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Cracked Bolts, Slides and Receivers

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tenOCEE View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Mar 05 2019 at 10:11am
It would be helpful and simple for spotters to look at this when they encounter a Universal for sale. At shows I see several on tables or being walked around. It takes a few seconds to look at the rail and then the serial. If you can only remember the first 4 digits that work ok for this project.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Mar 17 2019 at 6:38pm
Here's an Underwood posted on another site with the same resulting crack. The description is similar to the account I was told in that the bolt and slide came loose during operation.


Quote I was working on a friends Carbine. He was complaining that the slide and bolt flew out after firing a few rounds. found this. He told me that many years ago the slide and bolt were replaced because the bolt cracked and damaged the slide. This is a paperweight now, right? I guess I'm going to try and help him find another receiver or barreled receiver at this point.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote sleeplessnashadow Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 3:22am
Good find

For the Underwood receiver shown on the link: "the slide and bolt flew out after firing a few rounds ... He told me that many years ago the slide and bolt were replaced because the bolt cracked and damaged the slide."

If this assessment is correct it means the replacement bolt and slide were not what cracked the Underwood receiver.

Setting this assessment aside for the moment this Underwood receiver and the two Universal's shown in this thread show a pattern. That being the location of the crack being consistent with something pushing up or down on the receiver from above or below with the crack happening lengthwise above milled groove also running lengthwise that the slide handle lug moves back and forth in.

The example below obviously isn't cracked and was used as a visual aid only.

The first few images are to show the position of the slide handle lug in relation to the cracks shown in the prior pics.

(To view a larger version click on the image)




















Jim
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tenOCEE View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 8:15am
So there can only be so many things forcing the slide upwards, and the obvious one is the bolt's right lug rotating upward. There are two descriptions of the bolts flying free of the receiver.

So is the bolt being caused to over-rotate out of the receiver (by a force on it) taking the slide with it?
Is the left lug not engaged in the receiver at the time of over-rotation, or is just pulling free as the bolt disengages the receiver (probably)?
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Charles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charles Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 8:33am
I think this is a job for a metallurgist to test the strength of he damaged area and also compare thickness of the receiver around the damaged area with a genuine M1 carbine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 8:41am
That's the thinnest spot by my eye of the receiver. The receiver top plane is angled downward from right to left. The slide tab slot is approaching the downward surface to the same left from below wherein an abrupt 90 degree corner invites a crack to form there. Perhaps starting with a spec measurement of the thin spot? Too brittle of hardness and the metal cracks. Too little and it tears. Too much upward force from the bolt overstresses the slide tab internal corner inviting a crack.

Overcharged round? Firing out of battery? Fatigued/cracked bolt from the previous event distorted the metal?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote A Seabee Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 8:11pm
I posted that over on the CMP forum. My friend is not a collector, just enjoys shooting the carbine. He's had it about 40 years, almost all Underwood parts. Shame that it's junk. He is considering a Fulton Armory barreled receiver at this point. Thank God it didn't blow up in somebody's face.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 8:52pm
@Tenocee. I agree with your scenario. Another contributor could be excessive wear of the slide lug which would allow greater upward movement of the slide, increasing the force of inertia from the rotating bolt. This fits with the description of the bolt flying out of the receiver. The location of the crack is consistent with the location of the slide lug when the bolt completes it's rotation. It would be interesting to see if there is evidence of significant wear on the affected surfaces.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 8:56pm
Maybe A Seabee could get a side on shot, but looking at the surfaces you don't see much wear inside the receiver where the bolt rides. I know the top surface doesn't get a lot of wear, but it seems to be very lightly worn too. Of course poor hardness could result in slide slot wear.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote A Seabee Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 9:00pm
The slide and bolt were replaced years ago. My friend probably never fired it much after that, and I imagine the crack was either caused by that event, or the cause of that event. either way, the original slide and bolt are long gone. the parts that are there now look almost new.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote A Seabee Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 9:01pm
I will take some more pictures when I get back to town, out of town working this week.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 9:36pm
Another source of excessive force being exerted on the bolt/slide is a condition that caused a bolt and gas cylinder failure on my Universal. The surface of the barrel that serves as a stop for the gas piston becomes worn allowing excessive piston travel. Imagine the additional force exerted if the piston is allowed to travel 30% more than intended. This wear is caused by poor hardening of the barrel and/or high round count. Tenocee, did the Universal carbines you reported exhibit this condition?


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Post Options Post Options   Thanks (1) Thanks(1)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: Mar 18 2019 at 10:24pm
Here is a cut receiver to demonstrate just how thin the material is in the area of the crack. Keep in mind this picture is enlarged and the area looks thicker then it really is. Also note how it is midline of the rail. this is where we see the crack on other posted photos.
 
 
 
If a bolt breaks the piece can twist and exert forces in all directions. Lift is most likely what is happening to create the split. Like Tenosee pointed out that the area has a sharp corner to it which is a natural stress riser.
When they would heat treat a receiver they would bring it up to a "Critical" temperature. where the molecules align and the metal actually looses its ability to attract a magnet.
The material is left at temperature to "soak". Thin areas will achieve the critical temperature very fast but thicker areas take more time
Issues you will have is specific properties of the metal composition could cook off on the thinner sections. The thinner the material can over harden. this could make it fracture more easily.\
 
Here is another receiver that was demilled by smashing the rear section of it. the top it is orientated in attempt to show how easy the slide channel web cracked. I had to use a light to get the crack to show.
 
 
look at the same receiver from the bottom. think of how thin this is where the receiver is relieved. (Arrow)
I am unable to measure this area but can say it is clearly thinner then the web at the first picture.
The red line helps show how far it is cracked, but also that it is separated all the way up the bolt lock up area. Thin of how much energy is adsorbed here. Take a look at your receiver to see how little mass there is in this section.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sleeplessnashadow Quote  Post ReplyReply Direct Link To This Post Posted: Mar 19 2019 at 1:14am
This post is in reference the receivers (both the commercial Universal and the GI Underwood) that cracked on top of the right side of the receiver.

