Friday, April 18, 2014

Remington R51: Is it safe?

There are numerous articles and videos out there in which the safety of the R51 is questioned, on the basis of design and/or functioning. Here is one example.

Perceptions are hard to overcome, and there is a lot of misunderstanding about the difference between in battery and locked breech contributing to negative perceptions.

To be clear, when a firearm is in battery, the bolt is fully closed. This usually means the breechblock/bolt is in contact with the breech face, and if a round is in the gun, it is fully chambered and properly headspaced (headspace is the distance measured from the part of the chamber that stops forward motion of the cartridge (the datum reference) to the face of the bolt. This distance is part of the cartridge specification).

The breech is locked when the breech can not be opened or moved by direct pressure from the head of the cartridge case. On most firearms, this is coincident with the firearm being in battery.

What the linked article fails to explain fully is that unlike other systems that lock the breech when in battery—such that in battery and locked breech are almost synonymous, the Pedersen delayed lock only locks the breech when the firearm is out of battery.

The short distance the bolt/breechblock travels between battery and lock imparts the momentum to the slide which is necessary to unlock the bolt once it locks. Firing from an out of battery, fully locked breech position will not cycle the slide. Any thing less than fully locked may or may cycle the slide or may short cycle it.

Every out of battery condition I have seen on my gun is due to the apparent failure to finish ream the chamber to SAMMI specs. This leaves the chamber with no throat and without a throat, there is a lot of ammo that will headspace off the bullet on the lands instead of the case mouth. This creates the out of battery condition.

When the slide is out of battery with the breech locked, it is not possible to cycle the action through pressure on the bolt. It is also almost impossible to detect this condition looking at the ejection port. One must look at the muzzle, (from the side please) to see if and how far the muzzle extends past the slide. It will be flush when fully in battery.

Also note that when the slide is out of battery enough to unlock the bolt, the hammer will not strike the firing pin with enough force to ignite the primer. (I've been trying to make this happen with no success).

I have seen numerous reports involving failures to feed, cycle, eject, etc. and examples of bulged cases and primers. 

The bulged case pictured in the linked article appears to be bulged on one side only. Close inspection of the barrel with a chambered case shows that the rim and extractor groove of the case head extends past the breech face and is unsupported by the chamber walls. This is not a problem because the case head is solid brass.

Fully chambered case


When the case is extracted far enough for the bolt to lock, the exposed portion of the case is still solid brass and the thinner case walls are still supported by the chamber walls. Except for a small spot just above the feed ramp. This is where I believe the bulge is occurring. It is very similar to the infamous Glock bulge in .40 cal Glocks.

Case when out of battery


When a cartridge is headspaced off of the bullet on the lands, the bullet may be tightly engraved on the rifling. This condition causes an unsafe pressure spike when the gun is fired because more pressure than normal is needed to start the bullet in motion. Pressure is exerted in all directions, and will follow the path of least resistance. Until the bullet starts moving, the point of least resistance is the unsupported case wall above the feed ramp. So it bulges. If the bullet fails to move the case will probably rupture, but it would probably take a cartridge loaded seriously out of spec to create this condition and such a cartridge could cause a problem in any gun.

I have yet to see any report of a catastrophic failure such as a ruptured case or pierced primer, which would indicate that the bullet started to move a pressures dropped to safe levels before a rupture occurred.

IMO, (which is worth whatever you think) the gun is safe to fire in and out of battery with commercial ammo and safely loaded hand loads, but until the chamber is cut to SAMMI spec, is not functionally reliable with all ammunition.

No comments: