I believe Clark is saying "no", and in any meaningful or practical sense, I agree, the snail type breech is
not a reliable indicator for dating a [Hawken] rifle?
In a couple of specific cases, the type and style of breech bolster is useful in helping to date the rifles in chronological order but not in absolute terms.
To the first point of "no" in the general sense. Below is a composite image showing the snail on a number of S. Hawken rifles. I arranged these as if there is an evolutionary progression in the development of the snail. This is a false assumption. We really don't know the dates these rifles were made, though some are certainly earlier than others, so the order I have them is not necessarily the true chronological order.
We do see some differences in the "snail" during the J&S period versus the S. Hawken period. We often see one of two types of breech bolsters on J&S Hawken rifles:
What I call the "brazed on" breech (Rich Pierce has a more descriptive term--Conquistador Helmet breech)
The other is something I call the "comma" snail
Of course, we already know a rifle marked "J&S Hawken" is earlier than a rifle marked "S. Hawken" so the shape of the snail doesn't provide much new information except in the case of an unmarked rifle.
The two special cases I refer to involve (1) the Peterson Hawken that has been discussed in this thread and (2) the J&S Hawken rifle in the Montana Historical Society collection.
As mentioned in an earlier post, the Peterson Hawken may be the earliest surviving Hawken dating to the late 1820's or early 1830's. It has a very primitive "snail" or breech bolster. In fact, it's little more than a drum that has been brazed or forge welded to the false breech and filed to shape it a little. It may be an example of the Hawken brothers' early experimentation with the percussion system.
The style and shape of the breech bolster along with other features of the Peterson Hawken such as the trigger guard, barrel wedge escutcheons, patch box, and shape of the cheekpiece suggest a very early rifle.
The J&S Hawken rifle in the Montana Historical Society collection also has what appears to be an early, primitive breech bolster. It is a very early example of the "brazed on" bolster, though it could also be forge welded on the barrel.
The full length MHS rifle.
The breech and lock on the MHS J&S Hawken.
I believe the Peterson Hawken has a patent or false breech, but the MHS rifle does not. The breech bolster is an integral part of the barrel. It was either brazed on or forge welded on the barrel.
There is only a hint of a rear and front fence on the breech.
I might also point out that the lock plate appears to have been made for a flintlock as it has a beveled edge common to the flintlock period. The lock is marked "TRYON" over "PHILADa".
This rifle has the same type of trigger guard as the Peterson Hawken.
Both the MHS Hawken and the Peterson Hawken have shorter tangs than later Hawken rifles. The Peterson's tang is about 2/3 normal length an has two tang bolts. The MHS rifle tang is about half length with only one tang bolt.
So with these two rifles, the breech bolster helps build the case for these being early Hawken rifles.