Niche reloading topics

[AlexD]

Started this thread to avoid distracting the OP on "Thinking of reloading" with engineers' discussion of fine tuning items or just reloading items of interest that make no difference to the grouping.
On that original thread, Deermanagement suggested that a couple of thou error in the bullet concentricity, leads to 13 thou variation at the lands, which is interesting and I promised to do some measurements and post.

I happened to have some rounds sitting here that are ideal for this test as they cover the absolute full range of seating depths.

These are 100 rounds of 0.270 and 100 rounds of 0.284: I made them to check out Lapua's rep's reported remark that the texture on the tail end of Lapua bullets improves accuracy and Eric Cortina's claim that taking that texture further by counterboring the rear of the bullets (moving the CoG forwards), improves accuracy over a 1000 yard range: he had a 1.78" group at 1000 yards by doing that.

I attach photos of these unusual bullets and rounds I made. I shot 40 of these so far with results that seem to debunk Eric's claim, turning a 0.7" group at 200 yards on a slightly breezy day to into an 8" group! But before declaring Mr Cortina's claim debunked, I am trying it again, by spanning the full range of seating depths using five different bullets (boat tail and flat), and bullet weights from 130gn to 180gn, in two different calibres (0.270 and 0.284) to get a range of twist rates. The loads all use RS60, in a charge weight thats works fine for normal bullets in the two rifles involved in the test.

For the 0.270 loads I am using Nosler Accubonds and Speer, both 130gns, the former taking 56gn of RS60 and the latter 57gn, (using abbreviation gn instead of the ISO gr). I have also taken some Perigrine 0.270s 110gn, removed the bullet, machined it, and reseated to the standard depth to compare with the factory version.
For 0.280 I am using Sierra Gameking 160gn and Berger 180gn, with 52gns of RS60: don't copy it in another rifle - it is "quite" a high pressure load especially on jam but with no pressure signs in that rifle which has a rather heavy barrel. Seating using modified RCBS die for 0.270 and Franklin Arsenal comp die for 0.284 (much nicer). All cases were annealed before loading with my RF annealer, posted on another thread.

For seating depth, I am using the entire range, from bullets seated so deep the neck is right up to the Ogive, though to bullets seated so lightly that they are at hard jam and only just held by the neck. These bullets are ideal therefore exploring Deerhunter's observations.

The first problem was how to hold them to get an accurate measurement of concentricity: Deermanagement's measurements are in the 2''' range so looking for a means to holding the neck at 0.1''' (1/10,000") concentricity. Tried a watchmakers lathe first - it holds the base, which is not well aligned with the neck (visibly miles out). Of course a normal 3 jaw chuck won't work, because centre on normal 3 jaw chucks depends on which socket one puts the chuck key into last. Ended up using a collet chuck and collet block, on a granite bench.

Pictures of the concentricity measurement setup will be in the 2nd post (ones done today are a bit dark with bands as the lights strobe with the camera, will do more tomorrow with better lights on).

Measurements: not surprisingly, cheap bullets, short bullets, shallow seated do not seat as concentrically as expensive long bullets deep seated. Concentricity deviation on the shortest bullet in a Winchester case, hardly seated, was up to 10'''. Berger and Accubonds are 0.5 to 0.6''' concentricity error. So this ties in with Deermanager's observations.

Next step will be blue these up and see how much seating deviation there is, though the geometry based on the measured concentricity does give support to Deermanagement's numbers.

 

[Brave Echo Niner]

Started this thread to avoid distracting the OP on "Thinking of reloading" with engineers' discussion of fine tuning items or just reloading items of interest that make no difference to the grouping.
On that original thread, Deermanagement suggested that a couple of thou error in the bullet concentricity, leads to 13 thou variation at the lands, which is interesting and I promised to do some measurements and post.

I happened to have some rounds sitting here that are ideal for this test as they cover the absolute full range of seating depths.

