My 6.5CM journey

Ian

Notorious member
Think about it, Bret, what happens to the base of the bullet when the front encounters sudden, high resistance to movement in the throat right as the pressure is zooming up the front side of the curve?
 

Sevenfan

Member
I like the looks of the bullet except it looks like the nose is hanging in space. Does the top cartridge in the photo chamber as-is? How does an un-sized bullet fit nose-first into the muzzle? Use a bushing neck sizer die or Lee collet sizing die to give yourself about 1.5 thousandths loaded neck tension and start out with something like 2400 powder. I bet it shoots.
As is? Yes & no. I'm light on neck tension, another case using what I had to work with, so am seating bullets slightly long and finish when chambering. I'm using a Redding S die adjusted so it just touches the shoulder without bump. Ordered another bushing last week that will let me reduce neck diameter an additional .001".

Bullet noses (.258" diameter) are not sized and stop ~.010" forward of the top groove.

Fiver I haven't deprimed the brass after the match, will do that today and let you know.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Think about it, Bret, what happens to the base of the bullet when the front encounters sudden, high resistance to movement in the throat right as the pressure is zooming up the front side of the curve?
I get that, it's the putting it in words in an easily understandable and relatable form that others can grasp without overwhelming them that becomes the problem. And as you said, why is 100FPS less not a problem? Where's the cut off point? 50 fps less? 25? 33.4? There are limits that get pretty hard to quantify and they aren't absolutes, or at least I don't think they are. That's why sometimes when you or Fiver write something that probably seems clear to you, fellers like me struggle to see exactly what the whole picture you're trying to paint is. In your example, "obturation" means more than one thing and actually "obturation" isn't even the correct term, at least according to Felix. And then we add in your reference to it happening sort of repeatedly as the bullet proceeds...that's a lot to take in! Might be easy for some but it's taken others years before the idea clicks.
 

Ian

Notorious member
Obturation is what happens when something stops up a hole through something else.

At some point in increasing velocity/pressure during a load wirkup something that was working before (or wasn't but also wasn't affecting the system in an obviously detrimental way before the next increase), stops working and the groups blow up.

Usually the thing that causes groups to blow up is an unbalanced bullet due to launch damage in the throat. Maybe it was unbalanced before but not badly enough to show up until a certain limit was reached. Maybe that extra little bit of powder and pressure started riveting the bullet base or otherwise causing excessive deformation of the bullet at launch. Maybe both together. Maybe something else.

Our challenge is to find out what went wrong and fix it so we can push things to the next failure point, figure that out, and so on. Our tools are bullet alloy choice, bullet shape choice, neck tension, seating depth, powder and primer choice, neck hardness, lube, and of course powder and primer choice. Another useful tool is a bullet trap which can capture the bullet largely intact for our forensic study.

Here is a bullet which experienced an insanely crooked launch and did not group well at anything approaching the velocity potential of the chambering.. It simply did not fit the rifle. A bullet design change cured the issue.

20220616_183405.jpg
 

Bret4207

At the casting bench in the sky. RIP Bret.
Felix had another word that more accurate, at least he said, and he's the only rocket scientist I ever conversed with.

Agree on the crooked launch. Easy to see on a nice long rifle bullet, not so much on a short handgun bullet.
 

fiver

Well-Known Member
for those not seeing the crooked.
look at the lube grooves on the top, and those on the right side.

now... we are at the part where RPM enters the conversation.
yep it matters.
chuckle,, okay i said it.
however it isn't the RPM's that made things go wrong, they are just the magnifying glass that says hey look at those big groups.
it's up to you to say well hell... was it?
or was it something else [like Ian's picture] that shows the real cause.
not what caused the cause but what? caused the big groups in this instance.
maybe the bullet, maybe not finding the center line of the barrel, which then caused the off set engraving and the spinning just zooped things here and there because of the imbalance.
 

Bret4207

At the casting bench in the sky. RIP Bret.
And if you don't have enough info to figure it out, like not looking at recovered bullets, then where do you go? I know- HARDCAST!!!

I think what most people would like is a set in stone set of rules to follow that will always give you success. I don't think such a critter exists in this game. All it takes is one little variation and the walls start coming down...on your head. That's the fun and the challenge. It's also the headache.
 

Ian

Notorious member
Hardcast or an 18-twist, 30" long custom barrel.

Or you can find and fix the problem and quit blaming it on some mystical "threshold" which myopically fingers one factor as being the principal issue.
 

fiver

Well-Known Member
the fact is there is more than one way to get there.
i got a sort of confession some time back that 'one way' being used was with light bullets.
paper works, a coat works, center line and design works, only it works in conjunction with powder speed and ALLOY.

they all got a limit of sorts,,,,,,,, so do jacketed bullets.

if they didn't we wouldn't be changing the jump, buying different brands, changing powder, cutting necks, weighing cases, trimming meplats, shooting ladders, and all the other stuff we do.
ask a cast bullet guy about doing all that stuff.
98% of them just shrug and say,,, why?
well.
 

