Hey BCastelow, Any updates ? I just ordered my Wolff spring as well - I am in the exact same situation as you with my JM Pro - I am about to remove those plastic inserts for a larger Mag. VERY curious on your test fire results.Fix: Unconfirmed. Removed the magazine and removed plastic inserts at both ends (I used a wooded dowel to tap it out). Replaced the original spring with a Wolff 12 Ga EP Magazine Spring. Capacity is now 9+1. I have been able to check the loading and cycling but I haven't been able to test fire. I will let you know the outcome.