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View Full Version : 77 gr cast in 223 RPM problems



harrelson
02-10-2019, 11:07 AM
I have just tried to load the Elvis 77 by Arsenal molds in A ar15 1 in 9 twist . I want them to cycle the action reliably. 1st attempt was at around 1800 fps in a 1 in 9 twist barrel so i would expect 144,000 rpm . bullets were not stable at 75 yds and only 2 out of five were on the target . If i went to a 1 in 7 twist barrel to try and stabilize the 77 gr bullet I would be at 185,000 rpm . I have not tried them in this gun yet .

From what i have been reading 140,000 is about the fastest you can spin a cast bullet. If you check a copper jacket at full power it is around 252,000 rpm .

Has anyone had any luck with this bullet or is it to heavy to stabilize in a load that will cycle a Ar15
Is this somethig that will not work ?

I have loaded the 55gr lee bator with 3" groups at 100 yds and cycle all my ar rifles ok.

Bob Harrelson

garandsrus
02-10-2019, 12:03 PM
I don’t think a 1 in 9 twist will stabilize a 77gr jacketed bullet. 1 in 8 or 7 is a more common twist for heavy (77 to 80gr) jacketed bullets. The length of the bullet is the important part in stabilization, the weight just goes up as the bullet gets longer.

Larry Gibson
02-10-2019, 12:35 PM
harrelson

First of all the 140,000 RPM figure with ternary cast bullets has nothing to do with bullet stability. It has to do with best accuracy at 100 and farther yard ranges. If you are shooting only at 75 yards or so then the velocity/RPM can be increased until it no longer maintains what is acceptable or usable accuracy to you.

What powder/charge are you using?
Are you using any filler?

What is the length of your Arsenal 77 gr bullet? Stability is based basically on caliber, length of bullet, velocity and barrel twist. A 77 gr .224 bullet .94" long with be fully stabilized at 1800 fps in a 9" twist.

Were the 2 "on target" bullet holes round?

Do you know if the misses were keyholing or just missing the target? You can wildly miss a target with stabilized bullets that exceed the RPM Threshold BTW. The major adverse affect of exceeding the RPM Threshold is poor to wild accuracy, it is not destabilization of the bullet.

Screwbolts
02-10-2019, 12:57 PM
Is your mold dropping plain based boolitz as per the drawing?

mehavey
02-10-2019, 08:49 PM
what i have been reading 140,000 is about the fastest you can spin a cast bullet.
See http://castboolits.gunloads.com/showthread.php?368459-223-cast-bullets-w-ar15&p=4472544&viewfull=1#post4472544
That bullet is running 180,000 RPM

That said. I don't think a 77gr -- cast or jacketed -- is going to effectively stabilize in 1-to-9 -- especially at that speed.

Run your bullet dimensions/twist/speed through the calculator here
http://bergerbullets.com/twist-rate-calculator-3/
and tell us what you find.

harrelson
02-10-2019, 10:00 PM
Larry

I was using 19 gr of wc 844 with no fillers .
the length is .801"
The 2 that were on the target were not perfectly round . I will use a bigger target to try and see the rest of shots next time

harrelson
02-10-2019, 10:02 PM
Is your mold dropping plain based boolitz as per the drawing?

Plain base no gas check,

harrelson
02-10-2019, 10:09 PM
See http://castboolits.gunloads.com/showthread.php?368459-223-cast-bullets-w-ar15&p=4472544&viewfull=1#post4472544
That bullet is running 180,000 RPM

That said. I don't think a 77gr -- cast or jacketed -- is going to effectively stabilize in 1-to-9 -- especially at that speed.

Run your bullet dimensions/twist/speed through the calculator here
http://bergerbullets.com/twist-rate-calculator-3/
and tell us what you find.

I used the calculator and got SG = 2.15

5Shot
02-10-2019, 10:34 PM
I can stabilize a 75 Hornady in a 1:9, so that certainly isn't the issue with your gun. How about fit? Did you measure the throat in your gun? Are they sized to the throat?

brewer12345
02-10-2019, 10:37 PM
mehavey, thanks for posting that rotational stability calculator. I will shortly be trying to load 223 for the first time and with all the bullet weights out there picking projectiles is kind of confusing. The calculator makes things a lot clearer.

Larry Gibson
02-10-2019, 10:41 PM
Larry

I was using 19 gr of wc 844 with no fillers .
the length is .801"
The 2 that were on the target were not perfectly round . I will use a bigger target to try and see the rest of shots next time

A bullet of that length should be stable in a 9" twist at that velocity.

