Hi Charlie,
I bought an H&R Target Model (38-55) last winter, took over three months to get it due to out of stock conditions. At any rate I had plenty of time to get my loads ready. Here are a few things I've learned, your barrel may be a bit different than mine, but:
1. The chamber on my rifle was very tight, such that I had to not crimp the bullets in the cases, or at least very lightly crimp them. Suggest you wait to load the bullets so you can load the first one and see if it chambers. That's better than having 50-100 rounds loaded only to find out they won't chamber.
2. I slugged my bore with some lead fishing weights to find out the size of the bore and grooves, after doing this I ordered the sizing die.... .378 in. Your bore size certainly could be a bit different, but the minimal effort to slug the bore is worthwhile.
3. Since the chamber is so tight on my rifle, the extractor was not strong enough to pull the case out of the chamber. This issue seems to be lessening the more I shoot the rifle and I anticipate that it will cease after a few hundred rounds. I considered polishing the chamber but chose to let it "wear" in. I keep a 3/8"X3' dowel rod in my rifle case to knock any cases out that stick. If you are going to use your rifle to hunt with, the chamber polishing would be a better way to go.
4. The first few groups I shot were nice but not very impressive (iron sights and new bore), but after I mounted a 3X9 scope and fired more ammunition they really started to tighten up. Latest groups were .88 inches at 50 yards and 1.5 inches at 100 yards. Last night I polished the bore with 'Flitz' last night and will be trying it tomorrow if it isn't raining.
There are a lot of good folks at this web sight that are willing to share there experience. I think you will like this rifle and cartridge.
Roudy