Cast bullets in .223

[Larry Gibson]

morme@gte.net

Nice thing about the .222 is most all of them had/have 14" twists. Thus with well cast bullets of the correct alloy upwards of 2400 fps is still "easy" as they are still under the RPM threshold. It's the 2500 - 2600+ fps range where the "hard" begins.

Larry Gibson

[JIMinPHX]

I keep hearing Larry tout the virtues of keeping your RPMs below their limit. One of these days, when I get the time, I'm going to have to set up some tests & see what I can learn about the things that he keeps preaching. He seems fairly convinced of what he says & he seems to have a fairly extensive background, so his opinions are hard to just dismiss, even when I find them to be counter intuitive. Some day I'm just going to have to invest the time so that I can come to understand the nuts & bolts of what he is saying. Right now, I'm still a little foggy on the subject.

[Larry Gibson]

Jim

When ever you find the time to invest let me know if I can assist in any way. I've run tests with 12, 14 and 16" twist .22 Hornets. I've ran tests with 7, 8, 9, 10, 12 and 14" twist .223s. I've run tests with 9 and 14' twist 22-250s, I've run tests with 10 and 12" twist .244/6mms. I've run tests with 7.9, 8, 9 and 10" twist 6.5s. I've run tests with 10 and 12" twist 30-30s. I've run tests with 10, 12 and 14" twist .308Ws and I've ran tests with 10 and 12" twist '06s. The results are all the same; the slower the twist the easier it is to maintain consistent accuracy at higher velocity.

Regardless of the twist in all the tests above the accuracy loss started at close to the same RPM level. That same RPM level is where just about every other cartridge generally loses accuracy also, regardless of the twist. Remember here that RPM is governed by the velocity and the twist so the faster the twist the lower the velocity will be for a given RPM. Again I will emphasise that i am talking about a threshold that may be lower or it may be higher depending on the variable associated with cast bullets, their designs, alloys, powders used etc. It is not a limit.

Again Jim, I'll be glad to assist any way I can.

Larry Gibson

[45 2.1]

It is not a limit.

Larry Gibson

Thats about the only thing you say about it that I agree with. Accuracy, or the lack of it, depends entirely on what you choose to do and how you go about doing it. Bad choices = Bad Results.

[PatMarlin]

Here we go ...

Where's BA John? ...

[Larry Gibson]

Nice to know 45 2.1 finally understands that

That's all I have to say about that.

Larry Gibson

[JIMinPHX]

Larry, do you notice that the RPM limit varies with caliber, or do boolits of all diameters work to a similar limit in your experiance?

[Larry Gibson]

Larry, do you notice that the RPM limit varies with caliber, or do boolits of all diameters work to a similar limit in your experiance?

Jim

Let me just touch on semantics a bit since you mention "limit". The RPM threshold is not a limit. It is a threshold, it can be bumped up with advanced loading techniques and cast bullet designs. It also can be lowered by poor casting and loading techniques and improper alloys. For the normal run of the mill regular type cast bullet of medium caliber ( around 26 to .33 cals) and pushed with powders from 2400 up through 4350 the threshold hovers between 120,000 and 140,000 RPM. For example; a well cast 150 - 200 gr GC'd cast bullet with a bore riding nose pushed by 4895 in a 10" twist '06 will give its best accuracy in the 1850 -1950 fps range. 1950 fps is pushing the 140,000 RPM. Above that accuracy begins to go, perhaps not greatly at first but it is still going. At 2200 fps it is gone and the group dispersion as range increases will be non linear. You can push that bullet to 2200 fps if you pay attention to details and use a much slower burning powder. Above that and accuracy can and will go quickly. Thus the RPM threshold is just that, a threshold that may be pushed, lowered , crossed or what ever one wants to call it. It is however, not a "limit".

Now to answer the thrux of your question; Yes, I do find it caliber dependent. The smaller the caliber the lower the threshold and the harder it is to push the threshold to a higher fps/RPM level. This is because a defect that destroys accuracy in a small calibe r cast bullet like .224 up through .268 will have little effect on a larger bullet, especially those of .35 cal or larger. Additional the larger bores of .35 cal and above, usually have slower twists to begin with. They are ften at max fps with cast or jacketed before the RPM threshold is reached. Some aren't, like my M70 .375 H&H with it's 12" twist. Many don't want to push a 250 -300 cast bullet to it's RPM threshold at 2350+ fps. The 45-70 is another one; you aren't going to push the normal 300 - 550 gr cast bullets fast enough to get to the RPM threshold with their 18 - 22" twists.

