A couple of questions about OOB,s

[des547]

What in the heck can cause an out of barrel cartridge ignition ?

Why would any rifle manufacturer allow a gun design to be marketed if this malfunction was even remotely possible ?

I've owned dozens of semi auto .22 rifles and handguns over the years and all of them have functioned like they were intended to without all these FTE's, FTF and certainly an out of barrel ignition !!

My AR15-22 is waiting for me to return from vacation to fire its first rounds. Maybe I should clamp it in a bench vise and attach a long string !!!

Des

 

[BELT_FED]

if you shoot enough it will happen.. granted these guns are more prone to do it than most.. but ive had a ruger 10/22 blow the mag out of it and set my jacket on fire.. and ive had a 1919 beltfed gun blow a top cover off just to name a couple.. oobs happen when the bolt picks up a live round and loads it mst of the way into the chamber still leaving a small gap the brass case can not take the chamber pressure unless its completely in the chamber... the hammer strikes firing the round that is almost chambered and the case ruptures... using hot ammo and a clean gun r great ways to avoid this because hot ammo slings the bolt to the rear harder in return i bounces and slams shut harder clean guns mean that the bolt doesnt have to over come the grit and the same thing happens.. i hope this helps

 

[chuck s]

The M16/AR15 fire control parts acerbate the problem as the trigger will release the hammer long before the bolt is in battery. This is not a problem with the parent rifle as the firing pin can't reach the primer until the bolt has rotated behind the locking lugs and consequently retracted into the bolt carrier. You can verify this at your desk with the bolt carrier group in your hand.

With the M&P15-22, however, the cartridge is held tightly against the bolt face during feeding and the bolt does not lock to the receiver. At any point the hammer can strike the firing pin it will smack the primer. If it's only partially in the chamber neither the firing pin nor primer care, they just do their jobs and detonate.

Grab your M&P15-22, clear it, and ease the bolt forward about half way. Pull the trigger and the hammer will fall. Won't hit the firing pin until it's almost closed. The almost is the critical issue. Experiments (here) using a dime or two as a spacer and an empty case as a test cartridge show the firing pin will smack the primer about "one or two dimes" out of battery. That's enough gap for the gas pressure to blow out the back of the chamber or rupture the case. Extractor exit is a common result.

Next time you load your M&P15-22 ease the bolt forward and observe how it feeds. Note the cartridge is held tightly to the face of the bolt the entire feed process. Don't be stupid and pull the trigger to confirm the tests with the empty case.

Aggressive polishing of the chamber may help. I've not had an out of battery firing since doing this. Chamber has gotta be clean -- that's a given.

-- Chuck

 

[des547]

Thanks guys for the information. In the Smith ads for this rifle it says it has a target grade barrel and tight chambers generally go along with that type of barrel. I can see where clean would be the name of the game in helping to prevent this problem.

My first job when I get home is to clean the thing and give a close inspection to the face of the barrel and the chamber. A very slight chamfer to the outer edge of the chamber may be called for as a sharp edge can grab the side of the case sometimes. I have a neat way to polish the chamber if that is required. All of these things should have been done at the factory but that all takes hours and hours means the gun would cost more.

Des