Does COL change velocity?

  • Last Post 03 February 2018
nosee posted this 03 February 2018

My Conograph is wrong, or a longer col creates higher velocity! 

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John Carlson posted this 03 February 2018

In my experience, chambering the bullet more tightly into the lands (longer) will result in slightly higher velocity.  Possibly because the pressure has to build up a bit more before the bullet starts to move.  Likewise sizing the bullets larger results in higher velocity, at least to a point, possibly because it seals better, less blowby.

John Carlson. CBA Director of Military Competition.

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  • RicinYakima
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RicinYakima posted this 03 February 2018


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GP Idaho posted this 03 February 2018

I agree with John And Ric in most instances but then there are the small capacity cases where seating the bullets deeper has the effect of raising pressures. 9X19 and 40 S&W are notorious.  Gp

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BigMan54 posted this 03 February 2018

When I got my first(only) chronograph.

I tried seating the .25-06 with different brands of bullets of differing weights. Conclusions: 1) Sierra's because of the bullet profile cannot be seated as far out as Hornady. 2)Shorter jump lower velocity, however because of the more rounded ogive of Sierra, when seated to touch the rifling would give almost 100fps higher velocity. 3) Hornady; because of the combination of more gradual ogive and more bearing surface, needed a powder charge beyond MAX to reach the same velocity. Best of my recollection from 30yrs ago.

LYMAN #358156GC: seated in upper crimping groove in .38spl case over 10grs 2400 gave 1100+fps, When seated out and crimped in lower crimping groove gave 950fps.     THESE LOADS ARE BEYOND MAXIMUM, USE IN HEAVY FRAME .357MAG CHAMBERED GUN ONLY.  USE EXTREME CAUTION, WORK UP FROM STARTING LOADS ONLY.

Yeah, I know Old Skeeter Skelton advocated the use of the #353156 seated out in the lower crimping groove over 13.5grs of 2400. And I've shot about a gazillion of those loads in a New Model BlackHawk & S&W 19. But these tests used old Reloading Manual Data.  

Long time Caster/Reloader, Getting back into it after almost 10yrs. Life Member NRA 40+yrs, Life S.A.S.S. #375. Does this mean a description of me as a fumble-fingered knuckle-draggin' baboon. I also drool in my sleep. I firmly believe that true happiness is a warm gun. Did I mention how much I HATE auto-correct on this blasted tablet.

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