Low speed and large Melplats ??

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Last Post 15 April 2012

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Wayne S posted this 08 April 2012

Has anyone seen less that good results shooting rifle <.284 & .308> bullets with large <.180 +> melplats at low {-1150 fps} speeds. I've been trying to get an NOE 7 Hunter < basically a Seaco 071 with a .180 melplat> to shoot at around 1100-1200 fps. Something my grand children like to shoot, and a special purpose need for myself. The bullets go into about 3” at 100, while the RCBS 168 SP which with it's as cast Dia. is less that perfect goes into 1.5” at 100. "talk” on the Cast boolits forum suggests that large melplat designs at least in the .284-.308 size don't group well at low speeds. Thoughts & opinions

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onondaga posted this 08 April 2012

Wayne S:

The 30 cal. Lyman or RCBS silhouette molds do the accuracy thing for a lot of competitive silhouette shooters. They are both flat nose bullets suitable for paper, silhouette, or hunting. They also shoot better for people on this forum than for people on that other one.

Alloy selection is also important. Your desired speed 1100-1200 fps may be too slow for a popular alloy like Lyman #2 at 15 BHN and going to a softer alloy would be predictable for better accuracy. I'd aim for 11-12 BHN in that velocity.

Gary

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Wayne S posted this 08 April 2012

Gary, My RCBS 145 Sil has a melplat of .120, the 7 Hunter has a melplat of .190, .070 might not sound like much till you look at it on a “Mike” and the differences between the two bullets side by side. AND as I stated, the RCBS shot about 50% smaller groups.

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RicinYakima posted this 08 April 2012

Wayne,

I have been working with several 0.175+ melplats in 30 caliber for a couple of years. Yes, I have the same experience, poor grouping at certain muzzle speeds. My thoughts are that it is very unstable going from super to sub sonic. That is why it is so noticeable in your interest velocity range.

My groups got better in the 7.62 X 39 and the Lyman 311440 when MZ was dropped to no more than 1000 f/s with shotgun powder loads. An NEI 180 grain flat nose with 0.180” shoots better at a minimum of 1500 f/s. No proof in any of this, just reporting my experience.

HTH, Ric

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onondaga posted this 08 April 2012

Wayne S:

I know that is a big difference in meplat. Didn't know that was important for your purpose.

The RanchDog 30 cal. bullets have the largest meplat I know of in 30. cal if you are looking for a meat slapper. He also offers the service to modify his molds to plain base for part or all of the 6 cavity mold.

If you are just looking for sheer accuracy in 30 cal. actually the Lee CTL- 312-160-2R does the best for me out of my .308 Win Sako rifle. Checked, sized @.311"/lubed with Recluse, the all up 174 gr. #2 Alloy bullet at 2198 fps with H4895 shoots sub 1MOA @ 100 yards for me but that pointy nose is not a good deer killer at all compared to the silhouette or Ranchdog bullets that shoot borderline MOA @ 100 yards for my Sako..

Gary

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RicinYakima posted this 08 April 2012

Wayne,

HTH, Ric

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6pt-sika posted this 08 April 2012

Deleted on behalf of the person that started the thread .

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onondaga posted this 08 April 2012

In the 1100-1200 fps range I have wonderful accuracy in .223 with 2.9 grains Hodgdon TiteGroup at 1150 fps with a 60 grain RNGC and in the 7.62X39 I use 8 grains with a 150 grain FNGC for 1150 fps. Either groups 3/4 inch at 50 yards. The .223 in a Handi Ultra Varmint and the X39 in a Remington Spartan single shot.

The Titegroup is completely non position sensitive and ignites great and burns clean.

Gary

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Wayne S posted this 09 April 2012

Wayne S wrote: Has anyone seen less that good results shooting rifle <.284 & .308> bullets with large <.180 +> melplats at low {-1150 fps} speeds. I've been trying to get an NOE 7 Hunter < basically a Seaco 071 with a .180 melplat> to shoot at around 1100-1200 fps. Something my grand children like to shoot, and a special purpose need for myself. The bullets go into about 3” at 100, while the RCBS 168 SP which with it's as cast Dia. is less that perfect goes into 1.5” at 100. "talk” on the Cast boolits forum suggests that large melplat designs at least in the .284-.308 size don't group well at low speeds. Thoughts & opinions BEFORE anyone else offers anymore useless info, please read the above question, it asks a specific question about large melplat bullets in the .284 to .308 size, and if you have experienced a lack of accucary compaired to small melplat designs at low speeds. No where do I ask for opinions on what bullets you like, or powders you use . It's like asking how many combinations of numbers are there on two {2} dice that will equal 3 , ONLY one answer Rickin Yakima, Thanks, the transition from super to subsonic seams to be a big factor, and the large melplat probably helps the 7 Hunter drop into subsonic before it gets to 100 yds.

