I've done large vs. small lube groove shootouts in the past, and usually didn't see a significant difference. But a recent problem with the 7BR in cold temperatures made me wonder if bullet design could play a role in cold temperature performance. So let's see.
A "Loverider" design on the left vs. an "XC" design on the right, both based on the same basic 7mm 100 gr. GC design that I've been shooting for quite a while. I use the "XC" label loosely because it has minimal lube grooves similar to the 30 caliber NOE XC design, however it does not pretend to be an exact
copy of the XC.
Here's a 10 shot group with a cold rifle and cold ammo. The rifle and ammo were 33 degrees F. Starting with a cold clean barrel, one fouling shot was fired, then the 10 shots for group, pausing one minute between shot so the barrel never even got warm to the touch. Then I cleaned the barrel with Ed's Red and allowed the rifle to cool for an hour before repeating the same procedure with the XC bullet.
A previous target with the standard "Loverin" bullet is pasted into the photo for comparison.
Due to concerns about gas checks coming off in flight and smacking the chrono, I did not chrono these loads, but it normally runs 3150 fps with the usual load of 32.4 gr. LT30.
You can't prove much with a single group, so all I was looking for today was whether the bullet would shoot a group or whether it would spray bullets all over the target. Also whether any gas checks came off (neither experimental bullet shed any gas checks today). So far it does appear that bullet design may influence cold weather performance, but I'd like to repeat the cold weather shootout before jumping to conclusions (you can't shoot multiple cold groups in one range session because the barrel warms up after several shots are fired).
There are a lot of variables at play here so it may take a lot of testing and a lot of time to figure out what is going on.