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- Last updated: 23/11/2016
If proof was needed, fast moving small calibres are capable of superior downrange performance, primarily due to the enhanced Ballistic Coefficients (BC) of the bullets as compared to a similar weight in .224 or .243. That’s some statement but small calibres have enjoyed a renaissance of late and I for one am a big fan. I love my .14, .17, .20 and .22 calibre wildcats but my best to date has to be the .20 Satan developed nearly a decade ago…
Whereas the 20 Tactical is great for bullets up to 40-grains, the 20BR and 20-250 certainly are more efficient when pushing the heavier 50 and 55-grain projectiles. A .20 BR will push a 50-grainer at 3850 fps which equals a .22-250 and .220 Swift velocities but offers a better BC than the .224 projectile (over 0.3 as compared to 0.25), so downrange performance will correspondingly be better all round. The 55-grain Bergers are as wind-slippery as they get and have great BC`S of 0.381 better than a .243 Hornady 87-grain Match King!
The only compromise with small calibres is that as the bullets get heavier they become longer and therefore need a faster twist rate to stabilise. However, if you want to push a 50-55 grainer down a fast twist barrel quickly, pressures can rise alarmingly. A 50-grain Varmint Boat Tail needs 1 in 9 to stabilise it rather than the 1 in 12 common to the lighter .20 projectiles. The 55s prefer 1 in 8 or 1 in 8.5 though I have played with 1 in 6 twist’s and custom made 60-70 grain bullets.
RIFLE AND CARTRIDGE SPEC
I chose a Pac-Nor Super Match grade 29” tube and, as I wanted to be able to use heavier bullets, I had them make me a tight 1 in 8.5 twist to ensure the 50 and 55 grainers would stabilise. The barrel was mated to my RPA Quadlite switch barrel action.
It would be nice to push the 50 and 55-grain Bergers as high a velocity as possible, so needed a case that fulfilled these criteria. At first the .22-250 Rem was an obvious contender due to its easy availability but I hankered after something different. I really wanted a ¾ length .243 case but did not want the chore of resizing and forming brass, so I hit on the idea of using the 6x47 Swiss Match (SM) case in May 2003.
This is a match-quality .308 bolt face cartridge with a 47mm body and therefore represents a ¾ length .243/.308 case capacity. This was actually the Mark 1 version because as soon as the Lapua 6.5x47mm case came out I necked this down to .20 and this was the .20 Satan Mark 2 version. In reality both cases perform similarly despite the 6.5x47L having a small rifle primer unlike the SM case which has a large rifle primer.
The design and water capacity of 44-grains looked feasible and a reamer was ordered from Pacific Tool and Gauge that would entail minimal brass preparation and require no neck turning. I settled on a neck diameter on the reamer of 0.235” that would give 1.5 thou clearance on the neck and chamber wall, along with a length of 1.8215” and a 30° shoulder. I did actually design an improved case with a 40 and 45° shoulder and a small capacity case called a Pup if the load density was not optimum.
Case forming was easy. Virgin 6x47 SM brass was sorted by weight for consistency and batched accordingly. They were then run through a .22 BR FL die set with sizing button removed to initiate the first neck sizing procedure, being sure to lube with Imperial Sizing wax as I went. Next it was run through a .20 BR FL die with button removed to achieve the primary .20 neck diameter. I then trimmed the cases to 1.8215” to uncut the chamber/reamer spec and ran each one through a .204 expander mandrel to even out neck concentricity and give enough tension for the bullets for fire forming. De-burr the inside and out, and hey presto one .20 Satan cartridge ready for fire forming.
Medium burn rate powders such as Alliant Reloder 15, RL17, Varget or H 4350 would be good choices. I reckoned that 38-grains behind a 50-grain Berger would be about top dollar. So I reduced the load and started at 32-grains of RL 15 as a fire-forming load with a Federal 210 primer.
