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USA
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Posted: 5/15/2024 4:02:15 PM EDT
What options are there if your barrel/bolt have too small of a headspace and you have failure to extract issues?
Try to ream it out? Use some sandpaper to wear down the throat? |
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Posted: 5/15/2024 5:13:39 PM EDT
[Last Edit: j3_]
[#1]
Speaking of AR type rifle I would not expect failure to extract from inadequate headspace. Instead, I would expect the bolt to not fully close and the firing pin does not reach the primer causing failure to fire problems and along with that hard to hand extract unfired chambered or partially chambered rounds. But that is just me.
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Posted: 5/15/2024 5:14:16 PM EDT
[Last Edit: CATM]
[#2]
Are you certain the ammo isn't the issue? Try a couple different bolts before you attempt to ream the chamber. If it's a chrome or nitrided barrel, I would find another barrel and bolt combination that gives an acceptable headspace dimension. EDIT: what does a go, no-go and field gauge show? You're saying this combination of bolt and barrel will not lock on a "Go" dimension gauge?
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USA
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Posted: 5/15/2024 8:17:23 PM EDT
[#3]
Quote HistoryOriginally Posted By CATM: Are you certain the ammo isn't the issue? Try a couple different bolts before you attempt to ream the chamber. If it's a chrome or nitrided barrel, I would find another barrel and bolt combination that gives an acceptable headspace dimension. EDIT: what does a go, no-go and field gauge show? You're saying this combination of bolt and barrel will not lock on a "Go" dimension gauge? No go is good. I cheaped out and didn't get the go, I'm seeing that was a mistake. I just used a loaded round thinking "good enough". I'll try some different ammo and see if that helps. And ya it's a nitride barrel. I do have a spare bolt I'll try also that I forgot I had. |
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Posted: 5/15/2024 9:03:41 PM EDT
[#4]
If it's closing on ammo and you are firing it, then it has enough headspace. Now it may have tight headspace, but that's another issue. What makes you think you extraction issue has to do with headspace?
Also more details would be helpful. |
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MN, USA
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Posted: 5/16/2024 1:06:55 AM EDT
[#5]
Quote HistoryOriginally Posted By bpm990d: If it's closing on ammo and you are firing it, then it has enough headspace. Now it may have tight headspace, but that's another issue. What makes you think you extraction issue has to do with headspace? Also more details would be helpful. This ^^^ Been preaching it for years. Also, in agreement that we need more info. |
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AZ, USA
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Posted: 5/16/2024 4:03:36 PM EDT
[#6]
Quote HistoryOriginally Posted By j3_: Speaking of AR type rifle I would not expect failure to extract from inadequate headspace. Instead, I would expect the bolt to not fully close and the firing pin does not reach the primer causing failure to fire problems and along with that hard to hand extract unfired chambered or partially rounds. But that is just me. The AR, like many military weapons, uses a concept called "crush-up" - the longest allowable case is somewhat longer than the shortest allowable chamber. I don't remember exactly what this figure is, but I want to say it's like .003". I'll have to check my notes when I get home. Steel cases might present a problem in this regard. |
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AZ, USA
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Posted: 5/16/2024 4:11:54 PM EDT
[#7]
Originally Posted By CPT_CAVEMAN: What options are there if your barrel/bolt have too small of a headspace and you have failure to extract issues? Try to ream it out? Use some sandpaper to wear down the throat? What kind of ammo are you shooting? |
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NC, USA
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Posted: 5/16/2024 6:26:30 PM EDT
[Last Edit: lysanderxiii]
[#8]
Quote HistoryOriginally Posted By brownbomber: The AR, like many military weapons, uses a concept called "crush-up" - the longest allowable case is somewhat longer than the shortest allowable chamber. I don't remember exactly what this figure is, but I want to say it's like .003". I'll have to check my notes when I get home. Steel cases might present a problem in this regard. SAAMI specifications for the maximum cartridge case give the headspace as 1.4666". SAAMI specifications for the minimum chamber give the headspace as 1.4636". That gives a maximum crush up of 0.0030". SAAMI allows a crush as well. Military maximum case length is 1.4667" M16 minimum chamber is 1.4646", 0.0021" crush. M249 minimum chamber is 1.4611". 0.0056" crush. |
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Posted: 5/16/2024 8:03:16 PM EDT
[Last Edit: j3_]
[#9]
