Although there is no definitive evidence to date proving that Sikhs wore Punjab turban helmets, if we look at the collective body of secondary circumstantial evidence, it meets the threshold of evidence to allow us to make the assumption that they may likely have. If that is the case, then the most important question becomes why is this style helmet so rare and why did the Punjab turban helmet never achieve the level of popularity and high rate of adoption among Sikhs wearing helmets that the Indo-Persian style helmet did?
Looking at the number of 19th century or earlier helmets attributed to Punjab or the Sikhs, we find that there are less than a handful of surviving Punjab turban style helmets in existence in various museum and private collections around the world. On the other hand there are literally hundreds, if not thousands of surviving Indo-Persian style helmets attributed to Punjab and the Sikh Empire in various collections. Visual evidence of many paintings and drawings of Sikhs wearing the Indo-Persian style helmet provide conclusive proof that this style of helmet achieved overwhelming broad appeal in Punjab. The large disparity in adoption indicates that the Punjab turban helmet never achieved anywhere near the level of popularity or appeal that the traditional Indo-Persian style helmet did among 19th century Sikhs of the Sikh Empire in Punjab.
Of the surviving Punjab turban helmets in existence, although they share a similar general design of a main hemispherical bowl surmounted with a secondary smaller dome and the attachment of a camail of chain mail to the lower edges; their decorative design varies. In fact of all of the surviving turban helmets, there are no two helmets which are identical. Each surviving turban helmet has a distinct and unique design in terms of the gold inlay pattern work as well as the proportions and shape of the top-knot secondary domes. Unlike the Indo-Persian style helmets, where multiple examples of the same style of helmet exist, the distinct uniqueness of each of the surviving Punjab turban helmets indicate that they were not standardized or produced in any substantial numbers during their manufacture, for example to equip a group of soldiers with one style of helmet. Instead the Punjab turban helmets seem to have been produced in extremely small quantities, likely commissioned as ‘one-off’ helmets, each produced by a different artisans or craftsmen, thus accounting for the existing variations among the surviving Punjab turban helmets.
A display at the Royal Armouries featuring a Punjab turban helmet next to a traditional Indo-Persian style helmet attributed to Lahore reveals some striking differences between the two which may account for the relative lack of popularity or sucess of the turban helmet compared to the popular Indo-Persian style helmet among 19th century Sikhs of the Sikh Empire.
In terms of their relative size, there is a significant variation between the two helmets, with the Indo-Persian style helmet providing much more head protection with a larger main hemispherical bowl which would cover more of the wearers head than the turban helmet with its elliptical bowl and concave sides. The turban helmet also lacks the sliding nasal guard found on Indo-Persian helmets and thus provides no protection to the face of the wearer. These two characteristics mean that the Punjab turban helmet provided less safety and protection for the wearer compared to the Indo-Persian style helmet.
Another function of battle helmets, beyond providing safety for the head that was very important was the general appearance of the helmet in terms of its grandeur and intimidation factor directed towards the enemy on the battlefield or other soldiers of the Sikh Empire. Looking at the two helmets at the Royal Armouries display, one can observe that the Indo-Persian style helmet appears much grander and provides a more intimidating form than the relatively benign turban helmet beside it. During this era, troops of Maharaja Ranjit Singh’s cavalry were required to purchase their own horses, weapons and clothing. There was also a sense or rivalry among the troops as they would try to make the grandest or most imposing form compared to their contemporaries and in that regard the Indo-Persian style helmet fills that role better than does the Punjab turban helmet.
Description of cavalry officers under the command of its European Generals Jean Baptise Ventura and Claude Auguste Court:
Almost every one of the Sikh officers of these regular troops was dressed according to his own taste; some in English, others in French uniform, or in a mixture of both; some wore turbans, or caps with shawls wrapped round them, and others helmets and chakos: some had high boots with coloured tops, other shoes; some wore white, and others coloured pantaloons. (von Orlich, 1845) 
One of the key elements of helmet design that was so important to the Sikhs in terms of grandeur or intimidation was the kalgi plume and the helmets of the Sikh Empire were specially designed to optimize and maximize the display of these plumes. It was a sign of status among Sikh Sardars and men of importance to wear a large kalgi plume or set of plumes in their turbans or helmets.
Plumes have been made of herons' feathers in many countries, and here they are in great request, as no Sikh officer of any rank is ever seen without one in his turban ; and in those of the Surdars, or great men, the feathers, generally an uneven number, between ten and twenty, are fastened into a funnel-shaped stem, entirely covered with gold wire or thread, or sometimes richly ornamented with pearls, emeralds, and rubies. (Vigne,1842) 
In fact one of the key design elements that helps distinguish the style of Indo-Persian style helmets preferred by Sikhs as compared to those worn in Asia and Persia, was the prominence in the design given to porte-aigrette plume holder rather than a central spike at the very apex of the helmet to hold high a large bhatka kalgi plume, sometimes up to a foot in length or more. This prominent kalgi plume holder at the very top of the helmet is usually accompanied by two other porte-aigrette plume holders. In the Punjab turban helmets there is no kalgi plume holder at the apex of the helmet except in one helmet  and in general the helmets have none or a minimal configuration of plume holders. This de-emphasis of the kalgi plume in the Punjab turban helmet design may have significantly contributed to their lack of popularity among the Sikhs and instead the overwhelming preference for the Indo-Persian style helmet with its design optimized to prominently display the kalgi plumes on the wearers head.
Although today the Punjab turban helmet is commonly thought by many to be the quintessential and most common type of armoured helmet worn by the Sikhs of the Sikh Kingdoms of the 19th century, evidence indicates that this was never the case as the Punjab turban helmet failed to achieve any popularity among helmet wearing soldiers or nobles of the Sikh Empire, who overwhelmingly preferred the Indo-Persian style helmet.
The Punjab turban helmet represents a historic anomaly and was extremely rare even during the time of its manufacture and usage in the Sikh Empire and never achieved much popularity in the Sikh Empire due to a number of factors including its design. Its usage seems to have been primarily confined to a very tiny sample size of the cavalry of the Lahore Empire.
The Punjab turban helmet represents a truly unique and rare anomaly in the history of Sikh armour. Given its lack of popularity, overwhelming preference for the Indo-Persian style helmet and the extremely low rates of its manufacture and usage it is quite incredible that any of these rare types of helmets have survived at all.
1. Captain Leopold von Orlich, Translator H. Evens Lloyd, Travels in India, including Sinde and the Punjab, Vol I (London: 1845), 229
2. G. T. Vigne, Travels in Kashmir, Ladak, Iskardo, Volume 1, (London: 1842), 306-307
3. Davinder Singh Toor, “In Praise of Steel: Understanding Sikh Arms and Armour” (presentation, 2011)