Consistent HV Accuracy

[Larry Gibson]

HV consistent accuracy with cast bullets can be done. It doesn’t require any secret reloading technique. You don’t have to walk bare foot down the rice paper without tearing the paper to do it. You don’t need any secret ingredients or special formed cases etc., etc., etc. All it takes is a correct design of cast bullet and proper cast bullet loading techniques and you must control the RPM. Now before you …..:groner:……look at what I’ve done and then ask your self why you aren’t doing it.

The results I obtained today with the newly aquired 311466U mould is atypical of the accuracy I get with a regualr 2 cavity 311466 at HV in slower twists. Many of you may wonder why I always recommend the slower 12 or 14" twists for .30 cals, thereason is obvious. HV with cast bullets comes very easy with a loger barrel and a slower twist. Next time you are going to rebarrel give it some thought.

The target below was shot today in a drizzling rain with a slight cross wind. I was using my Palma .308W rifle which has a 14” twist 27.5” long barrel. The bullet was a 311466U cast of 80/20 linotype/lead and air cooled. They drop from the 4 cavity Lyman mould at .3105”. I do not weight sort these bullets but do give them a good visual inspection rejecting any with defects. I run about 10 - 12% rejects because I am persnickery about what is a "defect". I seat Hornady GCs and Lube them with Javelina in a Lyman 450 with a .311 H die. The scraper groove and first lube groove are not filled because I size the first 2 driving bands at .300. This gives a very short bore riding nose and allows the bullets to be seated so the full driving band is just off the leade and the GC does not protrude below the case necks. OAL is 2.608”.

The cases are LC92 cases that have been “match prepped” in the usual manner. The cases are well fire formed and neck sized. I use a Lyman .31 M die to expand the necks and bell the case mouth slightly. A couple days ago I posted a target I shot with 47 gr of AA4350. Velocity was 2530 at the muzzle and accuracy for 10 shots was 1.5 moa at 100 yards. For today I loaded 40 rounds with 48 gr of AA4350 which is a slightly compressed load. I used Remington 9 ½ LR primers for today’s loads. I fired 3 foulers on a separate target and then shot 8 shots for group over the Oehler M35P. The muzzle velocity was right at 2600 fps. That 8 shot groups measured 1.75 moa. I then shot a second 10 shot group at 100 yards without the chronograph. That group measured 1.35 moa. A 200 yard target was put up and I moved the elevation of the T16 4 moa up and shot a 9 shot group. That 200 yard group measured 2.88” which is 1.44 moa. I then corrected the elevation and windage for a 200 yard zero and fired the last 10 shots at 100 yards to see the point of impact. That group measured 1.55 moa. The average moa for the 3 groups at 100 yards and the 200 yard group of a total of 37 shots was 1.52 moa. Also note the linear dispersion of the group at 200 yards compared to the 100 yard groups.

The RPM of that 2600 fps load was 133,700 +/-. With a 10” twist barrel the RPM would have been 187,200 +/-. Today I put 37 shots at 2600 fps with a cast bullet into 1.5 moa without any trouble at all. Anyone done that lately with a 10” twist barrel? My point here is that it is easy with a longer barrel using a slower twist which controls the RPM and keeps them reasonable.

BTW; the BC of that bullet at that velocity is .23 as measured with Oehler M43. Zeroed at 200 yards it is 2.75” high at 2244 fps. The 200 yard velocity is 1916 fps. It drops 12.5” at 300 yards and still is pushing 1623 fps. It should hold sonic to 500 yards at 1173 fps. (Based on PointBlank Ballistic Software) Should be close enough for little deer to 300 yards, don’t ya think? Let me see now...I've a M788 in .308W that the barrel is about done for....hmmmm, a 26" barrel with a 14" twist and a tight neck chambering might just be in order...........

Larry Gibson

[Bret4207]

Larry, this is one of those posts I'll have to read 4 or 5 times before daring to come to a preliminary conclusion. But, do you think barrel length affects you outcome in any way?

