why do I need to resize cases from my AR-15
- Thread starter wtfTG
- Start date
1. Because the gas-operated extraction of a semi-auto happens under considerable residual
chamber pressure, and the shoulder is/can be blown forward "a little bit".
2. Because the bolt closure of an auto is spring-driven, with very little available torque to fully
close/rotate on a case that's just "a little bit" long.
You don't want to be around a bolt that hasn't quite "closed all the way." Now this is a lesser
catastropic risk with the AR bolt design, but can get real exciting with others like the Garand, M1A,
30 carbine, and a host of foreign military actions
chamber pressure, and the shoulder is/can be blown forward "a little bit".
2. Because the bolt closure of an auto is spring-driven, with very little available torque to fully
close/rotate on a case that's just "a little bit" long.
You don't want to be around a bolt that hasn't quite "closed all the way." Now this is a lesser
catastropic risk with the AR bolt design, but can get real exciting with others like the Garand, M1A,
30 carbine, and a host of foreign military actions
cryogenic419
New member
Brass in bolt action rifles is not subject to the split second stripping from a magazine and jamming into a chamber that you see in a semi auto. You could neck size only but kiss any sort of reliability goodbye.
The Importance of resizing
The most important issue of reloading the 5.56/2.23 AR-15 style semi-auto loader is the cannelure. Cannelure allows the bullet to be firmly grasped by the case mouth. There is no other reason for cannelure, period. As an auto loader rapidly ejects a casing and then slams home to the breach the loading cartridge is subject to severe forces which, if not perfectly aligned with the bore can cause the bullet to contact the face of the breach. If not for the cannelure insuring a firm grasp, the bullet could be shoved into the casing eventually leading to a stuck bullet somewhere down the barrel. The next round would then fire and cause an explosion.
Most bullet manufacturers list their trim length as being 1.750" which is exactly what the SS109 projectile calls for. You must set up your crimp and seat depth so that the overall cartridge length is no more than 2.260". Any longer OAL and the cartridge cannot be loaded into a magazine. You can trim a little less than 1.750" but do not exceed that length. Seat your bullet so the case mouth just touches the top of the cannelure. Yes, you can shoot non-cannelure bullets in your 5.56...if you don't cherish your eyesight. One other thing...if you shoot the same brass in the same rifle you only need to check your trim length and only neck size. Full-length sizing is to ensure any cartridge can fit any rifle of the same calibre. Go on ebay and buy some old Speer or Hornady manuals.
The most important issue of reloading the 5.56/2.23 AR-15 style semi-auto loader is the cannelure. Cannelure allows the bullet to be firmly grasped by the case mouth. There is no other reason for cannelure, period. As an auto loader rapidly ejects a casing and then slams home to the breach the loading cartridge is subject to severe forces which, if not perfectly aligned with the bore can cause the bullet to contact the face of the breach. If not for the cannelure insuring a firm grasp, the bullet could be shoved into the casing eventually leading to a stuck bullet somewhere down the barrel. The next round would then fire and cause an explosion.
Most bullet manufacturers list their trim length as being 1.750" which is exactly what the SS109 projectile calls for. You must set up your crimp and seat depth so that the overall cartridge length is no more than 2.260". Any longer OAL and the cartridge cannot be loaded into a magazine. You can trim a little less than 1.750" but do not exceed that length. Seat your bullet so the case mouth just touches the top of the cannelure. Yes, you can shoot non-cannelure bullets in your 5.56...if you don't cherish your eyesight. One other thing...if you shoot the same brass in the same rifle you only need to check your trim length and only neck size. Full-length sizing is to ensure any cartridge can fit any rifle of the same calibre. Go on ebay and buy some old Speer or Hornady manuals.
FWIW, the OP's issue is not that of neck tension and/or crimp. Neck tension
from a properly neck-sized case is just fine all by itself. (No crimp needed)
The issue is case headspace growth upon high-pressure extraction, and the
need to resize for reliable bolt closure next time around.
from a properly neck-sized case is just fine all by itself. (No crimp needed)
The issue is case headspace growth upon high-pressure extraction, and the
need to resize for reliable bolt closure next time around.
