Starting dose and needle questions

For ghk-cu I use 30 g 8 mm in the lower glute because other spots sting for hours. Everything else I do with 30 g 4 mm. Gauges from 29 to 32 feel about the same to me, though 32 g can twist too easily and may struggle with thicker solutions.

You probably wouldn't notice a 27 g at all so the sharpness isn't the real issue. The bending risk is higher with longer 30-31 g needles. I'd stick with 30 g or thicker up to 27 g for better strength, especially since these are water based. Anything past half an inch starts feeling flimsy. I once tried a 31 g half-inch around the love handle area with ghk-cu and it bent ninety degrees after withdrawal, leaving a blue lump under the skin.

I disagree with the previous post. With extra fat a 4-8 mm needle is unlikely to reach muscle anyway, and stopping short of full insertion makes it even less likely. Those lengths are intended for subq use, while 4 mm is more for Botox. High body-fat users trying 4-8 mm for supposed IM peptides are not actually reaching muscle.

This is one of those cases where ChatGPT actually helps. I entered your height weight and body fat and it suggested 25 g needles for IM, though 27 g versions exist too.

You also don't have to inject reta intramuscularly. I use 31 g 8 mm for glp-1 type peptides.

If you can pinch the skin easily you probably won't hit muscle. On the other hand if you aren't carrying much extra weight you might still end up with stretch marks or loose skin unless you're older.