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Posted: 8/28/2009 2:05:40 PM EDT
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I just bought a new DPMS AR-15 & find that most of my reloads that work fine in my Colt AR-15 will not properly chamber in the DPMS. As best I can deduce, it is a problem with the shoulder. The DPMS does headspace OK with a Foster GO gauge of 1.4636.
I use an RCBS full length length resizing die. In fact, I reloaded 5 more to make sure the die was set up according to the instructions and still have a problem. As best I can understand the RCBS die does not give the shoulder a bump, but simply resizes the case diameter. Is this true?? I would appreciate any thoughts/suggestions/comments as to how to make the reloads compatible with both guns. |
| The RCBS FL sizer die is supposed to give the shoulder a bump. Sometimes it helps to crowd the die a bit by screwing it down another quarter turn passed contact forcing an overcenter action with the press at Top Dead Center. Sometimes you can get another .001 to .002 out of the shoulder bump this way. Another thing to check is make sure there is ample clearance in the DPMS chamber relief for the case neck. Some chambers will not accept any brass not trimmed at or below 1.760. |
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I would appreciate any thoughts/suggestions/comments as to how to make the reloads compatible with both guns. Get a 223 case guage, such as the Dillon, and then adjust your size die so the headspacing falls between the upper and lower cuts on the case guage. Thats how I do it. |
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Might need a small based size die. I used FL for years without problems with my bushmaster. When I started getting more 223's, I started having problems with some of my brass not wanting to chamber easily in other rifles. The small base solved that problem. I can live with the shortened brass life as I normally start to get neck cracks on 3-5 loadings anyway, with 223 only for some reason. Besides, I get enough 223 brass for free to keep me broke so losing a few don;t hurt. I would rather have the brass rezised to min dimentions so it works every time.
Just thought I might throw that out there. |
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I would appreciate any thoughts/suggestions/comments as to how to make the reloads compatible with both guns. Get a 223 case guage, such as the Dillon, and then adjust your size die so the headspacing falls between the upper and lower cuts on the case guage. Thats how I do it. While I'm not saying not to use a case gage but I bought a few of them for calibers I reload for. I started to find that a fired case would fit in the case gage, indicating that the fired case was in spec. My fired case sure wouldn't chamber in my rifle so I stopped using them. Just my experience. |
, yes now I have a gauge. Heck it was only 1 jug 
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Wow, thanks for all the replies/suggestions.
Press is RCBS single stage and the die is full length resizing - not just neck resizing. Here is where I may have gone wrong –– when initially setting up the die, I did not 'over cam' it so that is something to try As for trimming the brass to less than 1.76, I'll give that a try –– 1.75 ??? If the above does not prove satisfactory, then I'll move on to a case gage and/or small base die. Again thanks for all the ideas. I'll post the results –– maybe 1 - 2 weeks. |
| "Shoulder bump" is internet slang for partial resizing. Full Length resizing means just what it says. Your DPMS's chamber appears to be tighter than the Colt chamber. Is it a .223? If you're reloading for more than one AR, you're going to have to resize for the one with the tightest chamber, unless you want to make custom ammo for each one. Just adjust the FL Die down until the cases will chamber in the DPMS. The Colt probably won't notice the difference. Welcome to the Big Time. |
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I like the RCBS Precision Mic for checking fired brass from different rifles plus setting the sizing die to bump the shoulder back to a measured amount. Here's a good article on the Precision Mic:
http://www.realguns.com/archives/035.htm Here's another article on using the Hornady Headspace set. Nice thing about this set is that it will check most calibers. I have both the RCBS Mic and Hornady sets. http://www.inlandshooters.net/index.php?contentid=99 Like previously stated, you may have to adjust your sizing die for hard contact with the shellholder to size the shoulder back enough. Also, I've seen shellholders out of spec. The distance from the top of the shellholder where it contacts the die to the shelf the case head sets on is supposed to be .125". |