These are 100 rounds of 0.270 and 100 rounds of 0.284: I made them to check out Lapua's rep's remark that the texture on the tail end of Lapua bullets improves accuracy and Eric Cortina's claim that taking that texture further by counterboring the rear of the bullets (moving the CoG forwards), improves accuracy over a 1000 yard range: he had a 1.78" group at 1000 yards by doing that.

I attach photos of these unusual bullets and rounds I made. I shot 40 of these so far with results that seem to debunk Eric's claim, turning a 0.7" group at 200 yards on a slightly breezy day to into an 8" group! But before declaring Mr Cortina's claim debunked, I am trying it again, by spanning the full range of seating depths using five different bullets (boat tail and flat), and bullet weights from 130gn to 180gn, in two different calibres (0.270 and 0.284). The loads all use RS60, in a charge weight thats works fine for normal bullets in the two rifles involved in the test.

For the 0.270 loads I am using Nosler Accubonds and Speer, both 130gns, the former taking 56gn of RS60 and the latter 57gn, (using abbreviation gn instead of the ISO gr). I have also taken some Perigrine 0.270s 110gn, removed the bullet, machined it, and reseated to the standard depth to compare with the factory version.
For 0.280 I am using Sierra Gameking 160gn and Berger 180gn, with 52gns of RS60: don't copy it in another rifle - it is "quite" a high pressure load especially on jam but with no pressure signs in that rifle which has a rather heavy barrel. Seating using modified RCBS die for 0.270 and Franklin Arsenal comp die for 0.284 (much nicer). All cases were annealed before loading with my RF annealer, posted on another thread.

For seating depth, I am using the entire range, from bullets seated so deep the neck is right up to the Ogive, though to bullets seated so lightly that they are at hard jam and only just held by the neck. These bullets are ideal therefore exploring Deerhunter's observations.

The first problem was how to hold them to get an accurate measurement of concentricty: Deermanagement's measurements are in the 2''' range so looking for a means to holding the neck at 0.1''' (1/10,000") concentricity. Tried a watchmakers lathe first - it holds the base, which is not well aligned with the neck (visibly miles out). Of course a normal 3 jaw chuck won't work, because centre on normal 3 jaw chucks depends on which socket one puts the chuck key into last. Ended up using a collet chuck and collet block, on a granite bench.

Pictures of the concentricity measurement setup will be in the 2nd post (ones done today are a bit dark with bands as the lights strobe with the camera, will do more tomorrow with better lights on).

Measurements: not surprisingly, cheap bullets, short bullets, do not seat as concentrically as long bullets. Concentricity deviation on the shortest bullet in a Winchester case, hardly seated, was up to 10'''. Berger and Accubonds are 0.5 to 0.6''' concentricity error. So this ties in with Deerhunter's observations.

Next step will be blue these up and see how much seating deviation there is, though the geometry based on the measured concentricity does give support to Deermanagement's numbers.

Was that claim about altering the bullets base not made by Mr Cortina on 1 April?

If it’s this video you’re referencing?

 

[AlexD]

It could be. I did see the date but he had it out before then.

Definitely does not work on the ones I tried so far: groups at 200 yards become an order of magnitude larger. However, from the outset the idea struck me as interesting as a means to explore moving the CoG relative to the Aerodynamic centre to look at aerodynamic jump so I thought, lets have an explore, moving the CoG forward by simple counterboring and moving it back further with tungsten tails in copper bullets and measure the aerodynamic jump component (hence them being testing on a slightly breezy day).

 

[Rory]

To my mind it defeats the object of having an aerodynamically efficient boat tail, the hollow base would be a drag fest.

 

[AlexD]

To my mind it defeats the object of having an aerodynamically efficient boat tail, the hollow base would be a drag fest.

