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Disappointments - And Correcting Horisontal And Vertical Errors
There is great satisfaction in the perfect shot on your game animal with iron sights. The shooter can have the knowledge that he is a fair cut above the average casual hunter. The sight adjustments need to be understood perfectly and applied correctly - and then the skill can be acquired by experience.
Horisontal Errors
In the diagramme measurements of a SAKO Model L61R Finnbear sights were used:
1. CA represents 100 metres to the target.
2. AB represents a 2 MOA (62mm) impact error to the right.
3. DE represents the lateral error correction calculation for (2) above by moving the bead centre line to the right.
4. AB1 represents a 3 MOA (93mm) impact error to the right.
5. DE1 reprents the lateral error correction calculation for (4) above by moving the bead cetre line to the right.
6. CD represents the distance between rear and front sights (463mm).
Calculation Principles
The angle subtended by the lateral error needs to be dermined in order to calculate the front sight correction adjustment related to the distance between rear and front sights.
Determine angle ACB
1. the tan function of angle ACB = 62mm ÷ 100,000 mm = 0.00062
2. Therefore angle ACB = arc tan 0.00062
= 0.036 degrees.
.
Determine lateral error correction
1. The tan function of angle ACB = DE ÷ CD
2. Therefore: the tan function of angle ACB = DE ÷ 463mm
3. Therefore: 0,00062 = DE ÷ 463
4. Therefore DE = 0,00062 x 463
= 0,29 mm.
Drift the front sight 0,29mm to the right to compensate for a 2 MOA error at 100 metres.
Because the error wil always be directly angular for horisontal discplacement, and for the average 600 mm (24”) barrel length of dangerous game rifles a rule of thumb of 0.15 mm (0.005”) per MOA error angle will be very close to being exactly correct.
Because the bullet is not a laser it does not follow the bore centre line and vertical errors are not linear. Out to 50 metres the error is small enough to use the same principle for bead adjustment of 5-thousandths of an inch for every 1 MOA vertical error.
Real Life Iron Sight Issues
It is a frustrating, disappointing experience for a dedicated hunter when a new rifle is consistently inaccurate - shooting patterns instead of tight groups. In 1984 I had that with a Ruger No. 1 in .270 Winchester which I had bought in a used but very pleasing condition. I needed a new rifle particularly for blesbok culling. Culling entails a lot of shooting even in one season, including load development because only brain shots are allowed and distances are hardly ever closer than 200 metres. I wanted to save my .308W Musgrave Model "Vrystaat" which I had been using very successfully and the single shot Ruger appealed to me. It turned out to be a total lemon and not nearky up to the job. Even with the best riflescope it shot all over the place. The gunshop was prepared to take it back and sold me a SAKO Model 85 Hunter which was
About two years ago I bought a Ruger Safari Express Magnum in .375 Holland & Holland Magnum. Casually seen it oozed "Africa" but later when I examined it closely it turned out to be one of the most faked (for sake of appearance) rifles to have come off a production line anywhere. I loaded a few cartridges with 300 gr Peregrine VRG-2 monolithic solids, did two off-hand shots with the Express "shallow V" iron sights to get a feel for the grip and trigger and then set up my Chrony.
The first bullet showed 2 760 ft/sec muzzle velocity - about 230 ft/sec too fast. That should have warned be about bullet distance above the light sensors but I did not consider that because my aim into the Chrony was good. The case and primer condition showed no overpressure whatsoever - and this should have warned me even more but I did not pay proper attention. The rifle shot 3 inches low at 50 metres. The shallow Express fixed blade was LOWER than the front sight I later determined. I should have checked the boresighting but being used to factory rifles that group 1/2 MOA on target off the shelf I did not do a boresight confirmation of the alignment of the system and had trusted Ruger.
The front bead installed on the Ruger Express Safari Magnum .375 H&H is way too high in relation to the rear sight.
I had ammunition and decided to flip the 100 yds blade up and check the impact elevation with that at 50 metres. The bullet went about 70 mm to the left of aim and still slightly low. Checking these popularly called Express sights carefully it turned out that the notches in the flip up blades were not alligned with the bore centreline and the shallow "V" and the front sight. Those flip-up blades clearly were rushed in manufacturing and assembly and never checked for alignment with the centre of the fixed shallow "V". Unlike other manufacturers Ruger certainly does not shoot each rifle to check the sights. What a disappointment in the Ruger name that experience was.
The iron sights on this Ruger Safari Magnum disqualified it immediately for Africa use. A total fake sighting system was slappped onto this expensive rifle for appearance only and with zero practical use. Removing the metal from the stock more features standard to an Africa big bore rifle - like the crossbolt - were also just fake, superficial additions with no internal application integrity. I drove the 300 miles round trip to the seller and back and cancelled the deal. While I own three Ruger M77s in the USA I was disgusted by the many things that were wrong on this expensive, much touted RSM.
