---
title: "Better MC (BMC4 / BMC5) FPS Boost, RAM Tuning & Crash Fixes in Prism Launcher"
description: "Fix Exit Code 1 crashes, garbage-collection lag spikes, and low FPS in Better MC (BMC4 / BMC5) (Fabric / Forge / NeoForge) using Prism Launcher on Windows."
canonical: https://prismlauncher.ink/modpacks/better-mc-bmc4-fps-and-crash-fix
updated: 2026-10-17
---

# Better MC (BMC4 / BMC5): FPS & Crash Fix Guide

Memory tuning (6 GB – 8 GB), Java 17 or Java 21 setup, and crash troubleshooting for Better MC (BMC4 / BMC5) in Prism Launcher.

## Facts (2026-10-17)

- **Target Modpack:** Better MC (BMC4 / BMC5)
- **Required Java:** Java 17 or Java 21
- **Optimal Heap RAM:** 6 GB – 8 GB
- **Loader:** Fabric / Forge / NeoForge

## Eliminating lag spikes and stutters in Better MC (BMC4 / BMC5)

When running [Better MC (BMC4 / BMC5)](https://prismlauncher.ink/modpacks/better-mc-bmc4) on Windows, stutter usually comes from either too little heap memory or an over-allocated heap (>12 GB) causing long JVM garbage-collection pauses.

Lock your instance memory inside the **6 GB – 8 GB** sweet spot and verify that `javaw.exe` is assigned to your dedicated NVIDIA or AMD GPU in Windows Graphics Settings.

## Fixing startup crashes and updating safely

1. Confirm your instance uses **Java 17 or Java 21** under Edit Instance → Settings → Java.
2. Before updating the modpack to a new release, right-click the tile and select [Copy Instance](https://prismlauncher.ink/instances/clone-and-group-instances-on-dashboard) so your existing world and configs have a rollback point.
3. If a crash persists, click **Upload** in the Minecraft Log tab to generate an [mclo.gs](https://prismlauncher.ink/words/mclogs-crash-log-upload) diagnostic link. Get the latest Prism build at [/download](https://prismlauncher.ink/download).

## FAQ

### Why does Better MC (BMC4 / BMC5) crash before reaching the title screen?

90% of pre-title-screen crashes on Better MC (BMC4 / BMC5) happen because Prism is pointing at the wrong Java major version instead of Java 17 or Java 21.

### Can I add extra performance mods or shaders to this pack?

Yes. Open Edit Instance → Mods → Download mods to add FerriteCore, ModernFix, or Iris/Oculus matching your loader.

## Related

- [Better MC (BMC4 / BMC5) on Prism Launcher](https://prismlauncher.ink/modpacks/better-mc-bmc4)
- [Prism Launcher Modpacks & Mod Downloader](https://prismlauncher.ink/modpacks)
- [How to Fix Minecraft Exit Code 1 & Exit Code -1 in Prism Launcher](https://prismlauncher.ink/howto/fix-minecraft-exit-code-1-prism-launcher)
- [Prism Launcher Java & JVM Configuration](https://prismlauncher.ink/java)
- [Fabulously Optimized on Prism Launcher](https://prismlauncher.ink/modpacks/fabulously-optimized)

## Download

Free and open source: [Download Prism Launcher](https://prismlauncher.ink/download)

Markdown mirror: https://prismlauncher.ink/modpacks/better-mc-bmc4-fps-and-crash-fix.md