My interest was the lateral spread from the aerodynamic jump, but interestingly the change did not affect the average vertical spread, i.e. the mean velocity to the target over 200 yards. I would expect the slightly lighter bullet to have a lower BC, so losing speed and dropping more, but apparently it is compensated over the relatively short 200 yard range by the lighter bullet going faster with the same load.
Of course with a group opening up greatly it is harder to get an accurate figure for change, so it is not 3 or 5 rounds needed but 40, hence my having 200 of these rounds to hand.

In conic theory, moving CoG forward should reduce cone diameter, but cone definitely increased a lot, probably due to reduced stabilty. I have the tungsten ended rounds too to check, that move CoG back (drilled out and tungsten slugs pressed into the bullet hard so it does not fly apart).

In terms of drag, the airflow is fully separated anyway, as the bullet is spinning at 300K rpm and moving supersonically so not expecting much change in drag. So a cavity at the rear should not make much difference, other than a lighter bullet of the same length and cross section has a lower BC. The big difference is the movement of CoG w.r.t. the Aerodynamic centre.

 

[AlexD]

Interesting and thought provoking,
Query is that SP are far less uniform than BT, and even those can vary, I've had some Nosler BT that varied by 0.01" bullet length and A Max that varied by 0.015".
if the COAL length to the Ogive varies due to runout variation, surely the further from the neck the greater the variation?
Compounded by the lack of consistency in bullet length, the length at the tip will vary even more according to the orientation of the the base of the cartridge to the tip of the bullet when measuring COAL, so if the cartridge is rotated through 360° the length will surely change even more?

Moved from the other thread, to avoid derailing it. Yes, there is a tall tolerance stack here.

Speer 130gns have a lot of variation. The tips are often deformed, at least in the boxes I have, but the ogives seem fine. On the Accubonds and Bergers, I sort them. Their weights vary a lot, so they are sorted for that, then I sort them for overall length, using a 1m tape and treating thou as mm or as 1/10th of a grain. The small espresso paper cups are good for holding the bullets in each group and come from Amazon in lots of colours so can be stacked against the ruler and still know which is the 158.2gn pot and which is the 158.3gn pot.

The Speer 130gns are short so they don't have so much to hold them straight in the case especially after the cases have been annealed the neck tension is on the low side.

In these measurements I was looking at ogive concentricity only. The numbers should be added to the COAl variation from the bullet tip variance.

Can you clarify what you mean by rotating it through 360 degrees? I turned them through 360 degrees on their axis to measure the ogive (in 6 places, as per the collet holder flats).

 

[Andy RV]

Have you measured the ogive and boat tail runout of the bullets alone to start with? Prior to loading? Certainly boat tail runout will have a far greater affect on performance than bullet to case concentricity.

There is a saying in the trade when it comes to bullet stability, put the mass in the ass.

You may well find that you’ve weakened the rear of the bullet sufficiently that it’s distorting upon muzzle exit as the blast accelerates pass?

 

[Andyquadra]

Was that claim about altering the bullets base not made by Mr Cortina on 1 April?

If it’s this video you’re referencing?

I watched the same video with interest just last week up until 7.45minutes! Yes, its an April fool joke

 

[AlexD]

Have you measured the ogive and boat tail runout of the bullets alone to start with? Prior to loading? Certainly boat tail runout will have a far greater affect on performance than bullet to case concentricity.

There is a saying in the trade when it comes to bullet stability, put the mass in the ass.

You may well find that you’ve weakened the rear of the bullet sufficiently that it’s distorting upon muzzle exit as the blast accelerates pass?

Mass in the rear helps stabilise, mass closer to the aerodynamic centre reduces aerodynamic jump, so a tradeoff.
The idea of drilling the rear and putting things into the cavity, seems an easy of exploring the jump tradeoff, but the reduction in stability from reducing mass in the hollow tails has meant that stability factor in the results far outweighs anything else, so one needs to run a lot of ammo to extract the information one is after. The tungsten rear loads are interesting, and hope to compile that data over the next week or two. Pushing a 130gn bullet to 155.
On the bullet distorting, the only measure I have is the hole size in the target, which seems unaffected so the bullets seems to be holding together.
The hollow tail bullets hold pressure in them at they leave the rifle, acting as a rocket for a metre or two so the cavity is as central as possible in the bullet.

