F OPEN, A NEW ERA?

[John T]

Hello.

A look at the current Berger bullet tables shows that 30 Cal high performance bullets are now on a par with the 7 mm.
7 mm 184 gr F-Open Hybrid Target G7 0.356 1:9 Twist
30 Cal 208 gr Long Range Hybrid Target G7 0.354 1:10 Twist.

The addition of a .308 barrel, chambered for the 300 RSAUM and throated for the 208 LRHT would not be too painful and it is likely to be significantly more consistent/accurate than the 7mm, even with a small increase in drift. Looks promising for Bisley 2025.

It would be interesting to hear from those who are already well ahead on this development road.

Regards, John T,
27.8.22

[Matt P]

Energy limits will be a problem. You won't stay under it and get near a 7mm SAUM, beside the extra recoil make the 30 harder to shoot consistently. Not being able to practice for the FCWC at Queens competitions (under pressure) here would be detrimental IMO.
Why would the 30 be more consistent ?? The groups I see shot at Queens events at a 1000 yards by the 7mm's is outstanding, in fact the level of accuracy/performance over the past few years by FO in general has come along leaps and bounds.
Matt P

[Frank Green]

Yes energy limits or velocities at some ranges will be an issue.

I do have a 300PRC up and running. Slinging 225 and 230gr bullets at 2900fps. Yes recoil is more but I’m ok with it. It does shoot a little flatter and cuts the wind better. Accuracy is awesome as well.

My gun weighs 21.75#. So just under the weight limit.

Later, Frank

[Frank Green]

I just fit up finally another barrel in 6.5PRC. Bullets are 150SMK and 147 Hornady’s. More for testing than anything else. Barrel life will be an issue.

[John T]

Matt and Frank, thanks for your responses.

Having spent a great effort to expand the topic, only to have the reply vanish, is more than disappointing, especially because it happens so often.

Matt, for a similar case volume, the larger the bore, the more efficient the case. The 300 RSAUM is vastly superior to the 7 RSAUM.

The choice of 30 Cal bullets under 220 gr will make the 7 mm redundant.

Regards,
John.
30.8.22

[PeteFox]

The choice of 30 Cal bullets under 220 gr will make the 7 mm redundant.

John
I disagree. In a perfect world without rules you may be correct, but rules we have in abundance. Muzzle energy being the most important here.
As I understand it, the muzzle energy limit for a number of rifle ranges is 3500 ft-lbf. Belmont and Bendigo?

To remain at approx 3500 ft-lbf:

A 180gn 7mm Berger hybrid speed is 2975fps (3537 ft-lbf)

A 208 gn .308 Berger hybrid speed is 2775 fps (3552 ft-lbf)

Given that the ballistics are very similar the 7mm will win every time by virtue of the MV.
Using the above numbers the 7mm terminal velocity will be faster and wind deflection less than the 208 hybrid.
Pete

[willow]

The choice of 30 Cal bullets under 220 gr will make the 7 mm redundant.

John
I disagree. In a perfect world without rules you may be correct, but rules we have in abundance. Muzzle energy being the most important here.
As I understand it, the muzzle energy limit for a number of rifle ranges is 3500 ft-lbf. Belmont and Bendigo?

To remain at approx 3500 ft-lbf:

A 180gn 7mm Berger hybrid speed is 2975fps (3537 ft-lbf)

A 208 gn .308 Berger hybrid speed is 2775 fps (3552 ft-lbf)

Given that the ballistics are very similar the 7mm will win every time by virtue of the MV.
Using the above numbers the 7mm terminal velocity will be faster and wind deflection less than the 208 hybrid.
Pete

Agree. Having said that, I do own a 300wsm which I run with Berger 215gr hybrids at 2900fps however I can't use it at Belmont and the same goes for Bendigo. While I do believe there may be an advantage at the longs in nasty conditions, there are so few ranges where I can truly exploit it, I do wonder whether it's a calibre I will persist with. I am about to join the 7 SAUM club specifically for the longs at 1000 yard ranges like Bendigo and Belmont just to give me that extra bit of horsepower the 284 gives up at the longs.

[Matt P]

Matt and Frank, thanks for your responses.

Having spent a great effort to expand the topic, only to have the reply vanish, is more than disappointing, especially because it happens so often.

Matt, for a similar case volume, the larger the bore, the more efficient the case. The 300 RSAUM is vastly superior to the 7 RSAUM.

The choice of 30 Cal bullets under 220 gr will make the 7 mm redundant.

Regards,
John.
30.8.22

John,
If it was "vastly superior", everyone would be using it. People would find a way, they always do but as an overall package the 30 just doesn't cut it in a 10kg gun.
At high level competition around the world I only see a handful of 30 cals in the results sheets.
Matt P

[AlanF]

Always an interesting topic to try to predict what is the "next big thing" with cartridges and bore size. I agree with the majority opinion that 7mm is currently the best bore size for F-Open but it may only take a technology advance or a rule change to bring something else into favour. Rules such as energy limits have a major bearing. Also, barrel life, performance and availability of components have a big influence on choices. If I had to guess, the next big thing will be LESS than 7mm. There's only so much you can do to improve a projectile's BC without increasing its weight. Reducing bore size without reducing bullet weight will significantly improve BC. This will come at a cost in terms of barrel life. However, its reasonable to expect improvements in barrel and propellant technology which will increase barrel life. On the other hand the trend for energy limit rules in recent times has been downwards, and that trend could continue.