From Sierra.
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.
Link to article.
http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm
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.
Link to article.
http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm
The cannelure is irrelevant. You do not need bullets with a cannelure for any semi-auto. The cannelure harkens back to when the only repeater was a lever action and much later to automatic weapons. Has nothing whatever to do with loading for a semi-auto. Ever see a match bullet with one?
FL sizing is important because of the forces involved with a semi. There was an article in one of the gun rags years and years ago that said something about how the case entered the chamber differently too.
"...residual chamber pressure..." No such thing. The action doesn't even start to open until chamber pressures have dropped to nothing. If there was such a thing as residual chamber pressure, that pressure would end up in the mag, receiver and shooter's face.
"...Slam-fires are an ever-present danger with Service Rifles (particularly with the M1 and M14 family)..." This is nonsense.
"...Go on E-Bay..." Buying or selling ANYTHING on E-Bay directly funds the people who are busy lobbying to take your firearms away from you.
FL sizing is important because of the forces involved with a semi. There was an article in one of the gun rags years and years ago that said something about how the case entered the chamber differently too.
"...residual chamber pressure..." No such thing. The action doesn't even start to open until chamber pressures have dropped to nothing. If there was such a thing as residual chamber pressure, that pressure would end up in the mag, receiver and shooter's face.
"...Slam-fires are an ever-present danger with Service Rifles (particularly with the M1 and M14 family)..." This is nonsense.
"...Go on E-Bay..." Buying or selling ANYTHING on E-Bay directly funds the people who are busy lobbying to take your firearms away from you.
That is incorrect. In fact I have seen rims mangled in an FN49 by extractors because the case was still firmly attached to the chamber walls when the bolt was opening. In fact the chamber pressure curve can still be as high as 12,000 psi when the bullet passes the gas port in a Garand and force is applied to the piston face in an attempt to cam the bolt open. That pressure may have dropped to zero when the case finally "unsticks" doesn't mean that life wasn't real miserable at the start.
From Zediker:
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.
But I will ask the counsel of the UncleNicks of the world before getting deeper.
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Thanks for posting that mehavey.
One can also check this same phenomenon with a tool like the Hornady Headspace gauge.
Testing different powders with different burn rates can cause the action to cycle at different times, thus changing the dimensions (head to Datum) of a fired case.
One can also check this same phenomenon with a tool like the Hornady Headspace gauge.
Testing different powders with different burn rates can cause the action to cycle at different times, thus changing the dimensions (head to Datum) of a fired case.
I will confirm the above bold section happens . I've measured this more then a few times with a comparator ( Hornady Headspace gauge ) . The measurement is from the head to the datum point ( middle of the shoulder-ish ) I've noticed the lower pressure rounds like 223 loads fired from my AR's have very inconsistent case head space measurements while full power 5.56 NATO loads give very consistent head to datum measurements from my AR's .
One of my chambers will produce a 5.56 NATO fired case measuring 1.460 from head to datum( my comparator measurement not actual size ) . I have measured ammo that were fired from that rifle as long as 1.463 and as low as 1.456 and everything in between .
If you understand that if your chamber is 1.460 you need to size your cases to 1.459 to 1.457 to feed reliably depending on the type of firearm . You then can see by those numbers if you have a case that measures 1.463 trying to fit in a space that's 1.460 , you're going to have a problem . Even if it was 1.460 the same as the chamber you will likely have issues because of # 2 in the quote Because the bolt closure of an auto is spring-driven, with very little available torque to fully close/rotate on a case that's just "a little bit" long.
So the rule is size your semi auto brass .003 shorter then your fire formed brass . Now that sounds simple right ? Well no not really because some cases from an AR may actually be longer then the chamber after firing . Well then how do you know what's the right sized fire formed case ? As I said above I've found factory NATO rounds to expand the cases pretty consistent So I'll use those and confirm buy sizing a case .002 longer then the fire formed case and try to slowly chamber it by riding the bolt home and trying to force the case in by tapping and the forward assist . If the case does not chamber I size it down another .001 and repeat until it chambers . This is usually my max case head space . I'll then FL size my cases .002 to .003 shorter .