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I would appreciate any thoughts/suggestions/comments as to how to make the reloads compatible with both guns. Get a 223 case gauge, such as the Dillon, and then adjust your size die so the headspacing falls between the upper and lower cuts on the case gauge. That's how I do it. The Dillon gauge is no good for this kind of precision measurements, my Colt 6920 head spaces perfectly between the two surfaces of my Dillon gauge but my new DD mid length barrel with a Young's NM BCG has less headspace and using the same setting on the drop in gauge will not work. You need a Hornady or Sinclair bump gauge set to see how much the shoulder is being pushed out on each gun and size accordingly. For example if using the Sinclair bump gauge(I use the Sinclair insert in the Hornady gauge set because it gives a much better measurement) measure some factory loaded rounds and then shoot five in each gun keeping them separated, then measure how much the shoulder got pushed out in each gun. In my 6920 it has .008" headspace and the DD barrel only has .005" headspace, so if you were to only bump the shoulders back .003" on the brass fired from the Colt rifle it wont fit the DD rifle even though it checks good in the Dillon gauge, you need more exact measurements when dealing with two guns. I set my sizing die (Hornady FL custom New Dimension sizing die) up to bump the shoulder back on the DD fired brass .003" and this gives my .006" headspace in the 6920. Now I really don't shoot the 6920 that much especially with my reloads so since it's just my SHTF gun and stays loaded with factory 5.56 ammo so the little extra headspace on the reloads if shoot through it isn't hurting anything and makes them safe to shoot in both guns. To be safe and really know what you need to do, you need to be able to get true measurements from both guns, so I suggest you invest in the Sinclair bump gauge set (or similar quality gauge set) so you can set your die up accordingly. The Sinclair bump gauge set really is much better than the Hornady inserts since it measures off the shoulder angle and not just off the datum point. After bumping my shoulder back .003" using the Sinclair gauge the Hornady gauge reads that it has only been bumped back .001", now this is with getting a beginning and after size with both gauges and is an accurate comparison, so according to the Hornady gauge you still need .002" more headspace at least when really you have already bumped the shoulder back .003", so the Hornady gauge is causing you(me) to way over size my brass so I stick with the Sinclair inserts only for everything I reload now with no problems chambering at all. JMHO EWP |
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Wow, thanks for all the replies/suggestions. Press is RCBS single stage and the die is full length resizing - not just neck resizing. Here is where I may have gone wrong –– when initially setting up the die, I did not 'over cam' it so that is something to try As for trimming the brass to less than 1.76, I'll give that a try –– 1.75 ??? If the above does not prove satisfactory, then I'll move on to a case gage and/or small base die. Again thanks for all the ideas. I'll post the results –– maybe 1 - 2 weeks. I had this problem with my dies too. I load for a bunch of different .223 rifles, AR's, bolt guns, Mini-14 etc. None of my dies, including my small base dies would correct the problem you and I are having. No matter which dies I used, I tried 4!, I could not get my ammo into the case gauge between the two steps. My soulution, fianlly, was to grind a few thousandths off the bottom of my old Dillon carbide die. Now I can get the exact headspace I want. I tried this with my small base die and it worked too. Ammo runs in all my guns without a hitch. |
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IMHO...........
The Colt has a generous chamber. The DPMS....might not have so generous a chamber. If you begin with that belief in your mind (that the chambers are different)...........things will go alot easier for you. So........... Your reloaded ammo (re-sized cases) was first set up to be used with the COLT and it works fine. I suspect that perhaps, you've been loading your ammo to the long end of the spectrum. Now, you have a new rifle (DPMS chamber) so, you need to adjust the die. The ammo for this rifle probably needs to be on the shorter end of the spectrum. BTW, you can make ammo to function with both rifles. But if, you want "ulitmate accuracy".............go ahead and play with the "fancy tools" that are mentioned by so many of the folks who suggest set backs of X inches. WARNING, you probably will end up making ammo to suit the individual rifle. So, perhaps two different die setting (or die sets permanently set for the individual riifle) will be needed in the end. Or consider a bit of compromise...........you might find a setting that will work with both rifles. But, going a "bit off"............and the ammo could bring things to a halt again. So, if you want a simple solution.........I suggest that you just set up your resizing die to re-size your brass to the shorter (min.) side of the acceptable spectrum. So that, the ammo that you make will function with both of your rifles (if not any future additions). This is ONE REASON why some people love the SB dies. Though for me, I would try it first with a F/L sizer die, set to the shorter end of the spectrum. You know....KISS. The downside to the latter approach is, a bit shorter case life and/or perhaps a bit of loss in accuracy (then again, you might not see it at all). Tools...........Examples…….. http://www.sinclairintl.com/prod_detail_list/Case-Gauges-Headspace-Tools They run from the simple and cheap (Wilson Case Gage) to the more expensive and complex. You get to choose how you like to do things and how much you want to spend. _________________________________ The DPMS does headspace OK with a Foster GO gauge of 1.4636.
