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Review of FX Elite performance and characteristics of its ST barrel ... long.

April 5 2012 at 10:29 PM

Yrrah  (Login Yrrah)

FX Royale Elite.Extensive review of some aspects of this rifle.
I am mindful that many shooters here are disdainful of reviews that are short on detail or smack of just advertisement blurb. I also realize that many don't like to read about every blade of grass someone has cut. I hope this report to be a fair compromise.

These results are relevant to the FX Elite rifle # 6007 of .25 calibre/ 6.35 mm. with Smooth Twist barrel shooting JSB Exact King 25.4 pellets and others as indicated..

This is a relatively new FX rifle model that shares some specifications with the FX Royale 500 . Numerous questions, suppositions, claims and opinions circulate in the airgun media regarding, in particular, the performance of the Smooth Twist ( ST ) barrels and their affect on pellet ballistics and accuracy in this line.

I have posted here of my rifles undoubted precision grouping ability a number of times:

This present present report addresses questions of :

1. Pellet spin-rate and its correspondence to barrel "rifling twist rate" and some implications.
2. The nature of physical pellet alterations as affected by the ST barrel configuration.
3. The influence of actual spin rate (as opposed to barrel twist rate ) and apparent alterations of pellet form on external ballistics; in particular it addresses the stability of pellet flight and of air resistance in flight and gives evidence based upon field testing.

Taking these three in turn:

1. The physical barrel "rifling twist rate" is nominally 1:16 inches, or an initial rate of one turn to 16 inches travel of the pellet. ... My tests of marked pellets shot through paper screens indicate an initial pellet in-flight spin rate of approximately one revolution in 70 to 80 inches of travel for JSB 25.4 gr King test pellets from this particular barrel at the particular test velocity. This test cannot be absolutely precise. But another conventionally rifled barrel, used as a control, and shot at the same velocity with the same pellets, shows consistent rates of 1:18 / 1:19 inches at muzzle for the test. This would be very close to the nominal twist rate for this barrel.

The first implication of this is that the test pellets shot through the ST barrel of this rifle do not have initial spin rates that correspond to the barrel's nominal left hand twist rate of 1:16". Their actual initial flight spin rate is approximately four and a half to five times slower than that of the actual rifling twist rate.

It should be emphasized that this should not necessarily be seen as being detrimental to field accuracy/ precision. On the contrary, the consistently excellent precision grouping, demonstrated here in previous research posts (as small as 0.25" at 52 yards and MOA at 100 yards), indicates otherwise (see referenced link). What it does do is to again raise the question as to the real role of an air rifle barrel's twist rate and its influence upon pellet stability. A diablo pellet is spin stabilized but also strongly drag stabilized, because of its shuttlecock shape, and most probably does not require the same spin rates that bullets require to prevent them from swapping ends.

[IMG][linked image][/IMG]

2. A reason for (1), above, is that the pellets are in fact "stripping" through the ST rifling but in doing so they follow the rifling sufficiently to pick up a consistent spin of the magnitude indicated. A close examination of recovered pellets after having been shot, seems to also verify this. Although the area ratio of the barrel's "lands" to the "grooves" of the "rifling" seems to be approximately in the ratio of 1:1:

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(Late Edit with added pic but of a .22 barrel with sleeve cover removed) : Outside of ST barrel muzzle showing the pressed lines that become the lands internally in the barrel.

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When shot through the barrel the pellets' heads and skirts have five conjoined "flats" that seem to have been swaged in stripping over the "lands". There is no visible evidence of markings that correspond to the "grooves" of the ST "rifling" seen in the above pic...

[IMG][linked image][/IMG]
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NOTE: There can be a distinct difference in the results emanating from the dynamics of shooting a pellet to those of one that has been merely pushed through the barrel (as is often reported in article reviews ). This would seem to be particularly so in this case of the ST barrel, given the great differences in the forces involved. With great care I managed to push some 0.25 pellets through the ST barrels in a way that shows the character of the barrel grooves as well as the lands; Edit: I had to encourage the barrel to rotate around the pellet to eventually get this result. I did not manage to be successful with the .22 barrel, every pushed pellet stripped with no evidence of the barrel grooves as high sections on the pellet.

[IMG][linked image][/IMG]
[IMG][linked image][/IMG]

Again, it would be a mistake to assume that this stripping would somehow result in reduced performance in accuracy, precision or velocity. None are truly compromised when judged by the field accuracy and results of precision grouping which I have attained so far.

