Extreme Velocity Spread Question - I'm perplexed
I just got back from the range and am perplexed on what just happened. I have been working hard on my extreme velocity spread on my .338/.300 RUM/50 degree shoulder wild-cat.
2 weekends ago, i did some load testing and found a powder charge and seating depth combination that shot .5" groups (100 yards) with a 19 FPS extreme velocity spread.
I loaded up 50 rounds of this exact combination combination and headed to the range to zero the rifle and get an average FPS reading for my ballistic program prior to heading off to a long-range shooting school.
I shot 13 rounds and got a 64 FPS Extreme Velocity spread on the same load i shot 2 weekends ago with a 19 FPS spread (based only on 5 shots however)
NOTE: 19 FPS 5 shots were loaded with a dry neck lube and the 13 rounds fired with 64 PFS spread were not.
Any thoughts as to what might be happening here?
Below is some key data points that may help you in the quest of solve the problem or at least identify where the problem may be.
The only real difference is that the dry neck lube was NOT used on these loads.
Chronograph Data from this morning's shooting. Sorted from slowest to fastest.
Note: if you throw out the 2,772 and 2,836 shots the spread drops to 28 FPS which is a lot better but not single digits or low teens that i was expecting.
Question: Does Dry Neck Lube make that much of a difference???
- PV-21 Chronograph was used.
- .300 Grain Verger VLD (Generation 2) in .338 caliber
- Bearing surface of all bullets was the same (measured with Davidson comparators x 2)
- Bullets were weighed on a digital scale and all were the exact same weight 300.4 grains
- All bullets were seated .010 longer than needed and then after each bullet was seated, i used the micrometer seating die to adjust each round down to the reading of 3.188 which in my rifle is .015 off the OGIVE.
- 93.0g of H1000 Powered (each load was exact loads)]All brass was trimmed to length, chamfered and de burred
- .363 Neck sizing busing was used on all brass
- Temperature was 75 degrees at the start of the shooting - 80 degrees at the end of the shooting
- All shooting was done in less than 1 hour time frame.