Lastly, I suspect that the headspace gauge that you used (Go Gauge) on the new rifle is the type for testing "headspace of the chamber".......like these for example........ http://www.sinclairintl.com/product/11244/Case-Gauges-Headspace-Tools If that was the case..........no wonder you're confused by the "headspace" subject. That tool is NOT USED to test/gauge ammo. Aloha, Mark |
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Try..........
http://www.sinclairintl.com/product/11245/Case-Gauges-Headspace-Tools or http://www.sinclairintl.com/product/11239/Case-Gauges-Headspace-Tools or http://www.sinclairintl.com/product/8809/Case-Gauges-Headspace-Tools For the "expensive" way to check your headspace on your home made ammo. Aloha, Mark |
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"Shoulder bump" is internet slang for partial resizing. Full Length resizing means just what it says. Your DPMS's chamber appears to be tighter than the Colt chamber. Is it a .223? If you're reloading for more than one AR, you're going to have to resize for the one with the tightest chamber, unless you want to make custom ammo for each one. Just adjust the FL Die down until the cases will chamber in the DPMS. The Colt probably won't notice the difference. Welcome to the Big Time. Shoulder bump isn't done when partial sizing, doesn't come anywhere near bumping the shoulder. Only when full sizing is done is when the die bumps the shoulder. 'Borg |
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EWP ––- You said "The Sinclair bump gauge set really is much better than the Hornady inserts" I have looked in both the Sinclair catalog & their web site, but cannot find the Sinclair bump gauge set. Can you supply an item/catalog number? TIA I bought the Hornady bump gauge set but use the Sinclair inserts in the Hornady comparator body, you can measure just cases or loaded ammo using the Hornady comparator body unlike the Sinclair complete set that offers two different (short and long) comparator bodies. I use the .223 & 6.8 SPC with good results, no problems chambering any rounds in three .223 rifles since I know just how much each rifle pushes the shoulder out and size accordingly to fit all three guns, I couldnt get this precise measurement using the Hornady inserts. On another note the Hornady(Custom-Grade New Dimension Dies) FL sizing die has more than enough shoulder bump for any combo of guns, it will bump the shoulder past(shorter) where the factory ammo was if screwed all the way down, just a thought to those that are not getting enough shoulder bump with your current dies, these dies will bump the shoulder plenty without even touching the shell plate/holder to the die.. |
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Any die that is designated as full length, by definition, pushes the shoulder back. I agree with diabolical chicken, try screwing the die down a bit. A guy at Redding told me that every 5 degrees of a turn of the die equals 0.001 inches. Well there are some guys on here with their FL dies adjusted all the way down were it touches the shell holder and then still having to cam over their press to get enough shoulder bump, these dies must have a deep shoulder bump if so much die adjustment is needed and is what I was referring to that the Hornady FL dies don't need to be adjusted deep like that to get the required shoulder bump needed. |
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Any die that is designated as full length, by definition, pushes the shoulder back. I agree with diabolical chicken, try screwing the die down a bit. A guy at Redding told me that every 5 degrees of a turn of the die equals 0.001 inches. Well there are some guys on here with their FL dies adjusted all the way down were it touches the shell holder and then still having to cam over their press to get enough shoulder bump, these dies must have a deep shoulder bump if so much die adjustment is needed and is what I was referring to that the Hornady FL dies don't need to be adjusted deep like that to get the required shoulder bump needed. As you know.........most will say to F/L resize ammo intended for use in an auto loader. Your regular F/L sizer die can be used to give F/L sizing or neck sizing. It's in the amount of adjustment that you give it. Some choose to buy a neck sizing ONLY die because, they like to do things that way. The general instructions are: bring the ram up to position. Then. screw the die down until it touches the shell holder. Next, screw the die an additional 1/8 turn (or whatever more). That will give a slight "cam over." But, whatever............. IMHO..........use a gauge (and/or YOUR ACTUAL firearm) to test for the "correct resizing." You don't want to make a 1000 or so rounds then find out that it won't chamber. Aloha, Mark |