Quote HistoryOriginally Posted By brownbomber: The AR, like many military weapons, uses a concept called "crush-up" - the longest allowable case is somewhat longer than the shortest allowable chamber. I don't remember exactly what this figure is, but I want to say it's like .003". I'll have to check my notes when I get home. Steel cases might present a problem in this regard. I have never ran into commercial ammo that I have purchased that the case was sized to cause a crush even if drawings, Saami, or govt. specs allowed it. I based my response on my own experiences only which has worked very well for me. If there is fault in it based on equal real world experiences that are different than mine I would consider those for my own use based on their value. Post up a manufacturer making cases or ammunition sized to utilize any allowed crush for an AR!5 if someone knows of one. At most wouldn't that crush scenario only apply to trying to extract an unfired round? |
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MN, USA
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Posted: 5/16/2024 10:39:45 PM EDT
[#10]
Quote HistoryOriginally Posted By j3_: I have never ran into commercial ammo that I have purchased that the case was sized to cause a crush even if drawings, Saami, or govt. specs allowed it. I based my response on my own experiences only which has worked very well for me. If there is fault in it based on equal real world experiences that are different than mine I would consider those for my own use based on their value. Post up a manufacturer making cases or ammunition sized to utilize any allowed crush for an AR!5 if someone knows of one. At most wouldn't that crush scenario only apply to trying to extract an unfired round? I'm fairly certain that no man'f are incorporating "crush" into their ammo specs. Folks are shooting that stuff in firearms other than AR's. Headspace will have little to no effect on extraction/ejection, IMO. Once it goes bang, everything changes. |
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AZ, USA
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Posted: 5/17/2024 11:13:14 AM EDT
[#11]
Quote HistoryOriginally Posted By lysanderxiii: SAAMI specifications for the maximum cartridge case give the headspace as 1.4666". SAAMI specifications for the minimum chamber give the headspace as 1.4636". That gives a maximum crush up of 0.0030". SAAMI allows a crush as well. Military maximum case length is 1.4667" M16 minimum chamber is 1.4646", 0.0021" crush. M249 minimum chamber is 1.4611". 0.0056" crush. Quote HistoryOriginally Posted By lysanderxiii: Originally Posted By brownbomber: The AR, like many military weapons, uses a concept called "crush-up" - the longest allowable case is somewhat longer than the shortest allowable chamber. I don't remember exactly what this figure is, but I want to say it's like .003". I'll have to check my notes when I get home. Steel cases might present a problem in this regard. SAAMI specifications for the maximum cartridge case give the headspace as 1.4666". SAAMI specifications for the minimum chamber give the headspace as 1.4636". That gives a maximum crush up of 0.0030". SAAMI allows a crush as well. Military maximum case length is 1.4667" M16 minimum chamber is 1.4646", 0.0021" crush. M249 minimum chamber is 1.4611". 0.0056" crush. M240 is -.009 crush to +.007 clearance. M60 is -.0025 crush to +.0065 clearance. The 1918 BAR is -.0092 crush to +.0087 clearance. The M14 and M14 National Match both DONT have any crush. The M1 Garand is -.0056 crush to +.0044 clearance. |
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AZ, USA
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Posted: 5/17/2024 11:18:55 AM EDT
[#12]
Quote HistoryOriginally Posted By j3_: I have never ran into commercial ammo that I have purchased that the case was sized to cause a crush even if drawings, Saami, or govt. specs allowed it. I based my response on my own experiences only which has worked very well for me. If there is fault in it based on equal real world experiences that are different than mine I would consider those for my own use based on their value. Post up a manufacturer making cases or ammunition sized to utilize any allowed crush for an AR!5 if someone knows of one. At most wouldn't that crush scenario only apply to trying to extract an unfired round? Quote HistoryOriginally Posted By j3_: Originally Posted By brownbomber: The AR, like many military weapons, uses a concept called "crush-up" - the longest allowable case is somewhat longer than the shortest allowable chamber. I don't remember exactly what this figure is, but I want to say it's like .003". I'll have to check my notes when I get home. Steel cases might present a problem in this regard. I have never ran into commercial ammo that I have purchased that the case was sized to cause a crush even if drawings, Saami, or govt. specs allowed it. I based my response on my own experiences only which has worked very well for me. If there is fault in it based on equal real world experiences that are different than mine I would consider those for my own use based on their value. Post up a manufacturer making cases or ammunition sized to utilize any allowed crush for an AR!5 if someone knows of one. At most wouldn't that crush scenario only apply to trying to extract an unfired round? If you have an AR15 minimum chamber and an 5.56mm maxiumum-length case, you have a very slight crush condition. I'm not sure if you'd even be able to feel that, because I've never done it before. I suspect that cartridge length and chamber length follow a normal-distributuon, with very few falling at the extremes (but I don't know that for a fact). Crush-up is discussed in this publication: Technical Notes Small Arms Design, by John Rocha |
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MT, USA
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Posted: 5/17/2024 11:18:57 AM EDT
[#13]
Is this a new barrel? What type of bore does it have, chrome lined or no? I had extraction issues with a DPMS barrel years ago. Stick with chrome lined or nitrided barrels.
