Discrepancy in load data

[toby]

Simple theory, all bullets are different regardless that they may all be 168 grain.

[LynnJr]

OP
The manufacturers know exactly what they are doing and there data is usually spot on.
You should be getting roughly 10 fps velocity change per 0.1 grain of powder change except when in a node.
That said you failed to post the C.O.A.L. of same bullet using same powder in same barrel length.
If you or anyone here were top look up the data from Sierra bullets on a 117 grain bullet in the 25-06 cartridge using two different Sierra reloading manuals it would appear to be a misprint as one lists the max load below the other books starting load.
This data can be found in the 50th anniversary book and the earlier 4th edition book if my memory is any good.
If you load your rounds to either books specs they both come out safe.
How is this possible your asking about now? You need to checkout the C.O.A.L. of each book.
By loading your rounds longer you are creating a larger pressure vessel thus reducing pressure from the same amount of powder burned.
To give you an extremely exaggerated example put your head in a small fish tank and have a buddy drop an M80 in it next to your head.
Now have your same buddy drop a similar M80 in the south end of Lake Tahoe while your head is in the north end of the lake.
In both examples the same amount of powder gets burned but in the much larger pressure vessel you most likely wouldn't even notice it and in the smaller one serious harm is likely.

The correct term is Freebore and it is how Roy Weatherby got more velocity out of his cartridges than anyone else of that era.

On the bearing surface statement that is generally a correct statement but as of late most manufacturers have solved or created a new issue depending on which side of the fence you sit.
The current trend in Monolithic Solids is to put waste bands on the bearing surfaces in order to reduce friction. Some solids have 4-6 ridges and some like the AAA-Harlow Boreriders have wide sections completely removed to reduce friction.
Length of the bullet no longer matters as todays bullets will have multiple designs in a single bullet.
Today we should probably say the total bearing surface friction producing area is larger thus creating higher pressure signs but nobody is going to do that.
Go back and look at barrel length and C.O.A.L. and let me know if your data now jives.

[pacrat]

Earlier versions of the Barnes all copper bullets had no driving bands. Increased bearing surface greatly effected pressure spiking. Especialy when you consider the construction difference between a soft lead w jacket and solid. Significant more pressure to engrave the solids.

Other solid copper bullets such as the Nosler E-tip the pressure spike cautions still apply. Hard engraving and increased bore bearing surface.

No matter which type bullet you choose. Remember there are no SAFE SHORTCUTS. Always start low and work up slow in small increments.

JM2c

[LynnJr]

Pacrat
We are in total agreement on the bearing surface. It is the surface area that matters most and not the bullets overall length.
Not only that but the barrel manufacturers are now creating barrels with different bore to groove ratios just for the solids so the combustion gases escaping around the bullet don't erode the throat as much. The solids don't slug up like the lead core jacketed bullets do so you don't need a lot of engraving.

[J-cat]

On that note, I have found Sierra's beating surface length to vary by as much as .050" between lots, which could contribute to the discrepancy.

[J-cat]

You should be getting roughly 10 fps velocity change per 0.1 grain of powder change except when in a node.

Could you explain the "when in a node" more.

[LynnJr]

As you increase your powder charge in a typical burn zone the charge weight and fps tend to go hand in hand with each other.
When you reach a node your fps will no longer keep up with your powder charge in nice even increments.
As you keep going up past the second node and reach pressure the velocity will skyrocket with the same amount of powder change.

If you generally use 44 grains of powder and use 0.4 tenth increments you should see uniform velocity from 40-46 grains except for the node at 44 grains. When you get into high pressure above 46 grains 0.4 grains of powder might make the velocity change 80-100 fps. This is only an example.

[J-cat]

I'm seeing about 5 FPS per .1gr of IMR4064 in the 41.something grain range with 175/185gr bullets in my 308. But I'm also not seeing any difference at all in average velocity between 41.6 and 41.7 grains. I checked the weights several times using a Gempro. So I'm wondering if I have reached powder charge nirvana.

[LynnJr]

If your varying your charge 0.1 and your velocity is only changing 5 fps you are most likely into a node.
It is important to note that nodes have width so if you only see this condition over 0.1 grains your powder is not of a optimum burn rate or your sededing an anomaly in your data.

[edwardm]

I've prepped some of those Federal cases but haven't loaded them yet.

Let me share with you what the consensus seems be on Federal .308 cases for reloading.

1) They are capable of good if not great accuracy with proper brass prep.
2) They are thinner, softer, and lighter than most other manufacturers.
3) The primer pockets are usually the first to go (enlarge too much) and the cases aren't suitable after that.

Anyway, load with them with confidence and I'd have a back-up plan after 4 firings.

Truth spoken. Gets worse - lately, Winchester 308 (not WCC surplus) brass has been worse. After 1 firing, about 20% of the primer pockets are loose and 5-10% will drop a primer with just a gentle rap of the case on my bench. In a pinch I'll use that stuff for one last load in a bolt gun - otherwise into the recycling bucket.

[JagerDog]

I want to start using 168 gr. A-max in my .308 win for target shooting, but the the load data that I'm looking at is inconsistent. I don't know what I should use for starting load and what is the absolute max load.

Here is a table of the different load data.


My rifle is a Savage 10 FCP-K. Using 168 gr. SMK's, I started at 41.0 gr Varget and worked my way up to 46.0 gr in 0.5 gr increments without noticing any pressure signs. My best groups at 100 yards were with 44.5 gr Varget
.
[B]Since it worked with 168 gr. SMK, can I start 168 gr. A-max at 41.0 gr?[/B]

Here are the components I want to use.
Bullets: 168 gr A-max
Powder: Varget
Primers: Winchester Large Rifle

Yes