On the other end of the scale look at all the trouble most everyone has with the 6.5 Swede with its 7.9" twist and it's RPM threshold around 1550 fps. Then throw in the .223s with 7, 8, 9, 10, 12 and 14" twist and you get the picture. The RPM threshold there is around 1500 fps with the 7" twist, 1750 fps with the 9" twist, 2200 fps with the 12" twist and 2600+ fps with the 14" twist. The .22 Hornet is in the same boat with its 12, 14 and 16" twists. I've definately found that hitting 140,000 RPM with with the slower twist makes accuracy difficult with the small bores, especially the .22 CFs. I However in .30 cal it is not difficult at all with a 14" twist .308W. I regularly shoot a 311466 at 2600+ fps out of my 27" barreled Palma rifle with 1.5 moa accuracy (consistent 10 shot groups) out to 300 yards. That still is not 140,000 RPM though but is very close at 133,000+ RPM. I'm planning on a 30" barreld '06 with a 14" twist or perhaps even a 16" twist to try for such consistent accuracy at 2700 or perhaps 2800 fps in the future......

Larry Gibson

[JIMinPHX]

Do you notice that Greenfield holds true? Does what you say in conjunction with Greenfield mean that the highest velocities for accuracy can only be achieved with short boolits because of the slow twist that you need to use to get high velocity?

[Larry Gibson]

Jim

Assuming you mean Greenhill as in the formula for computing twists needed(?). The formula generally holds true but there are variables with it. However, there are degrees of stabilization which are generally accepted as over stabilized, stabilized and under stabilized. All are stabilized and will fly point forward but the stabilized bullet will fly more efficiently. Note I said efficiently and not accurately. More accurately will happen only based on the qulaity of the bullets. We should not confuse stability with accuracy. However the two do go hand in hand given equal quality bullets. Given equal quality bullets a stabilzed bullet will be more accurate than either the over or under stabilized bullets. Twist and velocity being the deciding factors there.

Short cast bullets with little or no bore riding noses are most often the most accurate at high velocity/high RPM. Simply because there is less bullet "riding" (basically unsupported in the bore and/or grooves) to obturate unevenly, slump to one side or otherwise become unbalanced during accelleration in the barrel. These same short cast bullets also do better in accuracy at high velcoity in slower twist rilfes because the accelleration to 2600 fps in a 26"+ barrel is still a lot more severe, regardless of twist, than accelleration to 1800 fps in the same length barrel. Fore example; you will, more than likely, get better accuracy at a higher velocity in the same twist with a 225462 than with a 225415. The reason being the shorter bearing surface and longer nose of the 225415 lend itself to being more unbalanced during accelleration than does the 225462, even though the 225462 is heavier and longer.

In the Palma rifle I still get very good accuracy with the 311041 at 2400 fps that is only obtainable at 2200 fps in a 12" twist and at 1950 fps in a 10" twist. And at 2400 fps the 311041 is still quite stable out of the 14" twist to 300 yards anyways. The shorter 311466 with no nose to speak of still does much better upwards of 2600+ fps in the 14" twist. That is why you see me generally refer to "regular cast bullets" in my writings on the RPM threshold. By that I mean the common cast bullet with a bore riding nose. That is the bullet that will hit it's RPM threshold first.

Let me point out that the RPM threshold is not about the bullet losing stability (flying point forward). The RPM threshold is about when the centrifugal force, caused by unbalances in the bullet, over comes the rotational stability of the bullet making it's flight path a spiraled one with non linear dispersion as the range increases. For the regular cast bullet this occurs in the 120,000 to 140,000 RPM range.

Larry Gibson

[JKH]

Larry,

First let me say that I admire and respect men (and women as well) that have the ability to perform higher mathmatics and especially make it sound so easy, your explanations are very clear, I wish I had the knowledge of math to flly appreciate them.

Okay, being that a shorter boolit with little or no bore riding nose will tend to hold accuracy better at higher RPM thresholds, how would you say the LEE Bator boolit would fare at higher velocities in an AR15 barrel having a 1:8 twist rate? Also, how would that sme boolit fare given the use of lino-type alloy verses say #2 or water cooled wheel weight alloy?

I have been shooting some loads using WW alloy boolits that function the rifle properly and what few I have shot seem to have good accuracy (I need to get on a bench though and spend some quality time punching holes), however I would like to load .223/5.56 using cast boolits to at least starting velocities for standard 55 grain ball ammo and of course want decent accuracy too ;^ ) Do you think this may be achieveable with the Bator as described above?

Thanks

Jeff

[morme@gte.net]

What loads are you using for the Bator in your 1:8 rifle that cycle the action properly?

for me,
21gn 4064 cycled 9 out of 10 shots
15gn 4198 short cycled. the case was ejected, but a new round was not picked up. I manually loaded each round

I also tried
7.5gn Trail Boss (full case, no compression)
9.0 Blue Dot
9.0 Red Dot
10.5 2400

I used the powders on my shelf.

