In my gun, they did not show signs of tumbling at 25 and 50 yards. Midwayusa has them in 50 round boxes. They had more of a thump sound than the crack of the the high velocity rounds. They were reliable in my M4, no hiccups but they seemed dirtier than CCI or blazers. In a couple of handguns they showed obvious keyholing at 25 yards. Th M4 has a 13 .75 to 1 or so rifling twist. I think this is enough faster than the usual 16 to 1 twist to make a difference in rifle length barrels. I can't promise that they will work in someone elses gun.
I am curious about UK laws concerning tactical rimfires. My first thought would be that they would not be allowed. I would appreciate more info. Thanks for any responses.
They worked very well in my M4. They sounded different than high velocity, but not a lot quieter. The slightly quicker twist helps these in the colt/ umarex M4. On the other hand they were sootier than other ammo. The groups with these and the high velocity ammo overlapped at 50 yards with the 60 grainers shooting slighty higher.
I sighted in my iron sights today. I had to adjust the front sight to lower the point of impact. I am still having fun. Cleaned after 600 rounds . I had a stovepipe. Perfect until then.