throat angle

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Frank Green
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Re: throat angle

#31 Postby Frank Green » Tue Jan 15, 2019 5:38 am

Sorry I'm not allowed to say who did the testing and or give more details. The one page I can say it is a .308win and a 175smk. The other page is a .30cal. mag but again I cannot say the bullet. I don't want this to come across as bashing makers etc....Look at the bottom right of each graph sheet. I circled it on the 175. See now nice and smooth it flows. Now look at the next page bottom right corner. The bullet never goes to sleep/gets steady etc...even when pushed at 3000fps it got better but again never smooth.

Ammo/bullets where tested out to 2000+ meters. I forgot that part and was guessing it was 1000 or longer.

Later, Frank
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williada
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Re: throat angle

#32 Postby williada » Tue Jan 15, 2019 4:29 pm

Thank you for posting Frank. Raises lots of little things to think about and how we can bring it back to the topic of throat angles.

I wonder if bullet makers take into account the yaw of repose when bullets spin at different rates which alter the yaw of repose with the external force and direction of wind too. What is important about the yaw of repose and the angle of attack is that friction causes heat. The greater the yaw of repose, the greater the heat, the greater the wave drag. This heat is significant because Hornady have changed their polymer tip as it was melting. That issue is separate from aerodynamic design where models are assumed to balance the centre of pressure with the centre of gravity. IMO the instability of the bullet presented is suggestive of variable separation of the wave drag from the boundary layer of the body that is not optimised for heat variability and that effect on the pressure wave. The heat will diminish as the projectile passes back through the dreaded transonic zone as it slows down with distance and the wind vector may also change the lift characteristics towards the end of its trajectory although the spin rate does not diminish much leading to more erratic flight. It would seem the centre of pressure is somewhat more variable and harder to balance with the centre of gravity in this scenario so the design would not be optimised if spin rates were suitable. I would not otherwise think nutation would continue along the trajectory but only minor yaw bob if the fundamentals were covered.

I very much agree that the nose length reaches a point of diminishing returns.

Edit. Added pics.

Nose Shape.jpg


For others:

Unlike rockets and aircraft we have a spinning thing happening which drastically changes trim. The nose drag does not alter much in flight. We know that from rocket science. The essence of the VLD was a smaller tip to keep nose drag minimal and at the meplat, not further in front of it in its forward motion. The essence of the boat tail was to reduce parasitic drag. These two aspects allow the bullet to carry speed longer and effectively maintain a higher BC. But because of yaw of repose, because bullets spin, the bullets do not fly straight on but tilt up into the wind more so until the overturning moment in trajectory. That imposes an automatic limit to nose length and streamlining with the secant ogive. The longer the projectile the harder it’s got to spin for Sg which increases the tilt, puts pressure on jackets and core and may affect tractability out long if over spun too. At the other extreme is a tangent ogive formed by a circle at the junction of the body. In this context, air is like water. A circular drain provides the least resistance to water flow. Given the slight tilt then the limit of nose design should have some tangent influence in its balance.

A way around this can be a pointed tip but not for its minimal straight on presentation to the atmosphere but its cross sectional presentation due to tilt induced by yaw of repose which reduces the trade-off for a tangent influence in the nose shape. The surface area change is slight but the effect in the order of ½ minute can be seen on the target at 1000 yards with a 180 grain in a 7 mm SAUM. I also think a pointed bullet assists as a balancing factor in pressure in that it offsets a tendency for an uneven detachment of the body wave from the boundary layer (particularly in the transonic zone at extreme distance) and necessarily occurs before the major pressure wave on the body to act like a trim feature like front fins on a fish. The body wave commences at the junction of the ogive with parallel section of the bullet body.

My thinking is that the hybrid design assists in three ways. Firstly, it is not as twitchy as a VLD if it is shorter so there is less tilt, less heat, less change in drag. By “twichy” I mean the propensity to nose on like a weather vane into wind flow which of course the terrain can play havoc with because it rapidly changes drag. Secondly, the hybrid may provide a trim effect with the transition from secant to tangent before the junction of the ogive with the body; and thirdly a throat angle cut at tangent to the ogive which is based on a circle provides the least resistance. The latter should reduce in bore yaw if free bore dimensions are parallel and minimal in diameter.