Now it may seem like a lot to do or complicated but it's really not and you only need to do it once for each firearm . Once you have the correct measurement you can just size all cases accordingly .
I'll save the fact that an AR BCG flying home will set back a shoulder back .0015 to .0025 as it slams the case into the chamber for another day
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The Importance of resizing
The most important issue of reloading the 5.56/2.23 AR-15 style semi-auto loader is the cannelure. Cannelure allows the bullet to be firmly grasped by the case mouth. There is no other reason for cannelure, period. As an auto loader rapidly ejects a casing and then slams home to the breach the loading cartridge is subject to severe forces which, if not perfectly aligned with the bore can cause the bullet to contact the face of the breach. If not for the cannelure insuring a firm grasp, the bullet could be shoved into the casing eventually leading to a stuck bullet somewhere down the barrel. The next round would then fire and cause an explosion.
No crimp is needed for your semi auto AR. No cannelure is needed either. Proper case neck tension is all that's needed.
Most bullet manufacturers list their trim length as being 1.750" which is exactly what the SS109 projectile calls for.
Bullet manufactures? The trim length is for the cartridge case, (brass), not a "bullet"
You must set up your crimp and seat depth so that the overall cartridge length is no more than 2.260". Any longer OAL and the cartridge cannot be loaded into a magazine. You can trim a little less than 1.750" but do not exceed that length. Seat your bullet so the case mouth just touches the top of the cannelure. Yes, you can shoot non-cannelure bullets in your 5.56...if you don't cherish your eyesight.
What!?¿like I said, proper/tight neck tension/grip is all that's needed.
One other thing...if you shoot the same brass in the same rifle you only need to check your trim length and only neck size. Full-length sizing is to ensure any cartridge can fit any rifle of the same calibre. Go on ebay and buy some old Speer or Hornady manuals.
I would suggest you do the same thing, read before posting---.
Finianmac is offline Report Post
As said, you MUST full length re-size brass meant to be used in an AR rifle. I tried the collet type neck sizer made by lee for my AR. Out of 20 rounds 18 fired flawlessly, the other 2 hung up upon chambering, didn't go fully into battery.
I'm in the crowd that does NOT believe in pressure being still inside a fired case upon extraction. In any semi auto rifle. It all has to do with time. Not enough time for mechanical parts to move before the bullet is clear of the barrel. Look where the gas port is, just behind the muzzle. In an AR, the pressure has to fill the gas tube, it has to blow the bolt back to start the extraction process. The bullet is long gone by that time.
Same for a M-1 the gas port is way up front, the piston has to have pressure on it to begin to move that heavy operating rod that then has to rotate the bolt.
That is inconsistent with the principles of a gas operated firearm like the AR 15.
This may help.
https://en.m.wikipedia.org/wiki/Gas-operated_reloading
It would be for those who seat the bullet far enough out that they end up headspacing on the bullet instead of the case shoulder, but that's unusual and not recommended for the AR because of the associated slamfire risk.
The same risk applies for not sizing cases to narrow the sides of the case and set the shoulder back. Glen Zediker says to set it back 0.002" from the size at which it ejects from your gun, assuming your gun doesn't stretch the case. Most commercial cases, when new, are about 0.002" shorter at the shoulder than a SAAMI minimum chamber, and I believe that is where it came from.
The military has minimum bullet pull or extraction force numbers defined for ammunition, and that can require a crimp to meet. I do not know the criteria used to arrive at these specifications. Perhaps board member Hummer70 does, as he used to work at Aberdeen Proving Grounds doing testing, among other things.
