vertical groups at distance

[Seddo]

Hi guys,

I have a question that isn't related to F Class shooting but I think the answer could be know by a few of you that have done a lot of 1000y testing as the same thing will happen to a 308 at that range. If I can get my 300y vertical down i will give it a go in an f class match.

I have been playing with a 300 Whisper shooting 208 amax at 1050fps. Batching cases in 1gr lots and projectiles in 0.2 gr lots cut the 100y group in half to under 0.5" but hasn't stopped the 300y vertical. I have run them over the chrono and the ES was in the teens, i haven't tried it again since buying the magento speed.

All i can think to do next is:
measuring the bearing surface length
moly coating
neck turning

Does anyone have an idea which one has the most impact on reducing vertical at long range or do i have to do all of them?

I have given up on my current batch of cases and ordered some new ones, i will prep them and start the process again.

[bruce moulds]

seddo,
I don't know the answer to your issue, but will offer this.
you are at the bottom end of the trans sonic zone.
bullets do funny things here, due to strange airflow and also due to strange things happening to dynamic stability.
dynamic stability needs to be tested for.
a bullet that has a little "wiggle" will lose b.c. during that occurrence.
some bullets are safer in this regard than others.
gyroscopic stability could be above 1.4 and this can still happen.
talk to match rifle shooters and creedmoor shooters.
bpcr bullets can easily be launched at low velocity s.d., and can hold 1moa of vert at 1000 yd,
in this game spitzers are avoided like the plague due to lack of long range stability and accuracy
the old 45/70 500gn round nose was tested to 2 miles at sandy hook. you might find this on google.
the latest bullet developments in this area were by metford for long range bpcr, and his bullet basically resembled the 303 mk V1 bullet in shape, which he designed.
the modern equivalent is the money bullet, developed by dan Theodore.
this bullet is defined by having a round nose 50% to 55% of groove diameter, a secant ogive, and parallel sided bearing surface and a flat base.
this shape was proven mathematically and in practice by nasa to be the most stable in trans sonic and subsonic flight.
both the metford and money bullet have been shot at 1 mile in matches and are known to be able to hold 1 moa vert when started at about 1300 fps.interesting that metford cme to the same conclusion as nasa, he by trial and error, and nasa by computer.
at those speeds you could shoot cast bullets, and so invest in a money mould suited to paper patching, and probably get good results.
all the pointy boattails don't offer much drag benefit at these low speeds.
keep safe,
bruce.
p.s.
go to boomer's moulds website to see a money nosed bullet.
it is a grooved bullet. a patched bullet with no grooves and the same weight and nose will have 60% wind deflection of a grease grooved bullet.

[Seddo]

Bruce,

I have been reading how much the guys in the states like the 247gr NOE moulds and have been thinking about getting some to try. My casting set up at the moment is a brand new lee pot that's only been out of the box once in 2 years. I have been meaning to give casting a go so it looks like this might be the time to start.

I haven't done much testing here but a mate has used the 220 sierra RN bullets and he said they have the same trajectory so i don't think the BC has as much of an effect on subsonic bullets.

[Brad Y]

Dunno scott, but far out by todays 500m standards, my 284 doesnt seem tassie worthy. Vertical city!

[DaveMc]

Not only dynamic stability - what about gyroscopic stability? Not sure on your twist rate but possibly this is a high BC bullet with very low rpm due to low launch speed.

e.g. 308 launching from a 10 twist @ 2700 fps will be spinning at 12/10 * 2700 * 60 = 194,400 rpm

same twist at 1050 fps is 75600rpm.

Of course there is less lift forces to counteract but twist rate would need to be very high (guessing around 8 or better).

[Seddo]

Dave,

It's 1 in 8 and it has a 1.8 stability factor.

I might try cleaning up some necks on the old cases while I wait for the new ones.

