pure lead and velocity

[canuck4570]

in a 450 marlin is 1100 fps to fast for pure lead bullets ?
thank you

[leftiye]

Shouldn't be. Believe it or not boolits have been shot at 1000 fps and below sucessfully even when not lubed, so pure lead at those velocities should be no problemo (especially when lubed - and your boolit design carries a lot of lube). I don't quite understand your affinity for 1100 fps.. Even pure lead will sucessfuly shoot faster than that. Happens alla time with Black powder. 1200 fps or better still 1300 fps would give you nice expansion without the hollowpoint. And it should kick butt on almost anything in this hemisphere.

[canuck4570]

I hunt with what I shoot all year
a 1000+ round so recoil is a factor
I want to enjoy my shooting that is the reason why I shoot low velocity
and use a big bullet for knock down power and I wish it to expand up to 200 yards that is for the hollow point
the nightscope able me to dial in at different yardage easely

[SierraWhiskeyMC]

Something to keep in mind is the speed of sound at the temperatures you'll be hunting.

Here's an online calculator:
http://www.sengpielaudio.com/calculator-speedsound.htm

When your boolits get close to supersonic, they start getting buffeted around quite a bit, which really affects accuracy. Note that the speed of sound is affected a good bit by temperature. If you're going to be hunting in 20°F weather, the speed of sound will be about 1074 feet/sec, and you'd want to stay under 0.9 Mach (speed of sound) to avoid most of the buffeting. 1074 x 0.9 = 967 f/s. If you'd developed a load during hot summer months (say, 85°F), the speed of sound would be closer to 1145 f/s; x 0.9 = 1030 f/s.

Working up a load that shoots well at 85°F may be all over the place when you get into cold weather. You really want to avoid going transonic between the muzzle and the target.

Note that bullet stability is affected by temperature and altitude. One that's marginally stable at high summer temps and/or at high altitudes may be unstable at low altitude/low temps.

There's a spreadsheet containing Miller's stability formula available for download about halfway down this page: http://accurateshooter.wordpress.com/2008/06/03/calculating-bullet-rpm-spin-rates-and-stability/

It's accurate to within about 7%, which is a heck of a lot better than Greenhill's formula.

[canuck4570]

I did not mention it in my previous reply
I go and get by ballistic on JBMhttp://www.jbmballistics.com/~jbm/cgi-bin/jbmdist-5.0.cgi
I take this in account so I took the coldest temperature I hunt in and develop my load accordingly and it is has you say 1080 fps so I develop a bit under this speed
thank you for the stability chart its in my bookmark will read it carefuly
thank again for your experience
will learn something certainly....

[Leftoverdj]

Canuck, I follow your logic and sympathise to a degree. Nothing more is needed for the very little hunting I do. In Virginia woods, 100 yards is a long shot.

I would suggest adding maybe 2% tin though. It will impair expansion very little but do a lot to improve casting and prevent leading. I have a Lee HP mould for the .45-70, but saw some tests of cup pointed bullets that looked intriguing. Instead of an actual cavity, the meplat is made concave to encourage the bullet to rivet. It's said to be less likely to fail to expand because of plugging of the cavity, and to leave far more bullet weight should the expanded portion be wiped off.

[canuck4570]

when I will have the mold hollow pointed I will have a bunch of different plug made for experimenting

[SierraWhiskeyMC]

I did not mention it in my previous reply
I go and get by ballistic on JBMhttp://www.jbmballistics.com/~jbm/cgi-bin/jbmdist-5.0.cgi
I take this in account so I took the coldest temperature I hunt in and develop my load accordingly and it is has you say 1080 fps so I develop a bit under this speed.

Great that you're using some tools to help in developing loads. :)

Keep in mind that as your boolit approaches the speed of sound, the air that's forced out of the boolit's direct path can actually exceed the speed of sound, which creates a great deal of turbulence right next to the boolit; that's why I suggested multiplying the speed of sound at a given temperature by 0.9 to arrive at the maximum subsonic velocity you'd want. The 0.9 is just a "rule of thumb" type thing.

