconds, groups were horrendous) because I didn't have much time and wanted to chrono the rounds

Think that could be why it was just marginally higher?

 

[2506]

I think it was just one of those odd ball things that just happen. If you can do this and it repeats the same thing a couple more times then there may be a need to do some head scratching about it.

 

[Longtrain]

I agree with 2506, go back and try again, but
...this time try to pick a good day, plan to give yourself enough time to do everything right, be very methodical about your setup, target, ammo and note taking. Shoot your groups with the same speed, about a minute between shots, let it sit for 5-10 minutes between groupings to cool the barrel a bit. Trying to get the same conditions as possible to accurately make comparisons. Try to shoot good groups, weather may effect that result, if so, take it with a grain of salt. I always try my best, but if the wind is giving me fits, I’ll just crono my loads and check for ES and SD, etc. I’ll shoot for groups on a good weather day.

 

[BCBRAD]

As the barrel heats the bore will be more constricted to a point. As even more heat is applied the bore eventually becomes larger. At the macro level.