450Bushmaster.net

Is an enlarged port a must-have for the 450B? I wanted to use the Aero slickside upper and it doesn't come with enlarged port. It seems an easy enough mod to DIY so might go that way and open it up if it has issues. Was just wondering is anyone has used a standard port and has success.

TIA, Rod.

s4s4u wrote:Is an enlarged port a must-have for the 450B? I wanted to use the Aero slickside upper and it doesn't come with enlarged port. It seems an easy enough mod to DIY so might go that way and open it up if it has issues. Was just wondering is anyone has used a standard port and has success.

TIA, Rod.

Rod;

If the ejection port isn't enlarged at the factory, you will have to do it yourself. As you observed, its not difficult. Rat Tail Files, Dremel or Mill The 450b case will hang up at best or not pass at all on a port cut for 5.56.

Hoot

Thank you for the info.

For what it’s worth. I’ve seen tons of different recommendations on enlarged ports. Some came right from the specs on what a factory Bushmaster 450 port looks like. Others came from people’s personal recommendations. Most seem to show ports opened at a minimum at the front half to around the .60” - .61”. When I built my AR in 450 BM I used the Wilson Combat 450 BM builders kit with the barrel, matched BCG, spring and gas port/tube. They provide specs that showed opening the entire port up to .615 (front to back)!

I bought the Seekins IRMT upper and SP 223 lower for my build. When I received it I noticed the entire port was opened to .53” front to back vs a standard mil spec upper which is around .50”. I racked several rounds through the magazine and was shocked that it ejected them perfectly. Was somewhat skeptical that it would work but I decided to finish the build without opening it up past .53” as I really wasn’t keen on taking a dremel and hand files to my beautiful billet upper.

As crazy as it may seem the gun is flawless. Throws brass perfectly at around 4 o’clock and I could set up a bucket 10 feet away and probably land 90% of the spent cases in the bucket. Bottom line is I know first hand you don’t need to open the port up past .53”. The Seekins upper and Wilson combat build kit proved this to me. The gun is flawless. Not one hiccup in several hundred rounds and it’ll do 1” groups at 100 yards.

I just went thru this myself.

IMHO YES, ya need a more open port For reliability. Im lucky in that I have access to a Mill & Bridgport. I used a bridge port and a 3/8 & .630 end mill.

Just a few passes on each side. I choose to omit the door. But it can be retained by only opening FORWARD of its contact point then entire bottom of port. I opened top to shadow line at the top then bottom to line scored off door. Took maybe 15 minutes then 30 more carefully removing the "knobs" that held the door. Last a couple
Coats of alumi black and it was a invisible modification.

Im certain its been done with a dremil and files. Id just recomend NOT TO RUSH and be of proper state of mind not rushed or tired or fatagued. Its something thats gonna be very obvious if ya fudge or ham hand it.

Maybe ask around buddies and see if they have access to a mill or bridgeport. Its quick and easy.

You could also just buy a spec 450/458 upper.

GOOD LUCK!


CW

cwlongshot wrote:I just went thru this myself.

IMHO YES, ya need a more open port For reliability. Im lucky in that I have access to a Mill & Bridgport. I used a bridge port and a 3/8 & .630 end mill.

Just a few passes on each side. I choose to omit the door. But it can be retained by only opening FORWARD of its contact point then entire bottom of port. I opened top to shadow line at the top then bottom to line scored off door. Took maybe 15 minutes then 30 more carefully removing the "knobs" that held the door. Last a couple
Coats of alumi black and it was a invisible modification.

Im certain its been done with a dremil and files. Id just recomend NOT TO RUSH and be of proper state of mind not rushed or tired or fatagued. Its something thats gonna be very obvious if ya fudge or ham hand it.

Maybe ask around buddies and see if they have access to a mill or bridgeport. Its quick and easy.

You could also just buy a spec 450/458 upper.

GOOD LUCK!


CW

Plus one on the "not to rush" part.
I was in NO hurry. Taped the livin' hell outta the parts that needed keeping.
If I did a plumbing job that bad, I'd go back to retreading.
Thankfully it was a $39 PSA stripped lower.
I'm SO ashamed...
Dremel... 1 star. Do not recommend.