I went to my local gun club to continue the breaking in of my Colt Delta Elite 10mm, set up target and loaded a full magazine. When I fired the fifth round the slide locked partially open and I cleared gun (removed magazine) to check out the problem. Just looking at gun I saw nothing indicating a problem but noticed what looked like a scratch on the top of the barrel, so being a little upset I just packed up and came home to get the gun apart and see if something had broken. After cleaning the barrel I discovered it was crack and not scratched, barrel was cracked on top from breach to muzzle and it had scorch the slide inside above the barrel. This happened while shooting factory WW 175 gr Silvertips, which have never seemed as loud or as heavy recoiling as even Remington target ammo. This gun has a rather low round count, I have only shot two 50 round boxes of Remington 170 gr target ammo, two 20 round boxes WW Silvertips that were about 4 years old and 5 rounds from this box that was about 1 or 2 years old. The gun was cleaned after last use and barrel inspected as always, no issues noticed. While shooting I heard or felt nothing unusual on the fifth round, no squib or hot load sound. I had 5 nice shots to the target then slide jammed about 3/4 or more open and last fired round ejected properly. I have done a minor cleaning of barrel and wipe of slide to check it, wished I had not done that now as it may have aided in your investigation of the incident. This has really shaken my faith in the new Colt guns, when its repaired I will have to run four or five hundred rounds through it before using it for personal defense or hunting. I guess I am back to my S&W 3 629 44 magnum to carry now.