Hope I have not added to confusion. :? :) Its all your fault Bruce!! [-X :D :D

Who needs to read wind? Just joking.
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Last edited by williada on Thu Jan 17, 2019 7:12 am, edited 1 time in total.

bruce moulds
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Re: throat angle

#33 Postby bruce moulds » Tue Jan 15, 2019 5:02 pm

williada,
the essence of a vld might include small tips, but it also includes long ogives.
for the same meplat diameter, lengthening the nose is th single buggest reducer of drag.
this in turn lengthens the bullet, which as you say requires a faster twist and increases yaw of repose.
it also takes longer to precess and nutate, in itself making smaller groups less possible than shorter bullets and slower twists.
you could well be right that we are on the cusp of going too far.
could this be the reason berger sold the business?
their model might have reached it use by date. :idea:
i also wonder how badly the hornady plastic tips melted, or did the just want to enter a new price point in the market place :?:
please excuse the cynacism.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

wsftr
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Re: throat angle

#34 Postby wsftr » Tue Jan 15, 2019 5:31 pm

Frank, Peter and Williada - Thank you very much for your data and information
I've landed at leade angle not being a significant contributor but an influencer to some extent on precision.
Its interesting but most I have spoken to with the new 200s and fast twists that couldn't get them shooting to satisfaction have gone and changed to a known bullet and sub optimally seated into the case and walked away happy. My takeaway on that is twist is an influencer on precision (SR BR will state this) but we aren't there yet in that limit with these bullets.
Last edited by wsftr on Tue Jan 15, 2019 6:00 pm, edited 4 times in total.

pjifl
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Re: throat angle

#35 Postby pjifl » Tue Jan 15, 2019 5:33 pm

I am seeing some of the new Hornady ELD plastic tips fall out. Otherwise they seem a reasonable bullet and I have seen good scores with them. We did have a mystery miss with one, however, and I seriously suspect the projectile. It's a worry. That was a 6.5 147 grain ELD.
It was hot but not being driven at super speed.

The typical VLD secant ogive is I think a copy of some quite successful artillery shells favored by the Americans. Nothing new about it.

I would be happy to buy Berger VLDs if/when they become available again.

Peter Smith.

bruce moulds
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Re: throat angle

#36 Postby bruce moulds » Tue Jan 15, 2019 7:11 pm

plastic tips,
just 1 more thing to go wrong.
if humans have anything to do with something look out.
the less they have to do with it, the more likely a good outcome.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

Frank Green
Posts: 343
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#37 Postby Frank Green » Tue Jan 15, 2019 8:43 pm

All very interesting to say the least.

Not to get off subject about throat angle. I’ve shot a lot of the Hornady bullets both in handloaded form and in box ammo form. I haven’t expierenced and bullet failures/tip melting etc...I know it’s been talked about over here as well. I also know before Hornady redesigned the tip they abused certain lots of bullets that had claims against them and couldn’t get them to fail. We made barrels for them for testing. 4 groove and 5R. They shot the barrels smoking hot, little cleaning etc...like I said abused the barrels and the bullets. Word was they couldn’t get them to fail.

The Army about 2 years ago (right about the time the Hornady 147’s came out but where not included in the testing as the testing was well underway) in they’re search to pick a couple of primary bullets for the new 6.5CM and .260 Rem. Being used in military applications tested something to the tune of over thirty 6.5mm bullets. So Hornady 140 AMAX or the ELD-M bullets where included in the testing.

Shot out to a 1k yards and further. All of the bullets where tested for accuracy etc...the Hornady bullets where not picked in the end but from what I was told and probably out of concern of the tips falling off and or melting was the reason most likely but no tips where lost and they had no accuracy issues. During the testing the Hornady’s shot neck and neck with other bullets. There was no clear bullet that out performed another from a military use perspective.

I know there was also terminal effects of impact testing done as well and most likely as a guess as I know it’s been done in the past how the bullet flies after being shot thru an object/barrier like glass etc...

I wish I had an unlimited budget and not to mention time!

Frank Green
Posts: 343
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#38 Postby Frank Green » Tue Jan 15, 2019 8:48 pm

wsftr wrote:Frank, Peter and Williada - Thank you very much for your data and information
I've landed at leade angle not being a significant contributor but an influencer to some extent on precision.
Its interesting but most I have spoken to with the new 200s and fast twists that couldn't get them shooting to satisfaction have gone and changed to a known bullet and sub optimally seated into the case and walked away happy. My takeaway on that is twist is an influencer on precision (SR BR will state this) but we aren't there yet in that limit with these bullets.


