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Cracked Bolt - something else to look for |
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Marty Black
Moderator Group Editor in Chief Emeritus Joined: Dec 30 2015 Location: Pismo Beach, CA Status: Offline Points: 100336 |
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Posted: Mar 06 2017 at 5:02pm |
We all know that the carbine bolt design is structurally weak in the area between the right lug and the extractor hole. And most of us have heard stories about the right lug breaking off. But although I've been looking at carbines since the 1970s, maybe I've never looked close enough.
I recently sold an N14 bolt on ebay, but it was returned by the buyer, stating that it was cracked below the right lug. I couldn't believe that I hadn't noticed that myself, and when I re-examined the bolt I had my doubts. From a normal hand-to-eye distance, it looked like a scratch to me. But under a magnifying glass, I started to wonder. I removed the extractor, and - using a magnifying glass and a bright light shining up the extractor hole - a crack was easy to see, which extended all the way up the hole! Ouch! Anyhow, something else for us to keep in mind when examining bolts. I never bought any carbines or parts that appeared to be abused, but this one got by me. |
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Marty Black
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sling00
Hard Corps Joined: Apr 21 2016 Location: Tennessee Status: Offline Points: 941 |
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Hard lesson to learn but thanks for sharing. The picture is outstanding considering the magnification and great detail. Are the cracks typically in this area or are there other areas of concern with the other lug or machined areas? I guess a person could resort to dye penetrant testing the bolt if there was much liability as stake. Google provides several sites for the "how-to's" and materials.
Oh, and by the way I finally got all my CCNLs in 3 ring binders. That's soooo much better than thumbing through the stack. A 52 card pickup is one thing but a 3000 page pick-up and re-sort would be a disaster.
Thanks again |
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Charles
Grunt Joined: Mar 21 2016 Location: Maryland Status: Offline Points: 587 |
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I guess we shooters will be pulling the bolts out for inspection before our next trip to the range. Many thanks for your post.
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Charles
Co B 1st Batl.115 Inf. Reg. 29th. Divi. 4.2 Heavy Mortar Co Retired Life member NRA |
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Marty Black
Moderator Group Editor in Chief Emeritus Joined: Dec 30 2015 Location: Pismo Beach, CA Status: Offline Points: 100336 |
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To answer Sling's question, I'm no metallurgist nor a gunsmith, but everything I've read points to the area shown in the photo I posted: the rear of the right lug toward the extractor hole. I am still surprised at how small that crack is. When viewed in normal light at a "normal" hand-to-eye distance, it looks like a mere scratch.
The left lug and other parts of the bolt are not under stress. The "violence" of the carbine's action falls squarely on the right lug. In Carbine Club Newsletter 370, Brian Quick points out a small change that was made in the design of the round bolt in late 1944, that was made to relieve stress if the bolt initially hangs up against the edge of the receiver (upon firing) before the slide rotates it clear and takes it rearward. That impact/stress would occur at the rear of the right lug, where the crack originated in the N14 bolt photographed. (Sure wish I could remember who I got that bolt from, decades ago!) War Baby! p86 shows an early Inland bolt that broke at the right lug. Page 88 compares this early bolt with the improved bolt which incorporated a "strengthening web" to reinforce the weak area. This change was made at about the time that mass production started at Inland in May 1942. While we are on the subject, the extractor is extremely weak. Shooters should regularly clean behind the "claw" of the extractor with a GI toothbrush or a toothpick, or other means...(Or take the bolt apart to clean it, but that's not really necessary). Unburnt powder, oil, grease, and other firing residue gunk will build up behind the claw, and eventually limit the movement of the extractor. This stress will eventually break the extractor at the stem, or at the edge of the claw (what I call "the fingernail"). Examine an extractor and note how small, thin, and fragile that "fingernail" surface is. The "fingernail" is what grips the cannelure of the cartridge case to extract it after firing. If the extractor is not rotating about its stem because of gunk buildup, the stress will be placed on that "fingernail" and on the top of the stem, and one of them is gonna break. Thankfully, extractors are still cheap and easily available, and this failure is not dangerous like a bolt failure....but I've seen two guys at carbine matches take a piece of extractor shrapnel to the forehead when it came apart. Be good to your bolt, keep it clean, and enjoy firing your carbine! Regards, Marty Black |
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Marty Black
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Marty Black
Moderator Group Editor in Chief Emeritus Joined: Dec 30 2015 Location: Pismo Beach, CA Status: Offline Points: 100336 |
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One more thing...Why is it that I always think of one more thing AFTER I hit the Post Reply button?!
Anyhow, on the subject of the carbine's weak extractor, I'd recommend you never use that Wolf (or anyone else's) steel-cased ammunition in a carbine. That thin fragile extractor "fingernail" can barely handle the common soft brass cases....Don't abuse your extractor by battering it against a steel case. I remember, when Wolf ammo first came on the market 15-20 years ago, it enjoyed great popularity because it was so much cheaper than other ammo. But AR-15 shooters had trouble with those steel cases also. Not worth the savings in cost, in my opinion. For what it's worth...MB |
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Marty Black
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floydthecat
Hard Corps Joined: Oct 13 2016 Location: Mississippi Status: Offline Points: 1996 |
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The gook under the "fingernail" can foul it bad enough to start having extraction problems. I routinely rake under the lip with a dental-pick and remove any built-up deposits. There really isn't much room under there to become fouled. When I first disassembled one, I wondered how-in-the-world did it work...but it does. The first time I had extraction issues, I thought the lip was broken-off, but discovered it was completely plugged with deposits.
