Target Bullets

[Stuck]

Thank you all very much for the advice.

:goodjob:

[Alpha1]

No problem by the way if you are getting good results with the Amax and you all ready have a load that works with them then why bother to change. Amax are a good bullet.

[Laurie]

With the exception of the 208gn model, .30 A-Max bullets are a poor choice for 1,000 yard competition. Alongside the 168gn Sierra MK and its near copies - Hornady HPBT Match, Nosler CC, Speer Gold Medal Match - and the modern 180gn SMK, they suffer from a short boat-tail section with overly steep angles, 13.5, 12.9, 12.6-degrees for the 155, 168 and 178gn models respectively. The angle should be under 10-degrees, and recent thinking is that 7-8 is optimal.

The purpose of the boat-tail section is to reduce tail-drag. As the bullet passes through the air it creates a circular low-pressure area behind its base with turbulent air around its circumference which creates drag. At high velocities the bullet nose creates a high percentage of the overall resistance to its passage through the air because of the supersonic shockwaves created ahead of the nose. However, unlike nose induced drag, that at the rear is not velocity sensitive and remains constant throughout the flight. By the time the bullet's velocity drops close to the speed of sound it makes up a significant percentage of total drag, and once subsonic is the largest source of continuing drag.

The reason for putting a boat-tail rear onto bullets designed for LR shooting (originally for FMJs designed for machinegun ammunition) is that the amount of this drag is directly related to the bullet base area. So, if you take the 0.308" 200gn Berger Hybrid as an example the base dia is reduced from .308 to 0.259 and its area reduces even more, by just under 29% from 0.0745 sq in to 0.0530 sq in. So far so good, so why not use a 20-degree tail angle and reduce it a lot more? Go too steep and the air flowing along the sides of the bullet refuses to follow the tail section walls and you lose the benefit. In fact it gets worse as the airflow now breaks away from the bullet walls and creates turbulence at the bearing surface to tail section junction actually increasing drag over a comparable flat-base bullet. When the bullet speed drops into the transonic speed zone ~1.2-1.0 MACH, the turbulence usually becomes more severe in this instance to the point where the bullet may be destabilised. The combination of increased drag and turbulence also effectively degrades the bullet's BC at longer ranges which is why the 168gn Sierra MK for instance usually, but not always, ends up subsonic at 1K at .308 Win velocities and often creates oval holes in the target or even goes through it sideways due to the destabilising effect.

Interestingly, Hornady has apparently woken up to this issue and that its customers are much more likely to shoot beyond 500 or 600 yards than was the case even 10 years ago. The most recently introduced A-Max, the 208gn model has an 8.3-deg tail angle and the new HPBT models are radically redesigned compared to their A-Max stablemates. The 178gn HPBT has a longer more sharply radiused neck section (13.42 calibres v 9.59), a much shorter central bearing section (0.401 v 0.509-inches) to reduce friction in the barrel, and a longer less sharply angled tail section (0.185 v 0.135 inches and 8-deg angle v 12.6) than the same weight A-Max. The result is an increase in average G7 BC from 0.240 to 0.257 which is a lot better, marginally better than the 175gn Berger VLD for instance, but still behind the newest Bergers - 0.266 for the 168gn Hybrid and 0.264 for the 175gn LRBT. Moreover, this model (178gn Hornady HPBT) should remain stable at all ranges making it a viable 1K .308 Win bullet. (All measurements and figures from Bryan Litz's 'Applied Ballistics for Long Range Shooting 2nd edition.)

The 180gn Sierra MK is an interesting case. It used to have a long, shallow angle boat-tail section and was a favourite LR bullet in US conventional long-range prone disciplines, also used by Match Rifle shooters here. Around 25 or 30 years ago, the company redesigned it with a short steep (12.7-deg) boattail, result no longer any good at long ranges. Old timers still talk of the fabled long-range Sierra 180 and I've heard it suggested it's just a shooting myth, but Yorkshire shooter Ken Rathbone showed me some examples from a batch he'd picked up somewhere a year or two ago.

[Stuck]

Thanks very much for taking the time to explain that Laurie.

[GazMorris]

.