Which new 200’s are you guys having a problem with? Out of curiosity. The new SMK’s?

williada
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Re: throat angle

#39 Postby williada » Wed Jan 16, 2019 10:54 am

Peter, are the polymer tips falling out when manipulated with your fingers for instance? I know securing polymer to a stake can be difficult from when I was experimenting with bullet re-alignment tooling. I am not pushing the Hornady's, although I find them to be a great bullet as have other club members whose scores have improved since using them in 7 mm chamberings. I am fortunate to have a small pile of 180 Berger Hybrids left. But coming back to the Hornady's, I am confident they have got the design right going by club mates' X counts and like many manufacturers, there are gliches and materials might not be up to scratch at times. Sample batch testing is not necessarily a sure thing in terms of probability with regards to quality assurance in long production runs. The question then arises, how many failures are occurring in the sample size you are quoting to be statistical significance? I think I would only start to worry when more evidence is available although our gut feeling makes us wary. In the Juenke machine they stack up reasonably. Club mates have found just like any projectile they have to be batched for weight and ogive.

WSFTR I think the spin rate needs a little tweak upward from the Sg of 1.5 for long range closer to the transonic distance and a good 30 fps above it if possible. The Miller model is based on a linear application of muzzle velocity extrapolated for distance when perhaps the actual is not quite linear. Miller also had formulas for pointed bullets, but the market ran with the sales agenda as very few people pointed bullets. Given we like to start a bullet straight with a suitable leade angle then a little tweak to cover the rearward moving centre of pressure at very long distance would seem equally desirable i.e. around 1.7 Sg and below tractability issues. The subtleties are such that atmospheric temperature will play a larger role in air density and consequently bullet performance. I also think powder selection and full ignition is critical in maintaining the peak of the pressure curve in the right place and land angle does affect that.

bruce moulds
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Re: throat angle

#40 Postby bruce moulds » Wed Jan 16, 2019 12:48 pm

williada, i am glad to hear you mention higher Sg requirement for long range bullets.
i have believed this for some time but when mentioning it all i hear is crickets chirping.
i also believe this helps when going transonic and in that zone.
i believe also that there is a greater loss of spin at distance than the commonly held belief of "next to none", making a higher gyroscopic stability at the muzzle even more important.
spin decay seems to be related to time of flight, so faster bullets suffer from it less than slower bullets of the same design.
then there is still dynamic stability to test for, and this means in the field.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

pjifl
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Location: Innisfail, Far North QLD.

Re: throat angle

#41 Postby pjifl » Wed Jan 16, 2019 1:12 pm

I have not had a tip fall out but another club member has had two. One happened in the box of projectiles, the other he showed to me - it had been loaded but in his bullet box a tip had fallen out. He is not trying to straighten any - they are seated with a quality seater.
I would estimate that he has loaded and fired about 300 - 400. Another shooter is using 140 grain ELDs in a 6.5 and so far has not seen any problems.

We will fire that one and see where it prints on a 600y target just out of curiosity. The end result is a 'meplat' maybe 3 or 4 mm across.
This is the shooter who had a mystery miss. No one knows and we will never know. Maybe a burst projectile, maybe some tip failure on the way to the target. I think we only had one target up at the time.

The same shooter managed a 90-12 at 600y at one time using the same projectiles. These are 6.5s at 147 grainers. It is tantalizing but somehow I don't quite trust them. 1 in 8 inch twist.

I have some 7mm ELDs I want to really test but at the moment am using some stockpiled Berger Hunting 180s. The trouble is that these days I have to shoot from a rickety table and simply cannot produce the fine groups I once could because of my health. It's a real bugger !!!

Peter Smith.

Frank Green
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Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#42 Postby Frank Green » Wed Jan 16, 2019 2:13 pm

Peter, I can do a twist rate check again tomorrow on the 147’s for you. I know they will fly in a 1-8 but I feel the 1-8 is on the edge. I asked one of the ballistic guys at Hornady what he recommended on them. He said same thing they will fly in a 1-8 but he was more comfortable with a 1-7.5 twist.

We’ve been recommending to customers who are shooting the 147’s and 150gr Smk’s to go at least 1-7.5 twist. Use the 1-8 for 140’s and lighter bullets.

