How much to back off in powder to try a new bullet (same gr weight)?

[SGK]

So if I have a load with 168gr ELD-M of 44 gr of Varget (308) how far would you back off to try some 168gr Berger Hybrid Target?

 

[10at6]

Not much

 

[Park ranger]

Going from a Hornady to Berger not much, but I probably would if going from Berger to H. 1/2 grain or so

 

[spclark]

Depends on how bullets’ bearing surface length differs; longer surface = more resistance to engraving by lands when fired, higher pressures.

Too, if BTO dimension changes, and both bullets are seated to same dimension - either on or off lands - higher pressures will occur when longer bullet’s fired. Reason being, longer bullet will reduce case capacity more than shorter one.

Going from ELD to Hybrid will be different than going Hybrid > ELD.

When I switched from Berger 6mm 105 VLD to their then-new Hybrid, bearing surfaces were close enough no change was indicated yet I backed off 0.5 grain anyway, then worked up.

 

[Rsadams]

I would say what Sierra told me when going from a 168gr matchkings to a168gr tipped matchking.... 2/10s to 3/10s and work up... But safer and more is ALWAYS better , different bullets have different bearing surfaces... Plus you need to make sure if useing a longer bullet it's not into the lands creating more pressure unless you're putting it there... There's no substitute for safety in reloading... Back it down till your comfortable and work back up , your gut is normally correct....

Sorry Spclark you posted before I got done...

 

[Shynloco]

Most folks I've shot with start off at least 10 thou off and see how they group in three shot groups. Then move 5 thou either in or out at a time and retest. Keep in mind, most .308's I've tested don't like the jam, while others have loved it. What I do in testing a new bullet, is to find the "Accuracy Load" or recommended AOL in the Manufacturer Loading Manual. Load two or three 3/shot groups and see how they group. THEN start moving the bullet 5 thou inward toward the lands until you find the best grouping. Then move 2 thou and 1 thou at a time for fine tuning. Each rifle has it's own likes or dislikes, even of the same make and caliber. SO what someone recommends and says works in their rifles, may not be what your particular rifle likes. I've even seen two rifles, same caliber, same manufacturer (not custom but "across the counter" rifles with successive serial numbers) end up with two different Seating Depths using the same bullet. And then upon changing the barrels to Match Barrels, one liked the jam while the other not so much (ended up 10 thou off for best grouping). Hope that helps.

Alex

 

[spclark]

Sorry Spclark you posted before I got done...

No need for that. Your comments reiterate what I posted, we’re on the same page with this for the OP’s benefit.

 

[TheOtherZilla]

Whats the Berger load data say?

 

[SGK]

Whats the Berger load data say?

A very good point! 42.5gr is max listed load. (44gr was max load listed in Hornady manual) Seems like I should just start 4-5% below 42.5gr and ladder up (again). I find it interesting that the two manuals can be 1.5gr apart. It's not as if the tables are for specific profile bullets. All the Berger 168 gr are lumped in together, for example. while Hornady groups together 165-168gr. Hornady assumes 22" barrel, Berger 24". Mine (a Blaser sporter) is 23".

(50 thou jump has been the sweet spot in my testing with ELD-M.)

 

[Billy 30-06]

I would back off 1 full grain and work back up 1/2 grain at a time. This way you could dial in the new bullet.
Billy

 

[savagedasher]

Full 20 % Depends on case volume

 

[uncle-buck]

Am still learning how to use QuickLOAD, but it has been well worth the $160 when it comes to answering questions like those asked by the OP.

 

[Zero333]

If 44 gr was the sweet spot for the 168 eldm, I would back down to 43gr and re work the load up to 45'ish grains to find the sweet spot for the 168 berger.

 

[SGK]

I would back off 1 full grain and work back up 1/2 grain at a time.

If 44 gr was the sweet spot for the 168 eldm, I would back down to 43gr and re work the load up to 45'ish grains

Both of those starting points exceed the max listed load in the Berger manual...

Full 20 % Depends on case volume

I don't follow. Assume using same cases.

 

[savagedasher]

Many of cases can have as much as 3 grains of capacity differences

 

[SGK]

Depends on how bullets’ bearing surface length differs; longer surface = more resistance to engraving by lands when fired, higher pressures.

Too, if BTO dimension changes, and both bullets are seated to same dimension - either on or off lands - higher pressures will occur when longer bullet’s fired. Reason being, longer bullet will reduce case capacity more than shorter one.

Understood. I think I will examine a sample of each bullet more closely in this regard. I find it interesting that a bundle of 4 bullets for Berger produces a listed 42.5 gr max and a bundle of 8 bullets for Hornady produces a listed max of 44 gr. I view these listed max figures as a hard stop.

Am still learning how to use QuickLOAD, but it has been well worth the $160 when it comes to answering questions like those asked by the OP.

You are likely correct. To date I have been bugging a friend who has it to give me info. However, I've still to refine the inputs for him (case capacity, measured muzzle velocity etc). Unfortunately I don't have a way currently to run Windows.

@savagedasher FWIW I did an H2O capacity test of a sample of 16 RWS 308 cases I have here. Cleaned, resized and plugged using the 21st Century primer plug. While raw case weight varied a decent amount - ES of 5.3 gr; SD 1.4 gr - the variance in H2O capacity was much less - ES 1.0 gr and SD of 0.3 gr.