Risking stirring up a 30-page discourse on ballistics :groner: projectiles that are more aerodynamic (like spire points) may be more stable near the speed of sound than boolits with a big fat flat meplat (nose) depending on a lot of other variables.

But to keep it simple (too late! :-P), try experimenting with loads that range from about 0.85 Mach to 0.99 Mach with your particular boolits under relatively stable atmospheric conditions at a known temperature. Fire at least a 5-shot group with each load to see how accurate they are. That will give you "the real deal" kind of data from your rifle using your boolits that you can use to work up loads for colder weather.

If you don't have MS Excel installed, I could run the numbers for you in the stability calculator.
Post your rifle's caliber, rate of twist (inches per turn), boolit weight in grains, boolit length in inches, and I'll give you a ballpark idea of how they'll do.

Leftoverdj's right - a bit o' tin won't hurt expansion much, and will help a great deal in your boolits being fully formed. The most critical part of the boolit is the base; unless it is fully formed and nice & flat, put it in the melt pot for the next casting session.

[canuck4570]

ok here goes
450 malin
1/20 twist
bullet length is 1.395
weight cast is 575 on the dot
thanks
by the way I shoot a 30-06 in the same speeds and your are so correct
at 1150 accurate at 100 but at 200 yards not so good
took the speed down to 1055 and accurate at both 100 and 200

[canuck4570]

I went on JBM and after playing with the stability finder and figuring how to work it I have learned something
thank you Sierra
according to it the 575 gr bullet that I have is not a good candidate for my 1 in 20 twist....
this twist is more for the 400 to 500 gr bullets
thanks for quiding me to this part of ballistic learning....
canuck

[Echo]

ok here goes
450 malin
1/20 twist
bullet length is 1.395
weight cast is 575 on the dot
thanks
by the way I shoot a 30-06 in the same speeds and your are so correct
at 1150 accurate at 100 but at 200 yards not so good
took the speed down to 1055 and accurate at both 100 and 200

Or maybe kick the velocity up to 1500 fps and be accurate @ 100 and 200. It's when the boolit comes down through the speed of sound that produces the disturbance that reduces accuracy. I don't have the math necessary, but if the boolit haven't dropped below 1100 by 200 yards, it should still be about as accurate as at 100 yards.

[SierraWhiskeyMC]

I went on JBM and after playing with the stability finder and figuring how to work it I have learned something
thank you Sierra
according to it the 575 gr bullet that I have is not a good candidate for my 1 in 20 twist....
this twist is more for the 400 to 500 gr bullets
thanks for quiding me to this part of ballistic learning....
canuck

OK, plugged your numbers into the Miller spreadsheet, and found that your boolit actually should be plenty stable for your twist rate, bore diameter, boolit weight and length, even when you're shooting as slow as 540f/s at 0°F at sea level - give or take 7%.

JBM may be using the Greenhill formula, which "wants" a much higher twist rate.

Your "gotcha" is going to be the boolit leaving the muzzle. That's where the velocity is going to be the highest, and deviations in boolit base uniformity will hit you the hardest. If you're very close to supersonic, your boolit is going to get a lot of buffeting. If your boolit bases are not really square, it will create a pressure differential on the base of the boolit that will try to make it tumble during flight.

But like everything else, the proof's in the puddin'. As I suggested before, load up some boolits that will vary in velocity from about 0.85 Mach to near 1.0 Mach; five rounds of each load. See how they group. Try to start each set of 5 rounds with the rifle cooled off.

[canuck4570]

yes JBM is using the miller formula
with the 575 gr .458 at 40 degree and with a length of 1.395 at 1050 fps I am at 2.03
just a bit over the 2.00 limit
will try it just the same and see.....