Range report, explosion!!!

Post by **Pirate** » Sat Sep 17, 2005 6:25 pm

Needless to say being a gun test dummy is getting very exciting! I took the gun to
the range today with a new cocking stud welded on and proceeded to do some testing.
I loaded a starter tab with 2 rounds, the first round failed to fire, it had a nice impression
from the firing pin but didn't go off. the second round fired and ejected. the primer looked good.
A nice dimple with only slight signs of extrusion around the firing pin hole. I loaded another
2 round belt and fired the first round, it fired and ejected, when I fired the third round
there was an explosion the gun shuddered and some smoke came out of the receiver. I was wearing heavy welding
gloves and felt the concussion on my hand. I opened the top cover and the bolt was open about 3/4 of the way
and the blown case was stuck in the bolt, with part of the case wrapped around the bottom. I removed the bbl
and saw the front of the case in the chamber. the bullet left the bbl. I removed the bolt
and saw the firing pin sticking out about 1/4", way to far. after disassembling the bolt
I saw the pin was bent and wedged into the bolt. I had to drive it out with a punch.
I am not totally sure what happened at this point, obviously the bolt was not fully closed or locked.
the gun needs to be torn down and all parts thouroughly inspected before further testing can resume.

Post by **TOM R** » Sat Sep 17, 2005 7:01 pm

holy cow , got all your fingers and toes?

Post by **Pirate** » Sat Sep 17, 2005 7:45 pm

Official gun test dummy uniform includes:
heavy leather glcves
safety glasses
face shield
leather boots

any questions?

Post by **panaceabeachbum** » Sat Sep 17, 2005 7:55 pm

wow great to hear your ok , did the pin get shoved thru the bolt enough to do any damage to the bolt?

Post by **TOM R** » Sat Sep 17, 2005 7:57 pm

Pirate wrote:Official gun test dummy uniform includes:
heavy leather glcves
safety glasses
face shield
leather boots

any questions?

tink it should also include a set of weldin leathers with the leather apron attached

Post by **salt6** » Sat Sep 17, 2005 8:35 pm

Looks like it fired out of battery.

Post by **Blanksguy** » Sat Sep 17, 2005 8:37 pm

Pirate,

Has anyone looked at using the rear of the "wedge" as a stop/safety to where the firing-pin cannot hit the primers if the "wedge" has not fully seated the bolt-locking-rollers? Possibly a hole for the firing-pin all the way through....and a step inside for the FP-spring.....the shoulder of the firing-pin stopping on the rear of the "wedge" to where it will not protrude enough to fire the primer unless the "wedge" is fully forward and only protrude enough to hit the primer once the wedge has moved the rollers into the locked position.

Does anyone have access to one of BRP's SA bolt-Groups and their Trigger-Group.....might be better to post some clear digital photos with measurements of what BRP is using (if possible) instead of "re-inventing-the-wheel"?

Just a question at this point as the photos appear to show "early-unlocking" of an MG42....but with a semi-only (SA) MG42 it looks as if the firing-pin could still reach the primer with the system not fully locked.

Be safe, RichardS.
PS: Glad to hear no one was hurt.

Post by **Pirate** » Sat Sep 17, 2005 9:08 pm

Blanks guy,
That is exactly how mine is setup. the wedge is drilled through, the fp is stepped to
prevent excess protrusion. there is a forward spring to prevent slam fire and one in
the back to keep it centered. I think the bolt was not fully closed / locked. I marked the
bolt & receiver to make sure it is fully closed, but haven't had that problem for a while and
didn't check on this shot

Karbinator · Post by **Karbinator** » Sat Sep 17, 2005 10:36 pm

Partial chambered round / out of battery.

how bout a bounce spring now pirate?

Post by **Pirate** » Sat Sep 17, 2005 11:15 pm

Karbinator wrote:Partial chambered round / out of battery.

how bout a bounce spring now pirate?

anti bounce doesn't prevent an out of battery problem like this.

Karbinator · Post by **Karbinator** » Sat Sep 17, 2005 11:22 pm

Pirate wrote:
Karbinator wrote:Partial chambered round / out of battery.

how bout a bounce spring now pirate?
anti bounce doesn't prevent an out of battery problem like this.