Plain base no gas check,

No GC is probably the problem. Many PB cast bullets just do not do well above 1500 - 1600 fps especially the smaller caliber ones with bore riding noses. You might try a a Dacron filler with that as sometimes the Dacron filler will help somewhat. Other wise I suggest a GC design.

brewer12345
02-10-2019, 11:19 PM
No GC is probably the problem. Many PB cast bullets just do not do well above 1500 - 1600 fps especially the smaller caliber ones with bore riding noses. You might try a a Dacron filler with that as sometimes the Dacron filler will help somewhat. Other wise I suggest a GC design.

Larry, I am planning on casting PB boolits and powder coating for 223. I have my eye on a 60 grain mold meant for powder coating (no lube grooves) and plain base. For full tilt loads I will use jacketed, but I planned on doing something in the range of 1500 to 2000 FPS with the cast. Will be loading for a 1 in 9 twist. If I cast pretty hard (Lyman #2? Lino 50/50 with COWW?) and powder coat, can I get away with more than 1600 FPS or is that pushing it?

sigep1764
02-10-2019, 11:55 PM
Im using a 75 grainer from MP with a gas check and 15.5 grains of W748 out of a 1/7 twist. No idea the speed, I extrapolated from the Lyman Cast Boolit Handbook. Ive only shot at 25 yard indoor range, but it does just fine. Off a rest it was about quarter sized groups open sights. Off hand standing with irons, about fist sized. Im happy, didn't adjust my sights and I get to practice cheaply. Whats the book say for speed with your powder and weight? Are you getting full function? How low can you go getting full function? Maybe try some plain base gas checks?

mehavey
02-11-2019, 12:23 AM
At a 0.801" length, I agree the bullet "should" be stable.
harrelson: What alloy/lube(PC?)/sizing diameter are you using ?

FWIW: I ran QL --> 16" barrel/Elvis Bullet/H335*/19gr/2.26" OAL and got >31,000psi/2,125fps
Did they actually chrono >325fps slower than that?


* H335 ~ WC844

Tackleberry41
02-11-2019, 08:48 AM
I shoot the NOE 80gr out of a 1-9, subsonic and they are stable, as well as full power. Powder coating makes a difference.

Larry Gibson
02-11-2019, 10:42 AM
Larry, I am planning on casting PB boolits and powder coating for 223. I have my eye on a 60 grain mold meant for powder coating (no lube grooves) and plain base. For full tilt loads I will use jacketed, but I planned on doing something in the range of 1500 to 2000 FPS with the cast. Will be loading for a 1 in 9 twist. If I cast pretty hard (Lyman #2? Lino 50/50 with COWW?) and powder coat, can I get away with more than 1600 FPS or is that pushing it?

If you are set on PCing and not using a GC then whether or not you can "get away with it" (assuming a reasonably accurate closer range load that functions your AR) is mostly going to be dependent on your AR. To function reliably the time/pressure curve must have sufficient psi at the GP to function the action. Try the WC 844 with the Dacron filler to give a more consistent ignition and burn. You might also try RL7 and H4895 with the 77 gr bullet and with the one you're going to try.

Yes, casting them hard, PCing them and even heat treating them can help. I found it much easier to just use a GC than to do all that but that's just me. I suggest finding a load that functions reliably at the lowest velocity. If your PB bullet is going to shoot with reasonable accuracy (other factors than the RPM will make it unstable/inaccurate if it is) then it will do so at the lowest velocity that reliably functions the action with powders giving consistent ignition (RL7 and H4895 for example...perhaps with a Dacron filler if needed).

brewer12345
02-11-2019, 01:05 PM
Thanks, Larry. This is actually for a single shot break action rifle, so I don't have to deal with getting a semi auto action to cycle.

Larry Gibson
02-11-2019, 01:13 PM
Thanks, Larry. This is actually for a single shot break action rifle, so I don't have to deal with getting a semi auto action to cycle.

Ah, then you have far more favorable options, particularly with faster burning powders.

harrelson
02-17-2019, 08:30 PM
I started over today with the 77 gr bullets . i started with bullets lubed with Carnauba Red . This is the same lube i used last time . I dropped back to 1650 fps and got a 3" group at 75 yds but when i got to 1800 fps it was more of a pattern .

I also tried powder coated bullets and and the groups were all around 1" at 75 yds . I tried 3 different loads 15.5 gr wc844 1770 fps, 16gr wc844 1790 fps and 16.5 gr wc844 1860 fps . All of these rounds would cycle my rifle length gas system .

Both of the bullets were sized to .225" . I was using a 1 in 7 twist barrel today . I dont know why the powder coated ( shake n bake method ) bullets are shooting great . I will load some more and see how fast i can push them and keep accuracy.

Bob Harrelson