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onondaga posted this 09 April 2012

The talkers over at castboolits have their clique of superheroes with little ballistic science and a lot of petty arguments I hope don't start here..

The transition to subsonic speed with flat nose bullets causing a disturbance in bullet path is a theory and has not been proven . There is specialized photography capable demonstrating proof that the theory is correct or not by imaging of the air upset by the bullet on it's path during transition. A pattern of upset transition would be visible if it does , in fact, exist.. Supposing one way or the other is just supposing until there is proof. It seems just as likely that many other ballistic variables are equally capable of causing an upset in bullet path during transition to subsonic if there is an upset upon deceleration at all.

An approximately equal number of talkers at castboolits don't have any problem. There is also the highest percentage of shooters at castboolits that don't show pictures of their targets because they don't shoot well enough to be able to say if anything helps their group size or not and are merely looking for a place to lay blame for their lame marksmanship.

In reality there is only a handful of marksmen and a couple handfuls of mechanical shooting machines on the planet that could demonstrate what the armchair scientists at castboolits are showboating and huffed up about.

Why not consider percentage of draft angle on the flat nose bullet? That is a more likely design alteration to keep bullets on path better than meplat size in my opinion. Any way, hollow point boat tail bullets with huge BCs haven't been beaten yet. Those ballistic factors work with cast bullets and the low velocities in this topic. I don't see anybody machining HPBT cast molds and they would work fine at the low velocities.

Shoot what you have and do your best is a better suggestion.

Gary

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800Fahrenheit posted this 12 April 2012

Wayne S,

It's more likely bullet fit and/or alloy vs. pressure curve is(are) the culprit(s) rather than meplat diameter. You're questioning the aerodynamics of a 62% meplat in the transonic region which probably wouldn't even raise suspicion in the minds of accomplished old handgunners in the days of yore. :-)

I just took a look at a drawing of the NOE 7mm Hunter and the first question that comes to mind is: what is the nose diameter of your castings from the NOE mold vs. those from your RCBS mold? I get my best results from long bore riding designs when the nose portion is near .002” over bore diameter. Which, incidentally is the reason some don't like bore riders; i.e., when you open the bolt on a properly fitting bore riding design, you risk pulling the bullet from the case neck. Also, check your NOE 7 Hunter castings for roundness on the nose.

I see the drawing of NOE 7 specifies a .277” nose which happens to be the bore diameter for a modern SAAMI 7mm; therefore, you may be a little loose on the nose unless the mold actually casts a .278-.279” nose (in your alloy).

Good luck and don't get frustrated... your micrometer and your mind are your best friends.

800F

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RicinYakima posted this 13 April 2012

Since I don't read the “Boolites” site, I don't have an opinion on what you guys are talking about, what ever it is.

I base my opinion (yes I know what that is worth) on the studies of early jet aircraft and nose shape of the experiments of Franklin Mann. Harold Vaughn, M.E., Scandia National Labratories, also did some good articles in Precision Shooting about 20 years ago.

I have had the same issues as Wayne S. with big flat points that start out at 1200 f/s and are less than 1000 f/s at 100 yards.

FWIW, Ric

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800Fahrenheit posted this 13 April 2012

RicinYakima wrote: ...I base my opinion (yes I know what that is worth) on the studies of early jet aircraft and nose shape of the experiments of Franklin Mann. Harold Vaughn, M.E., Scandia National Labratories, also did some good articles in Precision Shooting about 20 years ago.

I have had the same issues as Wayne S. with big flat points that start out at 1200 f/s and are less than 1000 f/s at 100 yards.

FWIW, Ric What do you mean by big flat points? 60%, 70% meplats?

The wider the meplat, the heavier the nose (all else equal) and therefore, the farther forward the CG (center of gravity); therefore, we could be experiencing an under-stabilization ("under-twisting") effect by increasing the meplat. This under-stabilization will obviously be exaggerated the slower the bullet spins (as velocity degrades).