Sierra 2156
Very good cost effective bullet - great for up to 600
1. Hard to point - very sharp
2. you MUST Bearing surface sort and (variation range 0.000 to 0.025)
3. Weight sort them (+- 2.0 grain variations)
Great for up to 600 - for practice excellent bullet for cost effective training at 1000 yards
ENS Rating

I don't shoot F-TR but I do TR and I've given up on using Berger bullets because they're approximately twice the price of Sierra for only a marginal increase in performance out of a top quality target rifle with a good shooter. With this in mind, I use Sierra 2156s at all ranges from 300 to 1000 yards and get excellent results.

Your mileage may vary for F-TR and I know that ENS swears by pointed Bergers. He's been nagging me to have a go with them for TR smile2

Gaz

UPDATE - Minor clarification added.

[Laurie]

I'd generally agree with Tim's (ENS) evaluations with the possible exception of his view of the 185gn Berger Juggernaut. If you get a barrel that really likes them, MVs in the 2,775-2,825 fps range make it an impressive performer giving superb elevation consistency at up to 1,000 and reducing the wind effect compared to the 155s. You do knock the stuffing out of your barrel though and they are expensive as with all Bergers, and were frequently hard to get even before Sandy Hook got US shooters into panic buying mode.

Like Tim though I've gone off heavies and 185 is certainly as heavy as I'd go now in theory, heavier than I'm actually running in practice. Some people continue to get excellent F/TR results with 210s and heavier, but I reckon it's just too much hard work both in getting them to perform and in shooting them. It's probably no coincidence that the sole 230gn Berger Hybrid user in the GB F/TR national circuit, Steve Donaldson has thrown away more points and lost more matches as a result of cross-shooting than all other F/TR league shooters combined. (Heavy recoil = bi-pod jump = pointing at a neighbouring target after touchdown!)

There are two other bullets I'd suggest worth trying:

The Aussie 155gn Dyer designed HBC which although VLD-shaped seems to be more jump tolerant than Berger equivalents. Its BC is identical to that of the 155.5gn Berger while it's priced close to the 155gn Sierra MKs. Very consistent dimensions (not weighed them), but not very pretty as the manufacturer obviously doesn't run them in a polishing tumbler before sending them out, they also come loose so the importer / retailer Brian Fox (Fox Firearms at Diggle) sells them in polythene baggies or screw-top hard plastic containers.

The 168gn Berger Hybrid. 0.266 G7 BC (same as the 190gn SMK and considerably higher than either of Lapua's 185s) but capable of being driven much faster at over 2,900 fps. So far, I've not found the Hybrids as easy to 'tune' as Berger / Bryan Litz makes out and only got it to shoot well in my rifle by treating it as a VLD seated into the lands.

If I were in Gaz's shoes (and TR rifle sling), I'd almost certainly shoot Sierra's #2156 too providing my barrel liked it given the price differential with Berger 155s. (So far, I've had very little success in getting this bullet to group for me in maybe three rifles now while the older #2155 model is nearly always a doddle.) With the area of the TR target's five ring four times that of the F-Class equivalent (yes, that's correct - a halving of ring diameter produces a 75% area reduction, not 50% as most people assume), there is not quite so desperate a need to chase that marginal fraction of an MOA reduction in wind induced movement to just break the line on a minority of close but not close enough wind calls. With perfect aim and elevation, the TR shooter has a full MOA (plus a little bit bit given you get the higher score on just breaking the outside edge of the line) to play with either side of the target centre, the F/TR shooter half-MOA and a bit, with that reducing as elevation rises or drops.

What this comes down to is that with perfect aim/elevation, the TR shooter using the SMK at 3,000 fps has to read a true 90-deg crosswind to + or - 1.1 mph, let's say around 2 1/4 mph in a true quartering wind to stay in the 5-ring, while the F/TR shooter has half that margin of error before he/she drops a point. Switching to a pointed Berger 155.5 at the same MV increases both shooters' windreading error margin slightly - by 0.05 mph for the F/TR shooter, a tenth of 1 mph for the TR shooter in a true crosswind ~ a tenth or maybe a little more mph in a quartering wind change for the F/TR shooter. Have a mere quarter-MOA elevation variation and life gets still harder for the F/TR shooter as his target's 5-ring's width is reduced by a greater absolute amount than that of the TR shooter's target. Shoot half MOA high or low and the F/TR shooter now has to have made a perfect wind call to keep the 5 points while the TR shooter still has a reasonable if reduced degree of latitude.

