450Bushmaster.net

Guys-

What length gas system would you put on a 24" barreled 450 and why?

-Barttman

I would stick with the mid-length gas system so that factory loads would be able to cycle properly.

To tell you the truth, at 24", I think you could actually entertain a rifle length system. The dwell afforded by the additional 4 inches over the 20" rifle length upper like I have, may tip the scale. That having been said, a mid-length system would be a sure bet. If you're doing R&D, by all means try the Rifle Length, but if you're doing a one off and have to get it right on the first try, go with the mid-length. Just my opinion.

Hoot

I have never tested a 24" 450, but the very first prototype .458 SOCOM I built back in early 2001 had a 24" barrel on it and a rifle length gas system. I don't recall the exact gas port hole, but I do remember having trouble getting it to run without opening up the gas port pretty damn big. It was around .135", maybe .140".

Tony Rumore
Tromix

TonyRumore wrote:I have never tested a 24" 450, but the very first prototype .458 SOCOM I built back in early 2001 had a 24" barrel on it and a rifle length gas system. I don't recall the exact gas port hole, but I do remember having trouble getting it to run without opening up the gas port pretty damn big. It was around .135", maybe .140".

Tony Rumore
Tromix

Without digging out the 20" Franklin upper with rifle length port and pulling the gas block, I seem to recall having to open it up to .120+ to get it to start cycling potent loads reliably. What I did not see, before stopping last summer, was the premise as I understood it, behind the "Corvette" project. Namely a velocity improvement from being able to use slower powders. I suspect, the missing component was not just having a rifle length gas system, but a longer barrel as well. At .120+, it was just beginning to cycle heavy loads reliably. I'm not done with that project, since I would like it to cycle all reasonable load ranges reliably. Something that the mid-length system in the Bartz does and if you dismiss the really heavy loads, the carbine length original design does also. When you think about it. When Bushmaster rolled the carbine length 450b out of R&D and into production, it was designed to reliably function using the only available 250 FTX factory loada, under any adverse weather condition, clean or dirty. It did that. They threw us a few bones in publishing some really anemic (lawyer approved) alternative loads after the fact, but for the most part, if you wanted to expand its mission in terms of loads, you were on your own or within the scope of test results generated within this user forum. All points considered, the carbine length system, coupled with a known good quantity in Lil Gun powder, is amazingly diverse. That having been said and I realize I'm ruminating too much on this, the mid-length system, seems to be the best of both worlds in terms of broadening the diversity of successful loads in all but the shorter barrel designs. That's my take on it, but I do not consider myself a authoritative source on the subject. Just a good observer.

Hoot

I have a buddy wanting a 24" upper, been chattering on it for a year now, he just likes long barreled AR's, so will be interested on what system you go with Bartt.

I fiddled with a Franklin 20" upper last summer a bit. One thing I did notice was it more or less just dumped the empties out, no FTE or real flinging of them, didn't matter if it was factory of handloads, just dumped them out.

Al-

For what it's worth and just in the interest of passing along good information...

By their own admission Franklin has been having some trouble with their extractors. I have helped customers with Franklin guns that were just pooping out empties barely clearing the ejection port or not clearing at all. We replace their extractor with one of ours and immediately the brass ejects properly.

Franklin makes a good product and I believe Jay has fixed this problem. Anyone experiencing a similar issue should contact him. He is a good guy and will fix you up.

-Barttman

Bartt, did you ever get a 24" barrel tested???

Al-

We expect test barrels in any day now. We will run one in rifle length gas and one in mid length gas and see how she goes. I'm not optimistic on the rifle gas. At our SAAMI ~40k pressure even at full .125 bore we may not be able to get enough gas at rifle length....

I know Tim does it but I don't believe he is running SAAMI.

-Barttman

Al-

Preliminary testing on the 24" rifle gas upper is completed... success! She functioned flawlessly. Perfect ejection, cycling, feeding and open bolt on last round. We will continue testing and keep you BoyZ posted with results.

-Barttman