312290- Transonic and accuracy?.....

[waco]

My 312290 checked and lubed weigh in at 225gr. I have not ran these over my Chrony yet
I load them in my Rem.700 308 with 20gr SR4759 for a SWAG of 16-1800fps?

Anyway. This load shoots very well for me so far out to 80 yards(could not get a 100 yard spot that day)
Running the estimated BC(.259) at my estimated speed these are going transonic somewhere near the 300 yard range.

My question is does anyone have any first hand experience with this long heavy 30cal bullet at distance?
I know that some designs are not affected as much as others while dropping below the speed of sound.

My goal next time out is to try to ring some 12" steel at 500 yards with these things.
It looks like they will be dropping around 38 MOA at 500 yards. So almost 16 feet.

Looks like I have right at 35MOA adjustment left
in my scope after a 100 yard zero. I do have a mildot reticle so that helps.

Thoughts?.....
Walter

 

[fiver]

on the 311290 I'm seeing a bit more B.C. more like .305
I'm guessing 1800 fps would be a reasonable speed for your load.
from a 100 yd zero.
500yds is 15'7"s of drop or about 188"s with 1.17 seconds of flight time and a 60" correction for a 10 mph wind..
your remaining velocity is about 1125 fps at 350 yds and is what I would be more concerned with.
if you could put your load over the chrono and gain another 100 fps you only retain another 30 fps at 500 yds.[which is down to about 990 fps at 1800 MV]

you have enough weight and twist and a good nose shape to make it through the sub sonic transition at 350 yds but another 150 yds past that? [shrug]
maybe you could sneak up another 100yds closer to the dinger out there.??

 

[waco]

on the 311290 I'm seeing a bit more B.C. more like .305
I'm guessing 1800 fps would be a reasonable speed for your load.
from a 100 yd zero.
500yds is 15'7"s of drop or about 188"s with 1.17 seconds of flight time and a 60" correction for a 10 mph wind..
your remaining velocity is about 1125 fps at 350 yds and is what I would be more concerned with.
if you could put your load over the chrono and gain another 100 fps you only retain another 30 fps at 500 yds.[which is down to about 990 fps at 1800 MV]

you have enough weight and twist and a good nose shape to make it through the sub sonic transition at 350 yds but another 150 yds past that? [shrug]
maybe you could sneak up another 100yds closer to the dinger out there.??

I guess the proof will be in the pudding as they say....

 

[fiver]

yeah,, you don't know for sure until you shoot.
I was just using the numbers from the Lyman book but I am sure they are just rounded off calculations.

I was looking at a 32 cal bullet weighing right near the same and it was showing numbers much better than I would expect, it had a BC of about .450 airc. and retained a lot more velocity at distance.

 

[waco]

It will be a fun experiment none the less. Footage for a new video possibly!

 

[waco]

Lamar. What do you figure this same bullet over 27gr of H4895 would be doing?

 

[fiver]

off the top of my head poorly without a filler. [seriously you'll be fighting ignition and velocity inconsistency's]
but around the 1750 [real world] area would be about right.

this is why we keep on slowing down the powder speed.
we fill the case with more powder but we never hit high enough pressures to really accelerate the bullet.
to get high velocity we have to maintain a push without banging the bullet out of shape from the start, and then push even that edge through fitment, alloy, and design parameters to gain more and more velocity.[usually by moving up the powder speed]
without the fitment we are unsupported and the velocity's have to remain low.
the slower powders help you around the first hurdle with anything that has a decent design by allowing you to get most of the bullet into the barrel before pushing it along.
it's kind of a see-saw game where you keep pushing until your balanced then unbalance things again and then find the thing you need for the opposite side of the lever.
push that side down and start piling on the other end again unfortunately the plank starts getting fuller and fuller.

 

[waco]

This is that 4895 load at 80 yards. I asked only because I had no Chrony that day either. No filler in these.

 

[fiver]

the up and down holes are showing why the filler is used.

the up and down are velocity variations from the extreme end of ignition inconsistency's.

 

[JSH]

My findings, I had thought a different design may fair better, so I tried that. No luck. Some were better than others.
Jacketed or cast dropping back to sub sonic can do some odd things.
I played with sub sonic enough to swear off of it.

Anymore I find a good load at 100, then hope for the best before it drops to sub velocities.
On the other hand good friends Palma rifle shoots terrible groups at 100 through 300. Yet settles down and plays nice past that.

My thoughts, big piece of cardboard and give it a try.