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Any die that is designated as full length, by definition, pushes the shoulder back. I agree with diabolical chicken, try screwing the die down a bit. A guy at Redding told me that every 5 degrees of a turn of the die equals 0.001 inches. Well there are some guys on here with their FL dies adjusted all the way down were it touches the shell holder and then still having to cam over their press to get enough shoulder bump, these dies must have a deep shoulder bump if so much die adjustment is needed and is what I was referring to that the Hornady FL dies don't need to be adjusted deep like that to get the required shoulder bump needed. As you know.........most will say to F/L resize ammo intended for use in an auto loader. Your regular F/L sizer die can be used to give F/L sizing or neck sizing. It's in the amount of adjustment that you give it. Some choose to buy a neck sizing ONLY die because, they like to do things that way. The general instructions are: bring the ram up to position. Then. screw the die down until it touches the shell holder. Next, screw the die an additional 1/8 turn (or whatever more). That will give a slight "cam over." But, whatever............. IMHO..........use a gauge (and/or YOUR ACTUAL firearm) to test for the "correct resizing." You don't want to make a 1000 or so rounds then find out that it won't chamber. Aloha, Mark I use the Sinclair bump gauge and bump my shoulders back .003-4" with a FL sizer and call it a day, never had any problems with feeding or pressure in any of my reloads. |
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When you say "reloads" do you mean the whole round, including COL? Is it possible the dpms has a shorter throat and the bullet is hitting the lands? Anything is "possible." But, I doubt that DPMS is trying to re-invent the wheel. I suspect that DPMS knows that their customers will be using M193 and other common loads. Look at the specs for these common chambers......... http://www.radomski.us/njhp/cart_tech.htm Aloha, Mark |
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Any die that is designated as full length, by definition, pushes the shoulder back. I agree with diabolical chicken, try screwing the die down a bit. A guy at Redding told me that every 5 degrees of a turn of the die equals 0.001 inches. Well there are some guys on here with their FL dies adjusted all the way down were it touches the shell holder and then still having to cam over their press to get enough shoulder bump, these dies must have a deep shoulder bump if so much die adjustment is needed and is what I was referring to that the Hornady FL dies don't need to be adjusted deep like that to get the required shoulder bump needed. As you know.........most will say to F/L resize ammo intended for use in an auto loader. Your regular F/L sizer die can be used to give F/L sizing or neck sizing. It's in the amount of adjustment that you give it. Some choose to buy a neck sizing ONLY die because, they like to do things that way. The general instructions are: bring the ram up to position. Then. screw the die down until it touches the shell holder. Next, screw the die an additional 1/8 turn (or whatever more). That will give a slight "cam over." But, whatever............. IMHO..........use a gauge (and/or YOUR ACTUAL firearm) to test for the "correct resizing." You don't want to make a 1000 or so rounds then find out that it won't chamber. Aloha, Mark I use the Sinclair bump gauge and bump my shoulders back .003-4" with a FL sizer and call it a day, never had any problems with feeding or pressure in any of my reloads. Yes, your technique and gauge is GOOD. _______________________________________ And YES, I believe that die brands might vary some tiny bit. But, they would probably be generally made to SAAMI specs. _______________________________________ But "others" still have trouble........... I figure that the instructions may have some confused......because the subject comes up VERY often. Then, the instructions are ususally good for most single stage presses. A progressive is different (note the shell PLATE and note the flex involved). But, we don't usually make that distinction when repeating the instructions. I figure that a progressive reloader should already KNOW HOW TO set up his/her dies, BEFORE he/she made the move. Aloha, Mark |
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Tracemaker has given little facts about his situation. Unknown bullets, powder, COL,cases,chamber being 5.56 or .223. Its funny how a thread can take off on a tangent without knowing what the ell is really going on.
