Hello Mr Grayling
I have answered your questions on your BBS thread, but will copy my post here too.
The design of the Gem type airgun is American in origin and stems back to a design first pattented in around 1871 by Haviland and Gunn, the rights to which were bought up by Henry Quackenbush in about 1880-81 and marketed as their model No5, available in .21 calibre (the odd sized cal ensured the use HMQ's proprietary ammo, felted slugs, darts and rimfire rounds, the man was an aftersales genius!). Also in airgun only and dual air and rimfire versions (by virtue of a removable "floating" firing pin that replaced the breech washer when in use). The guns basic design (a quaterstocked break barrel, hinged at the breech and used to compress both the spring and cock the gun, and with an airchamber directly behind albeit running at a slight angle to the barrel) made its way to Europe pretty quickly with the Germans and Belgians jumping on the bandwagon. Eisenwerke Gaggenau were very much at the forefront, producing Gem pattern type guns from the early 1880's onwards in various light, medium and heavy weight patterns, these were imported into the uk and can be seen with various traders stamps on them like Lane Brothers, Arbenz, Hooton Jones..Friedrich Langenhan was another German maker of Gem patterns. The family of Marck was a little later on the Gem scene (1890's), a Belgian maker, working out of Liege, and producing guns into the 30's(and the best of the continental European makers too, IMHO) We also have the British offering, namely The Britannia, the poshest Gem pattern ever! :D...
So the basic Gem design was simple, relatively few parts, made from castings and machined to fit on a production line basis, thus spurring the start of the fashion for cheap mass-produced airguns that the working man could actually afford to buy. Working mans shooting clubs, bell target, gallery shooting, all owe a small dept to the humble Gem which hung on in there for a long time, with old stock still being sold up to the start of WW2, that is a span of nearly 70 years unaltered...and its legacy is that the basic break barrel and cocking design still exist to this day, so it must've had something going for it!
...so, when comparing it to say a BSA/Lincoln of early 1900's vintage, you're still not doing the humble Gem pattern justice because the design was 30 odd years old when these new British tap-loading underlevers were all the rage!...but if you are comparing them, do it with an old Beezer and a Britannia (no contest for me:D)...As for the alien design...looks are quirky but handle one (a good one) and see how quick it comes the shoulder and just sits on aim, doesn't matter if your big or small the design is forgiving and is surprisingly comfortable in use.
If you are in the market for a Gem pattern, go for a JM Gem preferably fitted with target sights if you can find one (although these are rare!...the 6 or so I've seen and heard about are all fitted with Giffard pattern sights!...and I own 3 of them) As for oomph (and without overspringing it) anywhere from 3 to 6fpe is a more realistic power level to achieve from most light/medium pattern Gems, some heavy models in .25 cal can achieve 9-10fpe, but they are usually difficult to cock at these power levels.
Re. Breech seals, I think you are a little confused because all Gem patterns have a breech seal of some description, usually leather, but some do not have piston seals, just relying on a close fit machined piston and cylinder bore to achieve a seal, usually with a buffer washer of leather or rubber in the front of the cylinder...but others do have traditional leather cup seals fitted... ( I make them for most Gem patterns if you ever need one:D)...and all the Gems I've seen have been smoothbore, usually in .177cal (most common) sometimes in .25 (not so common), and I've heard tell of .22 aswell (most .22 seem to have been rifled??), but never seen/owned one in .22 or rifled for that matter.
Was that £80 each? or for the pair?...and have you seen the prices asked on gunstar!!:eek:...Nearly all Gems were originally 2-tone with a nickel plated cylinder and blued barrel...all-blued Gems are much rarer by comparison, and usually being later examples....and you are forgiven for dismissing those Gems in favour of the light pattern Beezers, a light pattern is a pretty gun to behold
I've already touched on some of these questions but to recap...
Re. Average power - without overspringing, 3-6fpe from light/medium weight Gem and 5-8fpe from a heavy pattern.
Re. Problems to look out for - The usual problems exist with all old guns associated with wear and tear, and loss of original finish, no more so than with a Gem!..they are usually old and tired, and rarely looked after!...The oldest problem that affects most break barrel guns, namely a wobbly barrel, caused by excessive wear at the breech pivot point, but this is relatively easy to cure in the case of the Gem by making and fitting a new pivot pin. Other things to look for are cracks in the castings around the front and rear of the cylinder, barrel catch, and all pivot points...not to mention the use of makeshift pivot pins in various forms i.e. bolts, nails, screws, rollpins...you name it, if it's round-ish and mostly made of any sort of metal...then an example almost certainly exists somewhere of some bright spark who "gently" hammered it into the barrel point of a Gem at some point in time!...Stripped threads in the cylinder and/or the pinchbolt (the end of cylinder nearest the stock clamps around the endplug) Machined fit pistons can also be tired and slack, cured by fitting a leather cup seal, you can also cut the front of the piston off so you don't loose too much power through lost swept volume, but this is not strictly necessary because if the machine fit was too slack then you'll always gain power with a better piston seal anyway. Worn sears, bent trigger guards, bent barrels, cracked stocks, missing sights...the list goes on!
Re. Spare parts - Well, I did have one or two odd bits but sold them recently!...but they are not that hard to get a hold of with most folk having a bit of Gem in their spares bins somewhere, and scrappers usually come up fairly cheap.
Re. prices - it's all about condition
..the average Gem, in good working condition, £50-£100 depending on model. Nice Gems that retain most of their original finish can command much higher prices (nothing strange there, condition is paramount!) Scrappers can be got for £10-£30 depending on how bad it is, what's broken, missing ,etc.
Re. Rifled barrels - Well, I've never seen one but have heard of them, and, interestingly enough, all the rifled Gems I have heard about are in .22cal!...I have also heard tell that what is percieved as rifling in a Gem barrel, i.e. spiral lines running through the bore, is actually just a vestige is the manufacturing proccess!
I hope that goes someway towards answering your questions
Gems patterns always wanted, especially Jean Marck T-Bar Gems