[bruce moulds]

seddo,
that bullet looks like a bore riding nose type, which allows a heavier bullet that does not use up powder space.
these bullets need to be fairly hard cast so that the unlubed nose can't bump up ino the rifling and cause leading.
the bore riding nose also aligns th bullet well if the nose is a ggod fit.
the best way to select a mould is to measure your bore dia, measure your groove dia, and have a custom mould maker make you one to cast at required specs.
nose would ideally be 0.0005 smaller than bore, and driving bands 0.001 bigger than groove dia.
it would in this case be worth experimenting with alloys as soft as 16:1 lead/tin, to lyman no2 which is 90 lead, 5 tin, and 5 antimony.
there is another hard alloy called taracorp magnum which I could find the mix of if that helps.
start casting at 800 degrees f and try down to 750 in later batches.
the most consistent bullets are cast with a ladle, which is handy, because most of those pots with a valve can leak. blocking the hole and removing the valve mechanism can be done.
fluxing the alloy with beeswax is a good thing to do.
cast with a rhythm for consistency.
e.g.hold the ladle on the mould for the count of 5. when the sprue frosts count to 8. cut the sprue. get the mould back to the ladle fast and start again.
this will very with the mould and alloy.
do people like hawksbury river sell the type of bullet you might want to try. this can be a way to experiment without joining the mould a month club.
most of the commercial smokeless powder lubes are ok.
paper patch needs no lube and has a lot less drag, but you have to learn to do it.'patch to groove dia + 0.001. only thing here is the bullet might be too far back in the case.
dave is fight about gyroscopic stability. 2.0 is not too high at these velocities, and 1.4 should be regarded as absolute min.
keep safe,
bruce.

[AlanF]

Seddo,

If you are getting good (say 0.5 MOA) accuracy at the shorts and low (say 10fps SD) velocity variation, then you have nearly everything covered. If you then get bad vert at the longs, then projectile (BC) inconsistency is a prime candidate. Hornady A-Max have a reputation for some batches being excellent and others terrible. Before doing anything drastic, I would simply try a couple of different projectiles e.g. Berger have an excellent reputation for consistency.

Alan

[bruce moulds]

alan,
dynamic stability issues can cause consistent projectiles to have different bc due to some going a bit more sideways, then straightening up again.
a most interesting subject.
the old 175 matchking was noted for its ability to go through the trans sonic zone and out the other side with great accuracy, while the 168 has a bad name past 600 to 800 yd.
the 220 gn rn might well be a good bullet. a similar shape was used in the krag for palma match in its time, and would have well been in the danger zone at those ranges.

keep safe,
bruce.

[DaveMc]

Seddo,

If you are getting good (say 0.5 MOA) accuracy at the shorts and low (say 10fps SD) velocity variation, then you have nearly everything covered. If you then get bad vert at the longs, then projectile (BC) inconsistency is a prime candidate. Hornady A-Max have a reputation for some batches being excellent and others terrible. Before doing anything drastic, I would simply try a couple of different projectiles e.g. Berger have an excellent reputation for consistency.

Alan

I agree 100% with Alan here (including the AMAX variation thing). good short range accuracy and low velocity spreads definitively mean you don't need to look at brass, bedding, barrel, loads or anything like that. You are down to how the bullet is behaving out wide. BC variation is a possibility and Bruces explanation as well.

You are travelling in a zone that is beyond most F classers experience here. Whilst we do go subsonic we generally are doing it at much higher RPM and tend to try and stay above the transonic level where possible. You will probably get more insight into this by asking the question on some American sites where they deal with this exact case (literally) and projectile. Also the black powder boys will have some interesting knowledge (Bruce ??) but their projectiles are quite different.

This projectile is not going to behave the same as being shot out of a 308 and then slowing down as the spin rate hardly slows over the course of the range but velocity does significantly. You would need to send it out of a 1 in 4 twist for similar behaviour to the match rfle 1200 yard guys.

I know you are after high BC stuff but below the speed of sound it is less important. It would be really interesting to try a large round nose, flat based bullet to see this effect. You shouldn't have any issues with barrel life or powder costs so worth a try!! (e.g. Hornady 220 or 180 gr round nose)

[aaronraad]

Seddo

I'll see if I can PM you a pdf for an example of a transonic projectile that Byron Smalley was working on before he passed away last year.

Elliptical ogives (nose cone profiles) work best for subsonic projectiles combined with long boat tail designs. Optimum designs exist for hyper, super, tans and the subsonic regions.

BC's have to be recalculated unless you have the averages for the correct velocity range. Something like the Sierra MK 240gr (only uses a 6 cal tangent ogive) is a good place to start and you get a couple of BC figures from Sierra.

