Is a powder change needed for my mauser 43

[tony1]

I have brought a mauser 43 mould for my 1871/84 mauser however the wt of this bullet head is 340g, I have been using a 370g bullet head made for me.
as I have been using a 70 grains of fine black powder with the 370g head, will I need to change the wt of powder when shooting the 340g head
so I hit the same area at 100yrds with the new wight bullet.
hope you understand what I am asking.
thanks

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[Patrick Chadwick]

The answer is - in principle - yes. However, there are so many variables that play a role. For instance, if the diameter of the lighter bullet is just a tad (US unit of measurement) or gnat's whisker (British) larger, then it will be a wee bit tighter in the neck and may well achieve a higher velocity. On the other hand, if it is set to the same overall length, then there is a small space under the lighter bullet, causing reduced peak pressure and hence muzzle velocity ... and then, again, etc etc...

In other words, forget theory, you are going to have to try it out. As a first step, I suggest you load the cases with the lighter bullet to exactly the same overall length as for the heavier bullet, establish the difference in the height of the bullet base, and adjust the powder accordingly, to have the same packing density as before. Assuming, of course, that the seating depth was optimized in the first place...

Sorry I cannot be more precise!

Patrick

[fndrbass19]

haha. it's too bad we can't all agree on a standard unit of measurement.

[Patrick Chadwick]

Well, I grew up with imperial units, learnt CGS units (centimeter-gramm-second) units at school, changed to MKS (meter-kilogram-second) at university, did mechanical engineering with BSF, BSW, BSC, BA.... threads, changed to metric over here, now need (for Europeans) eccentric US threads...
So I have draws full of taps and dies - and some of them even match! Boy, do I know about different standards!

But the serious point of my posting was that there are so many variables that affect a BPCR, that the practical effects of bullet form and hardness, lubrication, neck tightness, seating depth, powder type, packing density, wads (yes/no/what material/how thick) + barrel condition, fouling, bedding etc. etc. that I would not bother with any kind of theoretical calculation but get down to the range and try it out, as recommended in the second part of my previous contribution.

BTW, Tony1, if you want to get the best accuracy from your 71/84, I think you are probably moving the wrong way. Heavier bullets are often more accurate - not because of the weight, but because a longer cylindrical section provides better guidance in the throat, allowing you to seat the bullet closer to the lands while still having a sufficient length in the case neck for good obturation.

Patrick