Checked chamber lengh for my 1893 Spanish Mauser and got 3.165" to the lands...

[Patrick Chadwick]

To put it quite bluntly (without intending to be rude!) - Stop messing around with plinker bullets!

I copied this from a previous thread on the same problem (in a Mosin-Nagant 91/30 sniper):

".. A possible problem is that the throat of the rifle is deep enough that the boat tail is coming free of the cartridge neck before the bullet is engaging the lands. This can actually lead to a worse internal ballistic performance and group size than with flat-base projectiles, as the gas blow-by on the bullet can cause it to be engraved with a slight skew**. Check the absolute maximum OAL you can use (with the bullet touching the lands) and if, in this position, the start of the boat tail is out of the case, stick to flat-base. That is precisely the situation with my 91/30. So the direct answer to your question is: yes I have tried HPBT, but the flat-base round-nose or spitzer types fly better in my rifle!

*Get the Sierra book for detailed trajectory values.

**I suggest that you get out your pocket calculator and work out how much skew over the length of the parallel section of an HPBT corresponds to 1 MOA. It is very, very, small."

and next day:

"Ah well, since no-one else worked it out yet...
Using the old rule of thumb:

1 MOA corresponds to 1" at 100 yds.
so
1 MOA is 1/1000" at 1/10 yd or 3.6"
and over half an inch (the approx. length of the parallel section on an HPBT)
1MOA is 1/1000" divided by 3.6 x2 or 7.2

About 1.4 tenths of a thousandth of an inch. Small enough for you?

So now it is clear why the bench-rest boys measure things like bullet run-out in the case.
And why they try to get the "slop" of the neck in the chamber down to well-nigh zero.
And why neck sizing your fired case, leaving an ever-so-tiny unsized ring at the bottom of the neck that provides automatic centering of the neck in the chamber improves accuracy.

It's not just nit-picky fiddling around - it really can make a difference - if you and your rifle are good enough."

Use the longest bullets you can find for the 7x57. Flat base bullets. Something in the 160-180 grain range. For instance, the S&B "SPCE" bullets produce excellent results, as they have a long cylindrical section up to the step. They also cut very clean holes!