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USA
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Posted: 5/17/2024 1:23:14 PM EDT
[#14]
Quote HistoryOriginally Posted By brownbomber: What kind of ammo are you shooting? Quote HistoryOriginally Posted By brownbomber: Originally Posted By CPT_CAVEMAN: What options are there if your barrel/bolt have too small of a headspace and you have failure to extract issues? Try to ream it out? Use some sandpaper to wear down the throat? What kind of ammo are you shooting? "Sergeant Major" |
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USA
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Posted: 5/17/2024 1:29:23 PM EDT
[#15]
Quote HistoryOriginally Posted By AZ_Gun_Nut: Is this a new barrel? What type of bore does it have, chrome lined or no? I had extraction issues with a DPMS barrel years ago. Stick with chrome lined or nitrided barrels. Brand new barrel, nitride. Thought it might be a tight chamber so used some flitz and a drill to "hone" it or remove a little material. Thought it might be a pressure curve issue, but that doesn't make complete sense. So super tight headspace I'm pretty sure is the issue and looking for the cheapest and/or quickest option to fix it. |
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AZ, USA
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Posted: 5/17/2024 1:42:18 PM EDT
[#16]
Quote HistoryOriginally Posted By CPT_CAVEMAN: "Sergeant Major" Quote HistoryOriginally Posted By CPT_CAVEMAN: Originally Posted By brownbomber: Originally Posted By CPT_CAVEMAN: What options are there if your barrel/bolt have too small of a headspace and you have failure to extract issues? Try to ream it out? Use some sandpaper to wear down the throat? What kind of ammo are you shooting? "Sergeant Major" Cold-worked steel cartridge cases do not have the elastic recovery that brass cases have. Large portions of the case are actually larger than the chamber after they are fired, not unlike a press-fit dowel pin. They must be yanked out with tremendous force, which sometimes exceeds the strength of the rim. The 7.62x39 case has much more taper and a much thicker rim for this reason. This phenomenon is discussed in many, many publications, including the Oerlikon Pocketbook. I don't think the extraction failures in your weapon are any indication of a headspace problem. |
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MN, USA
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Posted: 5/17/2024 2:27:32 PM EDT
[#17]
Quote HistoryOriginally Posted By CPT_CAVEMAN: "Sergeant Major" Is that the only ammo you have shot in it? |
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USA
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Posted: 5/17/2024 7:44:04 PM EDT
[#18]
Quote HistoryOriginally Posted By s4s4u: Is that the only ammo you have shot in it? Yes |
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MN, USA
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Posted: 5/17/2024 10:51:00 PM EDT
[#19]
Quote HistoryOriginally Posted By CPT_CAVEMAN: Yes So you are wanting to change the chamber dimensions of a rifle because one type of ammo is giving you problems, without ever trying any other ammo? I think that may be a bit....rash....no? |
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USA
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Posted: 5/18/2024 7:36:28 AM EDT
[#20]
Quote HistoryOriginally Posted By s4s4u: So you are wanting to change the chamber dimensions of a rifle because one type of ammo is giving you problems, without ever trying any other ammo? I think that may be a bit....rash....no? Well, when you put it that way lol. But it has worked in every other gun I've shot it in. |
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MN, USA
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Posted: 5/18/2024 10:42:31 AM EDT
[#21]
Quote HistoryOriginally Posted By CPT_CAVEMAN: Well, when you put it that way lol. But it has worked in every other gun I've shot it in. I suppose if it's all you shoot, we can't fault you for wanting to make the gun want to shoot it  |
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