Spotting Rifles

[MarkHolloway]

How are spotting rifles employed? I've always thought the spotting rifle is fired until it hits the target. Then the main weapon is fired. If this is correct then it would be dangerously time consuming. I'm curious because pilots of the XM551 had a spotting rifle on some versions.

[Doug_Kibbey]

Mark,
In my experience, spotting rifles were mostly about getting the range. I've never seen one on an M551, but maybe there was a time before the choke reticle on the Sheridan was introduced that one was tried as a way of ranging before firing the main gun.

Later, of course, a proper laser rangefinder was made available and retrofitted, as there was no rangefinder at all previous to that on the M551.

D.

[Maple_Leaf_Eh]

On the M40 infantry 106mm Recoilless Rifle, the .50 calibre spotting rifle is a big bolt action (?) that is mounted on top of the main tube. The round is shorter than the conventional .50 cal. Its ballistics are matched to the main projectile. So the gunner snaps off a spotting round and everyone watches. He then adjusts his point of aim and belches off the main round. When everyone's lungs refill and their hearts go back to regular rhythm, they can do it all over again.

From a gaming website:
It is a semi-automatic weapon with a 20-round detachable magazine. Note that this rifle fires a round that is slightly smaller than the one used by the Browning HMG. The bullet is shorter, lighter and has a lower muzzle velocity

Cartridge, Caliber .50, Ball, Spotter-Tracer, M48A1/ M48A2
Caliber: 12.7 x 77 mm
Weapon Used In: M8C Spotting Rifle
Weight Complete: 0.107 kg
Length Complete: 114.81 mm
Packaging: 10 rounds per cardboard box
Packaging Weight: 1.070 kg
NOTE: The projectile contains a tracer element and an incendiary filler. On impact, the incendiary filler produces a puff of white smoke which aids in adjusting fire. The tracer element burns out at 1500 m. The spotter-tracer round is designed so that its trajectory closely matches the trajectory of the M40 recoilless rifle service munitions.

Game stats for the M8C:

Length: 114 cm
WT empty: 11.072kg
WT loaded: 13.989kg
cal: 12.7×77mm
Muzzle Vel: 1732 fps
eff rng: 1500m
max rng: 3100m
type of fire: semiautomatic
ROF: (SS) 40 Rpm
feed device: 20 round box magazine
Feed device wt: 2.917kg

[MarkHolloway]

It just seems to me that this process would be way too time consuming. Here is a photo of an XM-551 with the spotting rifle port above the coax port. This is the one at Ft. Knox.

[Doug_Kibbey]

- Maple_Leaf_Eh

On the M40 infantry 106mm Recoilless Rifle, the .50 calibre spotting rifle is a big bolt action (?) that is mounted on top of the main tube. The round is shorter than the conventional .50 cal. Its ballistics are matched to the main projectile.

We operated M40 RR's in my Air Cav Troop in Vietnam (off of M151A1C's and two "unauthorized" M37 "Beeps"). My recollection is that the spotting rifle was semi-auto (with a big honkin' magazine), but I'm open to correction. It is correct that the round was ballistically matched to the main round, but there was not the expectation of a 1:1 correlation of a hit when fired. That would take forever unless the crew was shooting at a distant bunker (and probably unoccupied, or at least soon would be after a spotting round shot or two).

In practical terms, it was more likely to be used in perimeter defense, and at shorter ranges, though the RR crews practiced on more distant targets. I was in the Scout Section, so this was not a primary duty of mine.

Don, I am in possession of a manuscript photo of the spotter rifle* installed on the XM551 as of the last few days, but as it's in preparation to go to press by the author, I'm not in a position to post it. However, I'll let you know as soon as the publication is available, which should be very soon.

*NOT the same device as on the M40. Different caliber and designation entirely.

[MarkHolloway]

Doug, What's the name of the book? I might like to buy it.

[Doug_Kibbey]

- MarkHolloway

Doug, What's the name of the book? I might like to buy it.

David or I will post something as soon as it's out.

[Maple_Leaf_Eh]

I remembered it as a big bolt-action, but the text I posted called it a semi-auto. Any pictures of the spotting rifle show a tubular receiver.

Thanks for the mention of the inexact ballistic match. In theory any projectile can be matched to another for a given distance. The intervening distances of course the faster one (likely) will have a flatter flight.

[Jason_Bobrowich]

They are actually called ranging guns.....they are not rifles....most are heavy machine guns.

Both the late version Centurions and the early version Chieftains used them.

They work very well....and in an era before stereoscopic rangefinders or lasers to determine range all that tank crews had was the Mk.1 eyeball with well practiced range estimation.

The ranging guns allowed the crew to fire round at the target to confirm the range to the target.....they did not need to hit the target....the gunner could adjust the point of impact of the ranging gun (which was boresighted to the main gun) to the target.

Now....a ranging gun also usually only fired tracer rounds....so the fall of shot could be easily observed...and the key would be to use the ranging gun at ranges below trace burn out for the round....usually a .50 Cal round. If targets beyond trace burn out were engaged and the ranging gun was used then multiple rounds (about 3) could be fired to get a larger fall of shot and observable splash....the inherent problem with this is at longer ranges the rounds will spread over the Beaten Zone making it harder for the gunner to adjust the sight picture to the target.

Ideally the ranging gun rounds would be fired and then the fall of shot adjusted to the target by the gunner using standard corrections in elevation and azimuth....the ranging gun would have a similar trajectory of the main gun out to certain ranges....in the perfect world the gunner would get a hit on the target with the ranging gun and in very short order the main gun would be firing and getting a first round hit.

The key is for the Commander to get a good intital range estimation in the fire order to the gunner....then only minor corrections would be needed.

Like any other main gun engagement it took practice to be effective.

To the contrary that it would be dangerously time consuming....a tank in a proper fire position only firing a ranging gun at another tank would barely if at all be seen....there are very limited consequences of fire....i.e muzzle blast or noise from a single round of .50 Cal being fired.....compared to what is created by a main gun round. If the ranging gun round missed it would probably not even be noticed by the enemy tank crew...if you have ever actually worked on a tank there are plenty of other noises louder than a machine gun firing all around you....the follow up round from the main gun would for sure be noticed by the enemy tank crew as they were destroyed.

[Jens_O_Mehner]

The M2 HB on the barrel of the Merkava also doubles as a ranging gun I have been told by IDF armour troops.



Jens O.

[MarkHolloway]

Thanks, Jason! It never occurred to me that the tank crew probably wouldn't even know they were being engaged by the spotting rifle.

[Dontos]

- Jens_O_Mehner

The M2 HB on the barrel of the Merkava also doubles as a ranging gun I have been told by IDF armour troops.



Jens O.

Don

[Dontos]

I finally dug this image up, its the TM diagram of the M8C spotting rifle which mounts on the M40A2, 106mm RR.



Regards
Don

[MarkHolloway]

As seen on the Ontos?

[Dontos]

- MarkHolloway

As seen on the Ontos?

Only mounted on 4 of the 6 106mm RR's mounted on the Ontos. The top two RR's on each bank have the M8C. This is to allow the dismounting of two of the six, and still gives the Ontos ranging abilties for each 'bank' or side of the vehicle.

Technically, 4 of the 6 can be dismounted and have the stand alone capability of operation, but the vehicles BII only includes 2 ground mount tripods.

Don