FTF with new Centurion upper

[jackblack73]

It is interesting to see that the White and BCM springs have such a different number of windings since they are supposed to have the same spring rate. Doesn't that imply that the wire in the White spring is weaker? I wonder if a thinner wire is used to leave room for the coating. Or is the coating more of a surface treatment?

They’re made of different materials. Springco springs are chrome silicon while BCM’s are likely stainless steel.

[Disciple]

They’re made of different materials. Springco springs are chrome silicon while BCM’s are likely stainless steel.

This reference gives 207 GPa MOE for chrome silicon and music wire, but only 203 GPa for 17-7 PH. Wouldn't that require a greater number of windings on a CS spring to have the same spring constant as the 17-7 PH spring with the same wire diameter and dimensions, rather than fewer as observed on the Sprinco White? Am I remembering this backward? Don't more windings make for a softer spring?

[1168]

This reference gives 207 GPa MOE for chrome silicon and music wire, but only 203 GPa for 17-7 PH. Wouldn't that require a greater number of windings on a CS spring to have the same spring constant as the 17-7 PH spring with the same wire diameter and dimensions, rather than fewer as observed on the Sprinco White? Am I remembering this backward? Don't more windings make for a softer spring?

Yes, more windings with the same wire diameter, material, and treatments make a softer spring, because the actual wire is longer. Taking an existing spring and clipping coils off it does not reduce rate, it makes a stiffer spring with less preload. Blows peoples minds because they slept through physics. And CS makes a stiffer spring than 17 series, if all other things are equal, which they rarely are.

As for coatings, it would appear that neither Sprinco CS nor BCM SS use one. Tubbs does, or has, but it flakes off quickly.

Sprinco claims +15% force with Blue, which is quite believable.

[1168]

This reference gives 207 GPa MOE for chrome silicon and music wire, but only 203 GPa for 17-7 PH. Wouldn't that require a greater number of windings on a CS spring to have the same spring constant as the 17-7 PH spring with the same wire diameter and dimensions, rather than fewer as observed on the Sprinco White? Am I remembering this backward? Don't more windings make for a softer spring?

While we’re discussing spring force, I did a casual experiment this weekend with a gun. It’s baseline is with a Sprinco White and a H0 buffer, 16” midlength barrel. In that state, it will not run Tula steel cased ammo. Short strokes almost every round per mag if freshly lubed, and its a consistent bolt action within a few mags. It is sewing machine reliable with any brass cased ammo that I’ve tried. About 1500 rounds on it so far in somewhat harsh testing conditions, mostly PMC, with some Fed XM193, Fed XM855, Precision One 62gr, and probably some other stuff. When suppressed, I drop in a PWS H4.

Anyway, I tested a BCM SS spring with a H0, and it ran the same lot of steel cased ammo perfectly reliably across about a hundred rounds. Locked back on empty every time. I dropped in a Colt SS spring with a H2, and it cycled fine over a couple mags, but didn’t lock back. Much better than it did with a White and H0.

It would appear that the Sprinco White is stiffer than BCM or Colt 17-series springs.

[Disciple]

I appreciate your conducting that test and sharing the result. H0 means carbine buffer with three steel weights, correct?

[1168]

I appreciate your conducting that test and sharing the result. H0 means carbine buffer with three steel weights, correct?

Correct.

[Dutch110]

Centurion is taking the BCG back and will give a refund. I'll probably get another BCM or LMT to replace.

Did you ever find out what the issue was with the BCG?

[maximus83]

Did you ever find out what the issue was with the BCG?

They issued the refund and I asked what the issue was, haven't heard back yet.

[maximus83]

Took it out again today, 250 rounds with a new DD BCG. Once again: tried multiple loads, new ammo, old ammo, .223, 5.56, mags loaded to 30, dropping bolt with bolt catch vs CH, nothing I could do would make it fail.

So at this point, pretty confident in saying it was something with the Centurion BCG. With that one, nothing I could do would make it work. With the BCM/LMT/DD BCG's, nothing I could do would make it fail. Definitely be interested to hear the cause, if Centurion decides to let me know. Either way, they were totally cool about the refund and it's a great upper.

Next step is to try one of my heavier BCM MK2 buffers, like the T1 or T2 (5.6oz). The recoil with the T0 (3.8oz) was a little snappy as far as getting back on target.

[georgeib]

Took it out again today, 250 rounds with a new DD BCG. Once again: tried multiple loads, new ammo, old ammo, .223, 5.56, mags loaded to 30, dropping bolt with bolt catch vs CH, nothing I could do would make it fail.

So at this point, pretty confident in saying it was something with the Centurion BCG. With that one, nothing I could do would make it work. With the BCM/LMT/DD BCG's, nothing I could do would make it fail. Definitely be interested to hear the cause, if Centurion decides to let me know. Either way, they were totally cool about the refund and it's a great upper.

Next step is to try one of my heavier BCM MK2 buffers, like the T1 or T2 (5.6oz). The recoil with the T0 (3.8oz) was a little snappy as far as getting back on target.

Good to hear.

I bet it will work with the T2 (A5H2) buffer just fine.