When to work on Jump/Jam during load development process

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Gerard
Posts: 160
Joined: Fri Feb 26, 2016 1:36 pm
Location: Rifle Range QLD

When to work on Jump/Jam during load development process

#1 Postby Gerard » Wed Apr 26, 2017 12:59 pm

When load developing do you guys work on Jump/Jam after deciding powder load or before?

Maybe, it only makes sense to do this in parallel rather than sequentially..
But as a novice and without equipment I was concerned that messing with Jump/Jam once you have arrived at a potentially hot powder load would be dangerous given the increasing pressures as you bring the projectile closer to the lands.
So my (possibly erroneous) process has been to work on Jump first with the starting load (In my case 44 grains of 2208 for my 308 Winchester cases and HBC 155).
I then tested various jump distances (.020, .015. .010, .005 etc) and (due to the fact I do not have a crono) decided based on best grouping.

Then I started working on powder load gradually increasing from a starting point of 45.7 up to 46.7 and in my case arrived at 46.2 and a .015 jump as the best group.
Now of course, I would have much preferred to do this based on a crono stats and will definitely endeavour to do that next time, as grouping is entirely subjective to how the shooter performs on the day.

But even then, when do you think is the correct time in the development process to experiment with Jump/Jam?

(Was going to say when do you work on 'OAL', but want to be clear that I was talking about to distance between rifle lands and projectile ogive and I think OAL may refer to length of round to tip of projectile.. so excuse my lack of correct terminology here).

jasmay
Posts: 1291
Joined: Fri Sep 28, 2012 9:26 pm

Re: When to work on Jump/Jam during load development process

#2 Postby jasmay » Wed Apr 26, 2017 1:32 pm

Two things.

I always do a max charge test before I start load development, keep going up in set increments until I start to see signs of pressure, than I know where my max charge is, this is done AT the lands, not jammed or jumped, just at/touching them.

I always load developing in the early phases at the lands, this will negate most of the concern when jamming them with, as you have said maxing out pressure.

Gerard
Posts: 160
Joined: Fri Feb 26, 2016 1:36 pm
Location: Rifle Range QLD

Re: When to work on Jump/Jam during load development process

#3 Postby Gerard » Thu Apr 27, 2017 12:05 am

Thank you Jasmay, that sounds like a sensible and safer way to develop.


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