OzFclass

Can anyone tell me the difference between the british, american and australian minutes. All I know is that the british and american minutes are bigger (I think) but by how much I don't know.
And which do you prefer. Or is that personal preference thing.

Thanks.

As far as I'm aware MOA is a global standard.
There is a metric alternative of Milliradians but it too is a global standard as far as i know.
1 minute is 1/60 of a degree the world over. 1 Minute of Angle is the liniar distance that minute projects at any given distance. At 100yds it is 1 inch. Thats the same everywhere.

In TR parlance:

Historically, the British made vernier sights for military rifles while the long tom Enfileds were still around & based the screw pitches or whatever on that barrel length. When the SMLE came about, they didn't change & so their sights overcorrected.

Australia didn't start with peep sights until the SMLE, so based their mechanics on that. The Sportco/Omark was of similar dimensions (deliberately, more than likely) & the Central was still the duck's guts.

Come modern 30" plus barrels & the Pommy stuff was reading about MOA again but the Central & it's clones (with occasional exceptions) was more than a tad off again - hence the expression Aussie MOA.

Never have been a student of Stateside machinations, so can't answer that one.

Minute of angle is minute of angle. Go altering the site radius and you change the angle. So for fancy sights, they will be out unless it is prescribed for your barrel length in TR. John’s history lesson is correct.

Of more relevance is getting to observe changes and learning how much your sight alters you on the target because judging the conditions has more impact on your score. That process is an estimation to enable a quick response to change to keep you ahead of the pack.

In fact when Central brought out with their third minute sights, there was a huge advantage people overlooked. Some comments first. Some were too concerned that the movements were too fiddly, others relished the sight because constant nips in small amounts were insurance of keeping groups centred on the practice of altering on each shot as they thought. Smarter people used them to make adjustments for light and vertical from left or right winds as the strength of the wind increased or decreased. The next phase was the ¼ elevation, ½ wind movements, where the quarters allows for constant nipping of elevation for the above in about the right ratio 1-4 for windage.

Based on McCoy’s work, the wind allowance down range has been established with regard to deflection. The rule of thumb being, the first third of the range is equal to 60 % and the last two thirds of the range being equal to 40% of the wind allowance. You can break the last 40% of the range into 30% and 10% as a rule of thumb. What this means for long range, particularly at 1000 yards you can make alterations on wind zones if flags pick up or drop off in the different zones.

That’s where the central sight comes in handy if it has third minute adjustments. Consider that if the wind is blowing the same in the first instance across the range and you get a hit with 1 minute, then things change. The flag in front of you drops to zero while the wind in the last 40 percent remains constant. You can come off roughly on 60% in two 1/3 minute movements for the front flag and leave the remaining 1/3 in place for the wind that still exists downrange. So you use the sight in blocks of two 1/3 movements for an approximation of 60% rule sight and the last 1/3 movement as an approximation for the balance of the range. Remember it is the first 1/3 of the range that is most important. You can never correct a bullet once it is initially off course.

Ideally I would like a TR sight with thirds to use in blocks of 2/3 and 1/3 of the for wind and elevation in quarters to marry with vertical drift associated with wind speed and direction as well for apparent aiming mark shifts in different mirage densities.

It is of concern too many people rely on mirage at long range. In situations where we saw recently at the final Pennant at Rosedale at 900 and 1000 yards where 6 teams competed, the mirage was what you saw at the target. People were getting done in elevation due to apparent aiming mark shifts and caught with birds, 2's, 1's and misses because the flags up close did not correspond with the mirage value on the target face. This was correct because the mirage value was equal to roughly 10%. A couple of our best shooters were able to shoot possibles and other team members including those of less experience had better scores than other teams. The team won both the scratch and the handicap on the day and for the year. There is no substitute for knowing what is happening.