On Eric Cortina, I think he posted a failed test on 1st April as a joke but some of it got out earlier. He heard the joke from the Lapua man about them being better due to the lapua stamp on the base, tried drilling bullets, found it does not work and posted his experiment as a joke. Which led to the thought, that actually as a means to play with aerodynamic jump to develop rounds which perform more consistently in cross winds, it is not a bad idea as one can't change the mass distribution from the front very easily.

On the tail, a flat tail has a LOWER drag at supersonic speeds than a boat tail. This is why the X15 had a wedge tail: see https://www.nasa.gov/wp-content/uploads/2015/04/607076main_x15researchresults-ebook.pdf . Subsonically the opposite applies. I thought the reason for the boat tail was to reduce stability so the bullet does more damage then they somehow migrated to ELD match bullet profiles for reasons I do not know (despite looking for the data).

 

[Len the dog]

(drilled out and tungsten slugs pressed into the bullet hard so it does not fly apart).

At what point could this be classed as armour piercing, I don’t know the legalities on this practice but would be interested to know.

 

[AlexD]

At what point could this be classed as armour piercing, I don’t know the legalities on this practice but would be interested to know.

It would be inefficient as an armour piercing round because the tungsten is at the wrong end, has a blunt shape, and there is not a lot of it.

Legally I understand it comes down to what the projectile is designed to do.

• Section 5(1A)(e): any ammunition for military use which consists of, or incorporates, a missile designed, on account of its having a jacket and hard core, to penetrate armour plating, armour screening or body armour, e.g. armour piercing ammunition;

Which these rounds are not.

 

[Len the dog]

It would be inefficient as an armour piercing round because the tungsten is at the wrong end, has a blunt shape, and there is not a lot of it.

Legally I understand it comes down to what the projectile is designed to do.

• Section 5(1A)(e): any ammunition for military use which consists of, or incorporates, a missile designed, on account of its having a jacket and hard core, to penetrate armour plating, armour screening or body armour, e.g. armour piercing ammunition;

Which these rounds are not.

It would certainly not be designed for that purpose but I wouldn’t like to test it in court. Even though the intention is merely to alter the aerodynamics of the projectile for the purpose of greater accuracy, it still has a hard core that could potentially allow it to penetrate body armour.

 

[tim@tcs]

It would certainly not be designed for that purpose but I wouldn’t like to test it in court. Even though the intention is merely to alter the aerodynamics of the projectile for the purpose of greater accuracy, it still has a hard core that could potentially allow it to penetrate body armour.

Legally it’s down to intention however case law would take precedent. That said if you knowingly use a bullet weight and barrel twist rate combination that produced massive amounts of damage on hitting a target in theory you are intentionally creating inhumane ammunition!
Tokarev auto ammo will penetrate police body arm our but it’s not designed to do so and standard.308 fmj ball can penetrate 1/2 inch steel plate but it’s not designed to!
Moving the cog into the parallel portion of the projectile is a known way of increasing stability and MkV11 .303 had an inert filler in its nose which the Germans tried to claim was designed to make the projectile expand explosively and a serious study of their wounded was used in the complaint!
It wasn’t designed to do that and as such the Germans were rightly told to do one!

 

[DavyG]

I watched the same video with interest just last week up until 7.45minutes! Yes, its an April fool joke

Indeed…
My first thought was if you take away a solid copper base, drill a hole and countersink it…all that is going to do is invite all that initial pressure inside the bullet allowing weird and wonderful base expansion. Bye bye consistent neck tension.
DG

 

[Andy RV]

On the tail, a flat tail has a LOWER drag at supersonic speeds than a boat tail. This is why the X15 had a wedge tail: see https://www.nasa.gov/wp-content/uploads/2015/04/607076main_x15researchresults-ebook.pdf . Subsonically the opposite applies. I thought the reason for the boat tail was to reduce stability so the bullet does more damage then they somehow migrated to ELD match bullet profiles for reasons I do not know (despite looking for the data).

