Ok, I did some sleuthing around on the Internet and found the article shown below. Don't know who the is the author, but it confirms what Magnum Maniac and Jerry M wrote above. The year it was written , 2016.
St, Marks Florida. It's the onetime Olin Corp plant, now part of General Dynamics. It makes double-based ball powders only or those (Such as Hodgdon Hybrid 100V and some Alliant types) using the same slurry / distillation based process.
All Winchester and Hodgdon ball / 'spherical' grades are supplied by St. Marks as are nearly all propellants used in US military small arms ammo, the US government having decided way back in the 1950s with 7.62 adoption that this type would be the norm, sniper and special purpose ammo aside.
Ramshot / Accurate ball powder comes from PB Clermont in Belgium. Hodgdon extruded grades and IMR-8208 XBR from Thales / ADI in Mulwala, NSW, Australia. Other than 8208 XBR, IMR extruded rifle powders are also made by a General Dynamics Corp owned plant in Valleyfield, Ontario, Canada. (Hodgdon owns the IMR brand name and marketing rights IIRC.) This plant also makes some Accurate brand extruded numbers. All Vihtavuori powders come from the town of that name in Finland.
Alliant 'Reloder' extruded grades were all made by Bofors in Sweden until a few years ago, but some recent additions such as Re17 and Re33 are sourced from Nitrochemie Wimmins AG in Switzerland. Alliant has also started using spherical grades from St. Marks.
Health & Safety and the EPA is the primary reason that all extruded powders are made outside of the USA. Ball types manufacture uses non-inflammable / explosive slurries with material piped between processes until the little balls are distilled out at a late stage for chemical treatments and grading. This method also allows old out of date propellants to be recycled alongside fresh ingredients reducing costs.
Extruded powders start by dissolving cellulose in powerful acids, a dangerous exothermic process and whose products are immediately highly explosive and inflammable, then further inherently dangerous processes and solvents are used to convert 'guncotton' into usable propellants. Many of the materials used are corrosive and toxic, likewise creating waste and pollution issues that have to be dealt with nowadays, not just dumped into waste ground or rivers as would once have been done.
All this makes the manufacture of this type inherently riskier which in this day and age is also much more expensive. A guy in the handloading powder business stated years ago that the EPA hadn't banned extruded powder manufacture, but its regulations were so onerous that any such produced in the country, (USA), would be so expensive, nobody would buy them.
Extruded propellants are widely manufactured in Europe still, although many older plants have closed over the last 20-30 years. None at all are manufactured in the USA since the DuPont Corporation firstly moved propellant production to Canada then later sold that operation. No doubt, the American military's decision to switch to ball propellants was a major influence here as military demand is the largest single component of many explosive manufacturers' business. Nevertheless, the US market for sporting ammunition and her industry's manufacturing outputs probably exceeds all of that of Europe combined.
Yes, I know Europe has high safety and environmental standards - the UK has not manufactured propellants since the ICI Nobel plant in Scotland closed in the late 1980s or early 1990s. However, there is a big difference between having exacting regulations and having such that are so onerous that there might as well be a complete ban which is what my contacts in the American handloading powders business have told me about the EPA's attitudes to manufacturing this (extruded) form.
One area where the EC is becoming more restrictive than the US is fast appearing though. That is the EC REACH program which is steadily evaluating every chemical used and identifying risks to human health, then legally forcing their replacements with safer alternatives.
It is known that some traditional chemical burning rate deterrents and other such behavior modifiers long used in small arms propellants are deemed to be in the dangerous category, so many long established powders are now living on borrowed time. A little commented on element of the blurb about the new IMR Enduron powders is that they are 'environmentally friendly'. It actually goes a bit further than that as many existing powders will not be allowed to be sold in EC countries in a very few years time, nor will ammunition loaded with them. General Dynamics / IMR is getting itself geared up to this challenge with its new products. Once the new regulations start to apply no older long established IMR grades will be compliant, that also applying to many other makes. I don't know how this affects many existing European manufacturers other than Nitrochemie whose powders are already compliant, but I wouldn't be at all surprised if this doesn't sound the death knell for some as there is substantially more capacity than demand for powders, given the lack of wartime requirements, but western governments have long since stopped worrying about that.
So far at any rate, there seems to be no US equivalent to REACH in this field, so many older propellants will continue to be sold in this market, likewise loaded ammunition.