The 150’s accuracy wise shot great from a 7.5 twist barrel during testing but they we’re not seeing the bc numbers during testing. According to my calc’s and depending on velocity the 7.5 twist is right on the edge.

I’ll update the twist calc’s tomorrow.

For a fyi....my 6.5cm barrel is a 1-6.75 twist. I made the barrel before the bullet design was finalized. The actual length and weight of the bullet wasn’t known and I wanted a barrel ready to go when they became available. A 7 twist was talked about being enough but didn’t take any chances and went a little faster.

I’m running the 147/150 gr bullets at a honest 2700fps out of a 23” barrel.

williada
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Re: throat angle

#43 Postby williada » Wed Jan 16, 2019 2:23 pm

Bruce, I am glad to see you adding to the knowledge pool because there is not much we can get out of the law of diminishing returns and we are kicking a thimble full of nuances which of course if you have an inquiring mind are huge because they are there.

Peter, that is good to know and something to be brought to the attention of Hornady to fix. I feel your frustration with your health, but your creative, scientific thinking is just so important for critical review. Don't worry about group size because you are entitled to rest on your contribution and what you have achieved for others.

pjifl
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Joined: Fri Jun 17, 2005 12:15 pm
Location: Innisfail, Far North QLD.

Re: throat angle

#44 Postby pjifl » Wed Jan 16, 2019 4:12 pm

The 147 grain 6.5s in a 1 in 8 inch twist seems to perform OK. Hornady do mention this twist. I had wondered if faster would be needed but then there is more chance or burst projectiles. This is something I have seen with a tight barrel in a 6.5 if they are really pushed.
The barrel was not bought with 147s in mind - rather 140s. But getting any projectiles in Aust these days seems a drama and you take what you can get.

BTW, we shoot in the hot tropics at about 3000 ft elevation. This probably aids stability and is not typical of much of the shooting elsewhere. I feel that some of the advice these days to shooters for faster twist barrels is given to cover bullet makers when their products are used in the Arctic or Alaska.

Peter Smith.

KHGS
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Location: Cowra NSW

Re: throat angle

#45 Postby KHGS » Wed Jan 16, 2019 4:33 pm

pjifl wrote:I have not had a tip fall out but another club member has had two. One happened in the box of projectiles, the other he showed to me - it had been loaded but in his bullet box a tip had fallen out. He is not trying to straighten any - they are seated with a quality seater.
I would estimate that he has loaded and fired about 300 - 400. Another shooter is using 140 grain ELDs in a 6.5 and so far has not seen any problems.

We will fire that one and see where it prints on a 600y target just out of curiosity. The end result is a 'meplat' maybe 3 or 4 mm across.
This is the shooter who had a mystery miss. No one knows and we will never know. Maybe a burst projectile, maybe some tip failure on the way to the target. I think we only had one target up at the time.

The same shooter managed a 90-12 at 600y at one time using the same projectiles. These are 6.5s at 147 grainers. It is tantalizing but somehow I don't quite trust them. 1 in 8 inch twist.

I have some 7mm ELDs I want to really test but at the moment am using some stockpiled Berger Hunting 180s. The trouble is that these days I have to shoot from a rickety table and simply cannot produce the fine groups I once could because of my health. It's a real bugger !!!

Peter Smith.


Hang in there Peter, your posts are appreciated by us all, they are always informative, I never "skip" over any of your posts and I appreciate the sharing of your considerable knowledge.

I have used a limited number of 7mm ELDM's in both 162 & 180 grain weights with excellent results in a couple of 9" twist barrels, one of these barrels has 2500 + rounds through it. I think that problems may be experienced with plastic tipped bullets with rotational velocity out of short twist barrels, 8" & less. Roughness in the throat or even slight carbon build ups in this area also contribute to these "problems".

I do not in any way consider myself to be a ballistic expert, but I am reasonably observant, so based on my observations I think we can get too carried away on the importance of chasing ultra high B.C. Also in my opinion, I think we see too much emphasis put on chasing the higher velocities & burning barrels out trying to achieve short range BR style 100 yard groups, we do not compete at 100 yards, for me 600 yards is where I want to see sub X sized round groups, I also believe the shape of the group is very important. My thoughts for what they are worth!!!
Keith H.


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