[Larry Gibson]

Bret

I don't think barrel length is affecting the accuracy, I think it just effects the velocity achieved. One of the primary objectives to accuracy is to keep the bullt as close to balanced as we can. The rate of accelleration (time/pressure curve) affects obturation. Thus pushing the bullet as fast in shorter barrel requires faster accelleration which accentuates any uneven setback or obturation creating a more unbalanced bullet in the cast of cast bullets. By using a longer barrel (practicallity has it's limits here) we can use slower powders thereby lessoning the accelleration rate and maintaining a ballanced bullet at higher velocity.

With the older 2 cavity 311466 the pressure of a 45 gr AA4350 load was 39,400 psi. I won't be surprised to see the 48 gr load pushing well over 40,000 psi. That is kind of psi is necessary to achieve higher velocity levels. Basically the longer barrel helps us get there with less pressure.

In this case (is that a pun;-) ) I'm maxed out capacity wise with the .308W. I am not sure I have reached the practical limits of AA4350 in .30 cal though. If I use a faster powders in an attempt for higher velocity I can not maintain that level of accuracy at 2600 fps let alone higher velocity. If I use a slower powder I can not achievethe 2600 fps. I am looking at getting another 28" barrel with a 14" twist to use for a short chambered '06 with the case capacity about half way between the .308W and the regualr '06. The M788 won't do for this so I will probably use a very good M98 Huskvarna sporter I have. With the larger capacity perhaps even a slower powder will boost velocity and/or improve accuracy.

Larry Gibson

[crabo]

Larry, I appreciate your posts. I'm not into high velocity rifle cast, but I'm sure I'll be there someday and I welcome the primer.

[Doc Highwall]

Thanks for the information Larry, I do not have that mould but I do have the LEE C312-155-2R gr that I was thinking of trying in my Palma rifle with a 30" barrel and 13.5" twist.

[Larry Gibson]

Doc

I've tried my Lee C312-155-2R in my M70 Target with 12" twist. It lost accuracy right at 2150 fps (129,000 RPM) but still held 2 moa through 2300 fps (138,000 RPM). Accuracy got pretty bad after that. That was with RL19. I also tried the RCBS 30-150-FN and it faired a little worse with accuracy going south around 2100 fs In the Palma I am pushing 1.5 to 2 moa 10 shot groups at 2300+ (138,000) with the Lee bullet but accuracy goes quickly after that. My thought is the 2R nose is just too long. The 311466 has a very short, stubby nose and the sizing of the 1st 2 driving bands give it a shorter bore riding nose than the Lee bullet has. Without siziing the driving bands and seating the GC below the case neck accuracy goes south much quicker also. I'm sure I pushing 40,000 psi+ with that 48/AA4350 load so the part of the bullet is no doubt damaged on firing when seated below the case neck. The 311466 and the LBT bullet are the only designs I have been successfull with at HV in the 14" or faster twists above 2200 fps. I will get the Palma Rifle hooked up to the Oehler M43 this next week hopefully and know what the psi is.

Please do give your Lee bullet a try and see what you find. I'm sure it will prove interesting one way or the other. I can also send some 311466s for you to try?

Larry Gibson

[Bass Ackward]

Atta boy Larry.

I still disagree with some of your conclusions on too fast of twist rate and RPM.

But with the 308W case, I can see how you got there. Go to a less "improved" case design and slightly larger case capacity and you will see how 10 twist can still hold bore center with the right design. With that said it is still easier with less obstruction to forward motion. (less twist)

The straighter sides and steeper shoulder of the 308 enhance burning of powder that a sloped case and slight shoulder will elongate with the same burn rate and show you more. So what happens is that you MUST go to a slower powder with the 308 and then you DON'T have the barrel length to burn it. You eventually hit the same wall with the 06, but it gives you more options. All because of rifling height where the lead is too weak to hold bore center and launch well.