Kinda thinking out loud .... the thickness of the receiver was by design and existed/exists on all of the .30 caliber carbines made to specifications. So while it's a weak point if all other parts are to spec the design is a reliable one and the crack shouldn't happen.

The slide handle lug that moves back and forth in that channel below the crack, as well as the channel it moves in, allow for a bit of vertical movement of the lug so it can move back and forth without impediment. Most of us have seen or experienced some slides/receivers have more vertical and/or horizontal movement than others.

While every part on every gun has a lifespan, based on the rarity of the cracks in this particular location I don't think this was something reaching the end of its lifespan. Consistent with the Universal's not having been fired much.

The source of the upward lift that cracked the slide definitely looks like it was the slide handle lug. The question is what gave that lug enough energy to crack the receiver. Realizing it could have been a one time event or unseen or unnoticed damage that occurred over time by an event that was repeated.

The location/position of the right bolt lug in the slide cam cut when the lug passes through the area that was cracked, to me, is like an arrow pointing towards the source of the excessive energy. While it would be great to be able to examine the slides and bolts involved I don't think they were the cause of the excessive energy exerted on the slide handle lug. In part due to the number of bolts and slides involved yet the location of that crack is a rarity. The excessive energy that caused the crack(s) has not been happening consistently enough to point to a flaw in the bolt, slide, and/or receiver. Given the number of carbines built by this design.

So, to the point.

Where the arrows point for the source of the excessive energy is the pressure exerted in the chamber when a round is fired. This source being the primary source of over spec or unrestrained energy that can and has damaged many carbines and other semi-auto rifles. With that energy following the path(es) of least resistance.

One of the reasons I've bored you with this is the experiences I've had when trying to find why a carbine or one of it's parts has taken significant damage during firing.

When something happens that impacts the function of a carbine the normal focus is on repair. The time spent on what went wrong is limited for a variety of understandable reasons. I am not a gunsmith. There are many others with far more experience and knowledge than I have. The same holds true for most of us.

Analyzing what went wrong often requires the carbine as it was immediately after things went wrong. As well as the empty shell casings from the rounds fired and examples of the ammunition that was being used. Especially when the arrows point to the chamber being the source of the problem.

The cracks on these receivers is a rare location but obviously consistent enough that the cause was probably the same for each one. While at the same time not being an issue common enough to effect more carbines.

I'm glad we have this thread as everyone who reads it brings with them the bits and pieces of what they know that can be combined with those from others. Much thanks to tenOCEE for continuing to share his info and pics.

Hopefully one of us or a future visitor will be able to locate one of these carbines that still has the barrel attached to the receiver with all of it's parts when it failed.

Jim
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tenOCEE Quote  Post ReplyReply Direct Link To This Post Posted: Mar 19 2019 at 5:15am
If I find one in the 150 range I'd feel comfortable picking it up. The 350 range asked by the one pictured above in my side by side image is gouging by a poorly motivated individual.

Originally posted by jackp1028 jackp1028 wrote:

Another source of excessive force being exerted on the bolt/slide is a condition that caused a bolt and gas cylinder failure on my Universal. The surface of the barrel that serves as a stop for the gas piston becomes worn allowing excessive piston travel. Imagine the additional force exerted if the piston is allowed to travel 30% more than intended. This wear is caused by poor hardening of the barrel and/or high round count. Tenocee, did the Universal carbines you reported exhibit this condition?

I've only gotten to examine the one I owned and didn't notice that it was worn there. The parts were in excellent condition.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: Mar 19 2019 at 8:58am
I think this was mentioned, but if you see a cracked receiver in this location please take a good look at the small bolt lug locking area of the receiver.

Considering that it is the slide rotating that turns the bolt. If the small lug area had an issue it could prevent the bolt from rotating. The leverage across the beltway be contributing factor to the bolt cracking.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charles Quote  Post ReplyReply Direct Link To This Post Posted: Mar 19 2019 at 9:39am
As I mentioned in a previous post, after a through cleaning the action and before oiling, it seemed the action was locked up. But after oiling, particularly the back of the right lug with grease, the action worked smoothly.
Just my observation . 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RClark9595 Quote  Post ReplyReply Direct Link To This Post Posted: Mar 31 2019 at 10:53am
I'm beginning to think the cause is lack of lube failure, that bolt is forced to rotate violently at that point in an upward direction and the slide is in the perfect location to cause that crack. I think because of the forces involved, there should be a little extra oil added at that point.
These guns are often stored for years, even if it was oiled before it was put away, oil does break down over time
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Post Options Post Options   Thanks (0) Thanks(0)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 7:41pm
Here is a recent auction where there was a catastrophic failure. Can you see it?

The seller stated that the op rod could not come out....

Yet it sold north of $450

Would you think this was salvageable? 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote W5USMC Quote  Post ReplyReply Direct Link To This Post Posted: Dec 03 2019 at 8:01pm
Originally posted by New2brass New2brass wrote:

Would you think this was salvageable? 


The barrel looks like it is shot to me, can't really get a good look at the receiver for damage. Was there any other pictures? May be a really expensive adj rear sight and barrel band. Did SamT buy it?
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