Powder Charge for Finding Optimum COAL

[Rosco-Pico]

Good Morning!

I've got a silly question and would like some guidance if possible. Here's the info:

Model 70 Win .25-06
H4831SC
Norma Brass trimmed to 2.484
WLR Primer
Berger 115 VLD
COAL -- 3.250
Forster FL Benchrest Sizer and Ultra Micrometer

I've followed what was posted in Bergers Load Recipe for the above combination. My rifle seemed to prefer the lower side in powder weight, 49 grains to be exact. Book specifies 48.5 - 54.3. I know I doing this backwards, but I was looking for my COAL/CBTO. I used a Hornady/Stoney point gauge and a dummy round that's been fire formed with a 115gn VLD. When using Bergers recommended jump off lands with 6 rounds each at:

-- 0.010 off lands
-- 0.050 off lands
-- 0.090 off lands
-- 0.130 off lands

Should I keep the same powder charge of 49.00 grains while doing this? I know the pressure will decrease the further I seat it out. Will this be an issue?

Second, a 0.010 jump, the bullet is really hanging out there. Not concerned about neck tension. Just curious if only half of the bullet journal is seated in neck.

Thanks for the help!

 

[Ironicaintit]

I'd keep that same powder charge while you find your optimum COAL.
Once that dimension's found, you could then go back and retweek your powder charge.

Like dialing in a carburetor.... Make one change at a time.

 

[JimKirk]

I almost always find three nodes of accuracy ... one at the lower end, the middle and one somewhere close to maximum powder wise ... that being said .... I would work much more between the 0.010" & 0.050" settings ...in 0.010" increments and then once I found the "better" spot there ... jump down to 0.005" and work up or down and dial it closer ...

Just remember that every rifle is like children ... no two are the same ... even if they do look like twins ...

 

[Bart B.]

I only find one accuracy node for any given bullet and powder. It spans near a 10% spread in charge weight and almost .100" spread in cartridge OAL length plus near .100" spread in bullet jump to lands for over the counter sporting rifles.

The land's contact point on bullets in that rifle will advance .001" for every 25 to 30 rounds fired. So, seating bullets a given distance off the lands means changing your seater setting that much that often. I think that's a waste of time.

I don't think you'll see any significant accuracy change over the 2000 round "best accuracy" barrel life it'll have if you seat them .010" off the lands to start with. Then shoot at least 15 (20's better) shots per test group. If you shoot 5 or less shots per test group, any combination of the three node factors stated above in different settings can produce tiny groups once in a while.

However, there's no standard for determining accuracy nodes, so, any load with the details that shoots the smallest same size test groups all the time may well be the best "node."

 

[JimKirk]

I only report my findings ... Yours I am sure are better....

 

[243winxb]

Should I keep the same powder charge of 49.00 grains while doing this? I know the pressure will decrease the further I seat it out. Will this be an issue?

Second, a 0.010 jump, the bullet is really hanging out there. Not concerned about neck tension. Just curious if only half of the bullet journal is seated in neck.

I dont agree with the Berger method, to much adjustment. The full diameter of the bullet shank should be in contact with the case neck. If COL is to long for the magazine or bullet is into the rifling, make the COL shorter so the round fits. Use the starting powder charge and work up for accuracy. Take the best load, now vari the COL by .010" to fine tune. This works for all bullets, not just VLD ones.

 

[Bart B.]

The full diameter of the bullet shank should be in contact with the case neck.

I've no idea where that myth comes from. Nor what theory there is that makes it so popular. It's known as seating bullets one caliber deep. And one of many myths amongst reloaders. But never a standard for commercial or arsenal precision and accurate ammo. Seldom, if ever, counters a query about seating bullets some amount from the lands.

 

[DownInTheDark]

I tried messing around with the COAL for my 35 Whelen, and noticed I was the biggest variable in accuracy.

 

[Bart B.]

When the COAL is increased for a given load reducing bullet jump distance to the lands, peak pressure and bullet velocity go up. Consider this when adjusting COAL is the last part of your load workup routine.

Pressure tests for a given load starting with the bullet touching the lands show a drop as bullet jump increases from zero to some value. Increasing it further starts peak pressure going back up.

Here's a great thread on jumping bullets and seating depths; pay close attention to Unclenick's comments.

https://thefiringline.com/forums/showthread.php?t=581192