Selecting a practice load - correct me if wrong...

[miko]

Let's say my carry load is .357 Mag 125 grains.

I want to practice with mild loads that cost less and put less wear on the gun and brass. At the same time I might want a practice load to reasonably reproduce some ballistic aspects of the carry load - specifically the point of impact (at close range) and felt recoil.

If I replace the 125 grain bullet with, say, 158 grain bullet (126% weight), I can drop the muzzle velocity to 79% for similar recoil/muzzle flip, etc.
Such a drop in muzzle velocity would mean 63% of original energy.
That means at least 37% less powder.

With bullets of 180 grain (144% weight), velocity can be reduced to 69% and energy to 48% - 52% less.

Sure, heavy bullets cost more but so does powder. What say you?

miko

 

[Cellar Dweller]

1. POI would be off, but at short range (like you stated) it shouldn't matter much, BUT:

2. You can't arbitrarily reduce powder by % and get the same results. From Accurate's 2003 edition, which is the most handy reference I have at the moment:

125 XTP start charge 158 XTP start charge % change
No. 2 7.6 5.9 77.6%
No. 5 10.4 8.8 84.6%
No. 7 11.9 10.3 86.5%
No. 9 15.3 13.5 88.2%
4100 17.3 14.2 82.1%

So the manufacturer's MINIMUM recommendation is not a simple formula, plus all are above your calculated % by quite a bit. YMMV, you may get it to work or you may have squibs. POI would definitely be off but, since I don't have a ballistic calculator handy, couldn't tell you how much.

 

[CZ57]

Bullet cost is a more significant cost factor than powder. Then, you can go to a slightly faster than magnum powder to build the same velocity, like AA#7 which is a good one, or Blue Dot has always been fairly popular for this and you will reduce cost through lower chargeweights. Building magnum loads with something like Unique doesn't excite me personally and I wouldn't use a powder that fast to do it, but certainly not with a powder faster than Unique. I agree with practicing with a load that feels like your carry or defense load. Really hard cast lead bullets like those from LaserCast/Oregon Trails might be an option to consider.

 

[Steve C]

According to your calc's if you take a 125gr JHP full power load from a 4" barrel at 1,450 fps and use the 79% of the velocity for a 158gr bullet you get 1,146 fps (rounded) which is quite easily obtained using a 158gr cast. About a 100 fps less than full power factory.

A load of 12.3grs of AA#9 set off with a CCI550 primer pushes a 158gr LSWC out the muzzle of my S&W 66 4" at 1,268 fps average.

If I wanted 1,150 or so I'd be looking at trying 6.5grs of Unique. You'd need a chrono to run both your 125gr defense load and your reload through to see what the real velocities are.

 

[joneb]

I've had good luck with AA#5 for 140gr Raineer plated using wsp and 8.3 gr of powder for reduced .357 mag loads. Duplicating POI with 158gr bullets could be a challenge, I don't think recoil is the only factor in POI, the dwell time of the bullet in the barrel could be a factor as well.

 

[only1asterisk]

If I replace the 125 grain bullet with, say, 158 grain bullet (126% weight), I can drop the muzzle velocity to 79% for similar recoil/muzzle flip, etc.
Such a drop in muzzle velocity would mean 63% of original energy.
That means at least 37% less powder.

With bullets of 180 grain (144% weight), velocity can be reduced to 69% and energy to 48% - 52% less.

Maybe not exactly. The recoil will feel different and the difference in muzzle blast will likely be pronounced between a 180 grainer and 125 loaded to the same powerfactor. Finding two dissimilar loads with the same POI is mostly luck, but at if your shooting is under 25 yards or so, you should have no problem finding something that is close enough for good practice.

David

 

[Steve C]

One thing is that while the recoil with a heavier bullet may be the same the fact that its moving slower will give it more dwell time in the barrel thus making it print higher, how much is something to find out through experementation. At under 15 yds pretty much everything shoots to point of aim in my pistols.

 

[Bullet]

miko
Let's say my carry load is .357 Mag 125 grains.

I want to practice with mild loads that cost less and put less wear on the gun and brass.

This is why a lot of people like 357’s - Practice mild load = 38 Specials.

miko
At the same time I might want a practice load to reasonably reproduce some ballistic aspects of the carry load - specifically the point of impact (at close range) and felt recoil.

Then load some 357 Mag 125gr to reasonably reproduce the ballistic of your carry load.