Hello and thank you for letting me joining this group!
    I recently acquired a new Dan Wesson Silverback 10mm. This is my first encounter with 10mm and my knowledge is limited regarding this round. To be honest i was always a .45 person but I have to admit I think 10mm will be a fantastic choice for me and I am very excited! I am not new to reloading (dillion 650xl) about 20k in various round types. Please be kind as i have done some research regarding shooting 40 cal from this weapon (saying it was safe). However, the headspace issue seems to worry me some.
   This weapon would be used primarily for target but would like to get into 3 gun competitions at some time. I do not need to run these rounds at its full potential so this is why I am considering using 40 cal cases and adjust the overall length to compensate for the difference. i currently dont shoot my other 40 very often but have around 6K cases for reloading.
   I tried researching any stickys regarding this topic but I didnt find much luck.

So my questions are:
   1. can I use 40 cal cases with in any type of variation (adjusting powder and OAL)?
   2. I would be using 800x powder
   3. I fully understand that using 10mm cases is the best option, just curios as 10mm cases are difficult for me to acquire at the moment.
   4. Oh yeah does anyone make separate magazine followers to convert 45 magazines to 10mm?

I value everyones input and figure there are experts here but please be patient with me.

1.  There is a user here, and I am drawing a blank on which one, that has done a fair bit of load work-ups with "Long 40".
2.  800X is a great powder, but as I am sure you know it meters slightly worse than corn flakes.  Longshot might make a good option too.
3.  40 brass is certainly prevalent and cheap
4.  Not sure a follower is needed.  Some mags work fine and some don't.  Just have to try and see.

I will add that, especially with Glock, I suggest a dedicated 40 caliber barrel.  However, with a Glock that is a $130 drop in commitment.  Not so much with a 1911, where the barrel is gonna run closer to $200 and you still have to have it fit to your gun, and you need a bushing.

Generally straight wall rimless cases that are supposed to headspace on the case mouth actually headspace on the rim/extractor interface.  However, if your extractor doesn't hold onto the brass, that brass is gonna have a short life and will appear to be overloaded.  What can happen is the firing pin will knock the brass off the extractor hook and forward into the chamber while also setting off the primer.  As the gas expands, the case accelerates towards the breech face of the slide and impacts with added velocity.  The momentum of this impact makes the brass look like it was subjected to higher pressure than actually occurred.  Primers will also be flattened or malformed as the will partially unseat before being violently re-seated.

This doesn't happen in most guns.  So, you will probably be fine.

Another concern with this plan is if you have 40 S&W pistols about the house.  Ammo loaded long and with data to make use of the extra case capacity created by seating long could have an issue in a 40 chamber.  The bullet could be seated into the lands creating a pressure spike. It could also be forced by the lands to a short COAL, creating an even larger pressure spike.  As long as the ammo is carefully marked and understood to be not 40 S&W ammo, this concern is mitigated.  But it still exists.

Welcome to the forum and congrats on the Silverback.  Fine gun in the best mm!

sqlbullet, has pointed out many of the things that are associated with using the shorter case of S&W40.
Being the Silver Back is a 1911 style one thing to be concerned about is the extractor itself.  Some 1911 extractors are bent to shape and specific to hold the casing properly.  If the 40casing is being slammed around that could take its toll on the extractor's settings.

Having a conversion barrel is usually the preferred method for best results when using the shorter cartridge case.  They bring the best reliability and accuracy as well.

All that being said yes some are shooting the 40S&W  in their 10mm firearms and most of them work just fine.  Loading the bullets long can help center the bullet to the 10mm chamber for less case movement. 

Another word of CAUTION is that the possibility of the bullet being shaved as it passes over the end of chamber cut.  Shaving can disrupt accuracy and even roll up on the end of the chamber cut, causing a stoppage failure to feed and the deposit there which can be fairly difficult to remove.

Great points! I did find followers on the Wilson combat site to convert the mags from 45 to 10mm and a new 40 cal Dan Wesson barrel is only 100 bucks. But I wonder if I would need to have it refitted to the weapon?

Not sure about the fitting as it may actually fit as is.  What needs to happen with the fitting process is fitting to the slide to where the barrel wit drop into the slide properly.  The barrel hood plays a part in this fit.  Trimming the barrel hood length (using sandpaper or  honing stone to gently shorten)  where it rest against the breech of the slide is what allows it to drop into battery and the locking surfaces mate with the slide cuts.  The ramp will be an important part of the fit so that ammo doesn't catch or snag for reliability.