From very briefly skimming over the ‘wedge’ section in the doc it sounds like they choose the wedge profile as provided the best geometry for the control surfaces, and your statement seems to contradict its self?…

Anyway there is no doubt that a boat tail provides an aerodynamic advantage at supersonic velocities.

 

[Lancaster]

Barnes used to produce the MRX years ago, Copper Bullet, Tungsten core, overcame the issue of Copper bullets being long for weight.
They were pricey, but very good, sadly they were discontinued, I guess due to cost.

Drilling the base of a bullet may cause them to act like a Diablo airgun pellet and the base could be pushed out like the skirt on a pellet.

 

[AlexD]

Indeed…
My first thought was if you take away a solid copper base, drill a hole and countersink it…all that is going to do is invite all that initial pressure inside the bullet allowing weird and wonderful base expansion. Bye bye consistent neck tension.
DG

The cases are annealed and have minimal neck tensions so the bullet should move out of the case fast: looking at the pressure peak and distance travelled in GRT it looks fine in theory. Empirically, the holes the bullets make in the target are not enlarged even with the biggest counterbores in the hot 0.284 180gn bullet in jam + RS60 52gn load.
The wild seating depth test would have also flagged any tendency for the pressure to swage the base.
As soon as the bullet leaves the case there is nothing to expand the base because the pressure is applied on all sides. Once the bullet starts moving down the barrel, any tendency for base expansion is constrained by the barrel wall and worst it can do is fit the rifling which the straight part of the bullet is going to do anyway.
On the rear shape X15 page 30: "A wedge shape was used because it is more effective than the conventional tail as a stabilizing surface at hypersonic speeds". A conventional tail is a boat shape.

 

[User00044]

My understanding of what you're trying to achieve is a bullet with weight bias to the rear , in an attempt to improve stability and reduce aerodynamic jump . I applaude you for the effort you're putting into this , but am unsure as to your end game .
Bullets with a rear weight bias already exist . The new Hornady ELD-VT , essentially they have taken a bullet of a heavier cup and core design and reduced the core . In doing so they have created a larger void behind the polymer tip effectively moving the weight bias back .
If the rear bias does have a positive effect on reducing the diameter of the conical movement during flight it may contribute to the higher BC figures claimed by Hornady . Although I've yet to see any hard figures . I would hazard a guess and say their ballistic guys are fully aware this .
I look forward to your results !

 

[AlexD]

but am unsure as to your end game .

End game is both a goal and a process. Process is to explore and learn more: some engineers make fine handbuilt watches when they slide towards retirement, some make cameras, others play with gun parts - all are fine mechanisms with lots to learn.

Goal of this path is to make a very Scottish bullet, that has as low as possible aerodynamic jump, so it shoots micro groups in the wind, where one corrects only for windage + distance and nothing else. As you know we have a wee breeze here from time to time. This time of year, it seems all the time.

On the ELD-VT, they increase the space between the aerodynamic centre and the CoG so it no doubt flies straight in a tighter cone but one would expect it to have more aerodynamic jump.

By the way here are the pictures I promised Deermanager on the setup to measure concentricity as finely as that discussion needed. Collets in collet block, holding the neck of the cartridge, on granite block, with dial indicator on the ogive (normally vertically, not 45 degrees in the pic). The bolts on the ground plate are for the fixture that line up the collet block in the right place each time, when I slide a fixture over them and the collet, and does not touch the bullet, but fixtures gets in the way of the photo so is off here. The second clamp behind the collet block ensures the collet block cannot slide backwards, so one measures the same place of the ogive each time one rotates the block.

 

[Klenchblaize]

More toys - got to have one of these funky looking bits of kit!

K