Larry,


I have been shooting some loads using WW alloy boolits that function the rifle properly and what few I have shot seem to have good accuracy (I need to get on a bench though and spend some quality time punching holes), however I would like to load .223/5.56 using cast boolits to at least starting velocities for standard 55 grain ball ammo and of course want decent accuracy too ;^ ) Do you think this may be achieveable with the Bator as described above?

Thanks

Jeff

[Larry Gibson]

Jeff

Okay, being that a shorter boolit with little or no bore riding nose will tend to hold accuracy better at higher RPM thresholds, how would you say the LEE Bator boolit would fare at higher velocities in an AR15 barrel having a 1:8 twist rate?

It's going to fair a little better than with a 7" twist....how's that for a "non-answer" I do not have any 1st hand experience with the Bator but would expect it to perfom as well as any. Most of my .223 cast bullet experience in ARs is with 7, 9 and 12" twists. I do have some limited experience with 225462 in an "over the course" match AR with 8" twist. i was attempting to develop a load for 200 yard reduced NMC that would hold 2 moa and function reliably. Best accuracy (1.5 moa for 20 shots!) was down around 1500 fps but reliable functioning was non exhistant. At around 1800 fps functioning was reliable but accuracy was only M193 equivelent (around 2 -3 moa at 200 yards). That is pushing 162,000 RPM. On advise of another forum member who claimed "good" accuracy at 2800 - 2900 fps from his 7" twist AR I pushed velocities up to 2900 fps. At 200 yards at 2400 fps about half of the shots held inside the 7 ring on an SR200 yard target. At 2900 fps only 7 of 20 shots hit on the entire target frame. The same loads were shooting roughly 5 - 6 moa at 100 yards. We can readlily see the non linear expansion of the group size from 100 to 200 yards.

So how do I think you will fair? If you cast and load correctly loads in the 1800 -2000 fps range you may equal M193 ball type accuracy, at least out to 100 yards. You may do a little better, you may do worse as there are variables of alloy, powder, accuracy of the rifle, your shooting ability, etc. involved. Just remember, at 2000 fps with that 8" twist you are pushing 180,000 RPM so you better load 'em right.

Also, how would that sme boolit fare given the use of lino-type alloy verses say #2 or water cooled awheel weight lloy?

Many years back I gave up on straight linotype for the small bullets. The reason being I had really high hopes for them in the .22 Hornet (16" twist) and the .223 (12" twist) pushing cast to 2500 - 2600 fps. I was unable to get wthe accuracy wanted with either twist above 2000 fps with linotype alloy. I then recovered some of the bullets (225415 and 225438) that had been shot into snow. Close inspection showed the linotype was chipping away behind the rifling on some of the driving bands. The loss of even a bit of alloy from one side will greatly unbalance such a small bullet.

I switched to 60/40, 70/30 and 80/20 linotype lead alloys and began imediately to have success with both cartridges. with excellent loads in the 22 Hornet in the 2500+ fps range and in the .223 in the 2200 + fps range. In a 14" twist .223 I was able to push to 2400+ fps with the same accuracy. The reason being is that "hard" by BHN alone is only half of the equation. The other half of "hard" is a malleable alloy. Linotype is to heavy in antimony and is brittle. WQ'd WW + 2% tin also works for me up though 2100 - 2200 fps.

I have been shooting some loads using WW alloy boolits that function the rifle properly and what few I have shot seem to have good accuracy (I need to get on a bench though and spend some quality time punching holes), however I would like to load .223/5.56 using cast boolits to at least starting velocities for standard 55 grain ball ammo and of course want decent accuracy too ;^ ) Do you think this may be achieveable with the Bator as described above?

Starting velocities with ball type ammo and that accuracy? If you mean upwards of 2700 - 2800 fps then, in my experience, I would have to say the chances are slim to none with slim being gone. However, if you do everything right, you may get acceptable foreign made ball type accuracy at least to 100 yards perhaps a bit over 2000 fps. Some may claim otherwise and I say more power to them but with what I've learned and experienced (I've tried very, very hard to get accuracy at high velocity with the .223 and several other cartridges) it's just not in the cards with cast bullets.

Now if your AR had a 24" barrel with a 14" twist we might get somewhere........

Larry Gibson

[JIMinPHX]

Let me point out that the RPM threshold is not about the bullet losing stability (flying point forward). The RPM threshold is about when the centrifugal force, caused by unbalances in the bullet, over comes the rotational stability of the bullet making it's flight path a spiraled one with non linear dispersion as the range increases. For the regular cast bullet this occurs in the 120,000 to 140,000 RPM range.

Larry Gibson

That's why I had asked you before if you saw the threshold being diameter dependent. A lot of forces on a rotating body are square factors, while others are linear. Doubling a diameter would give 4 x to the square forces & 2 x to the linear forces.

