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Posted: 9/18/2010 1:14:39 PM EDT
| I have been using the Lee 'Modern Reloading' (second edition) book as my current guide for bullet/powder, etc. reference. On page 40, it states that it is necessary to full-length resize when using (among others) autoloaders; I shoot both AR15 in 5.56 and 7.62 configuration(s). It seems to me that if using the same brass in the individual arms, each is 'fire formed' to the chambers used and by default only need to be neck sized. Does anyone have any insight into this? I tend to use the bulk of my reloads as 'shoot um up' ammo and at lowest powder charge and would like to get as much use out of the brass as possible. As a general rule, I currently full-length resize every time in the overall process. |
| Adjust your FL resizer to bump your shoulders ~.003. Kind of splits the difference between neck sizing and complete FL resizing where often shoulders are bumped .005 - .006 which is needless IMHO. .003 bump gives you the benefit of eased chambering/extraction, yet it doesn't overwork the brass. |
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Brass fired in your rifle is indeed fire formed to fit. How do you plan to get it back into the chamber in the same orientation on the next shot?
Autoloaders need brass sized with a little clearance for reliable operation. Fresh brass that springs back will work pretty well with neck sizing. Once or maybe twice. Then the case becomes work hardened and does not spring back as far to provide that little bit of clearance. Size full length. |
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Quoted:
As a general rule, I currently full-length resize every time in the overall process. Keep doing that and you will be fine. You may look into annealing if you want to extend brass life. Your cases will most likely split at the necks when they fail, and annealing, if done properly, could help with this issue. jonblack |
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Here is an explanation on so called fire formed brass from the M-14. Although not as drastic as the M-14 this occures in other semi-autos as well.
For one, the M14 has about the quickest operation of any auto-loading rifle — so much so that the bolt can unlock before the case has fully retracted from its expanded dimensions. We’re talking about milliseconds, but that’s all we have devoted to the entire process. The net result is that some amount of additional expansion frequently occurs in a case fired through an M14. Compounding this condition is that LC brass is liable not to contract as readily as other cases fired in other rifles. It’s very, very (comparatively) hot and getting jerked on by an extractor, and most seem to think this is responsible for a lot of the additional measured case growth. Don’t be fooled into thinking that brass from an M14 “fire formed” to fit the chamber; it may well have “fire deformed.” A spent case from a 14 will often have the shoulder blown farther forward than chamber specs should allow, and may also exhibit more case head expansion than it “should.” Here is a good article on loading for the sevice rifle. http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm Note the section on "Sizing". Sizing Full length sizing is the only option in the Service Rifle world. Minimal sizing does have its place in bolt actions, particularly where top accuracy is the goal. It can also be used in some other types of actions when reliability is not a top priority. However, anything other than full length resizing is a potentially serious problem with the Service Rifle. The case needs to be resized to the point that it will enter the chamber freely, completely and with absolutely no hint of resistance whatsoever. Failure to follow this simple practice is an invitation to some major headaches. The most common problem is the failure to fully chamber the round. This is troublesome at best. Considering the force with which the bolt slams home, it can also wedge the round tightly enough in the chamber that it is very difficult to extract without damaging the rifle. In the worst case scenario, it sets the stage for an out-of-battery firing when the trigger is pulled. Improper or insufficient resizing, particularly when combined with a high primer, is also a leading cause of slam-fires. Despite the oft-repeated advice that autoloaders, pumpguns and lever-actions require small base dies, the Service Rifles may be the exception that proves the rule. While it’s true that all of these action types lack the powerful camming forces of a bolt-action, the more generous chamber dimensions common to most Service Rifles are normally compatible with standard dies. Please understand that this is a general statement, and that there are exceptions to this. The point is, you don’t need to automatically go to a small base die set. Most of the standard reloading dies produced by reputable firms, such as RCBS, will resize fired brass properly to work in these rifles. Neck Sizing Neck sizing is a popular technique among accuracy-minded reloaders and frequently an effective way to improve accuracy. In essence, it amounts to sizing only the neck portion of the case while leaving the remainder of the shoulder and body untouched. This provides that “custom-fit” of the brass to chamber that so many shooters are working toward. Chambering a cartridge that has been neck-sized will normally give some slight resistance to closing the bolt. This is perfectly normal and to be expected when using this technique. While it’s a minor detail with the powerful camming forces of a bolt-action, this can be a serious problem with a service rifle. It can cause a failure to fully seat and chamber, effectively jamming the rifle. If the lugs have partially engaged, this can be a very difficult stoppage to clear. Under extreme circumstances, it can even lead to a slam-fire. The solution to these aggravating and potentially dangerous problems is simple: Don’t neck size for semi-auto rifles. For any reason. Ever. Whatever minor accuracy improvements are gained —and there is not always an improvement — are more than offset by the problems that are going to occur. Neck sizing is perhaps the best single illustration of a technique that is beneficial for a bolt-action, but is dangerously out of place in a Service Rifle. Stick to full length sizing—ALWAYS—when reloading for autoloaders. |
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I resize all M1A brass to SAAMI minimum haedspace, despit the fact that it comes from my chamber .006" longer than that. I routinely see fire in the chamber as the case is extracted, that can only mean that the pressure's are still high if there's "fire in the hole".
As stated in the longer post, this causes the brass to stretch more than it should and accounts for the longer than normal measuremets we find in these rifles. The net result is I feel comfortable firing these loaded rounds in any rifle, because they will fit without issues. My AR10's exhibit .002" case headspace upon firing. This tells me their actions are much less violent than my M1A's. Their headspace may be even longer, without measuring who knows. Always full length resize semi-autos. A case that doesn't allow the bolt to fully close could blow up a rifle, maybe yours. |
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