The Lapua subsonic 200gr 30 cal projectile is also another obvious starting point but I don't believe the projectiles are available as a reloading component and loaded ammunition is expensive.

Other than that look at the Corbin swaging website for some basic design ideas on subsonics.

You will need to give some thought to ricochet unless you use a frangible design. Anything hard like a target frame might cause an issue, much like subsonic .22 rimfire solid lead projectiles.

I'd suggest using Trailboss, magnum projectiles and a firm crimp. The second detonation effects can be action destroying to say the least. Good luck!

Aaron

[aaronraad]

Seddo

I'll see if I can PM you a pdf for an example of a transonic projectile that Byron Smalley was working on before he passed away last year.

Aaron

Found the a link to a copy of the old webpage https://www.cmpdsites.com/_superiorballistics/45caliber.htm

[bruce moulds]

my 40 and 45 cal money and elliptical nosed bullets have calculated b.c. of about 0.45.
trajectory and velocity fed into jbm brings them up to between 0.55 and 0.6 g1 bc at the velocities they fly at.
the trajectory suggests a bc variation during flight to my simple mind.
I am not sure that there is a lot of scientific data on trans and sub sonic flight available to civilians, and possibly not a lot of knowledge generally, due to focus on higher speeds.
cast bullets with noses like the one in the link do not work well out of bpcr and muzzle loaders, but this could be for any reason.
our bpcr bullets start in the trans sonic zone, and become subsonic at about 300. from then on to 1000, or a mile even, they are subsonic.
+/- 1.5 gn wt in a 540 gn bullet seems to make little difference to long range accuracy.
3 seconds time of flight to 1000 makes me wonder how much decay of spin happens relative to say a 308 tr load.
when you shoot these bullets at these speeds, it is amazing how you can learn their characteristics in the wind when there is a good minimal vert load.
Kenny wasserburger recently made 4 out of 5 hits on a 3 moa bull at 1 mile with a 45/110 using black powder and a money bullet at about 1300 mv.
keep safe,
bruce.

[Seddo]

Dave & Alan,
I will sort through my old cases and pull the best ones and see if I can do some more groups from 50y, 100y, 200y and 300y and see what the results are. I shoudl be able to get some Hornady RN projies off a mate so I will give them a shot next. As for other projies I have a 50 pack of 230 bergers and some 225gr Hornady Match.

Aaron,
Cant use traillboss, the case isn't big enough with a 200gr+ projie so the easiest option is 2205 followed by 2400 and 296, cant remember what the VV powder was but I cant get any so it doesnt matter. I'm picking up a pack of Lapua 308 200gr factory ammo this week so I will pull one and see what the projie looks like.

[DenisA]

[/quote]

I agree 100% with Alan here (including the AMAX variation thing). good short range accuracy and low velocity spreads definitively mean you don't need to look at brass, bedding, barrel, loads or anything like that. You are down to how the bullet is behaving out wide. BC variation is a possibility and Bruces explanation as well.

[/quote]

G'day Dave, I'm not challenging your advise. I know your far more knowledgable and experienced than myself, but the above is not inline with my understanding.

Page 181 of Applied Ballistics (The Nature of Bullet Dispersion) talks about 2 types of dispersion. Angular dispersion which is linear as it is based on distance and is a result of aiming and form inaccuracies and such, and then Launch dynamics dispersion which is parabolic as its based time of flight and directly affected by bullet inconsistancies and rfile setup flaws (bedding, etc) . The reason being, slight lateral velocity can be applied to the bullet and exaggerates as the bullet is subject to reducing velocity and longer flight. Its a great chapter.

Launch dynamics dispersion being parabolic is a major reason that makes long range so much harder than short range.

The issue of the OP seems to be directly subject to the majority of long range idiosyncrasies that we are all deaing with IMO.

According to my ballistics program, zerod at 100 yards, a 208g Amax bullet launched at 1050fps drops approx 32 moa (100 inches) by the time it hits 300 yards. Thats long range shooting for that cartridge by my understanding of the term.
This bullets only shedding approx 30 fps per 100 yards and dropping altittude and an incredibly fast rate. Approx. 50moa at 400y and then 68 moa at 500 yards.

P.S
I would have thought that a FB bullet would much more suitable to this cartridge for best short range groups.

As always, I stand to be corrected and appreciate more food for thought.