By the shape of the loops, it is a Mccord shell. 

Tim, I think you played triple what that helmet is worth. Maybe in Europe it’s a good deal but here in the states you got taken. Don’t worry we have all been screwed a time or two.  If I were you I would get on US and started searching completed auctions to get a better idea of what this stuff is worth.  Your helmet appears to have a Korean War era overpaint(light olive drab) and the chinstraps being hand sewn really really hurts the value. I would value that set up at around $160-200 US dollars on a good day.   Remember, no matter what people tell you, this stuff is not rare. I think the US made something like 22 million M1 helmets during WWII. Post a picture or two on here before you buy, people here are happy to help.  Not trying to ruin your day, sorry about that but next time take your time and do your research. This hobby can be very very dangerous as far as crooks and grifters and getting tipped off.   Amd really this helmet is not collectible at all, poor example. 

Greetings! Are the crimps at the front seam Circles or ovals?  They look like circles? If so its a Schluter. If they are oval, its a McCord... The chin straps look like someone threw them on for effect. Maybe glued on? And then some sloppy sewing? And the 101 on the liner also for sales effect.  Judging by what you could find in the States on ebay that is comparable to this, In my opinion..... I personally think you paid too much. It is all WW2 produced though.  

Hello everyone, I wanted to share my first major purchase to kickstart my collection and would love to hear your thoughts and expertise.I believe the helmet dates to around 1943 due to the fixed bales. The liner seems to match as well; it has a Firestone stamp inside with “23” underneath.The heat stamp on the shell is almost completely worn away.I paid €450 for the helmet, and I’m curious to hear whether you think that’s a fair price for this helmet

No I would not sell.

I thought I would join so I could learn new information about things I enjoy.   I have a small collection of militaria and while I spend a very long time collecting webbing from the US specifically WWI and WWII I've also collected other nations equipment  but not as much so.  I do enjoy vintage camping also and stoves among other things.  I also enjoy helmets but I do not have the collection many do.    Anyway  I look forward to meeting folks and learning

There really isn't a great explanation for why an older hallmark sometimes shows up on later era pieces.   Sometimes, firms reserved their older hallmarks for prestige lines.   Other times, the finishing jeweler may have accidentally grabbed the wrong stamp from a bin of hallmark stamps on the bench   Some jewelry companies were very strict about which hallmarks could be used.  Others practically desultory.  The three-cartouche (European like) Robbins hallmark is normally associated with the WW1 and before era.  Robbins seems to have retained this older hallmark and used it in later eras for higher end items (it occasionally shows up on 14k badges from the WW2 period).   Warm regards!   Chris

greetings  would you sell it thanks

Identified. Robbins   Now the follow up question, why/when was this hallmark used? It is on a WW2 jump badge.

With Marbles you can only get a general date range that straddles WWII and the information floating around, as Charlie noted, is contradictory and not always consistent. I can say that the attributed Marbles knives that I have and seen to WWII service members have either the left facing serif or no serif. I think that is about as good as it's going to get, a general idea. There is no difference being between the commercial pattern and those procured by the US Government, the only way to determine if they are "GI" is if they were so kind the inscribe/stamp something on the scabbard or knife itself. Those procured by the USAAC/USAAF were Local Purchases (1930's-1941) or Purchase Orders through Wright Field and contractors for several sustenance kits. Then there are procurements by the US Navy through Local Purchasing Offices. With all that said I do not think there is any viable way to determine quantities since most if not all purchases were small and sporadic from a multitude of sources. This then leaves a good measure of a guessing game that will likely never be resolved.