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Posted: 3/10/2007 12:27:46 PM EDT
| Did the original MP5's bolt lock back after the last round? And also I heard someone say that the new clones do not have the bolt delay mechanism anymore built into the bolt assembly. So is that true? Thanks |
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The original 9mm guns had no hold-open provision, that came with the introduction of the .40/10mm guns. The H&K roller locked mechanism is just that -- a locking mechanism. It is NOT a delayed blowback mechanism in the usual sense. The key which is most often misunderstood is the fact that unlocking of this "mechanism" occurs as a result of a rapid DECREASE in pressure against the boltface. The bolt does NOT unlock as a result of an INCREASE in pressure against the boltface, which is how a true blowback action works. |
Methinks you have this quite backwards, unless the 9mm guns are different from the larger ones. How does a drop in pressure cause something to move? The chamber pressure is exactly what pushes the bolt back. However, the timing of the mechanism is such that the actual opening happens after the peak chamber pressure has dropped. |
IIRQ, the fired round (barrel pressure) pushes against the bolt face, which puts pressure against the rollers rearward, which translates to the rollers forcing the lock backwards, and since the wedge shape lock is fixed to the carrier, push back on the carrier (increasing the B/C gap) until the time comes that the carrier is moved back far enough for the bolt/roller to clear the trunion, and the B/C moves reward in cycle. As for the bolt being locked, not in the sense of a lugged system, but that the back of the bolt is holding the live case tight against the chamber shoulders, and the rollers are just wedged into the trunion slots via the wedged lock. Simply, instead of the B/C being much heaver or the recoil spring being much stronger, the roller system plays out as a way of adding the needed mass/tension to the blow back system, and the system of the action is delayed/corrected via the roller wedging system to put the action into tune. As for the fluted chamber, Since the action is a blow back in design (delayed in the nature of not just B/C mass and spring tension alone, but the roller/lock wedging release as well) with the chamber/barrel bore still under high pressure during spent case extractions, the flutes in the chamber serve to release the pressure bound case from the chamber wall (gases flowing between the chamber wall and spent case) so the case can be extracted by the bolt. |
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