Madbull TightBore Inner Barrel (363mm for the M4)

Madbull close up

One of the few upgrades I’ve done to my Classic Army M15A4 RIS is to install a Madbull TightBore Inner Barrel to it, so today that’s what I’m going to review.

First things first, I’ll tell you a bit about the gun it is installed in. It is a Classic Army M15A4 RIS purchased brand new at Airsoft Atlanta. When I first bought the gun I was pretty pleased with it, but the groupings were about 5-8″ at 60 feet and I wanted to tighten it up a bit and make the gun a bit more consistent. It was off to Evike to make the purchase of a tightbore and a new hop up bucking and rubber.

First I needed to consider what type of tightbore I wanted and to do that I needed to consider the following:

  • Inner Diameter
  • Materials
  • Cost

I didn’t want to use a 6.01 as I just felt that left too little room for error. I always use high quality bb’s, but I’m not a fanatic about religously cleaning my barrel… even a bit dirt could cause a problem in a 6.01. I didn’t want to get a 6.04 as the stock barrel was a 6.08 and I just felt it wasn’t enough of an upgrade. So I settled on the Madbull 6.03 inner barrel.


The Madbull Inner Barrel is made from aluminum which makes it lighter than the Prometheus barrels which are steel, and stronger than the stock or Systema barrels made of brass. All in all I feel it’s a good comprise. There is a info sheet on Madbull’s website detailing the construction and manufacturing process of their inner barrels here.

The barrel is gorgeous, and it’s almost a shame it get covered up by the bland flat grey outer barrel of my M4. The barrel is coated in a shiny black finish with the Madbull logo etched into the side.

MadBull Inner Barrel Logo


I unfortunately do not have any pictures of the install process as it turned out to be more than I wanted to deal with. Taking apart the gun and removing the stock inner barrel was not a challenge, rather it was putting in the new one that became a real pain. Turns out that the generation 1 Madbull inner barrels were over coated with the finish, and as such did not fit properly, nor easily. I ended up having to wrap the end of the barrel with several layers of electrical tape, then put that end losely in my drill and spin it while holding 400 grit sand paper around the other end to grind it down. After a few minutes of that it fit nicely. I never want to have to do that again though. Now it seems Madbull has addressed this issue as they now state this on their product page:

“What is different from Ver 1 and Ver 2?
Based on the feedbacks from users, we did a lot of imporvement on Ver 2.
Ver 2 is using new machine and new coating process.
Ver 2 is using different packing (10pcs packing) to prevent “bending” during the shipment.”


After installing this I saw an immediate improvement in the groupings. The grouping went from 5-8 inches down to 2 inches or so. There’s not a whole lot more to say here, so that about wraps up the performance aspect.


Over all I have to say this is the best buy when it comes to airsoft inner barrels. You get the strength of aircraft grade aluminum, while keeping weight down. My only complaint with the barrel was the installation. I would (and have) recommend this barrel to everyone!

On a side note, Evike’s packaging of the item was horrid. Below you’ll see pictures of it, as it arrived. I took these pictures as evidence in the need to file a claim with the shipper (UPS) in the event it was damaged. While it was not damaged, I think a lot more could have been done to protect the contents. The barrel was enclosed in a plastic tube (not real stiff) from Madbull, but all that was done to supplement the packaging was to throw a few sheets of very loosely crumpled newspaper in a box that was almost the exact length of the barrel. I was not amused.

Picture one of the Madbull shipmentPicture 2 of the Madbull shipment




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