That's why I like the 06 family for HV cast in any bore diameter. Improved case designs for cast are just like fast twists, they make it more difficult and in the end, still limit you.

So if you actually WANT a good HV cast rifle and you are going to rebarrel, look at the 06, long barrel and 14 twist. :grin:

You gotta a lot of followers out there that will be nodding their heads when they read your posts and benefit from your work.

[45 2.1]

Atta boy Larry.
So if you actually WANT a good HV cast rifle and you are going to rebarrel, look at the 06, long barrel and 14 twist. :grin:

You gotta a lot of followers out there that will be nodding their heads when they read your posts and benefit from your work.

So, all I need to do this is a long slow custom twist barrel. I'm sure everyone here has those................... Same goes to Larry with a long slow custom twist barrel. Several guys here have wrote about this before, namely 357 Maximum with a 35 Whelen rifle. Not much new on that. ;) Please, if your gonna use a normal cast boolit, then use a normal rifle to go with it, if you got any that is.

[Larry Gibson]

Bass

As you know I have worked the '06 with 10" twist (2 rifles) barrels forwards and backwards (there's a little pun there) not only with this bullet but with your LBT bullet. The twist is still the limiting factor to achieving HV with cast bullets. Measurements of velcoity, pressure MAP and time /pressure curves show there is no difference between the "burning of powder that a sloped case and slight shoulder will elongate with the same burn rate ". That sounds good in theory and may apply to some cartridge comparisons. However, measurements of internal ballistics shows clearly it is not a factor with the use of slow burning powders in the .308W and the '06.

Like you, I can occasionally squeak out a 3 shot group 1 -1.5 moa group around 2500 fps with the '06 using either bullet. You've also admitted you can only do it when "conditons' are just right. Stretch that to 5 shot groups and accuracy goes to 3+ moa. Try 7 - 10 shot groups for a statistaclly valid analysis of accuracy and the groups get really bad. The point is that slower twist barrel will shoot cast bullets more accurately at a higher velcoity and it will do it with consistency. The reason is the RPM are controlled with the slower twist barrel and kept under 140,000. Now considering you never did show me consistent 5 shot 1 moa groups with your bullet out of the 10" twist '06. Do you think you can show me 37 consecutive shots that average 1.5 moa out of your 10" twist '06?

My whole point here is not to say you can't or you never will. It is simply to point out that the adverse affect of RPM at HV with cast bullets is very difficult to overcome. If one wants to shoot cast bullets and is going to rebarrel then the easy way is to use a slower twist so the projected velocity does not produce more than 140,000 RPM, preferably around 130 -135,000 RPM. Then accuracy is easily obtained without any secret loading techniques know only to one or two. Anyone can then shoot cast bullets at HV with very good and consistent accuracy. For some time now I have gone out and shot the same consitent accuracy with the 2530 fps load. For two days now I have fired 87 rounds into the same 1.5 moa accuracy with the 2600 fps load. That is without cleaning the barrel either. Can you do that with your 10" twist 06?

I do indeed think the '06 has more potential here than the .308W. I have menioned this numerous times before. However, it may have just a little too much capacity for 100% loading density with slower powders that will burn efficiently at lower pressures. That's why I mention a short chambered '06 case like a 30x57 or 30x60. I am definately going to build one. I am also considering a 16" twist as I am staying with 150 - 155 gr bullets for this. The 14" twist is going to hit the RPM threshold around 2700 fps but the 16" twist barrel will allow 3000 fps and still stay under the RPM threshold. If that is not doable with the short chambers then I can easily ream the chamber to a full '06 chamber. 3000 fps is very doable in a 28" barrel with 150 - 155 gr bullets in the '06. Should prove interesting, Ya think?