The neat but really useless Express sights on the Ruger RSM. The open "V" is way too low in relation to the front sight and the notches on the flip-up blades are out of line.
With fondness one remembers the days when the Winchester Model 70 in .375 H&H from 1952 to 1963 was the American made rifle that was perfect in every way for Africa hunting. Not a single design or factory build and assembly issue existed in those rifles.
Useful Iron Sights In My Gunsafe
SAKO Model L61R Finnbear .375 H&H
While not top of the line and certainly not in the traditional "Africa" style the SAKO Model L61R Finnbear is a pleasingly accurate rifle with a useful set of iron sights:
This entry level rifle has a rear sight assembly that is overly involved for the needs of hunting dangerous game. Range adjustments from below 100 metres to 500 metres is superfluous as nobody should shoot at any wild game - and certainly not any dangerous animal - beyond 100 yards.
That said - fine horisontal adjustment of the "U"-notch is easily achieved without high friction or difficult movement of the sight blade. What all the capabilities do is to enable the shooter to really finely adjust his bullet impact point for a specific bullet in order to have it exactly where he wants it.
Readers who know my ways will remember that I am a firm believer in using only a single weight bullet in any one calibre - and for the .375 H&H that is 300 gr at 2 550 ft/sec. No matter what I hunt, that is the bullet weight.
The front sight on the SAKO is drift adjustable and it has the all-important shiny bead for when a clear sight picture on a dark body is all-important. No rifle intended for dark skinned dangerous game should be without this feature.
Lee Enfield N0. 4 Mk. I .303 Brit
This 80 years old Lee Enfield No. 4 Mk. I in .303 Brit is my daily carry rifle. I customised it to be as lightweight as my Musgrave Ambidex .22 LR. This is a very pleasing rifle and calibre for big game hunting. It is dedicated to 168 gr Peregrine VRG-3 controlled expansion monolithic copper bullets at 2 650 ft/sec. Recoil impulse is sharp but the rifle is pleasingly accurate.
The sight protector hood was removed for the photograph. The bead is drift adjustable.
I cut a small, neat slot into the top of the hood to ensure sufficient light onto the silver bead.
The sight arrangement is dedicated to print at 100 metres with the bead top radius fully enclosed in the "U" notch in the shallow "V" of the rear sight.
Despite its age and many thousands of cordite and fulminate of mercury primers the bore is perfect and it shoots where you aim.
The photograph on the right is of a SA Hunting Rifle Competition life size target of an impala. The red lines show the scoring for competitions.
The circle shows the cenre of the heart's top chambers behind the shoulder which is a full score of 30 points. The rest of the heart allows 25 points and anywhere in the lung allows 15 points - as does the neck vertebra columns. A shot anywhere outside these on the body gets you a minus 15 point penalty. The brain centre is 31 points and the rest of the brain 30 points.
At 50 metres with the bead top radius halfway down into the rear blade "U" notch the Enfield prints in the centre of the circle (the heart's top chambers). With the bead's top radius level with the top of the "U" slot the shot is about 50 mm higher as is shown in the photo and will be on target at 100 metres. Certainly the latter is also a killing shot but but the animal will go somewhat further before dying than with a bullet through the heart's top chambers. That of course is the reason for the competition scoring.
The Musgraves (sadly NOT in my gunsafe! )
This model certainly is not an entry level rifle. Depending on the buyer's choice of wood this rifle will cost between $2 500 and $3 500. The photo is added to show what in my mind - and of course the mind of the Musgrave designer - must be the final word in rear sight design for a dangerous game rifle: One single "U" notch with a distinct horisontal top line and a white centre line. The shooter sets his bead picture in that "U" as is dictated by his own preference. Being a DG setup most likely the 50 metre arrangement will be with the top radius of the bead at the horisontal edge of the sight blade.
The single rear rear sight on this Musgrave in .375 H&H is the final word for a dangerous game rifle. It is factory regulated for a 300 gr bullet at 50 metres with a hold where the top radius of the bead is level with the top edge of the sight blade. The sight assembly can be adjusted vertically along a ramp, increasing the sight heigt in the direction of the shooter. Horisontal adjustment is done by drifting the front sight (not shown).
If the reader has iron sights on any of his rifles he should familiarise himself with them and become proficient to 150 yards (just under 140 metres) distance. By applying the principles discussed in this two-post series it should prove to be a pleasing time at the range and a satisfying hunt. Stalk your mule deer to 50 yards and kill it with open sights and that will be like going after Cape buffalo in South Africa.