Dear James,
In reference to the sight adjustment calculator, details of which you forwarded on 24 May last, it is advised that the figures are basically correct, but it also appears that the originator has his facts mixed. It is stated that “one vernier will cause a shot displacement of one inch per every one hundred yards away from target”, and then shows a table of varying sight movements necessary to achieve that condition.
The true fact is that, in any sight, the movement corresponding to one “minute” is a fixed amount determined by the pitch of the screw and number of detents in the control nuts. In a CENTRAL sight this is 1/120 inch.
The mathematics have been over complicated by the introduction of trigonometry, whereas the basics may be determined by consideration of simple ratios…
A movement of 1/120” of the sight on a rifle having a 30” sight radius will give 1” movement on the target at 3600” (100 yards).
If - A = the peep movement for one vernier = 1/120 inch. B = the sight radius (in inches) C = displacement at the target, then D = distance of target in inches.
Then the basic rule is AB = CD and also:- AD = BC
In the case of CENTRAL sights, dimension A = 1/120” and D = 3600 (100 yards). These are fixed and cannot be varied.
Substituting figures:- 1/120 x 3600 = 30 = B x C…and…………………………………..C = 30/B Thus the movement of ONE MINUTE or VERNIER projected onto a target at 100 yards is:-
For 28” sight radius – movement is 1.071” (=30/28). 29” 1.034” (=30/29). 30” 1.000” 31” 0.968” 32” 0.937” 33” 0.909” 34” 0.882” 35” 0.857” 36” 0.833” 45” 0.666”
A table showing this movement has been included in the instruction Sheet packed with CENTRAL sights for many years. (Copy enclosed).
This is the basic of the mathematics of CENTRAL sights made since about 1935. Please note the emphasis, and our discussion will be restricted to current sights for the moment.
The movement of 1 inch at the target 100 yards away subtends an angle of approximately 1 minute (actually 0.954929”); hence the general use of that term, but the movement of 1 inch for each 100 yards is quite precise for a rifle having a 30” sight radius and a CENTRAL sight.
It is not difficult to understand that there is not a wide selection of screw threads that will give the movement of 1/120 inch which is required, and that it is not very convenient to change to concept of 1” per 100 yards without causing many problems for shooters who are used to that movement.
It is a fundamental fact that the sight radius affects the accurate alignment of the firearm (compare a short barrel pistol with a long barrel pistol or a rifle) and it follows a longer sight radius and allows more precise alignment with the target. However, it is useful only if the shooter is capable of using it effectively.
The movement of the sight of (say) a 33” s.r. (10% longer) is 0.9091” and you must compensate by increasing the movement of the sight by 10%, i.e. 11 minutes instead of 10; 22 instead of 20; 33 instead of 30, etc… as is shown on the upper part of the calculator.
It is noted on the calculator diagram that the ½ minute sight has 6 indents. This is correct for the current production, but when CENTRAL were first made the rifle in use was the Long Lee Enfield having a sight radius of 36”. On these sights there were 5 indents on the wind arm control nut, and 10 on the elevation nuts (which had a coarser thread). This gave 1” adjustment at 100 yards range with the 36” sight radius.
When the S.M.L.E. was adopted, the control nuts on CENTRAL sights were changed (to 6 and 12 indents) to again give 1” per 100 yards, and the Bisley model sights carry a notation to that effect.
However, Parker Hale did NOT change their sights when the S.M.L.E. was adopted and the P.H. sights still give 1” per 100 yards for a 36” sight radius and 1.2” for a 30” sight radius, having a sight movement for one vernier of 1/100”.
How many shooters use Parker Hale sights believing they are moving 1” per 100 yards? Most would not know or care?
How many shooters can determine that they need “exactly” 20 minutes of wind, say, and then decide that as they are using a 33” sight radius that it must be increased to 22 minutes? Would not most of them say “about 20”, and then adjust as necessary to get into the centre?
The answer to those questions is the answer to how useful the calculator would be.
Have fun with it, but do not let it cloud your skill by attempting to be too technical – it is much more practical to know how many minutes from ring to ring on each target for your rifle, using the information we have been publishing for years, and move your sight accordingly.
Yours faithfully,
Rod. Johnson.

Just wondering if Scott is referring to scope clicks. The MOA of a scope click varies between manufacturers. For some, 1 MOA = 1 inch at 100yds, for others 1 MOA = 1.047 inches at 100 yards, with the latter being almost exactly 1 MOA. 1 MOA can be exactly defined as 1/21,600th of a full circle.

Alan

Previous to precision long range shooting we all accepted that 1" was equal to 1 Moa at 100 yards.
As Alan points out it is actually 1.047".
Hey, a lot of people will say that is splitting hairs?!!
Well, Leupold scopes for one have 1/4 inch clicks! Not 1/4 Moa as they quote?!

So what ? Well that is almost 5% variation.
If you wind 20Moa on a Leupold scope by clicks you will actually have 19 real!
Makes a difference in our sport but especially if long range hunting or competing at steel targets etc.
Check it out for yourselves if you card to differ.
Shane

I was referring to t/r sights and not scope minutes. Sorry guys I should have mentioned that. I was aware of different manufacturers of scopes having 1 moa/100m and 1"/100m depending on the brand of scope. And reading what you guys have posted it is looking the same for peeps. Not so much being the country of origin but certainly being a combination of sight radius and thred pitch being the deciding factor in amount of movement per click.
Thanks guys.