Bio bb's have had a fairly poor rap in the past due to poor quality. Bioval bb's have been around for some time now with great success and no issues with respect tight bore problems. In fact the slightly smaller diameter 5.92mm provides perfect clearance. The smaller diameter offers superior flight adjustment with your hop-up.
No Bio bb's come close, and most regular bb's show no performance advantages.
If your local dealer does not sell them, contact me and we can sell them to you.
www.mach1airsoft.com