What do you think the spring is for?

smoggle · Post by **smoggle** » Sun Sep 18, 2005 12:57 am

Did you have an "out of battery" explosion in your shorts? Probably would have if I did it.

Karbinator · Post by **Karbinator** » Sun Sep 18, 2005 10:45 am

In Myrvang's Univ.Mach.Gn book on page 159 under Tackling the "Bolt Bounce" problem :

....the troops experienced a lot of trouble with the phenomenon Known as "bolt bounce", wherein
the Mg42 would fire while the mechanism was not completely locked".
....""Bolt bounce" occurs to some extent on any open-bolt firing Mchngun when the bolt flies forward
to fire the round as soon as it chambers, But the bolt, rebounding from it's initial contact with the
barrel breech, bounces in and out of its locking recess before it settles. Problems arise if the cartridge
is fired before the bolt has settled"

"To solve the problems related to the bolt bounce (and delayed detonation of primers, which is listed as the
main probable cause),3 possible actions were listed:
1.shorten headspace by 0.2mm to wedge the cartridge tighter
2.Introduce a strong spring with plunger to be mounted inside the bolt carrer to stop the bolt locking wedge
from bouncing back
3.introduce a bolt locking wedged..which the company had created..designed to take up the slack in the bolt head
......have to be individually fitted to each bolt

pg162...
"Given normal detonation in the cartridge, this cycle should be uninterupted. however, during the fully locked portion
of this cycle, the safety margin for the bolt rollers in the barrel locking piece allows only 1 to 1.5mm of bounce. This
is incorporated in the design, but when irregularities occur and the bolt rollers bounce more than allowed for in the
saftey margin, the pressure inside the cartridge case will start to work on the bolt face and the bolt rollers will start
to move inward, away from their locked position. In other words, the farther the bolt rollers bounce, the worse the results.
..italics above are mine to note that the NEW Irregularites are from the SEMI design ie..

So the argument for not having the spring in semi is the bolt has enough time to settle (since fire
rate is single shots)??

Karbinator · Post by **Karbinator** » Sun Sep 18, 2005 12:32 pm

pg 163-165

An interseting observation was made on a shadowgraph of a virtually immediate detonation of
a cartridge....which caused an unusually fast acceleration of the pressure in the locking area,
which in turn threw the bolt locking wedge rearward(italics mine). THe backup device (spring)
caught the bolt locking wedge, and the bolt rollers remained well withing the 1-1.5mm safety margin....

When measuring the empty cartridge cases from the shooting trials with the bolt catch, it
found that only 10% of them had shoulder deformations..... and the Mg functioned perfectly
during the 2,000 rounds fired.

Karbinator · Post by **Karbinator** » Sun Sep 18, 2005 9:30 pm

2 weeks ago...
This one blew the barrel outwards--bending the gate.
Everything you see here stayed in the gun...jamming up the next
round from being fired. The Center piece (missing) from the cartridge pounded
into my shoe.

[/img]

Post by **panaceabeachbum** » Mon Sep 19, 2005 11:04 am

Gonna post my .02 cause I aint had a kick in the nadsack in a day or two, . I agree as well as most of the guys on weaponeer with Karb that the bounce spring does aid in keeping the locking piece wedged against the roller. Dont think so then just compare how easily the rollers move in and out of the locking position when the spring assembly is out. Dont think there is a fair amount of resistance then put the spring assembly back in and again try to reposition the roller with your fingers. Like other safety features we can include why leave it out?? hell at worst it increases bolt mass which we know to be good. There is a good post at weaponeer detailing how someonelse built a new spring guide to center around firing pin. Some will lead, some will follow, and a few will loose a finger or two , good thing you had on gloves I usally test with a car tire cradle and a piece of string, ground mount will be used on this project.

