linear velocity increase normal with .5gr changes?

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AShorvath

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I went out and did some more shooting yesterday and I had some odd chrono readings. I shot a total of 5 rounds at each charge and here are the averages for the 150gr ttsx in a 300wsm. Using H4350.

All 5 shots in each group were within a 50fps spread.

67gr - 3151fps
67.5gr - 3160fps
68gr - 3181fps
68.5gr - 3165fps

Considering the 68.5gr is recommended MAX (no pressure signs etc) should it not be close to the max velocity (3310fps according to Barnes).

What is the average velocity increase supposed to be? I am worried that since my 68.5gr readings might be incorrect, my other reading might not be super accurate either.

Andrew
 
145 fps less than the Barnes manual?. Not unusual, IMO.
Consider that they stand to gain market share by publishing higher vels.. They no doubt put effort into finding a fast barrel to develop their published data.

I've found the 4350's to be a wee bit sudden when they "hit the wall". Nice and progressive within normal working psi's, then a 1/2 grain more and ... pressure signs.
 
Ambient temp, barell length , chamber dimentions , atmospheric pressure ( altitude ) all also play into the velocity generated ! Also with the chrono data that you provided, it may well be that you hit the point of diminishing returns as far as adding powder / velocity gain! Your listed velocity is going down insted of up! Might well be that insted of going faster now you are just generating pressure ?
 
Usually speed is gained in a linear fashion, when you stop gaining speed you are usually maxed out pressure wise. Your results tell me that you might want to try a little slower powder, no promises though! Don't try to live by velocities in a book, no two barrels are exactly alike.
 
And, the negative change in velocity with an incremental increase in load can be a precursor to excess pressure. Time to back off. Or, go ahead and chase velocity w/o regard for the results of thousands of rounds tested through pressure barrels by ballistic technicians. What do they know, anyway?
 
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