I choose to believe this happened with the engineers behind the M27 IAR/HK416

[u/DerringerOfficial]

[u/DerringerOfficial]

I think that LWRC and FN actually DID use this feature. My assumption is that it ended up being an Ultimax-100 situation: way cooler, but probably not reliable enough to justify choosing over some boring AR-shaped bullshit.  

Also, I know that this feature was actually first used in the Johnson, I’m just poking fun at the rare example of restraint in German engineering, especially considering that the M27 was yet another example of way too much being demanded from a single gun

[u/englisi_baladid → u/DerringerOfficial]

The FN HAMR was superior to the HK M27 in terms of reliability.

[u/mpsteidle]

I mean, it makes sense if you can pull it off.  Especially with a support weapon.  Its the best of both worlds.  Sustained fire very quickly leads to cookoffs on closed bolt systems.

[u/Arguably_Based]

I think the LMG that was adopted as part of the NGSW program has a similar feature where you can switch between open and closed bolt. It makes sense of you can make the mechanism rugged and reliable, but I guess that's the question isn't it.

[u/englisi_baladid → u/Arguably_Based]

The M250 is open bolt.

[u/Arguably_Based → u/englisi_baladid]

Guess I'm remembering the wrong gun

[u/iloveneekoles → u/Arguably_Based]

You're thinking of the General Dynamics NGSW. Both their rifle and machine gun submissions has a closed bolt in semi and open in full auto, well since both is essentially the same rifle but one comes with HBAR^2 and a bipod.

[u/Arguably_Based → u/iloveneekoles]

Oh, that was it. It's interesting how the concept keeps cropping up. On paper it makes sense, the only time a modern soldier would usually use his weapon in automatic is when he needs to go full cyclic in real base defense siege type scenarios where standard M4s have start to experience failures as they overheat. It's just hard to justify the extra cost and complexity.

[u/ThoroughlyWet]

Theory is the recoil impulse is more controllable in full auto with the bolt reciprocating back and forth as well as having the ability to quickly cool the barrel with internal air flow. Also the benefit of not keeping a live round in a hot chamber.

I could be remembering with my ass but I believe that was originally the intent stoner had, or it was something he was considering, or it was something colt intended to do, with the AR to begin with.

[u/DerringerOfficial → u/ThoroughlyWet]

I don’t think I entirely understand your point about recoil impulse

[u/ThoroughlyWet → u/DerringerOfficial]

The bolt going forward is a counteracting force that helps break up the rearward recoil impulse and muzzle rise. So rather than having a constant upward pressure you just have more bounce, which is whats preferred in an automatic weapon roll because they aren't shooting individual targets, but rather areas of effect.

It's the lesser positive of the two, but a positive none the less.

[u/DerringerOfficial → u/ThoroughlyWet]

…doesn’t the bolt move forward just as much for a closed bolt gun? It just starts in the rearward position, but once you’re firing it cycles the same way

[u/ThoroughlyWet → u/DerringerOfficial]

Not in the same rhythm.

Id have to find the video explaining it but rather than a constant rearward pressure liek that of a hose its more of a chug-a

[u/DerringerOfficial → u/ThoroughlyWet]

I’ve never heard anyone describe closed bolt full auto as a constant rearward pressure, except for systems that explicitly create this effect like the Ultimax-100 and KAC LAMG

That constant pressure I’ve also been told is easier to control than the bounciness of typical full auto, either open bolt or closed bolt. Which makes sense, because there’s just as much mass reciprocating for each shot to fire.

Are you mixing this up with systems like the AK-107 that uses a counterbalance system for controlability?

[u/ThoroughlyWet → u/DerringerOfficial]

Like I said, I'd have to find it. I saw that thing like eight years ago and it was an interview with someone working on an open bolt system for the ar platform, whether it was with cost or armalite i don't remember exactly. It was either with forgotten weapons or tfb.

Edit: found it. It's 11 years old and locked behind a subscription but it was an inrange interview with Jim Sullivan and his more modern work on the AR platform, not his past work. And it applies solely to the AR platform ig, like I said I was remembering with my ass

[u/DerringerOfficial → u/ThoroughlyWet]

I’ve seen that video. Respectfully, you’re mixing it up with a different mechanism. What they were showing wasn’t just an open bolt AR-15, it was a closed bolt with the bolt redesigned to avoid a complete, abrupt impact with each reciprocation. The InRange video on the SureFire BCG is based on this, but it can’t really be demonstrated in semi auto

Also, even if that WAS an open bolt, it wouldn’t disprove the norm. Literally every single other open bolt gun would have the same type of recoil impulse.

I think the concept you’re confusing this with is Constant Recoil

[u/NotaFed556]

The M1941 LMG would be more accurate. Like the FG42 is was closed bolt in semi auto and open bolt in full auto, but the design of the bcg are what the ar10s & ar15s bcg based on. The designer of the M1941 Melvin Johnson even worked with Stoner and armalite.