The English were long noted for having a higher percentage of bad teeth, even among their Gentry. It is mostly genetic agravated by diet.

On other forums members have posted old photos of their ancestors in uniform, and the Britsh/English soldiers were as hale and hardy as any I've seen even compared to today's troopers.

The illusion of the "Sunken Chest" is more a matter of posture than actual physique. An example would be the actor Gregory Peck, a large powerfully built man his shoulders forwards stance always gave the illusion of a sunken chest.
The British Uniform of WW1 and earlier added to this appearance. The tight bodice with looser fitted tail of the uniform jacket, compared to the straight up and down tunic of the German and American counterparts.
The Germans copied the British style uniform jacket for their own dress uniforms in WW2.

Its said that the Germans themselves considered the Enfield superior for most forms of combat. The saying went that Germans went to war with a hunting rifle, Americans went to war with a target rifle, and the British went to war with a fighting rifle.

Only the trend towards higher pressure cartridges has given the forwards lockup rifles the edge as a sniper rifle.
In practice the Enfield bolt allows the sniper to cycle his bolt with a great deal less movement of his body, making it easier to remain hidden.

Back to the wire wrapped rifles.

The rifle grenade launchers of WW1 were very hard on a rifle, the kick was brutal. I've seen Garands reduced to junk from being used as designated grenade launcher guns.
To prevent damage to regular issue rifles the British took the worst examples they had and converted them to grenade launcher only duty. These guns usually had shot out or corroded bores. the wire wrap was intended to keep handguards from spliting due to shock.
Every WW1 and WW2 wire wrap I've examined had a terrible bore, and a couple I've seen taken out of the wood were pitted on the outside of the barrel like the surface of the moon. Actions were often loose as a goose. The soldier issued one of these was expected to never fire live ammo in it if he could avoid it.

The Later Ishapore Wire wraps were most often regular issue rifles in good to fine condition. They were already obsolete and only used for this purpose because there were still huge stocks of .303 blanks to be used up. No need damaging a perfectly good .308 Ishy when the older guns were available.
The few reports I've read of test firing the Ishy wire wraps indicate most can be expected to be good shooters.

PS
The Australians took old Lithgow rifles and cut the barrel back to about nine inches, cut the stock to a pistol grip, then installed a grenade launcher cup. The shortened barrel was run through a firing port on armored vechicles and the cup put on the outside. These were used to launch smoke grenades.
I first learned of these when studying prop guns used in Sci Fi movies. The dwarfs in Star Wars carried these old smoke grenade projectors tricked out to look like rayguns.
The guns without the launcer cup are occasionally seen in Australian Sci Fi films used as sawed off rifle/pistols.

Also a field modification of battle damaged No.1 Enfields favored by the Chinese was to cut the barrel back to around 12-14 inches and solder a half of a brass coin to the barrel as a front sight. The foreend was sometimes discarded altogether. Sometimes the rear sight was removed and a slot cut in the charger guide to use as a rear sight.
Parts removed were used to repair rifles in better condition.
These cut down rifles were carried by bicycle messengers, runners, and ammo handlers for self defense.
Theres also a dedicated grenade launcher version of the No.4 favored by Asian rebel groups.
Its cut short and a tube barrel jacket supports and guides the more modern anti tank grenades , usually old Nato issue grenades.
The original ladder peep sight is moved to the reciver ring.
Apparently this combination has proven remarkable accurate, allowing more precise placement of the grenade than the standard set ups.