Larry Gibson

[Larry Gibson]

45 2.1

Nice to see you add something positive to another thread. The fact is this is what I said in the 1st post;

"[Many of you may wonder why I always recommend the slower 12 or 14" twists for .30 cals, thereason is obvious. HV with cast bullets comes very easy with a loger barrel and a slower twist. Next time you are going to rebarrel give it some thought. /I]

If one is going to rebarrel and wants to shoot cast bullets accurately at HV consistently then the slower twist to control the RPM is the way to do it. Then anyone with rudementary knowledge of cast bullet loading can be successfull. It requires no "sage advise" from a "master". All you have to do is control the RPMs. If they want to shoot HV cast bullets form faster twist barrels [I]that they and I also then they will find it difficult and any results they get are not consistent, especially when one is talking 2500 - 2600 fps. That is just what every one has found out and is why everyone isn't shooting cast bullets at that HV, now isn't it?

Another topic;
Now, if you want to criticise about my 6.5 loads then you and I both agreed (during our telephone conversation) I had pushed the 3rd GB bullet to it's potential at 2100 fps with 1.5 moa accuracy. It would be a moot point to further criticise me for not achieving what starmetal claims becuase I do not have that Kurtz design bullet that he uses and which you say is needed. Neither he nor you will send me any kurtz bullets to test. So how can you logically criticise me? Well that's anyones guess. BTW; I'm not going to buy the mould jus to prove you right. You want to be proven right you might help a little instead of just criticise. I'll gladly PM my address if you want to send some 6.5 Kurtz bullets:-)

Larry Gibson

[45 2.1]

Another topic;
It would be a moot point to further criticise me for not achieving what starmetal claims becuase I do not have that Kurtz design bullet that he uses and which you say is needed. Neither he nor you will send me any kurtz bullets to test. So how can you logically criticise me? Easily, you were told it was the easiest to learn with, not that any of the others won't shoot sub MOA because they will, even the one your using will do 2400 fps and above. Joe even learned this himself recently. I can assure you he was suprised. Well that's anyones guess. BTW; I'm not going to buy the mould just to prove you right. I suspect you won't do anything at all to help prove i'm correct and everything to prove i'm wrong. Your cheating yourself and others because of it. You'll spend several hundred for a new barrel, but nothing for something that works easily and cheaply with common rifles. You want to be proven right you might help a little instead of just criticise. I have, but you can't follow directions too well and interject your own methods, which don't work to well, in place of them. I'll gladly PM my address if you want to send some 6.5 Kurtz bullets:-)
You'll probably get those boolits about 12 days after your obituary (or the twelth of never) is in the paper, the mail is extremely slow from here to there. Not that those boolits would do you any good either. The real trick is getting them started concentrically into the bore. You been told that many times, just when will it sink in? [smilie=1:[smilie=1:[smilie=1:

[MT Gianni]

Larry, wouldn't it be easier to have a 323466 copy made and use an 8mm 98 Mauser? The 29" bbl would fit your needs as would a slightly larger case. Lapping the lugs and drilling and tapping the receiver/ welding the bolt would all be pluses for a sale once the testing was done. It would verify that it is the twist rate as the 8mm is 1 in 9.5 AIRC.

[Larry Gibson]

MT Gianni

If we loo close theLyman 323470 is precisely an enlarged 311466. I've been shooting it for years in numerous M98s including the 29" barreled ones. I've also been shooting the 311466 in 29" M91 nd M1909 Argentines in 7.65 and also my 29" barreled M10 Ross .303. The longer barrels help a bit when slow powders are used but the RPM still is still there and best accuracy is under 140,000. However, acceptable accuracy can be had up through 2200 fps with the longer barrels. Above that the adverse affects of the increasing RPM take their toll on accuracy. The longer barrels allow us to "cushion the effect of acceleration on the bullet, the barrels twist and the velocity still determine the RPM.

Larry Gibson

[HangFireW8]

Larry,

Bench resters run the slowest twist barrels they can get away with for bullet length, hi power shooters have been running 1-13" barrels for years. Cast boolits are known to be fragile, so everything you say makes sense.