[macguru]

The push to lower energy limits at our ranges may mean that 30 cal high velocity, high BC projectiles are out of the question. Indeed, it may lead to a resurgence of interest in 6.5mm cartridges like the 6.5prc, 6.5-284 etc

[John T]

I must be brief so I do not suffer vanishment.
Australia won at Raton in 2013 because it was more SKILLFUL.
Australia won at Connaught because its SKILL had improved and was still better.
Everyone would agree with Matt that since Canada, "accuracy/performance ... has come along leaps and bounds."
But that has nothing to do with the 7 RSAUM, now that the 180+ bullets have taken it up to and maybe beyond its competitive limit.
Put simply, today's shooters have done this with their SKILL.
Their SKILL needs to move to the next level of challenge.
Rember the old adage; "You can't shoot better than your rifle." YES YOU CAN. The best now shoot better than the limit of the 7 RSAUM.

TO BE CONTINUED.

[John T]

There are two old propositions that relate to the performance of a rifle case.
1. EFFICIENCY; the degree to which there is even and complete ignition of the whole of the powder charge before any powder has left the mouth,
promotes,
CONSISTENCY; the constant rate of bullet propulsion.
promotes,
ACCURACY; the repeating POI at the target, particularly in the vertical plane.

2. The ratio of the powder charge CAPACITY of the case to the CROSS-SECTIONAL AREA OF THE BORE is indicative of case EFFICIENCY. the lower the
ratio, the higher the efficiency.

I accept both propositions as valid.

If you do not accept one or both, your comments are welcome.

Regards,
John T.
2.9.22

[John T]

Hello again.

It has been established that the ratio of the capacity of a case to the cross-sectional area of the bore is indicative of the degree of efficiency of the case. As it requires cubic inches to be divided by square inches, it cannot have a quantitative value.

However, the resultant value can be used when comparing the relative efficiency of cases.

Many lists, charts etc. have been published which list numerous cases in order of their ratio values, usually in ascending order of those values. Say case number 7 in the list has a ratio value of 2.4 and case number 12 has a value of 3.2. The relative ratio values tell us that case 12 (3.2) is less
efficient than case 7 (2.4). But the ratio values, on their own, are of no use in making a mathematical calculation of the difference.

[John T]

Sorry, suffered a glitch with my keyboard.

I was about to suggest that the ratio be given a title; "INDICATIVE EFFICIENCY RATIO, IER" and that the ratio value be called the "INDICATIVE EFFICIENCY VALUE, IEV".

The methods and means on which the lists are based and constructed vary so much that the Standard could be, from time to time, the length of the Prime Minister's nose. Take your pick. And I have. Not that it matters much in the big picture, the relativity stays much the same.

In one index of 33 cases, the 6 Dasher is ranked 14th, the last of the White Hats. The 284 WIN (20) and the 300 WSM (22) are Yellow Hats. The 7 RSAUM (26), the 6.5-284 (28) and the 50 BMG (33) are the Brown Hats, declared OVERBORE.

My list is short. I make it shorter by providing some extracts.
308 WIN 2.39
6 DASHER 2.92
7x57 2.93
300 RSAUM 3.36
300 RCM 3.62
300 WSM 3.74
"7-284 NORMA" 3.79
7 RSAUM 3.96

My proposition is that the 300 RSAUM is substantially more efficient than the 7 RSAUM, and has more inherent accuracy, more than sufficient to overcome any B.C. deficiencies.

Regards,
John T.
5.9.22

]

[Tim L]

Sorry, I can't accept either propositions as delivered.

"EFFICIENCY; the degree to which there is even and complete ignition of the whole of the powder charge before any powder has left the mouth,"

This is dependent on so much more than just the case dimensions. All 308s are not equal. Primers and flash hole being an obious one, powder selection and the host of factors involved there being another.

"promotes," no, this it does not do.

CONSISTENCY; the constant rate of bullet propulsion.

Im not sure propulsion is the right word, assuming you mean acceleration, bullets don't accelerate at a constant rate. But that aside, This ignores burn rate, expansion rate, barrel dimensions and material properties and a lot more besides the case.

"promotes,
ACCURACY; the repeating POI at the target, particularly in the vertical plane."

No. Way too many variables are simply being ignored to arrive at this conclusion.

"2. The ratio of the powder charge CAPACITY of the case to the CROSS-SECTIONAL AREA OF THE BORE is indicative of case EFFICIENCY. the lower the
ratio, the higher the efficiency."

Again no. Capacity might indicate the potential for efficiency and that is a big might. But the actual efficiency is dependent on a lot of other factors.

Don't get me wrong, if this thought process gets your bullets in the middle of the target then run with it. But as a proposition of how to select a case?? Nah.
Not one company has produced a case they hoped would be inaccurate. They are all capable, in just my short shooting life "ultimate accuracy" has come from 6.5x284, 284, 284 Shehane and the 7 SAUM.
And they have all been beaten, on occasion, by a list of other calibres too long to mention.
Everyone wants to make shooting a science, it's not. Its a skill.