I sent them an email saying I really want one of their XDm 5.25s in 10mm. Got no response yet.

Shot one is 45acp the other weekend and its a sweet shooter. 10mm would get some real pep with that 5 1/4" barrel.

The theory that I have been tossing around in my head s that the flutes act much like a pressure washer accelerating high speed fluid in a direction perpendicular to the bullet path. I have seen pressure washers cut skin. Imagine what it could do to much more fragile lung tissue. I am sure that someone with some advanced math could calculate the speed of the fluid that is generated by a projectile traveling at 1200+ fps through a fluid. Thats how I believe it creates such an extreme wound channel.

I didn't mention in my first post but this is my first loadings for 10mm. I've been handloading since the late 80's but mostly rifle.... and 41mag, but I sold that several years ago. It was a Taurus Ti frame revolver that was plain painful to shoot. A 25oz gun shooting full house 41mag will bruise the hand.

In testing this load I also ran some Underwood 200gr XTP and 220 lead just to get a measure of the web expansion. Following are the velocities I got. Funny how the lead got essentially the same mean velocity even though it was 20gr heavier. The lead with the wide meplate isn't 100% reliable in my gun. Stovepipes now and then which is not a good thing for a defensive round.

I have been thinking about working on a 200 gr XTP load as well, but decided to start with the 200gr Xtreme RNFP plated lead first because I wanted a deep penetrating round for big animal protection, second because it is way cheaper. From what I read the XTP seems to penetrate less when it is driven faster.

I do want to do some penetration tests on the Xtreme bullet at some point but I first want to make sure it is not stripping the copper plating at the speeds I would like to push it. Don't usually get much penetration when the bullet goes through the target sideways.

Load                       ft/sec     ft/sec  ft/sec   ft/sec  ft/sec  Mean        SD Underwood 200xtp   1201   1156   1173   1161   1157   1169.6   18.8095720313 Underwood 220lead   1184   1148   1166   1144   1160   1160.4   15.8996855315

These were all loaded with COAL of 1.250". I do realize that these are well over Hodgdon list of 8.2 grains for a 200 grain jacketed bullet but are in line with loads posted for Swampfox pull downs and his were with jacketed bullets. I am sure these exceed SAAMI pressures for the 10mm but with the tank like build and full supported chamber of the all steel Witness and springs to support a closed action I wanted to push the limits a bit to see what the 10mm could really do.

Guess I should have stated that these are above max recommended loads in my post, although I found no list of max loads for this particular bullet. I modified my original post a bit to show that MAX load is exceeded.

I finally got to shoot some loads I worked up for my Witness.
Using Longshot powder and 200gr Xtreme plated bullets CCI300 primer
Cases were single use Starline brass all from previously shot Underwood ammo.
Eaa Witness Standard with 4.5" barrel w/ flat bottom FP stop, 20lb hammer spring, at 8.6gr I swapped the 20lb recoil spring for a 22lb because I was seeing a bit more velocity variation than I like... and I had one.
Primers were obviously flatter in the heavier loads but nothing I would call alarming and none of the brass measured at the web showed excessive expansion.
I wasn't really noting the accuracy this time out so I'm thinking since the velocity is a know, I want to run at least a partial test again to see if I see any accuracy nodes. It was also cold as crap here so kinda rushed a bit.
I was noticing that the higher velocity loads seemed to be going off target more so I hope the plating isnt stripping but I was shooting at 25 yards at a small target(paper plate) and I find shooting over the chrony distracts my accuracy a bit. I think I'm more worried about not hitting the Chrony than I am in hitting the target.
Anyway, The velocity seems pretty linear even though I dropped to 1gr increments at 9.0gr. Almost get 1300fps from a 4.5" barrel. Not sure of what the pressure is to do that but it's definitely a snappy load. Got a few errors on the Chrony at the upper limits, probably too close to the gun and the blast messed up the reading.

Loadft/sec   ft/sec   ft/sec   ft/sec   ft/sec   Mean   SD             Delta 7.2   1005   1020   1004   Error    1010   1010   7.320063752    7.4   1021   1012   1038   1044   1032   1029   12.9151074328   20 7.6   1055   1067   1074   1101   1074   1074   16.8730554435   45 7.8   1068   1086   1043   1087   1039   1065   22.8757513538   -10 8.0   1078   1098   1103   1119   1092   1098   15.0166574177   33 8.2   1075   1108   1131   1078   1101   1099   23.04994577           1 Warning MAX LOAD recommended by Hodgdon for 200gr jacketed bullet 8.4   1140   1130   1103   1121   1147   1128   17.195929751          30 8.6   1152   1159   1160   1160   1160   1158   3.4928498393          30 8.8   1113   1167   1170   1140   1159   1150   23.6579796263   -8 9.0   1188   1188   1173   1176   1186   1182   7.155417528           32 9.1   1182   1193   1201   1167   1206   1190   15.6428897586   8 9.2   1200   1188   1163   1190   1167   1182   15.8839541676   -8 9.3   1192   1213   1212   1207   1208   1206   8.443932733           25 9.4   1239   1258   1212   1200   1219   1226   22.9847775713   19 9.5   1228   1217   1216   1221   1260   1228   18.2838726751   3 9.6   1213   1252   1240   1239   1252   1239   15.9279628327   11 9.7   1237   1262   1242   1283   1283   1261   21.8242983851   22 9.8   1274   1256   1249   1275   1245   1260   13.9892816113   -2 9.9   Error    1295   1295   1272   1282   1286   11.1654228163   26 10.0   1237   1294   1294   Error   Error     1275   32.9089653438   -11

Warning the MAX LOAD recommended by Hodgdon for Longshot with 200gr jacketed bullet is exceeded in this loading

Can you describe how it jammed? I find that many Witness jams are caused by a poorly designed magazine/follower. These jams typically present as rounds nose diving into the feed ramp but not always. The magazines were re-designed in about 2010/2011 so if your gun is brand new it more that likely has the new style magazine.

I plan to use 220s as a woods defense round. I hike and bow hunt in some pretty remote areas with lots of bear. I like the penetration of the heavy hard cast. May never have to use it but it is there if needed. I would probably go with the 180 or 200 XTP if I was hunting deer, but PA doesn't allow semi auto pistols for hunting. Lots of old school thinking in this State... hard to change minds.

Yep. Waiting for the 220 hard cast also. Was hoping for today but maybe next week.

Been waiting to get some 220 Hard Cast... Might have to buy from my iPhone since I won't be home at 6.