I am, however, now glancing at a bunch of mil surplus bangers that may never see rebarreling unless the lottery is won. They are my primary platforms for cast boolits (not counting handguns) and you know how they go, rifling rates from 7-3/4" to 10" and everything in between.

Did a lot of rebarreling when I was single, of my several custom rebarrels I have exactly one slower-than-usual twist rifle and a bunch of standard twists. The one slow twist is a very custom 3 groove Lilja, .0001" undersized, 1-15" 220 Swift. That is the last rifle I will shoot cast boolits from, which means I really do hope to get around to it in the next 30 years or so before I die, but all the other rifles come first.

So my problem now is, how do I file this information so I can find it then?

-HF

[Larry Gibson]

HangfireW8

I've been trying to explain to several here that the concept of controlling RPM for better accuracy wasn't my idea. When you prove it to them they still don't want to believe it. Oh well....

I also have numerous milsurps and other rifles with standard twists from the fast 6.5 Swedes to the standard 10" of my M1903s. I have lots of great cast bullet loads for those that keep the velocity/RPM where best accuracy is obtainable. Those are a joy to shoot with those loads which are pretty much similar to most loads that 99.99999% of the cast bullet shooters use with such rifles. I also have a couple that I do push the RPM to it's limit with quite successfully, contrary to others claims. The oy does come when I load cast for the 12" twist .30s and the 14 & 16" twist.22 CFs. Lastly my real joy as of late, not counting the success with the palma rifle, is the M91 Argentine I rebarreled to .35 Remington with a 26" shilen barrel having a 16" twist. The RCBS 35-200-FN can be driven as fast as the case capcity allows (2350 fps so far) with excellent accuracy. I was going to sgort chaber it with a .35 Whelen reamer making a 35x57 but it isn't broke as a .35 Remington so I can't bring myself to do it.

As to saving the info? Hard copy and fold the paper up and put it in the magazine of the most likely rifle for the conversion;-)

Larry Gibson

[leftiye]

Larry, we all know slower twists help................

So do a lot of other thangs. More is necessary to grow collard greens than sunlight.

[mpmarty]

Larry I too found I couldn't pack enough slow powder into the 308 to get decent acceleration and velocity. My solution was to dump the little 308 and move up to a much better case. I reform 284 Winchester to 30 caliber and the case capacity is nearly that of the '06 but is short enough to work in a 788 action. Works great in a 10" twist barrel.

[Bass Ackward]

Larry,

I applaud your efforts. I want to always promote testing. Doesn't mean that I have to mention mine though. I draw solace in the fact that others here are achieving great results. If they exceed mine, so much the better. Gives me more to shoot for. (Enjoy the pun)

See, I don't have the twist rate phobia. My phobia is low rifling height. I equate slow twists to the use of a GC. It widens the window for accuracy without requiring more form the operator to achieve it.

RPM arguments are solely based upon the strength of lead alloys and the failure to build rifles of correct rifling height for lead bullets in the applicable bore diameter. This failure results in a lowering velocity level as bore diameter is increased for the masses. This was true ever since this discussion began .... and it remains so today. Still others over come.

[scrapcan]

well good info being relayed by all in this post, it will be filed somewhere for the future.

I too have a commercial mauser action that should wear a barrel other than the 22-250 barrel it now has. I think 30-06 or 35 would be good to play with. I have a 308 win barrel that I go from Waksupi, but have not mounted it as I hate to lose the standard length action to a short action cartridge, just as it is now. But as I have the 308 barrel I gues it needs to be mounted and played with, probably too fast of a twist for this discussion though.

and it never hurts ot see several ways to work on something.

[w30wcf]

Larry,
Thank you for the very interesting report. Do you think that going to a slightly faster powder like Varget, 4064, or 4895 with loadings approximating 2600 f.p.s. would give better accuracy? I know that shooters in the Palma matches use those 3 powders.