3. In order to investigate the question of any possible positive and/ or negative influences of ST rifling on pellet flight characteristics, four approaches were undertaken namely 3a, 3b, 3c and 3d:

3a. A 50 to 100 yards "pellet drop test" comparison between the ST barrel Elite and a conventionally rifled BSA Hornet was made:

[IMG][linked image][/IMG]

This indicates that on a level playing field:
Given equal muzzle velocity of 880 fps and kinetic energy of 43.7 fpe ; with unselected pellets JSB Kings (best pellet for each rifle); with both rifles zeroed to 50 yards; under the same set of conditions; with only one group allowed to be shot at each range, not cherry picked from a number of groups; there was no obvious difference in drop from 50 yards to 100 yards ( 13.70 inches for the ST barrel and 13.75 inches for the conventionally rifled BSA barrel ); and no significant difference in grouping precision ( ctc 0.35 inches for both ST and BSA barrels at 50 yards, and 1.05 inches ctc ST barrel to 1.00 inch for the BSA Special Hornet barrel at 100 yd for 5 shot groups at each range ). ...

The implication of (3a) is that: at the specific MV 880 fps / Mach 0.78 at prevailing conditions, the air resistance of the same pellets shot from the two different barrels was similar, with no advantage in trajectory of the one over the other; and by implication, no differences in drag or ballistic coefficients. (However it will be seen in (3b) below, that this may not necessarily be the case at the higher muzzle velocity of 900 fps and Mach 0.80 when a velocity decay test over 55 yards was undertaken and a BC computed see (3b).

3b. A velocity decay test and computed ballistic coefficient were undertaken with 5 of JSB King pellets being shot over a chronograph at each distance of 18 inches and then at 55 yards at average velocity of 900 fps +/- 3 fps ST barrel and 898.2 fps +/- 2.5 fps for the BSA at 18 inches. The average velocities at 55 yards were 746 fps ST Elite barrel, 31.4 fpe, BC 0.0361 ( 0.0313 corrected to sea level ); and 760 fps, 32.6 fpe, BC 0.0407 ( 0.0352 corrected for sea level ) for the BSA Hornet. (Steve Woodwards BC calculator used).

This result indicates what appears to be a significant difference between the two rifles when the initial velocity of this pellet is increased to Mach 0.80. ... It is not in accord with the popular conjecture that the smoother rifling engravings on the ST barrel's projected pellets should necessarily automatically translate to an air resistance advantage in flight when compared to the engravings incurred from a conventionally rifled barrel. One school of reasoning in PB bullet ballistics is that the rifling engraving is of little consequence to air resistance as the boundary layer acts to moderate the possible influence.
This was a dramatic difference and so I shall repeat this test when time and ambient conditions permit to see if the results will be replicated.

3c. I have taken numerous slow motion video clips of pellets in flight from both the ST Elite barrel and the BSA Hornet's barrel. ...
My technique of taking movie clips through the scope sight is a personal adaptation of the method introduced to us all and made popular by Ted in Madison whose clips are well represented on YouTube.
My own innovations and techniques now allow for very reasonable flight analysis throughout virtually the whole of the pellet's journey. This has been enabled by tracking the pellet's flight from very close to the rifle out to quite long ranges.
JSB Kings and some other pellets' flight in calm and windy conditions show exceptional stability:

For Example: JSB Kings shot from the Elite and tracked to 50 yards in light wind showing beautifully stable flight:

And JSB Kings to 71 yards in relative calm:

These are representative of many clips taken of JSB Kings in flight.
They all support the notion of the very stable flight of this pellet when projected from the Elite 6007 ST barrel regardless of the empirically established slow projected spin rate of 1: 70 to 1:80 inches, which varies dramatically from the 1:16 to 1:19 inch rates generally representative of the air rifle barrels; and of stable flight regardless of the pellets' surface and form changes that may have resulted from "stripping" through the ST 1:16 inch rifling.

Another example of arguably by far the best expanding hunting .25 cal pellet marketed today: FX Elite and 26 gr JSB Predator Polymag .25 hunting pellet to 50 yards showing excellent stability and accuracy in some wind:.

3d. The fourth approach to establishing the stability status of flight, because of or in spite of the actual slow spin rate, was to examine the evidence of the apparent spatial attitude of the pellets to the target at the point of impact.
This pilot study was carried out at the extreme target range of 183 yards/ approx 167 metres and involved examining pellets that had impacted on a steel disc; on a very hard dead eucalyptus tree; that had penetrated some thick hard tree bark; or that had impacted hard ground.