How often do chambering issues relate to shoulder bump? Should the thread have been called shoulder bump? Has anyone ever heard of a tight chamber? |
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Tracemaker has given little facts about his situation. Unknown bullets, powder, COL,cases,chamber being 5.56 or .223. Its funny how a thread can take off on a tangent without knowing what the ell is really going on. How often do chambering issues relate to shoulder bump? Should the thread have been called shoulder bump? Has anyone ever heard of a tight chamber? Not likely, but anythings possible |
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Tracemaker has given little facts about his situation. Unknown bullets, powder, COL,cases,chamber being 5.56 or .223. Its funny how a thread can take off on a tangent without knowing what the ell is really going on. How often do chambering issues relate to shoulder bump? Should the thread have been called shoulder bump? Has anyone ever heard of a tight chamber? Gearhead: You are correct, the entire picture has not been laid out. The thread bumps along however because some low risk, or low probability assumptions are being made. The chamber met the "go gage" requirement so the DPMS is not a "out of spec tight chamber" lenghtwise. It could be tight radially, but that is yet to be determined. If a full sizing die will squeeze the case body down enough to address a tight diameter in the DPMS chamber, that might solve the problem (hence the SB recommendation). Or, if a full sizing die will not only squeeze the case body down, but compress the case body column near the shoulder that might solve the problem. COL problems and "into the lands" are very rare in AR-15 chambers. Jump to lands in my AR's varies from .14 to .10 inch depending on bullet used. Magazine feed COL restrictions usually filter out COL and "into the lands" problems. .223 chambers in 5.56 AR's are rare but not zero in occurence. I think most here ruled out powder, because nothing has been fired yet. Cases....well they are all originating from the same stream, dividing into two different chambers after sizing. |
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Tracemaker has given little facts about his situation. Unknown bullets, powder, COL,cases,chamber being 5.56 or .223. Its funny how a thread can take off on a tangent without knowing what the ell is really going on. How often do chambering issues relate to shoulder bump? Should the thread have been called shoulder bump? Has anyone ever heard of a tight chamber? Gearhead: You are correct, the entire picture has not been laid out. The thread bumps along however because some low risk, or low probability assumptions are being made. The chamber met the "go gage" requirement so the DPMS is not a "out of spec tight chamber" lenghtwise. It could be tight radially, but that is yet to be determined. If a full sizing die will squeeze the case body down enough to address a tight diameter in the DPMS chamber, that might solve the problem (hence the SB recommendation). Or, if a full sizing die will not only squeeze the case body down, but compress the case body column near the shoulder that might solve the problem. COL problems and "into the lands" are very rare in AR-15 chambers. Jump to lands in my AR's varies from .14 to .10 inch depending on bullet used. Magazine feed COL restrictions usually filter out COL and "into the lands" problems. .223 chambers in 5.56 AR's are rare but not zero in occurence. I think most here ruled out powder, because nothing has been fired yet. Cases....well they are all originating from the same stream, dividing into two different chambers after sizing. Tracemaker said his reloads "work fine" in his colt. I assumed that meant they/something has been fired. ALso I was wondering how far it fails to chamber? There isnt a pic? or a reference to how far the bolt stays open? WTF? Hey Ive learned alot about shoulder bump. I have had chambering issues with my .458Socom so things like this intrigue me. Never issues with .223 though .Wish we had some virtual 3D gunscan ways to figure these things out. |