The shots totally blow out the cases to correct chamber dimension and recorded a sedate 3533 fps velocity and 1386ft/lbs energy. This was a good safe staring point but obviously a long way to go to achieve that 4000 fps target. I upped the charge to 34-grains which achieved 3725 fps/1540ft/lbs, 36-grains yielded 3828 fps/1627 ft/lbs! I tentatively increased the powder to 36.5-grains and achieved 3950 fps. 37-grains yielded 4012 fps/ 1791 ft/lbs with no pressure signs and a stunning ¼” grouping.
I pushed on to 37.5 to achieve 4136 fps but groups opened up to 0.5”, 38-grains made a whopping 4175 fps. What struck me was not the high velocity from that 50-grain Berger but the consistency with less than 15fps variation. I had my load with 37-grains of RL 15, a 50-grain Berger bullet ignited with a Federal 210 primer would shoot 0.25” 3-shot groups with less than 15 fps variation and a staggering 4018 fps average velocity, pretty good. Other powders like Vit N140, Varget and H4350 had similar results with the 50 grain Berger’s
Now the 55-grain little Berger ‘torpedoes’ as I call them are 0.915” long and boy are these sexy! Extremely sharp, slender with a boat tail and best of all a BC of 0.381. Again medium powders but this time Reloder RL17 is just right. I started at 34-grains that gave a sedate 3507 fps, upping to 35-grains gave 3598 fps. 36-grains jumped this to 3691 fps and 37 produced a healthy 3811 fps. I pushed it one more grain to 38 and 3978 fps was my result but the bolt was a tad sticky so this was max in this RPA. Varget topped out at 38-grains and 3901 fps with H4350 achieving 3889 fps with a 40-grain payload.
DOWN RANGE PERFORMANCE
This means down range BC advantage against either .22 or .243 bullets. Similarly compare the 50- grain .204 Berger to that of their .224 Match bullet. The former has a BC of 0.296 whilst the traditional .224 bullet can only manage 0.241 even the venerable Nosler 40-grain Ballistic tip can only manage a BC of 0.242.
Even better is the astonishing Berger 55-grain .204 bullet with a BC of 0.381! Whilst the same weight .224 bullet is only 0.267, even a 0.243 of 55 grains is a lowly 0.240 BC if you launch these at the same velocity the smaller .204 will outperform the rest by a long shot, literally.
Think of it this way; my .20 Satan Wildcat round can push a 55-grain Berger at 3800 fps/1764 ft/lbs whilst a .224 calibre 55 grain Nosler Ballistic tip pushed by a .22-250 can generate the same 3800fps and 1764ft/lbs. Looks good, but wait; due to the better BC of the smaller .204 at 300 yards it only drops -5” and has a wind drift value of -5.3” compared to -6.8” drop and -10.1”wind drift of the larger bore.
If that does not convince you look at the 500 yard figures, the .20 Satan drops only -26.1” compared to the .22-250’s whopping -37.9”. Wind drift figures are just as impressive with Berger’s 55-grain .204 drifting only -16” in a 10mph 3 o’clock wind whilst the .224 started at the same initial velocity is pushed 32.9” off the target, which is over double the value!
If you are still not convinced about .20 calibres, think on this; the gap between .17 and .22 centrefire, in fact 0.172 and 0.224 calibres is some 0.052 thousandths of an inch which in ballistic terms is huge. That’s like having a 0.243 and 0.308 calibre with no 0.257, 0.264, 0.277 and 0.284 calibres between them, and where would we be without the 25-06, 6.5x55mm, .270 Win or any of the 7mm calibres. Makes you think doesn’t it?
One down side is case prep and run at full throttle the .20 Satan barrel life for top accuracy is only 1000 rounds but that’s 1000 dead crows!
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Zxreuu06 May 2022 at 05:02 AM
sure why bother reading the artical;
ivan taylor06 Feb 2014 at 06:54 PM
Alternatively just use any widely available .22 centerfire in what ever commercial chambering that takes your fancy. Minor theoretical exterior ballistic improvements are just not worth faffing about with custom barrels and custom manufactured dies. Hardly a value for money exercise.
Wilf17 Jul 2013 at 01:26 PM