.450 cycling problems

[thsoccer3]

Thank you for the input. The shop 1 mile from my house has springs in stock for $3, so I can definitely purchase a proper spring before firing with the cut spring.

Being that the 450 upper cycles on the BRO lower, this is why my attention is drawn to the buffer and spring. It also cycles on the M&P15 lower.

With all buffers being identical weight in the 3 lowers, the spring has my attention as the likely culprit, but I am far from an expert. I did notice the spring was 1/2" longer and stiffer than the two lowers that allow the ammunition to cycle, so I cut it, as I had read that this was an acceptable practice.

Since I will be visiting the parts store anyway, what length spring and weight buffer do you recommend for the 450? My plan is to have this lower specifically setup for the 450 and not interchange it.

[plant_one]

you could have always tested it by swapping the springs/buffers to a different lower thats known to work.

thats what i'd do - or move one of the spring buffers from a working lower into your trouble maker

[Texas Sheepdawg]

I built my first stripped lower and just returned from the range. I need expert advice.

My 450 Bushmaster 18" complete upper from Bear Creek Arsenal is short cycling. Shooting Hornady 250grn FTX, the casing ejects, but the next ammunition will not load. I have had this upper for a few years and used to shoot it on an M&P15 without modifications to the buffer or spring.

To troubleshoot, I put the 450 BM upper onto my Black Rain Ordinance lower, and the next ammunition loaded and action cycled correctly. I then put the 5.56 Black Rain Ordinance onto my built lower, and the 5.56 also cycled correctly.

Because of this, I am assuming my carbine buffer and spring in my built lower (adjustable buttstock) is not adequate for the 450 BM action. I do not see any markings on the buffer or spring. Do I need to replace the buffer (heavier?), spring (stiffer?), or both? I am also up for any other recommendations or ideas.

Thanks in advance.

buffer.JPG

Carbine buffers need carbine buffer springs. Make sure it’s not a rifle buffer spring. Also. JP buffer springs are polished and they really do help reduce drag during cycling. They run about $17 for either rifle of carbine spring. Midway USA has them.
Some of the “milspec” springs you see nowadays are very coarse. You can run your fingernail on a coil and it actually feels like 1000 grit sand paper. A polished spring will reflect like chrome or a mirror.