P365 XL bullet diameter? (.355, .356, or .357)

.355" is the upper limit for diameter of 9mm bullets. Of the three choices, this would be mine.

Thanks!

. 355

Wait, Slug your barrel and use outside micrometers to measure the slug dia., see a machinist if you must to have him measure for you. Meister bullets in Mo. has a great kit that I use. See my older thread on slugging the barrel. If you purchase coated bullets like SnS, purchase them 0.001" larger than your slug size. I am not sure what Brazos is offering you, coated, plated, or jacketed it makes a difference on the size that you order.

As a reloader I use whatever is cheaper or on sale. Either of those diameters will work. If you were shooting a rifle at long distances with a large caliber than I would slug barrel and purchase accordingly. That being said would go with.355.

Slug your barrel and measure it with a micrometer. A pair of calipers are not going to be accurate enough. Generally you want to go .001 over your grove diameter with cast bullets. So for a 9mm, that’s .356. If you look at the Lyman cast bullet reloading manual, all of their 9mm loads were done with .356 bullets. I order .356 bullets from brazos, and I’ve been very happy with the results. For my own cast bullets, I have a .355, .356 and .357 sizers and size accordingly depending on what gun it’s for.

You’ll find out pretty quickly if you have undersized bullets.

I use 147 grain in all of my stuff. I had to use 358 in my Beretta to keep from leading. They run fine in my Sigs too. I have a new shipment from Brazos that just got shipped and I ordered them in 357. I slugged my 320 barrel and came out 356 so ordered 357. The Sig barrels are a lot tighter than the Beretta 92's. I tested some 135 grain from Brazos and they ran really good too. I think my next batch I order will be 135 grain in 357.