Back in the mid 1990's I experimented with some higher velocity loads in my Rem 788 .30-30 with the intent being for the 385 meter NRA High Power Silhouette Turkey target. I have a 301618 paper patched mold that I had converted to conventional form (opened the last 3 driving bands to .310"). I made some bullets in Monotype alloy which weighed 160 grs. w/ gas check. Lube was M&N.

With a capacity load of 748, the bullet exited the 22" barrel at 2,610 f.p.s. avg and the first 5 shot group went into 7/8" at 100 yards. I was pretty estatic to say the least. Subsequent groups ran closer to 1.32" average and they sure were effective on the steel turkeys.....that is, if I did my part......

w30wcf

[Larry Gibson]

w30wcf

I tested Varget with the larger diameter 311466 but results were not good. I am thinking this may have been the result of the base of the bullet being seated below the case neck. I am going to retest with this 311466 with the 1st 2 driving bands sized so the base of the bullet is at te base of the neck. I use Varget with 175 gr MKs in my M70 target rifle with great success and they are not at max MAP psi so I believe the psi will be in the low 40,000s with the 153 cast 311466.

I also have a very nice M98 action in '06 that is in need of a new barrel. I am going to get a 28 - 30" barrel with a 16" twist and chamber it in 30-06 also. I am going to attempt 3000 fp with 2 moa or less at 200 yards. Should prove interesting.

Larry Gibson

[Larry Gibson]

Larry I too found I couldn't pack enough slow powder into the 308 to get decent acceleration and velocity. My solution was to dump the little 308 and move up to a much better case. I reform 284 Winchester to 30 caliber and the case capacity is nearly that of the '06 but is short enough to work in a 788 action. Works great in a 10" twist barrel.

Marty

Does that .284 case feed through the M788 magazine?

Larry Gibson

[Von Gruff]

Larry this a very interesting thread. I see you mentioned earlier that you used a 80/20 lino/lead mix.

Did you have a specific reason for adding the 20% pb?


What is the formula for working out the rpm?

I run a 160gn gc lino at 2415 (and this follows some origional loadings ) from my 1 in 9 x 25 in 7x57 for papar and play but softnose the boolit for meat. Figure I have a usable 250 yd range for goat - deer sized animals with good expansion and have done so to 185yds to date, so not sure if I can or need to get more from it than I have but may have a bit of a further play.

Von Gruff.

[Larry Gibson]

Von Gruff

The bullet you use is about as close to a perfect design for HV as I believe on can get. There is very little room for uneven set back of the chipping off of bullet parts. I use the 80/20 alloy becuase the linotype provides the strenght and the lead added makes it a little more maleable. I've found that with the Loven design bullets many times straight linotype is too brittle and parts of the driving bands can chip away from the pressure of torque with the rifling during accelleration. I discovered this with recovered bullets years ago. Also the 80/20 alloy, being slightly more ductile, seems to set back evenly during accelleration which leads to a more balance bullet. The more balanced the bullet the less adverse affect the higher RPM can have on it during flight.

I use the old method of RPM calculation where he twist is divided by 12". That gives a constant for each twist which is then divided into the velcity and that is then multiplied by 60 to get RPM. I also use the standard formula occasionally when I don't have my list of twist constants handy. Both come out quite close to each other and the difference is negligable. I usually also round off the RPM to the nearest hundred because any velocity quoted is also an average. A +/- a hundred or so RPM which falls in the ES of the velocity is not really meaningful when we are talking RPM in the 140,000 - 200,000 range. We don't have to be exact to the 1 RPM.

