Starting a load workup for a bullet with no published data available.

[amlevin]

When starting out with an "odd weight" bullet, one that isn't in any of the load manuals, what do you all use for that initial load range. Do you just start with data for the next highest weight listed in Powder Mfr's data or reduce the charge a little from recommended loads using a the next lightest bullet?

As an example, most powder manufacturers list powder charge ranges for 175 gr bullets and 180 grain bullets but not the popular 178 gr A-Max.

This is also the case with 69 gr bullets and 75 gr bullets but not 73 gr bullets like the Berger .224" 73 gr.

The list goes on with lots of bullets that are "tweener weights".

Just interested in how others go about determining the starting points for a load workup without wasting a lot of components?

Not so much interested in specific loads for the bullets I mentioned but the process in general. SWAG? Extrapolate a load based on charge weight value differences and bullet weight differences from published data? I know that one could just shoot a "Ladder Test" but what would be a realistic "mid-point" for any of these tests or do you just start real low and stop when the bolt won't lift

 

[ShootDots]

First you have to find out IF POSSIBLE, if your intended bullet has a longer or shorter bearing surface than the next heaviest projectile. EXAMPLE: The Berger 108's have a CONSIDERABLY longer bearing surface than the Berger 105 VLD's.. The difference in weight is small, almost insignificant, BUT the difference in bearing surface is GREAT! The 108's will build pressure FASTER than the 105's and MORE OF IT with the same charge of the same powder.

So if you are looking for a 178 AMAX, I would look to a 180gr HUNTING bullet, that PROBABLY has a longer bearing surface, and work from that load. If the hunting bullet does have a longer bearing surface, the load manual will show LOWER powder charges for the same powder BECAUSE it will build more pressure than a shorter bearing surface. That should get you safely started..

 

[spclark]

Weight ought to be your first consideration when trying to interpolate starting loads for an unpublished bullet. Do your research, find a few published loads for bullets of that weight range THEN compare the bearing surface length of your bullet against the "known" choices.

Two bullets of equal weight but dramatically different bearing surfaces will behave differently in a given chamber / barrel. The one with greater bearing surface will need reduced load as friction AND the energy needed to deform bullet jacket to the lands and grooves will affect pressure curves.

Remember too you're starting from a little better than scratch this way so starting on the low end of suggested loads for not-quite-the-same bullet is a good idea.

(I'd drafted my post but got sidetracked before posting it. ShootDots & I are in agreement here I think....)

 

[ShootDots]

I believe we are on the exact same page Mr. Clark...

 

[amlevin]

Thank you gentlemen for your replies. I have been paying attention to bearing surface whenever I changed bullet mfr's but stayed within the same weight.

I've been measuring the bearing surface by marking up the side of the bullet jacket then dragging the bullet across a piece of bond paper lying on a flat surface (usually a small sheet of glass). Using my calipers I then measure the length of the wiped area. Never have been able to wrap my head around just using two bullet comparator devices on my calipers.

Now, if only bullet manufacturer's would just publish the "bearing surface lengths" for at least their match grade bullets :

 

[spclark]

You're likely to get a more accurate reading with the mark'n'drag operation; that's a clever trick, I'll remember that next time. Few of us have access to optical comparators I'd think.

The dueling comparator method doesn't account for the curved / angled profiles front & back, adding two uncertainty factors to any dimension derived.

BTW, Berger does publish dimensional data for all their bullets, not just their match (target) line:

http://www.bergerbullets.com/pdf/Quick-Reference-Sheets.pdf