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Tracemaker has given little facts about his situation. Unknown bullets, powder, COL,cases,chamber being 5.56 or .223. Its funny how a thread can take off on a tangent without knowing what the ell is really going on. How often do chambering issues relate to shoulder bump? Should the thread have been called shoulder bump? Has anyone ever heard of a tight chamber? Gearhead: You are correct, the entire picture has not been laid out. The thread bumps along however because some low risk, or low probability assumptions are being made. The chamber met the "go gage" requirement so the DPMS is not a "out of spec tight chamber" lenghtwise. It could be tight radially, but that is yet to be determined. If a full sizing die will squeeze the case body down enough to address a tight diameter in the DPMS chamber, that might solve the problem (hence the SB recommendation). Or, if a full sizing die will not only squeeze the case body down, but compress the case body column near the shoulder that might solve the problem. COL problems and "into the lands" are very rare in AR-15 chambers. Jump to lands in my AR's varies from .14 to .10 inch depending on bullet used. Magazine feed COL restrictions usually filter out COL and "into the lands" problems. .223 chambers in 5.56 AR's are rare but not zero in occurence. I think most here ruled out powder, because nothing has been fired yet. Cases....well they are all originating from the same stream, dividing into two different chambers after sizing. Tracemaker said his reloads "work fine" in his colt. I assumed that meant they/something has been fired. ALso I was wondering how far it fails to chamber? There isnt a pic? or a reference to how far the bolt stays open? WTF? Hey Ive learned alot about shoulder bump. I have had chambering issues with my .458Socom so things like this intrigue me. Never issues with .223 though .Wish we had some virtual 3D gunscan ways to figure these things out. 21st Century CADCAM meets late 19th early 20th century ammo design. I guess that is what you are referring to. One of the neatest things I have seen lately is the LS-DYNA analysis and graphic simulation of a .243 case and primer cup during peak pressure. The link to it is up top in the tacked links thread. In the longrun though, I think it bids ill of the future of reloading, because the 21st century primer, brass and powder and bullet are probably, as we know it, going to go away. |
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"Shoulder bump" is internet slang for partial resizing. Full Length resizing means just what it says. Your DPMS's chamber appears to be tighter than the Colt chamber. Is it a .223? If you're reloading for more than one AR, you're going to have to resize for the one with the tightest chamber, unless you want to make custom ammo for each one. Just adjust the FL Die down until the cases will chamber in the DPMS. The Colt probably won't notice the difference. Welcome to the Big Time. Shoulder bump isn't done when partial sizing, doesn't come anywhere near bumping the shoulder. Only when full sizing is done is when the die bumps the shoulder. 'Borg When you FULL LENGTH resize, you not only set the shoulder back to min spec you also reduce the diameter of the case body. Partial resizing is "bumping" the shoulder back just enough to permit the case to chamber in addition to reducing the neck diameter enough to hold a bullet. Excuse me while I go to Sinclair's website to find a "Bump" gage. |
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"Shoulder bump" is internet slang for partial resizing. Full Length resizing means just what it says. Your DPMS's chamber appears to be tighter than the Colt chamber. Is it a .223? If you're reloading for more than one AR, you're going to have to resize for the one with the tightest chamber, unless you want to make custom ammo for each one. Just adjust the FL Die down until the cases will chamber in the DPMS. The Colt probably won't notice the difference. Welcome to the Big Time. Shoulder bump isn't done when partial sizing, doesn't come anywhere near bumping the shoulder. Only when full sizing is done is when the die bumps the shoulder. 'Borg When you FULL LENGTH resize, you not only set the shoulder back to min spec you also reduce the diameter of the case body. Partial resizing is "bumping" the shoulder back just enough to permit the case to chamber in addition to reducing the neck diameter enough to hold a bullet. Excuse me while I go to Sinclair's website to find a "Bump" gage. I'll have to agree with Borg. The shoulder doesn't get bumped back until the last few thousanths of stroke with a properly set die. As the case goes into the die, the neck and maybe part of the body is shaped, then the last is the body near the web and the shoulder gets moved back. At least that's the way I see it. |