Then the swing link and associated surfaces are the next part of the fitting process...here you will need some color markers to see where the mating surfaces rub or drag.

Quote from: Zeuslewis on April 09 2019 05:43:31 PM MDT
...and a new 40 cal Dan Wesson barrel is only 100 bucks. But I wonder if I would need to have it refitted to the weapon?

I don't think that barrel won't fit your gun.  Your Silverback has a ramped barrel.  I believe it is a Clark/Para style ramp, but am not sure.  I don't see a 40 S&W 5" ramped barrel on their parts page, but I didn't search hard.  The other ramped barrels I did find were $180.

These are "match" barrels so they will require fitting.  Barrel hood, upper lugs and lower lugs, as well as fitting a bushing to the barrel and then to the frame.

Here is a walk through of fitting an un-ramped Kart EZ fit barrel in a 1911 build.  The steps would be pretty much the same for your ramped barrel.

http://how-i-did-it.org/1911-project/the_kart_of_barrel_fitting.html

Welcome to the forum. I too shoot pistol games with 10mm, however mine is a Glock.

Do yourself a favor and leave the 800-X on the shelf at the LGS. It is a drop-and-trickle proposition. It will get old soon. Like said by Shadow, Longshot will be a substitute.

For gamer loads, I actually go with a quicker burner than either and throttle down velocities. The quicker burn speed gives better results at modest velocities.

My favorite powder for hard hitting heavies is No. 9.

Welcome. First, I wouldn't mess around shooting .40s out of any 10mm 1911 with an internal extractor. Starline has plenty of 10mm brass in stock and there are other options for buying used brass online.

I would concur that 800x is excellent for the hot stuff, but LongShot meters much better.

Those follower and spring kits on Wilson Combat's site aren't meant to convert from .45 to 10mm. They're replacements for worn parts. The internal width of 10mm mags is reduced by a indentation stamped down the side of the mag body. The 10m follower rides on that indentation and is narrower at the front than a .45 follower. There is also a difference in the feed lips. As mentioned previously, some 10mm 1911s will run with 47D mags (.45) and some will not. If yours won't run on them, I really doubt the 10mm follower would help. It would slop around in the mag body.

Congrats on your new gun!

I really appreciate everyone's input and I can tell there are some very knowledgeable people in this group to help. I had one more question about powder, would the 700x be an acceptable powder?

There's probably some load data for 700X out there for 10mm. It not really well suited. 700X works better for low pressure stuff like .45acp and .38Special. It doesn't meter that much better than 800X.

Since you seem to like powders that don't meter well give BlueDot a try. Many members here, myself included, will attest that 10.4gr with 180gr bullets is a very accurate load.

Don't fool around.   Use only cartridges designed for your gun.  Buy starline brass and either 180 grain FMJ or hardcast.  Use AA#5 for FBI or .40 equivalent loads, and AA#9 for 10mm loads.

AA #5, AA #7, & AA #9 are going to meter very, very well through your Dillon. These 3 powders will run the gamut from mild to wild in your 10mm.

I am using 8.9 gr of AA #5 under a 155 gr Federal HST (pulled bullets from RMR)  loads and it works great in my XDM 10 4.5 for velocities around 1150 fps. Soft shooting and very accurate. The velocity closely matches the Federal .40 S&W 155gr HST Tactical LE loading.

Quote from: Zeuslewis on April 12 2019 02:03:15 AM MDT
I really appreciate everyone's input and I can tell there are some very knowledgeable people in this group to help. I had one more question about powder, would the 700x be an acceptable powder?

This is a link to so much 10mm data and you can see data for the IMR HI Skor 700X powder as well...
http://10mm-firearms.com/reloading-10mm-ammo/10mm-load-data-collection/

Quote from: Zeuslewis on April 12 2019 02:03:15 AM MDT
I really appreciate everyone's input and I can tell there are some very knowledgeable people in this group to help. I had one more question about powder, would the 700x be an acceptable powder?

I would characterize 700-X as a powder that could he made to work if you needed to. Then only for loads that will barely make the action cycle. Very quick burning, and the 10mm favors in the burn speed of Unique and slower, with Accurate No. 9 and 2400 being on the extreme slow end.

If i had some to burn and wanted to make some soft shooting 10mm, I'd start with 40 SW max data as a start charge. Work up until the slide cycles then stop.