Worked up some loads for my Mosin

[Kicker96FS]

So today I got up and figured I would head over to the club to see how the reloads I worked up for my Mosin worked before I start myself into a reloading frenzy.

After tumbling, decaping and resizing, trimming and priming, I grabbed my brand new Hornady reloading bible #8 and found the page for the bullet I was using, the Hornady #3131. It is a 303 cal. at .3105.

I used IMR #4895 powder.

I made four loads, five rounds each as follows:

40 grain
42 grain
43.3 grain
44.5 grain

Shot them at 50 yards.

The 40 was not too bad, not a real tight group but all about 3" from each other,

The 42 was way cool, All shots in a one inch square!

The 43.3 was not cool, 6" apart.

The 44.5 was nuts! Over a 12" spread!

So I guess the 42 wins! Now to crank out some ammo!

 

[Tyke]

Why would small percentage changes in powder load have such a great effect on precision?

 

[Kicker96FS]

Short answer, it does as you can see. For the long answer, wait for Dukeinmaine to chime in.

Something to do with pressure, too much, not enough, and just right.

 

[bpm990d]

What kind of groups do you get with ball ammo at 50 yards?

B

 

[EddieCoyle]

Why would small percentage changes in powder load have such a great effect on precision?

Kicker96FS's group size differences are an order of magnitude bigger than anything I've experienced with small changes in powder charge.

But...

Changing the powder charge changes the velocity. Different velocities can have an effect on barrel harmonics and bullet stabilization both of which can cause group size to change.

 

[Slowdive]

Wow. I usually only see fractions of an inch of difference @ 100 yards. Generally I only see the difference if I shoot dozens of groups and measure the average group size and the standard deviation. When I settled on my current .308 load, I shot 50 five shot groups with 2 loads. The average difference was < 0.2".

Barrel harmonics can be a strange thing...I have some different 45-70 loads that print groups 10" apart @ 100yards. With that level of sensitivity, it'll be interesting to see if your groups hold together when the weather gets warm and humid.

ETA: I thought this was a good article on ladder testing. http://www.6mmbr.com/laddertest.html

 

[EddieCoyle]

Generally I only see the difference if I shoot dozens of groups and measure the average group size and the standard deviation.

I've found the same to be true once you're doing most everything else 'right' and you're using a good rifle. But if you have an AK or Mini 14 or some other rifle with tons of barrel whip, charge weight and velocity makes more of a difference. I don't load 7.62x54R so I can't speak for what happens with a Mosin.

If you have an AR with a good barrel or a decent bolt gun, and you pick good bullets, use a 'competition' seating die, seat bullets to the right depth, sort your brass by headstamp, number of times fired, and weight, and then prep it right, it takes many groups to determine the best charge weight. Even then, I'm not sure if powder charge has as much of an effect as other stuff.

If you go full retard on brass prep by doing things like uniforming primer pockets, deburring flash holes, checking flash hole diameter, and measuring neck concentricity, then I think maybe that charge weight (and velocity) will have a more obvious impact on velocity, provided you can shoot well enough to tell the difference.

I'll let you know when/if I get there. That's why this hobby is so f-ing fascinating.