I am working on a load for a 7mm mauser I have with a commercial barrel form a unknown maker with that being said does the fired brass being darkened/black just around the outside of the neck of brass tell me anything?

Nothing is easy...it could be brass is very hard, needing annealed...more likely you're operating at very low pressures, using data the lawyers insisted on to make the 7x57 safe in rolling blocks.

140 grain sierra's with 41 grains of IMR 4895

That should be a high enough pressure to expand the necks. Maybe your brass could stand to be annealed. According to Lyman #50, 38 gr should put you around 44,800 CUP...your charge weight of 41 gr should have you up around the SAAMI limit of 46,000 CUP. But, nothing is easy or girls would be doing it, a typical throat will be the old pattern reamer that digests 175 gr round nose bullets, and like in any cartridge...a lot of freebore reduces pressures dramatically and thusly, velocity. So, if a resized case springs back and doesn't hold the bullet firmly, try annealing.
Once you have eliminated that, you can judiciously adjust your load upward. A little soot on the neck is of no great concern. A chronograph is your friend, I am of the opinion that if you stay within published velocities for your class of rifle strength, you will not get into trouble. You never stated what action you have, but personally I have heard no evidence of '93's and 95's coming unglued. They do not however have a safety lug. Thousands were made into 7.62 x 51 as the 1916. When they came into this country, they were tested by Samco at HP White Laboratories...no rifle tested failed below 92,000 PSI. Sorry about the long windy, but there is so much bad info out there on these rifles on the interweb.

You may trust the strength of any Spanish-built small ring pre-1898 style military Mausers, but I don't. IMO, Spanish-built military Mausers are at the opposite end of the quality spectrum of the Swedish-built military Mausers, the Spanish-built rifles being among the poorest quality and the Swedish-built rifles being excellent quality.

I think it is a Karabiner 98a with a after market safety/trigger, and commercial barrel. There is no signs of pressure (as the handle having any stiffness on opening). the previous owner's estate had handloads that he had loaded and written down on the box but they were with RL-19 and looked to be right at the top of range or even a little over published, not wanting to believe that info i started over, I am using new Remington brass, Remington 9-1/2 primers. I dug around and found some info on loaddata that put 42 grains of IMR 4895 at the top and compressed, so I figured I would start a little less. The previous owner was reloading at over the 3.00 COAL, i loaded to 3.00.

Barsness, who forgot more than I'll ever know likes 4350, but I could never get my BRNO to digest that stuff (fully bedded barrel). With light bullets, 139-145 my notebook says: 140 Sierra, 50 gr of Win 760 gives 2700 fps (23 5/8 bbl length) "good groups but overly destructive on deer". Ditto 42 gr 4895. Then,48 gr 760/H414 at 2650, 1" grps (5 shot) 145 Speer flat base.
Anyway, you have a good stout action, have fun. I've only owned two 7x57's and I had to work at it to get them to my personal preference of sub 1 1/2 inch 5 shot groups at a hundred, so I'm no guru.

captjohn,
How old is your brass, and also how many reloads on the brass. I am asking because I have a sportified Brno made Peruvian large ring M98 Mauser that seemed to be hard on brass (even with mid range loads). First indications were "brass being darkened/black". Granted this was brass I had reloaded about 3 or 4 times previous. Very close inspection with a magnifying glass showed some hair-line cracks near the base of the neck on some brass. I had received that brass from a fellow who told me he only reloaded it twice. I now suspect that was not the case, and it had been reloaded a lot more than he indicated. Anyway I threw out that brass and started over with new brass and never had any more problems with that rifle.

This probably not the issue in your case, but you might inspect for 'hair-line cracks'.

Annealing as suggested by "flintlocke" is a good idea. It would tend to provide a tighter neck fit when seating your bullets.

CJ

Anneal them, even though the brass is new it can still be hard. Stuff happens.


ETA: As flintlock said, I don't stress about a bit of soot on the necks.