Re: VLD Bullets - How much should MV increase?
Ok, lets see...
You know, the funny thing with this is that different powders will really play a major role here. For example, by nitration content, a lot of VV's powders are very clean burning, and ignite efficiently, often completely converting from solid to gas in half the time/pressure ratio that different powders of similar speeds will. Another route to explanation; if you use a very slow burner, such as...H870, Retumbo, 5010...you would notice a LOT more velocity drop for those four inches, especailly with a bullet of that weight, and also because the shank length is quite short <minimum bullet-bore friction>. The bottom line is it is hard to approximate right to the last fps because of all the variables.
Here's what I found; assuming you were using H870 <I don't know what YOU were using, but H870 was a powder I found would work, and would match up with the pressure/velocity situ. rather nicely> with a 30" tube and 156gr projectile, I snarffed up some figures that got me to 3450fps. Chop 4" off, the speed drops to about 3320fps. BUT!--remember, the type of powder used will likely have the biggest effect--a faster burning powder will show less of a decrease, presumably. My earlier guess was based on RE25 for powder. I'd say you should be above 3300, anyhow. I used 3450 as you indicated that to be the accurate load, and for me, if it isn't accurate, it isn't worth a d*mn!