I will be taking a rifle to the range over the holiday to begin breaking in and zeroing.  I would like to shoot one, clean, shoot one, etc. for the first 5 rounds.  I will be using hopes number 9 and the temps will most likely be in the 20's.  Are there any issues using that solvent and cleaning a rifle in below freezing temperatures?  I could leave the solvent in my truck while I'm not using it.  The range I'm using is about 15 minutes drive time from my house so my other option is to shoot one then drive home and clean at home then go back to the range for the next shot.  I'd really like to get this done over the holiday so I can begin load development this Saturday.  Saturday is going to be 45 to 50 degrees so it will be right in the middle of the range of temps I will ever shoot in.  I will be using a temperature stable powder, but I still think doing load development in the middle range of temps is more ideal than doing it on one extreme end or the other.

I'd go pay homage to the barrel gods.

Unless you're chasing the absolute every bit of accuracy you don't need to do that type of break in. In the 90's the guys I knew who were shooting for the USAF Hi-Power team did not follow any type of barrel break in. They would shoot a new barrel 20 to 40 rounds at 600 yards and then just clean them.

I will admit this made me laugh...

I shot for the Natl. Guard Rifle Team (Penna./High Master).  We never did any barrel break-in.  Either the rifle shot or it didn't.

I will admit that I have done the barrel break-in stuff.  Just once on a new Remington (.308 SPS Tactical).  Don't do it any more.  You should clean/inspect any firearm prior to shooting.  Just saying.

As an example, my BIL and I purchased the same rifle (the Remington above).  He never did any knid of barrel break-in.  Shot junk ammo, never cleaned it.  He sold it to me.  When I looked down the bore it seemed that it had hair growing in it.  I mean you could hardly see through it.  After normal cleaning I shot it and compared it to my Remington.  His (never taken care of rifle) out shot mine.  It is what it is.

I agree that barrel break in is not necessary.  The people who make barrels like Shilen, Lilja, Schneider, Obermeyer, Kreiger and so on know how to put exactly the kind of finish in the throat, and barrel that they think works best.

It would be incredibly arrogant for someone like me to think that I can do a better job finishing out their barrels (by break in) than they can.  If they thought a barrel would shoot better by having something else done to it, they would have already done it.  Otherwise, people like myself would buy barrels from barrel makers who DO  finish their barrels so they shoot good from the start.

You are way, WAY overthinking this.  Go shoot the gun, stop worrying about break in, the temperature of the solvent, and so on.

But they DO recommend break in to polish the reamer marks in the throat that are not affected lapping by of the bore.  The bullet must exit the case mouth and fully pass through the reamed throat into the lands and grooves of the bore.  Irregularities in the throat upset bullet stability, introducing yaw, and catch and hold copper which builds up in tight match grade throats.  This affects both pressure and velocity and has a strong permanent effect on cleaning later.

I know for a fact that Krieger and Lilja strongly recommend this and suspect all the others mentioned do to.

Is breaking in the rifle going to cost you that much time/money?  If it works, great!  If not, you're outa little extra time with your gun. Clean, shoot, ...

I have never breacked in a bore. At least not cleaning after every shot.
I keep my bores clean. But some fouling is also healthy for accuracy.

This might be kind a religious issue. But I believe a bore needs some shots to stabilize.

As far as I understand it stabilizes due to some fouling. And fouling should be partially removed when your groups start to spread.

Please correct me if I am telling just nonsense. But my groups are competition groups.

Break-in is barrel dependent. Some barrels need it, some don't. You gotta just shoot some rounds and throw a few patches down the bore to see what's up. If the patches come out clean after like... 3-5 patches... then no break-in is really needed. Depends on the barrel and depends on who chambered it. My Bartlein barrel, chambered by Jon Beanland didn't really need any break in. I shot 5 rounds, put a few patches with some cleaner down the barrel. Came out clean after 4 patches. I shot 5 more rounds, tried it again, patches came out clean in like 3-4 again. So I called it good enough. At about 600 rounds or so, I noticed a drop in accuracy. So I thoroughly cleaned the barrel and the rifle is back to shooting great again. I suspect that at around 1200-1400 rounds, I'll notice another drop in accuracy and I'll clean it again.