Yes, the size of the meplat will affect where the shock wave hits on the bullet but the shock wave can also be moved by the configuration of the ogive. I'm going to have Tom at Accurate Molds cut a couple different designs in a .30 caliber 4-cavity mold. The only difference between the two designs will be the diameter of the meplat (same radius ogive; therefore, one design will need to be a tiny bit shorter and a few grains less than the other) and I'm going to shoot the heck out of these two designs from the same 10” twist '06.

Actually, I could add a negligible amount of length to the driving bands of the shorter version in order to keep the weights of the two designs equal.

800F

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RicinYakima posted this 13 April 2012

Thank you for the reply, 800F. Well this percentage of melplat is a pretty recent term, so I am calculating mine are 58.3 % and 68.5%.

I am well aware of the factors you are suggesting. However, a 1903 Springfield barrel will shoot Lyman 311284, 215 grains, at a MV of 1000f/s with complete stability out to two hundred yards. And it will do this at any velocity I have tried up to 1600 f/s, the fastest I have ever shot that bullet. The same rifle will shoot the Lyman 311440, 155 grains, well at less than 1000 f/s and over 1400 f/s. It makes poor 100 yard groups if shot at 1100 to 1200 f/s MV.

For what it is worth, bullet rotations per second have little if any relationship to forward speed through the air. The RPM's don't drop very much even if the bullet goes from 3000 f/s to 1000 f/s. RPM is a mechanical result of the the pitch of the lands and forward speed as it clears the muzzle.

You have a great idea there with two bullets so close togather. I eagerly await your results!

Best wishes,

Ric

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800Fahrenheit posted this 13 April 2012

RicinYakima wrote: Thank you for the reply, 800F. Well this percentage of melplat is a pretty recent term, so I am calculating mine are 58.3 % and 68.5%.

OK, I will probably compare 60% vs 70% meplats and I might go with plan B (in contrast to my previous post) which is to maintain the same bullet weight and B.C. by altering the radius ogive.

OK, CG is way back on this one and it's got a good B.C. The same rifle will shoot the Lyman 311440, 155 grains, well at less than 1000 f/s and over 1400 f/s. It makes poor 100 yard groups if shot at 1100 to 1200 f/s MV.

Very interesting. Are you using the same powder behind 311440 at all velocity levels or are you slowing the powder burn rate as you go up in velocity? I'm assuming you've done an adequate amount of testing and are controlling bullet hardness and casting quality throughout your testing. This transonic thing is very interesting to me. According to Lyman's data you should be entering transonic at 100 yards if you start this bullet at 1400 fps (depending on where you live and the time of day/year). I'd like to know how your loads that are shooting well at 100 yards after leaving the muzzle at 1500-1600 fps will group at 150 or even 200 yards. Would it be possible to give this a try? Are you talking about consistent 1MOA loads at 100 yards? What powder(s) are you using?

I'm sorry but that's not completely true. Bullet rotation (revolutions per second) is a function of velocity which is always a diminishing factor. Bullet rotation in revolutions per second is calculated by the product of (velocity in feet per second) x (revolutions per foot). For example: a 30-'06 launching 311284 at 1600 fps from a 10” twist would impart 1600 ft/sec x 1.2 revs/ft or 1920 revs/second to the bullet at the muzzle and roughly 1000 ft/sec x 1.2 revs/ft (1200 revs/sec) at approx. 500 yards.

You have a great idea there with two bullets so close togather. I eagerly await your results!

Best wishes,

Ric Regards, 800

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frnkeore posted this 13 April 2012

800, I'm not sure that I'm following you here.

Are you saying that rps decrease in a direct relationship to velocity? That's how I'm reading it, maybe I'm wrong. If so, I'm sorry.

rps decrease as a product of the mass and the diameter of the mass. i.e. large diameter flywheel stays in rotation longer that a small diameter flywheel.

Bullet rotation and velocity are not connected to each other after the bullet leaves the barrel.

Frank

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frnkeore posted this 13 April 2012

I'll add some more things here regarding this issue.

The transsonic range runs from appox 900+ fps to 1100+ fps. The speed of sound is 1120 fps at sea level under stadard atmospheric conditions. So it varies some depening on a lot of things.

The shock wave is never really in contact with the bullet, it preceeds it. The biggest problem with SS shock waves is the power it takes to push them, hence you loose velocity at a higher rate than subsonic.