Larry Gibson

[Von Gruff]

Larry,
Using that formula I see that I am running at 193,200 rpm so since that is way higher than your prefered 140,000 I have to imagine that not only is the boolit design working in my favour but I also must be getting good even fill out in the mould. It may also explain why faster loads were not up to accuracy requirements for hunting to the 250yd limit I set myself, that is 1 1/4 - 1 1/2 in at 100yds. I try to be as meticulous with my brass prep and loading and like you only do a visual on the boolits especially the base and GC shank. I use a TCBK wool wad (that is The Cast Bullet Kid to us here or Jeffinnz to you guys on the forum) over my 39gn H4350 that takes my 75%load density to just on the 100%
Have been using my own lube of 2/3 bees wax to 1/3 vaseline. How much effect would the lube have on the resulting effectiveness of the load.
Have been using Hornady GC to date but am waiting on one of Pats checkmakers to try some copper I have sourced.

This has been a very imformative thread and the learning goes on.
Thanks.

Von Gruff.

[felix]

I think we mentioned this before in some long time ago thread: A better measure than RPM would be the circumference speed. There is more consistency in forces described by the dynamic pull of a point from the center of rotation. In other words, rotational inertia of the boolit would me more emphatic and a possible more accurate description. For example, a 22 can withstand much more rotation than a 45 for the same "accuracy" potential. But, using a certain caliber like 308, it seems the 140K RPM appears to be the ball park number. ... felix

[Marlin Junky]

I think we mentioned this before in some long time ago thread: A better measure than RPM would be the circumference speed. There is more consistency in forces described by the dynamic pull of a point from the center of rotation. In other words, rotational inertia of the boolit would me more emphatic and a possible more accurate description. For example, a 22 can withstand much more rotation than a 45 for the same "accuracy" potential. But, using a certain caliber like 308, it seems the 240K RPM appears to be the ball park number. ... felix

Felix,

And this is with respect to internal ballistics, agreed?

Another question: What is the boolit material in the equation that yielded your 240K number?

MJ

[felix]

Felix,

And this is with respect to internal ballistics, agreed?

Another question: What is the boolit material in the equation that yielded your 240K number?

MJ


Should be 140K... Thanks, that is Larry's number, not mine. Simple to calculate, though, right? ... felix

[Marlin Junky]

Should be 140K... Thanks, that is Larry's number, not mine. Simple to calculate, though, right? ... felix

What I'm saying is that boolit material should be a variable in the equation, especially if we're talking about internal ballistics.

You didn't address my other question.

MJ

[Larry Gibson]

MJ

Not really sure what direction you are headed with internal ballistics; the RPM threshold has to do with external ballistics. Felix and I did have some discusion regards what he is talking about. However in practice the RPM threshold holds for all calibers. The difference is how far from the center of spin is the imbalance and to what relation ship is that if the center of spin does not coincide with the center of form or if the axis of spin does not coincide with the line of flight. Basically the farther from the center of spun the greater the affect. I.e., given two equal imalances; one at the cnetrer of the bullet and one on the outer surface. The one on the outer surface will have the greater affect. Also given the same imbalance, say a .5 gr wrinkle, in the same location on a 130 gr 6.5 bullet and a 200 gr .35 caliber bullet the imbalance on the 6.5 bullet will have a greater affect because it is a larger % of that bullets mass. Lots of variables and they all do affect the bullet in flight (external ballistics).

Larry Gibson

[geargnasher]

What I'm saying is that boolit material should be a variable in the equation, especially if we're talking about internal ballistics.

You didn't address my other question.

MJ

Axe to grind much?

Gear

[Marlin Junky]

MJ

Not really sure what direction you are headed with internal ballistics; the RPM threshold has to do with external ballistics.
Larry Gibson

Larry,

Just last week you said the RPM threshold has nothing to do with a boolit spinning in air. In case you've forgotten that conversation, follow the link:

http://castboolits.gunloads.com/showpost.php?p=998731&postcount=28 (second paragraph)

You're not being very convincing but don't sweat it on my behalf because I'm not taking your RPM bait anymore.

MJ

[Marlin Junky]

Axe to grind much?