Pirate in looking over your build pics, wonderful I cant thank you enough, I notice that the hammer is heavily radiused to clear the bottom of the bolt. As the back of your firing pin is unsupported it will have to be hit VERY sqaure so as not to bend. I notice the pin bent instead of breaking so I bet this is key to your problem . Just my opinion but I think the round faced hammer is striking the unhardened and unsopported pin off the centerline plane bending it upward causing it to bind after the first few wacks of the hammer. At this point it only has to be slightly off center/bent to contact the buffer screw outside the clearance hole and in turn getting shoved way far forward upon recoil. I know this doesnt totaly explain why it fired out of battery(although protruding firing pin would) but maybe it helps. One of my guys is in the shop now machining a bolt extension from solid that will have a removable guide bushing to support the rear of the pin. I will probably just machine a new heavy carrier as i am not real keen on welding the extension on. If it works out and we get enough intrest I will run a couple of dozen from 4130 and send them to harden. Best of luck and buy some string. RichardT

Post by **Pirate** » Mon Sep 19, 2005 3:32 pm

The hammer I am using is not the one in the photo. the one currently in the gun is
ground so that it hits the fp squarely. the pin bent because the bolt slammed into the hammer, it hit it so hard it drove it out the front of the bolt till it got stopped on one
of the shoulders.
In addition, the firing pin is not long enough to hit the buffer screw. the buffer I have is recessed, and the pin doesn't reach the bolt to hit it.

Post by **Pirate** » Mon Sep 19, 2005 5:37 pm

Hi Karbinator, was that a .308? how many rounds have you had blow like that?
was the cartridge chambered fully or was the bolt partially open?

Post by **panaceabeachbum** » Mon Sep 19, 2005 11:46 pm

Pirate wrote:The hammer I am using is not the one in the photo. the one currently in the gun is
ground so that it hits the fp squarely. the pin bent because the bolt slammed into the hammer, it hit it so hard it drove it out the front of the bolt till it got stopped on one
of the shoulders.
In addition, the firing pin is not long enough to hit the buffer screw. the buffer I have is recessed, and the pin doesn't reach the bolt to hit it.

Hi just trying to help,

I am unclear on the bolt slamming into the hammer statement, doesnt it do this as normal course during firing and recocking, mine do. Must be one hell of a hammer spring if it will bend a firing pin before reckocking the hammer

I wonder if your firing pin just doesnt hit the buffer under hand pressure but still hits it during recoil? the buffers in my guns all have springs requiring hundreds of pound of force to compress so there would be no way of knowing for sure since you cant budge it by hand to check.
Just because the screw appears recessed does not mean it will stay that way when the bolt compresses the buffer spring at a few hundred miles an hour. All the buffers appear to have a recessed screw, that distance is the distance the spring will travel before the carrier bottoms on the screw. If the bolt carrier is stock length and your not bottiming on the recoil spring, ie you cut it after installing carrier extension then the buffer bolt is the only staitionery object that halts rearward travel of the carrier after the buffer spring is compressed. That screw is the final stop. If the pin sticks out ANY at all and your spring is cut to the proper length so as not to be fully compressed by the extension then the pin will hit the buffer screw , especialy when it goes off unlocked. I know your firing pin has to stick out of the back of the carrier some or the hammer couldnt hit it, do you have the relief hole drilled in the buffer screw? If you dont have this relief and the firing pins sticks out (as it has to) there will be an unwanted collision. Maybe this isnt your problem , but I bet its what shoved that pin thru the bolt, just trying to offer an alternate view point in hopes of helping. Please keep us posted.

Post by **Pirate** » Tue Sep 20, 2005 9:16 pm

The bolt was not locked / fully closed when the round fired, the bolt came back at mach5,
not a normal condition, sort of like .308 blow back operated!
during normal operation it doesn't hit.
This build violates my first rule of building, ALWAYS start with NEW or LIKE NEW parts.
This is the first time I have broken this rule and it has led to problems. the kit I have is a whole gun
but not from one whole gun. there is a mix of new used and heavily used stuff and not really the
kind of parts to start a build like this. I am more than likely going to try to get another
kit in better condition with all the same vintage parts. up to this point it is an R&D project and
when I have it working to my satisfaction will modify a better set of internals.I apriciate input from
members, however sometimes others do not understand what the problem is or exactly how it
occured. and feel rebuffed when thier advice is not taken, even if it is not pertinent.
This is a forum for BUILDERS, no politics or other bs here, and the forum revolves around input
from the members. We need to keep Ideas flowing here.