I think that I have picked your brain enough for now. I have enough things to look into to keep me busy for more than a month.

I have a Bator mold that came from the current off-spec batch that I've been using as a cut up mold. I've altered it to produce several different boolit base geometries, including plain base. Once I finish my tests with the different Bator varieties, I'm going to put your RPM theories on my to-test list. I'll be testing your suggestions on whichever version of the Bator shows the most promise in my earlier experiments.

Thank you for taking the time to spell it all out for me.

Jim

[JIMinPHX]

What loads are you using for the Bator in your 1:8 rifle that cycle the action properly?

I'm not an AR guy, so please forgive me if this is a stupid question. Can't you adjust some kind of gas bushing or gas tube position or something to get those things to cycle with reduced loads?

[JKH]

morme@gte.net,
I am using 18.5 grains AA2230C (surplus canister powder, sightly slower than AA2230, same load data), CCI small rifle primers & various brass from commercial to steel.
My At has an Armalite M15(T) 24" bill barrel. Function so far is 100% with bolt lock back on empty mag, I have to shoot a lot more before I'm confidant in the load both for function & accuracy before I load any large quantities.

Larry,
Thank you for the well thought out & documented answer, I will keep working with the load I have & use WCWW, as long as I can get function with reasonable accuracy to 100 that will do. What should I play with the lino-type for? I have an early 60's Flaigg's bill barreled FN 98 commercial Mauser in '06, any suggestions? It weighs about 15 pounds

[morme@gte.net]

I'm not an AR guy, so please forgive me if this is a stupid question. Can't you adjust some kind of gas bushing or gas tube position or something to get those things to cycle with reduced loads?

sorta

you can open the gas port, lighten the carrier, lighten the buffer, and use a weaker spring.

larger gas port requires an adjustable gas tube or gas block so that you don't slam the carrier when used with normal loads

all the other "fixes" mean swapping out parts until it works, if it can be made to work with just lighter components (generally not)

the mechanical parts are hit and miss, and are probably not enough. The typical subsonic rifle has the gas port located 4.7" from the chamber. Gas port locations are below, in inches from the chamber.

Rifle 13.2
Mid length 9.8
Carbine 7.8
Pistol 4.7

I have a 18" barrel with a rifle gas port, which means the port is 4.8" from the muzzle. If I used a pistol gas port location, the port would be 13.3" from the muzzle. You can see that there would be gas pressure on the bolt carrier for a much longer time (from the time the bullet passes the gas port to the time it exits the muzzle.)

using a pistol gas port location with standard loads can bust up the bolt etc. In theory, you can use an adjustable gas block, but it does not work well.

For dedicated suppressed subsonic barrels like the 300 blackout, you only shoot subsonic.

[JKH]

Jim,
an AR15 is a direct impingement system, function is directly effected by port pressure as well as powder burn rate. You can bleed off gas in a shorter gas system such as a carbine or pistol were port pressure is much higher but cannot increase pressure when too low by mechanical means. A piston driven upper is much different in some respects & can be expected to behave much like an FAL or similar piston/tappet operated semi-auto.
HTH
Jeff

[JIMinPHX]

Geeze, that sounds like a real can of worms. It's a lot easier to change that sort of thing on some other types of gas guns.

[Larry Gibson]

morme@gte.net,
Larry,
Thank you for the well thought out & documented answer, I will keep working with the load I have & use WCWW, as long as I can get function with reasonable accuracy to 100 that will do. What should I play with the lino-type for? I have an early 60's Flaigg's bill barreled FN 98 commercial Mauser in '06, any suggestions? It weighs about 15 pounds

I like linotype and it generally works well in .30 cals, particularly if the bullet has thick driving bands. However, for regular loads in the best accuracy range of 1800 - 1950 fps I would mix it with lead at 60/40 LT/lead. Mixing the lead in it does lower the BHN but you can WQ if you want (I do not). The BHN on my alloy runs 16 - 18 with the Lee tester. The addition of the lead stretches out the supply of linotype but more importantly it makes for a "hard" yet malleable alloy and is not brittle like straight linotype. With the 60/40 alloy or 70/40 alloy I would use a 311299 over 4895 (28 - 32 g) with a 3/4 gr dacron filler. The RCBS 308-168-sil or the 311291 are also very good candidates.

If you want to push the envelope with higher velocity I suggest a 311466 or the LBT 150 gr SP cast of LT/lead at 80/20. Use these over slower powders like AA4350 or RL19 and, if you do everything else right, decent accuracy can be had upwards of 2400 fps. Developing these loads that will give consistent accuracy is not for the faint of heart or those who get frustrated easily.

Larry Gibson