Tomme boy

Well-Known Member
@waco has a post on the other site and this is what they are trying to tell him about his new Ruger in 223. It seems that a certain person has everyone believing in something that he can not do. So everyone just repeats what he says.

Quote" Because I would be limited to a velocity of 1300-1400 fps in order to stay under the RPM threshold, 120,000-140,000 RPM. At 1400 fps you're upwards of 120,000 RPM, bullets tend to become unstable when you exceed the threshold. I could shoot them at 1250-1300 fps but I don't need another 22 RF."

"If you use an alloy like Lyman #2 or harder and a gas check you can easily go to 140,000, which is 1555 fps. I use Lyman #2 and a gas check in my CZ-527 (223 Rem) and groups start to deteriorate just past 140,000."
 

Ian

Notorious member
:rofl:

80 yards, 7-twist no-name m4gery barrel on a plastic AR with 4MOA reflex sight. Chrono read 3,009 for five done as an S&Gs test at another member's range. Ammo was loaded for the MVP but I wanted to see how it would do from this barrel after attempting multiple times to firelap the 3-4 different choke points out of it. This was the Lyman mould Walter gave me with the damaged cavities. Anyone care to do the arithmetic?

20200723_155019.jpg
 

waco

Springfield, Oregon
I’m sure the RPM’s are off the chart. You must have got real lucky there….
 

Bret4207

At the casting bench in the sky. RIP Bret.
@waco has a post on the other site and this is what they are trying to tell him about his new Ruger in 223. It seems that a certain person has everyone believing in something that he can not do. So everyone just repeats what he says.

Quote" Because I would be limited to a velocity of 1300-1400 fps in order to stay under the RPM threshold, 120,000-140,000 RPM. At 1400 fps you're upwards of 120,000 RPM, bullets tend to become unstable when you exceed the threshold. I could shoot them at 1250-1300 fps but I don't need another 22 RF."

"If you use an alloy like Lyman #2 or harder and a gas check you can easily go to 140,000, which is 1555 fps. I use Lyman #2 and a gas check in my CZ-527 (223 Rem) and groups start to deteriorate just past 140,000."
Witchcraft!!! Anyone who can exceed the RPM Threshold is practicing witchcraft!!!

Gaaa! Can't say I miss that place. Proudly "Perma Banned"!!!

The weird part is I enjoyed talking back and forth with Larry! Just had to avoid his Holy Grail.
 
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Bret4207

At the casting bench in the sky. RIP Bret.
I’m sure the RPM’s are off the chart. You must have got real lucky there….
Nah!, easy explanation. The bullets were spinning wildly out of control, but they just happened to spin wildly out of control towards each other. Makes perfect sense. If the target had been 3 yards further way it would have been a 6 foot pattern!
 

Bret4207

At the casting bench in the sky. RIP Bret.
the fact is there is more than one way to get there.
i got a sort of confession some time back that 'one way' being used was with light bullets.
paper works, a coat works, center line and design works, only it works in conjunction with powder speed and ALLOY.

they all got a limit of sorts,,,,,,,, so do jacketed bullets.

if they didn't we wouldn't be changing the jump, buying different brands, changing powder, cutting necks, weighing cases, trimming meplats, shooting ladders, and all the other stuff we do.
ask a cast bullet guy about doing all that stuff.
98% of them just shrug and say,,, why?
well.
It's the anti-intuitive stuff that boggles the mind. Like, harder isn't necessarily going to work better or at all.

I still haven't figured the 1st way to get to where I want to be if things exceed 2200 or get under 7mm. The concept of many ways to the goal isn't hard to grasp, but many get stuck in the Great Traffic Circle of Choices!
 

Ian

Notorious member
Air cooled wheelweights bumped with a little Roto Superhard and tin. 7-twist. Over 300,000 rpm. The MVP was running that same load at 10 into 1.5" @100 per it's usual won't group under an inch, but it has a 9" twist. It ain't HOW you do it, it's the WAY you do it.
 
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Tomme boy

Well-Known Member
Being as consistent as you can casting the bullets. Sorting for ANY defect. Making sure your gas checks are seated properly. And sized to what your barrel wants. Just doing these things can get you far ahead of everyone that says you can't do it.

For my 223, if I don't do any of the above, 2200 fps is easy. and will hold right at 1" This is with a 1-9 twist. I know I have not got my alloy figured out yet. But 2650 fps is still 1.5" groups at 100 yds right now. This is on a factory Savage Axis with a heavy barrel. I have yet to shoot them in my White Oak Armament barrel on my AR15. But every jacketed is under 1" and several under 1/2" It has a much tighter throat than my savage and is a 1-8 tw. I was waiting to shoot it more to get the throat broken in more. I have to seat the same cast 65gr 0.035" shorter in the WOA barrel. So until then i am not going to shoot any cast in it. Maybe! I guess I need a base line to start from.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Bullet runout was a big issue for me. When you lay a loaded cartridge on a flatish surface and it rolls a little and you can spot the wobble, it's time to re-evaluate your loading practices!!! Fast relaoding doesn't mean good reloading sometimes.