Those that have impacted on the steel plough disc and flattened, seem to have obviously met it head on with point-on stability. (Late edit for picture insertion here)

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The steel disc target (below) with a five shot group, the best of three groups shot with an aim-off at the left edge of the disc of approx 12 inches to account for a light left to right breeze. The ctc group size is approx 54 mm or 2.12 inches or 1.11 MOA at the range of 183 yards.

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Close scrutiny will indicate the characteristic white dot of compressed paint where the heads of the pellets made first contact before the lead flattened and blasted away the surrounding paint - thus forming the typical point of impact signature markings. It should be noted that the pellets are descending from a flight mid-range trajectory apex of approximately 31 inches above the line of sight, and that the steel plough disc is slightly concave. Therefore there will naturally be a slightly off-centre head impact even from a perfectly stable non-gyrating flight.

This pellet was shot onto the very hard dead trunk of the eucalyptus tree above the target. It too has obviously remained stable and impacted "point-on".

[IMG][linked image][/IMG]

[IMG][linked image][/IMG]

This one was shot into bare ground at the same 183 yards off to one side of the target disc. It was the only one I recovered there and can be seen to have impacted dirt on the head indicating it too was still flying "point-on".

[IMG][linked image][/IMG]

The following picture shows a pellet that was shot into some very thick loose hard tree bark. It has penetrated one layer of bark and lodged in the second layer behind the first. It too has obviously retained its "point-on" attitude at 183 yards even after penetration of the first layer of dead bark.

[IMG][linked image][/IMG]

All of this supports an assertion that, despite or perhaps because of, the actual slow flight spin rate induced by the ST barrel format, the pellets are remaining stable to the range of 183 yards/ approx 167 metres. Further tests to longer range will be undertaken.

Initial velocity for these test shots was an average 915 fps which may be higher than ideal. Where indicated, performance comparisons are to a BSA Hornet which has been modified by John Bowkett of UK with installation of his own regulator and fill valve designs; barrel crowning; chamber preparation; and power increase to 45 to 50 fpe in .25 calibre; otherwise the barrel is a hammer forged BSA factory barrel as installed in the unregulated BSA Lonestar .25 rifles. This is an exceptional rifle by any standards.

In summary: To date the evidence I have supports the following in respect of the FX Elite S/N 6007 smooth twist barrel:

It seems as accurate as the best I have.

Actual pellet spin rate does not correspond to rifling twist rate and is about four to five times slower from this ST barrel. Accuracy/ grouping is excellent with the big 4 viz., JSB Kings, JSB Predator Polymags, Baracuda/ Kodiaks and Benjamin domes.

Pellets strip through the "rifling" and show no real evidence of the rifling's "grooves". In doing so they do pick up a relatively slow spin. The spin is apparently sufficient to stabilize the 4 popular pellets.

The actual but slow induced spin rate, combined with the drag stabilizing effects of the test diabolo pellets shape, are sufficient for precision grouping in some wind that approaches the best I have attained with conventional rifling at that range. .

The apparently more limited engraving of the ST rifling upon the test pellets does not appear to have any benefit in improving resistance to air friction in flight at a velocity of Mach 0.78 out to 100 yards as judged by pellet drop.

At an initial velocity of Mach 0.80 the velocity decay over 55 yards, was for some unknown reason, greater than that from the conventional rifled barrel when all other controllable factors were kept equal. (This deserves re-visiting and at even higher mach numbers ). This is somewhat at odds with the drop test results.

Slow motion videos indicate very stable pellet flight with no apparent precession, or spiral flight, for the JSB King and Polymag test pellets to the test ranges of 50 or 71 yards filmed .

JSB King pellets recovered at extreme range, 183 yards, show that they arrive at the POI with a "point-on" attitude - again indicating excellent flight stability in the prevailing light wind conditions.

Precision grouping in a light breeze to 183 yards is well within expectations with a 5 shot group of 2.12 inches ctc from a very limited number of 3 groups. For comparison, the best 5 shot group I have shot to date at that range is 1.45 inches ctc shooting 15.9 gr JSB Exact pellets in more perfect conditions. Very few groups have ever been shot at this specific range.

The sight was zeroed for the 183 yards tests with 172 clicks on the Bushnell 6500 scope set at 16X . Dave Eades' CG Ballistica Programme was used for all sight zero adjustments.

Link to my third post # 3 and which incorporates links to posts # 1 and # 2 for any who may be interested in the complete to date package:

I hope some have read to this point and enjoyed it ....... Best regards, Yrrah, Harry Fuller in OZ.

This message has been edited by Yrrah on Aug 27, 2014 9:14 AM

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