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Any die that is designated as full length, by definition, pushes the shoulder back. I agree with diabolical chicken, try screwing the die down a bit. A guy at Redding told me that every 5 degrees of a turn of the die equals 0.001 inches. Well there are some guys on here with their FL dies adjusted all the way down were it touches the shell holder and then still having to cam over their press to get enough shoulder bump, these dies must have a deep shoulder bump if so much die adjustment is needed and is what I was referring to that the Hornady FL dies don't need to be adjusted deep like that to get the required shoulder bump needed. I agree I tried over caming mine and had them turned down as far as they will go and still they wouldn't set the shoulder back at all. That's 4 different dies! By grinding just a few thousandths off the bottom of the die they work perfectly. |
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"Shoulder bump" is internet slang for partial resizing. Full Length resizing means just what it says. Your DPMS's chamber appears to be tighter than the Colt chamber. Is it a .223? If you're reloading for more than one AR, you're going to have to resize for the one with the tightest chamber, unless you want to make custom ammo for each one. Just adjust the FL Die down until the cases will chamber in the DPMS. The Colt probably won't notice the difference. Welcome to the Big Time. Shoulder bump isn't done when partial sizing, doesn't come anywhere near bumping the shoulder. Only when full sizing is done is when the die bumps the shoulder. 'Borg When you FULL LENGTH resize, you not only set the shoulder back to min spec you also reduce the diameter of the case body. Partial resizing is "bumping" the shoulder back just enough to permit the case to chamber in addition to reducing the neck diameter enough to hold a bullet. Excuse me while I go to Sinclair's website to find a "Bump" gage. I'll have to agree with Borg. The shoulder doesn't get bumped back until the last few thousanths of stroke with a properly set die. As the case goes into the die, the neck and maybe part of the body is shaped, then the last is the body near the web and the shoulder gets moved back. At least that's the way I see it. Take a fired case from a rifle that has max headspace (almost chambers a Field Reject gauge) and "bump the shoulder back a few thousandths". Then try to chamber that "resized" case in a match-chambered rifle that barely chambers a GO gauge. In my experience, it won't go. I went through this with my first M1 Garands which had headspace that varied from over spec to under spec. My original point was that people shouldn't refer to full length resizing as simply "bumping the shoulder back". Nor should they refer to case guages as "bump" gauges. I no longer "partial" resize cases for gas guns. They are resized to SAAMI minimum spec and loaded into chambers that won't chamber a NO-GO gauge. |
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This thread started with a question about relaods which chamber in a Colt but not chamber in a DPMS.
I bought a case gauge and checked the reloads –– many were beyond spec, meaning the shoulder was too far out; i.e. needing to be bumped. Some were 0.006" - 0.008" long. Set up the resizing die to over-cam and then measured the cases –– still the shoulder was long. As someone suggested, I ground about 0.006" off the bottom of the die and can now adjust the die to move the shoulder back to exactly the amount I want –– 0.000 - 0.002 less than spec. Reloaded 61 using this method and everyone chamered and fired. So, thanks for all the suggestions and info. For me, the problem is solved. |
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Thanks for the follow-up. Many problems do not get the closure that you provided here, so thanks again.
Grinding off the die then, solves the problem with your DPMS. If the RCBS precision mike before fixing the die, shows +.006 over SAAMI/ANSI minimum and that still works in the Colt, then the Colt chamber was the loose chamber, not the DPMS chamber was undersize. For reference: The Mil C 70599A Sec. 3.4.1 Headspace requirement for the chamber is: (for new AR's) 1.4646" to 1.4706". I am sure this would be based on the NATO chamber. That gives you a .006 float. |
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Based on what I/we now know –– the Colt chamber is clearly more loose than the DPMS.
However the learning experience for me was to get the die 'straightened out' or said more accurately –– shortened! I did not realize how sensitive the die position was in order to attain SAAMI/ANSI dimensions. Having only reloaded for 1 gun, using brass previously fired in that gun, I never had any problems. Thanks to everyone who contributed in this thread. |
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