Many people are going to say that such a minimal benefit isn't worth an extra £20 for a box of bullets (and the cost of the pointing die), but with a point on the aggregate score usually equalling an overall F/TR place in an F-Class league round (and sometimes two or three places at the top of the leaderboard), those one or two shots that just squeak 'in' to whatever ring over the course of four or five stages can be the differrence between getting the event winner's shield or having done 'really well' but just out of the top three 'on the podium'.

[Alpha1]

Interesting read thanks for that.

[GazMorris]

If I were in Gaz's shoes (and TR rifle sling), I'd almost certainly shoot Sierra's #2156 too providing my barrel liked it given the price differential with Berger 155s. (So far, I've had very little success in getting this bullet to group for me in maybe three rifles now while the older #2155 model is nearly always a doddle.)

Hi Laurie,

How much have you tried jumping the 2156s? I've found them to group better with a longer jump of about 40 thou than with shorter jumps like 20 thou or 10 thou in both my old Swing and new Barnard rifles (both with 30", 1/13" twist, 0.298x3065 barrels.) I've also found the 2155 to be incredibly tolerant of different loads and seating depths but haven't had as much trouble as other people seem to with the 2156.

With the area of the TR target's five ring four times that of the F-Class equivalent (yes, that's correct - a halving of ring diameter produces a 75% area reduction, not 50% as most people assume), there is not quite so desperate a need to chase that marginal fraction of an MOA reduction in wind induced movement to just break the line on a minority of close but not close enough wind calls. With perfect aim and elevation, the TR shooter has a full MOA (plus a little bit bit given you get the higher score on just breaking the outside edge of the line) to play with either side of the target centre, the F/TR shooter half-MOA and a bit, with that reducing as elevation rises or drops.

What this comes down to is that with perfect aim/elevation, the TR shooter using the SMK at 3,000 fps has to read a true 90-deg crosswind to + or - 1.1 mph, let's say around 2 1/4 mph in a true quartering wind to stay in the 5-ring, while the F/TR shooter has half that margin of error before he/she drops a point. Switching to a pointed Berger 155.5 at the same MV increases both shooters' windreading error margin slightly - by 0.05 mph for the F/TR shooter, a tenth of 1 mph for the TR shooter in a true crosswind ~ a tenth or maybe a little more mph in a quartering wind change for the F/TR shooter. Have a mere quarter-MOA elevation variation and life gets still harder for the F/TR shooter as his target's 5-ring's width is reduced by a greater absolute amount than that of the TR shooter's target. Shoot half MOA high or low and the F/TR shooter now has to have made a perfect wind call to keep the 5 points while the TR shooter still has a reasonable if reduced degree of latitude.

Many people are going to say that such a minimal benefit isn't worth an extra £20 for a box of bullets (and the cost of the pointing die), but with a point on the aggregate score usually equalling an overall F/TR place in an F-Class league round (and sometimes two or three places at the top of the leaderboard), those one or two shots that just squeak 'in' to whatever ring over the course of four or five stages can be the differrence between getting the event winner's shield or having done 'really well' but just out of the top three 'on the podium'.

What you say makes perfect, logical sense; however I'm much more of a fan of a good Monte Carlo analysis than this kind of "common sense" analysis as it gives you a useful numerical comparison, i.e. it shows you how much the benefit really is on the kind of statistical basis you allude to, rather than just showing that there is a benefit, which is obvious from a numerical comparison of BCs alone. (I recognise that we're in danger of getting into a TR vs. F-TR dick measuring competition here, which I have no intention of pursuing!)

Gaz

[Steve E]

For what it is worth,a 2156 at 2.9" COL, 2980fps will hold the V bull at 1200yds out of my well worn 30" 1/13 Kreiger.
It will nail the V bull at all normal TR distances with very little effort. I have also shot on the F-Class 600 and 1000yd targets and it will easily hold the bull on those targets without having to batch weigh and measure bearing surfaces or point them. Out of the box they are probably better than the ability of the shooters using them.
Shoot more worry less.

[Stuck]

For what it is worth,a 2156 at 2.9" COL, 2980fps will hold the V bull at 1200yds out of my well worn 30" 1/13 Kreiger.
It will nail the V bull at all normal TR distances with very little effort. I have also shot on the F-Class 600 and 1000yd targets and it will easily hold the bull on those targets without having to batch weigh and measure bearing surfaces or point them. Out of the box they are probably better than the ability of the shooters using them.
Shoot more worry less.

Steve,

I won't ask you to post your load data for obvious reasons but could I ask what powder you are using?

Mick.