Gear

What does that mean? Your comment certainly doesn't shed any light on the subject, so I can only conclude you enjoy living in the shadow of Larry's RPM theory. :-)

MJ

[Larry Gibson]

Larry,

Just last week you said the RPM threshold has nothing to do with a boolit spinning in air. In case you've forgotten that conversation, follow the link:

http://castboolits.gunloads.com/showpost.php?p=998731&postcount=28 (second paragraph)

You're not being very convincing but don't sweat it on my behalf because I'm not taking your RPM bait anymore.

MJ

MJ

That is not what I said at all. If you read the entire post it was in response to Bass and, I believe, your posts refering to the different charactoristics of rifling having the greater effect. I disagreed with that premiss. The charactoristics of the rifling, given good rifling and a smooth bore, have nothing to do with the RPM threshold. I have consistantly told you on that thread and probably others that the adverse affect of the centrafugal force of increased RPM when it happens, is the RPM threshold and it occurs during the external ballistic phase, i.e. when the bullet is in flight.

I am not "baiting" you, I am trying to help you achieve your HV with accuracy goal using lubed cast bullets. If you really want that '06 to shoot accurately at 2700 fps you will get one with a 14" twist barrel. However, you probably won't so please tell us how you make out with a 10" twist barrel, especially when you can shoot 37 consective shots into 1.5 moa at 100 & 200 yards at 2600 - 2700 fps. If you find you can't do that then I'll still be gald to help you.

Larry Gibson

PS; you might also want to remember that the concept of controlling the RPM with cast bullets is not "Larry's theory". The RPM threshold concept has been around a lot longer tha Larry has been discussing it here. Larry only uses it successfully, as do most cast bullet bench resters, and trys to hellp others, such as yourself, to understand how it works so they/you might be as successful with cast lubed bullets at high velocity.

[Larry Gibson]

Von Gruff

Yours is an excellent example of how the RPM threshold can be pushed higher. The choice of bullet is superb and the loading techniques you use are excellent. Your faster loads are not up to your accuracy standards because you have reached the RPM threshold for your load in that rifle. Well done:-) In keeping the RPM under 140,000 is a simple way of achieving accuracy without having to get too meticulous. I imagine that 99% of all rifle cast shooters find such "accuracy" loads that are below the RPM threshold of 140,000 RPM. If one is going to exceed that RPM threshold then one must get meticulous as you and the others of us do. It is unfortunate that many think the 140,000 RPM threshold is a "limit". It is not. However even when we push it to a higher RPM level it is still there and the increased RPM will eventually adversely affect the accuracy. Again, well done; you wouldn't want to sell that mould would you? ;-)

Larry Gibson

[Shooternz]

Bret


In this case (is that a pun;-) ) I'm maxed out capacity wise with the .308W. I am not sure I have reached the practical limits of AA4350 in .30 cal though. If I use a faster powders in an attempt for higher velocity I can not maintain that level of accuracy at 2600 fps let alone higher velocity. If I use a slower powder I can not achievethe 2600 fps. I am looking at getting another 28" barrel with a 14" twist to use for a short chambered '06 with the case capacity about half way between the .308W and the regualr '06. The M788 won't do for this so I will probably use a very good M98 Huskvarna sporter I have. With the larger capacity perhaps even a slower powder will boost velocity and/or improve accuracy.

Larry Gibson

Hi Larry,
Have you looked at the 7.5 Swiss case for your short 06 it's about half way between the 08 at 06 case and if you can scource Norma brass it's pretty good
I have a stalled project on a K31 that has been rebarreled with a 13" True-flite barrel the Gunsmith stuffed up the chamber trying to use a 284 body reamer
I got a chambering reamer from PT&G looks the business just run out of funds to finish it, the plan is to build a 7.5 Swiss on a Barnard P action that I have, the 7.5 Swiss would be perfect in a M98, I have one in .308 could rechamber it jeez more money.

Robert.

[Larry Gibson]

Shooternz

No I had not thought of that! Seems like a good idea.....as with you too many irons in the fire.

Larry Gibson