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NewScotlander
Grunt Advanced Collector Joined: Jan 02 2016 Location: New York Status: Offline Points: 682 |
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IMO if you are shooting your carbine on a regular basis, you should update the slide to the 7160091 configuration (increased dwell). Refer to CCNL 363, pages 4-6. The increased dwell delayed the opening of the bolt until chamber pressure had been reduced somewhat. The lower chamber pressure reduced stress on the right bolt lug.
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gene of oregon
Grunt Joined: Jan 23 2016 Location: silverton, or Status: Offline Points: 157 |
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Very good info. here. I try to remember to exchange the flat bolt with a round when out plunking. I'll have to pick up that slide also and have both in the shooting bag. Thanks
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The flag does not fly because of the wind that blows it. The flag flies because each soldier's last breath blows by it!
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Marty Black
Moderator Group Editor in Chief Emeritus Joined: Dec 30 2015 Location: Pismo Beach, CA Status: Offline Points: 100336 |
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Good stuff, guys....thanks for your responses. Good point on the late-type slide, NewScotlander.
Yeah, Floyd - if a shooter finds that his spent casing is not being extracted, it could be a dirty rusty chamber...but the smarter bet is either the "fingernail" has been chipped or broken off, or there is too much gunk under the extractor. That's been my experience at CMP Clinics and Carbine Matches. The military has always been big on scrubbing out the chamber area with a brush, and I still do that as a matter of habit, but in my experience, the carbine's chamber stays quite clean without any extra effort. After all, with the "straight case" of a carbine cartridge, you clean the chamber every time you push a cleaning rod and patch all the way thru the barrel. Also, I've found that the sharpness of the "fingernail" design tends to make tiny brass shavings from the case, which usually get stuck on the bolt face, in the "magazine area" of the receiver, and under the extractor. In my experience, that Aguila Mexican ammo is dirtier than other brands, and tends to build up that gunk quite quickly. When CMP stopped issuing GI Lake City ammo for the Camp Perry Carbine Match, and switched to Aguila, I couldn't believe how dirty my carbine was, after only 50 rounds. For a year or two afterwards, CMP continued to issue Aguila, and we were all required to use it....but I didn't. I brought my own GI Lake City ammo, loading my mags in secrecy, and gave away my issued box of Aguila. (Please don't tell anyone!) Then, in a cost-cutting measure, CMP stopped issuing ammo for the matches altogether. Now, it's strictly BYOA. But I digress... Enjoy! MB |
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Marty Black
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SWANEEDMB
On Point Joined: Jul 31 2016 Location: Iowa Status: Offline Points: 119 |
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Would be nice to know how the buyer found the crack, we have been doing some real 'bolt' looking at. Not to hi-jack this thread but looking at some bolts found one marked 'AOB' on right lug, 'H' on left lug, is a round bolt, bolt has an 'X' on top. ?
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Marty Black
Moderator Group Editor in Chief Emeritus Joined: Dec 30 2015 Location: Pismo Beach, CA Status: Offline Points: 100336 |
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Swanee, that's an IBM bolt, made by Auto Ordnance. Most AOB round bolts have that H on the left lug, meaning unknown. The X on top of some IBM and Quality Hardware bolts: A Chief of Ordnance memo, dated 4 Sep 1944, indicated that "bolts C57148 produced with round body (lightening cut omitted), but not including (all 5 other) revisions that were to be incorporated simultaneously, were authorized acceptable and are identified by letter X stamped on top approximately 1/2" to rear from lug."
The 6 total changes made in the "new" bolt design are listed in NL 370-6, and were standardized in November 1943. See Newsletters 329 (IBM, Chris Albright) and 370 (Round bolt, Brian Quick). Regards, MB |
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Marty Black
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m1a1fan
Hard Corps Got Para? Joined: Jan 01 2016 Location: Virginia Status: Offline Points: 1736 |
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Hands free googles come in handy especially if one shoots their carbines. Nothing better than hands free vs. struggling with a loop:
https://www.amazon.com/SE-MH1047L-Illuminated-Multi-Power-Magnifier/dp/B003UCODIA/ref=pd_lpo_60_bs_t_2/167-4478712-8569040?_encoding=UTF8&psc=1&refRID=N521N079DF7FVTFKPY9K |
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SWANEEDMB
On Point Joined: Jul 31 2016 Location: Iowa Status: Offline Points: 119 |
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Thanks Marty for your reply on my bolt, didn't want to hi-jack thread but we are unable to start a new one, maybe because pic's we tried to post at one time were to big, don't know who or how to rectifie, we do have a 'bring back' IBM and would like to share. Thanks
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