Cartridge is from Ammo Manufacture: * Mystery Winchester (old) 175 gr JHP (being investigated)(supplied by Intercooler)
Ballistics Information: 10mm Auto
Muzzle Velocity: ? ? fps
Muzzle Energy: ? ? ft. lbs
Brass Make/Headstamp: Winchester - Brass
Bullet Make/Weight/Construction/Info; Length 0. 6380"/Dia. 0.4000": 180gr Winchester JHP
Actual weight 180.2 grains  Crimp Diameter 0.3955" 
HP depth  HP 0.2750" / HP dia. 0.1200" (straight) / mouth 0.1920"
C.O.A.L.: 1.2520"
Primer: Large Pistol Nickle color  (red sealant)
Case: Diameter 0.4210" Crimp Diameter 0.4195" (heavy crimp)Length 0.9890"
Powder Description/Positive ID/Type/Charge Weight: Accurate #9  12.0 grains  **

* (being investigated) (Not Hornady) (Winchester casing new appears unfired)
** (AA#9 fine micro bead)

They were all Winchester brass with the red primer sealer.

Being they are 180's in Winchester brass  It doesn't look like the bullet in your other pull-down and more like an XTP.

These are the things that concern me as I look over the mystery of this cartridge...

Hornady Frontier 175 gr JHP bullet actual weight is 180 gr

Brass casing is headstamped Winchester and it is new and unfired

The powder is Accurate Arms #9 (not a Winchester brand)

Your test confirm performance where it would be for the loading with a 180gr bullet
Hornady Frontier 170gr JHP
EAA Elite Limited 4.75" 1172, 1191, 1194, 1177, 1195. Average = 1185.5 FPS/ 531 LBS

I contacted the seller to see if they knew any additional information. Any idea what bullet that is?

   These may remain an unknown unless someone can figure it out. The seller said he thinks he has another pack of these and will send it to me.


Maybe I should put unknown on the sheet and update the weight to 180gr?

It looks like the other load with an XTP bullet.

I have a theory! 

In the past I tested a Winchester brass cartridge with the red sealer on it. I found it and they were Precision Cartridge:

http://10mm-firearms.com/factory-10mm-ammo/precision-cartridge-in-the-morning-check-these-out/msg3072/#msg3072

I think these were done by them and possibly put in this box.

Here is what was found in 11 more of these that IC sent to do specials

8 had 11.8 grains
2 had 12.0 grains
1 had 10.8 grains

The bullets were all in the 180 grain range  COL was 1.2500- 1.2525"