Sight adjustment when shooting cast bullets

[Dombo63]

The Singer sight on my No 4 is spot on when using HPS Target ammo or my own handholds, 174gn SMK and a worked-up load of N140.
200gn cast bullets are much slower so will drop further for a given distance. Is there an easy way to calculate what the sight settings should be when using these bullets at different ranges?
One method i thought of was to run a ballistics calculator using the cast bullet's weight and MV then compare the resultant bullet drops to a table of standard FMJ rounds at normal MV and match them off. So if a cast bullet travelling at 1650 fps drops 18 inches at 300 yards, and a jacketed round at 2450 fps drops 15 inches at 200 yards, set the sight to approx 300 when shooting cast at 200.
Is this correct or am i missing something?

[bewildered]

I use 190g lead bullets in front of 16g of Alliant 2400 powder giving me 1550fps in my 308 target rifle.
My scope is zeroed on 200yds using a 145g fmj home load about equivalent to RG 145g ammo.

By a process of trial and error, skill (not much!) and good luck plus the help of a good spotter (vital) to watch the shot fall on the bank I needed to increase the elevation by 13 mins to get the lead bullets in the bull at 200yds and by 22mins for 300yds.

[andrew375]

The easiest way I found was to simply work back through the distances, make sure you let the marker know what you are doing. Targets are big enough that just a cranking up the rear sight by guess work will put you on paper first shot. A problem comes going from 300 to 500 yards as that is quite a step, but the more experienced you get the more accurate your feel for that "educated guess".

Write everything down so you only have to learn it once!

I've also used ballistics software, I mainly use the simple spread sheet type, like ballistics calculator97 as I don't have to put up with the hassle of installing the software and are usually simpler to use. I use the calculator to make a zeroing target as you get at from the range office at Bisley. This can be frighteningly accurate, like being just half a minute out at 1000 yards. As always accuracy of the result is dependent upon the accuracy of input data. Bullet weight is irrelevant to this exercise you need the ballistic coefficient which is usually listed nowadays by the mould maker. Also, if not already, your velocity value should come by chronographing the ammunition in your rifle.

For distances greater than 200 yards velocity is your friend. Apart from anything else I have found that best accuracy with cast bullets in centre-fire rifles, apart from pistol chamberings, comes at over 2000 fps. My K31 wont do anything with the Lee .310-150fp at under 2000 fps but I consistently get 3 moa ten shot groups when pushing them at 2160fps. This is with the issue sights and no sling so those groups contain a lot of operator error. I've never achieved any useful accuracy with the often quoted 16 grains of 2400, but in the K31 a load to give me 2190fps the above mentioned bullet gives the above mentioned accuracy.

[Dombo63]

Thanks both. I was looking to shoot them beyond 200 yards but to get the MV over 2000fps would I need to go back to N140 rather than Alliant Unique?
And my other question would be re leading as I had heard that at FMJ velocities was bullets leave a lot of lead in the barrel.
These bullets I have are all gas-checked and lubed btw.

[dromia]

If you are shooting over 200 yrds at known distance then why go over 2000 fps.

My 600 yrd target loads go around 1600-1800 fps depending on calibre and bullet weight with N110 or N120 powders.

[andrew375]

I've been up to 1900 fps with GM3 with no problems, I just feel better with a slower powder so I can keep the peak pressure down. Powders like N110, N120, Loxex S040, D060 and vectan tubal 3000 all work good. I don't use that many different powders as I buy in bulk, 4Kg minimum, when I find something at a good price. I use a lot of N140 because I can use it in a wide variety of applications.

The reasons for going for over 2000fps are; that is where I get best accuracy and when shooting outside you have the wind to contend with so the less time the bullet spends in the air the better. But mainly it is the accuracy. Like I said I've simply never achieved anything like accuracy with the much vaunted Ed Harris loads with 2400. The only real exception is my .375 Holland & Holland with a 280 gr. plain base and GM3 for 1700 fps, this will shoot .6 minute groups all day so long as I do my bit.

As for leading that is more a function of bullet fit, bullet hardness and/or peak pressure than velocity. Usually bullet fit is the problem. Bullets must be at the groove diameter of YOUR barrel or larger. The problem with commercially cast bullets, apart from usually being too hard, is they are sized to "nominal size" which is invariably too small; .308" for .30 cals and worst of all .311 for .303. Tenths of a thousands of an inch make all the difference. For example recommended bullet size for 7.5 Swiss is .308", but my K31 slugs out at 3088". Bullets drop form my mould at .310". I use a .309" sizing die to lube and seat gas checks. This bullet will give me sub 2" 10 shot groups at 50 metres consistently. That was until I used a new batch of bullets which just made a random pattern! Measuring the bullets showed they were .308"; I'd put the wrong sizing die in the machine! Fortunately only 100 or so had to go back in the pot. BTW I use the .308 die for my 7.62 target rifle that has a .3072" barrel.