Re: Same case, different caliber

12 November 2004, 08:36

denton

Re: Same case, different caliber - is there a rule?

Changing the bullet diameter changes the optimum powder speed. All other factors equal, bigger bores will want faster powders.

You absolutely cannot safely use loads designed for the 243 in the 308, or vice versa, even though they are the same case. Piston info offered earlier is dead on.

13 November 2004, 15:00

Mike375

Here is a reasonably good figure to use.

In the following bore sizes

270, 30, 338, 375, 416 and 458 the percentage change between each calibre is almost identical.

If you move down one calibre, such as 30 to 270 then the small calibre will use about the same load with a bullet that weighs 60% of the larger calibre. That is, top loads for a 110 grain 270 will be about the same as top loads for a 180 grain in 30 calibre, using the same case of course.

A 30/06 with 150 grain bullets would be similar to the 338/06 with 250 grainers and ditto for the 30/378 and 338/378.

Mike

12 November 2004, 06:21

ricciardelli

Not really...

12 November 2004, 17:55

jeffeosso

NO!!

jeffe

14 November 2004, 13:31

Hot Core

Quote:

In general, can you load a case with the same charge in different calibers, if the bullet SD is the same (and design, etc.) with similar pressures?...

Hey Taylor, There are perhaps some examples where your premise could in fact be shown to be "True". The problem is it doesn't hold true in all examples using the same case and changing the caliber. Therefore, it can be misleading and get a person into trouble while they believe they are in fact SAFE.

Just saw a post on the GunSmithing Board where a new fellow to AR mentioned he had total confidence in his chronograph and kept dumping in Powder until it registered what he thought the velocity should be from some randomly selected Manuals. He ended up sticking his Bolt and later determined he had a chronograph problem. He completely forgot the very most basic rules of Reloading and was lucky that he didn't blow-up his rifle.

---

There are only a few rules that apply to all cartridges and they are fairly easy to remember:

1. Always develop a load from below after refrencing multiple data sources and STOP adding Powder when "ANY" of the colloquial Pressure Indicators tell you that you might have gone too far. Then back off a bit and Fine Tune the Loads accuracy by varying the Seating Depth.
2. An inexpensive 0.0001" capable Micrometer is the best relative Pressure Indicator in existance.
3. HSGS = Reloaders Pyrite(aka Fool's Gold)

Just that simple.

14 November 2004, 16:38

Mike375

Great pattern!
Why didn't you keep going with smaller bores?

The percentage change is not the same, although 257 and 284 fit OK.

One I did leave out is 510 and 458 to 510 fits the pattern but I have never loaded for anything in 510 calibre but I would bet it would hold OK.

The one variation is if the "new calibre" has very big free bore. You see this with loading between the 378, 416 and 460 Wbys. The 378 and 460 have huge freebore but the 416 Wby has normal freebore. When the 416 Wby loads are used as the benchmark both the 378 and 460 use quite a bit more powder than predicted.

Mike

15 November 2004, 07:43

Jerry Eden

Bwana-Be:

Here is some actuall experience, not hypothetical!
I load for 6mm-06, 6.5mm-06, 270, 30-06, 338-06, and 35 Whelen. Other than the 28 caliber, that covers most of the popular cases built upon the 30-06.

The loads are not interchangable at all,

I cannot load the same charge of 4064 in the 338-06 as I can the 35 Whelen, even though they are close in bore diameter, without the 338 pressures going up to high. Also in one of my 270's I can load 58 grains of a particular IMR powder, and I can only get 54 grains of the same powder to work with safe pressures in the 6.5-06, again very close to one another in bore diameter.

All of this still leads us back to the statement, that all firearms are different, and a prudent reloader starts his load charges low and works up.

Jerry