Sharper noses have higher BC's in supersonic flight. A small rounded nose is best for subsonic flight and a small mepat can to a great extent act as round nose.

Supersonic speeds can be exceeded in the boundery layer of a wing or projectile, too, at sharper or uneven portions (i.e. mepat edges) causing those areas to create small localized shock waves and turbulance.

Food for thought in this discussion.

Frank

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800Fahrenheit posted this 14 April 2012

frnkeore wrote: 800, I'm not sure that I'm following you here.

Are you saying that rps decrease in a direct relationship to velocity? That's how I'm reading it, maybe I'm wrong. If so, I'm sorry.

rps decrease as a product of the mass and the diameter of the mass. i.e. large diameter flywheel stays in rotation longer that a small diameter flywheel.

Bullet rotation and velocity are not connected to each other after the bullet leaves the barrel.

Frank Frank,

Assuming bullet stability, the number of bullet rotations from the muzzle to the target depends on rate of twist and distance from the muzzle to the target and is a constant, correct?

The time it takes to perform that number of rotations depends on the mean velocity in feet per second from the muzzle to the target, correct? This time span is usually referred to as time of flight (let's abbreviate to tof).

As velocity is increased, tof decreases; conversely, if velocity is decreased tof increases, correct? In other words, tof is inversely proportional to velocity. OK so far?

OK, here we go:

Assuming the number of bullet revolutions (let's shorten that to revs) is constant what happens to the quotient: revs/tof when tof becomes small? Doesn't revs/tof increase as tof decreases? You betcha, revs divided by tof becomes large as tof becomes small. Remember, we're talking about a rate, (i.e., something with respect to time) not the absolute number of revolutions which is a constant. Conversely, revs/tof becomes small as tof becomes large. It follows, since revs/tof is inversely proportional to tof and tof is inversely proportional to velocity (step 3) that revs/tof is directly proportional to velocity. Finally, tof is usually expressed in seconds (or fractions of a second); therefore, revs/tof is expressed as RPS (revs per second), or can be converted to RPM (revs per minute) by multiplying RPS by 60sec/min.

Regards, 800F

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Ken Campbell Iowa posted this 14 April 2012

hey, this is fun!

it is important that the spinning bullet is a small flywheel, and the rotational velocity will only be diminished by friction of the air, and this will have very little effect in the few seconds to reach our normal targets.

since the bullet takes longer to arrive at a farther target, the total number of rotations ( spins ) will be greater ..... if a close target takes one second and a farther target takes 3 seconds to contact.... the bullet will rotate 3 times as much for the far target.

interestingly, the bullet near the far target is spinning 3 times as much per foot ( ooops i should'nt have gone this far. ) ken

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800Fahrenheit posted this 15 April 2012

Ken Campbell, Iowa wrote: ...the bullet near the far target is spinning 3 times as much per foot ( ooops i should'nt have gone this far. ) ken

What? Are you trying to confuse yourself? The number of spins per unit length is dependent on the rate of twist cut into the barrel (assuming the bullet is in stable flight). The units on RPS or RPM is the number of revolutions per unit time which is dependent on velocity (feet per second). Please tell me you get this simple concept. Perhaps I'm missing the joke, I'm kinda new here.

800F

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RicinYakima posted this 15 April 2012

800Fahrenheit wrote: Ken Campbell, Iowa wrote: ...the bullet near the far target is spinning 3 times as much per footÃ‚Â ( ooops i should'nt have gone this far.Ã‚Â Ã‚Â )Ã‚Â Ã‚Â ken

What? Are you trying to confuse yourself? The number of spins per unit length is dependent on the rate of twist cut into the barrel (assuming the bullet is in stable flight).Ã‚Â The units on RPS or RPM is the number of revolutions per unit time which is dependent on velocity (feet per second). Please tell me you get this simple concept.Ã‚Â Perhaps I'm missing the joke, I'm kinda new here.

800F

800F,

My last time on this subject. Your error is that RPS or RPM is generated by the twist in the barrel, BUT once the bullet leaves the barrel, the bullet's RPS/RPM is totally independent of forward velocity. When the bullet is not confined within the barrel, RPS/RPM has no relationship to bullet velocity as it flys through the air.

No, it is not a joke, but you have to separate internal and external ballistic principles.

Best wishes, Ric