Most case necks have about 0.001" interference fit with the bullet. In theory, since cartridge brass expands about .0011%/°F, for .223, if you could heat the neck more than 90°F hotter than the bullet underneath it, the bullet would then be loose in the neck. When you place a round in a hot chamber, the neck will likely touch the chamber on one side, and the shoulder of the case may be in contact with the chamber, so heat will enter the neck before the bullet. But heat transfers rather well from brass to copper, and the lead under the bullet, while not as fast a conductor of heat as copper is, does expand more per degree than brass (0.0016%/°F), so I think it would be hard to arrive at that much net temperature difference and for the lead core of a bullet not to be overwhelming the difference, but I suspect concern that it might happen in a full auto chamber may be one reason for the military insisting on crimps.
The full auto scenario is not normally a concern for a target shooter or a hunter. This is why there is not normally a need to crimp. Indeed, target bullets makers recommend against creating crimp indentations in them for fear of causing imbalance or loss of ballistic coefficient. Nonetheless, experiments by Lee and others have found that you can sometimes actually gain accuracy, at least at short range, with crimps. You have to experiment with that on your own, as it is likely to be one of those things individual to the rifle.
For bullets that possess crimp cannelures, if you are using a hard-to-ignite powder or one on the slow end of the range of choices, you may get some ignition consistency improvement from using a crimp in conjunction with a magnum primer. You can test this with a chronograph. It if reduces the velocity SD, it is likely helping. If not, it likely isn't.
If you shoot long range (say, 500 yards and beyond) even if the crimp improves SD and accuracy at short range, I would do some side-by-side grouping of your best crimped and non-crimped loads for the same bullet at your longest range. This is to see if bullet distortion or velocity variability opens your groups up more in those situations.
The same risk applies for not sizing cases to narrow the sides of the case and set the shoulder back. Glen Zediker says to set it back 0.002" from the size at which it ejects from your gun, assuming your gun doesn't stretch the case. Most commercial cases, when new, are about 0.002" shorter at the shoulder than a SAAMI minimum chamber, and I believe that is where it came from.
The military has minimum bullet pull or extraction force numbers defined for ammunition, and that can require a crimp to meet. I do not know the criteria used to arrive at these specifications. Perhaps board member Hummer70 does, as he used to work at Aberdeen Proving Grounds doing testing, among other things.
Most case necks have about 0.001" interference fit with the bullet. In theory, since cartridge brass expands about .0011%/°F, for .223, if you could heat the neck more than 90°F hotter than the bullet underneath it, the bullet would then be loose in the neck. When you place a round in a hot chamber, the neck will likely touch the chamber on one side, and the shoulder of the case may be in contact with the chamber, so heat will enter the neck before the bullet. But heat transfers rather well from brass to copper, and the lead under the bullet, while not as fast a conductor of heat as copper is, does expand more per degree than brass (0.0016%/°F), so I think it would be hard to arrive at that much net temperature difference and for the lead core of a bullet not to be overwhelming the difference, but I suspect concern that it might happen in a full auto chamber may be one reason for the military insisting on crimps.
The full auto scenario is not normally a concern for a target shooter or a hunter. This is why there is not normally a need to crimp. Indeed, target bullets makers recommend against creating crimp indentations in them for fear of causing imbalance or loss of ballistic coefficient. Nonetheless, experiments by Lee and others have found that you can sometimes actually gain accuracy, at least at short range, with crimps. You have to experiment with that on your own, as it is likely to be one of those things individual to the rifle.
For bullets that possess crimp cannelures, if you are using a hard-to-ignite powder or one on the slow end of the range of choices, you may get some ignition consistency improvement from using a crimp in conjunction with a magnum primer. You can test this with a chronograph. It if reduces the velocity SD, it is likely helping. If not, it likely isn't.
If you shoot long range (say, 500 yards and beyond) even if the crimp improves SD and accuracy at short range, I would do some side-by-side grouping of your best crimped and non-crimped loads for the same bullet at your longest range. This is to see if bullet distortion or velocity variability opens your groups up more in those situations.
stubbicatt
New member
I remember reading somewhere that the original chambers, and maybe still, of Colt M16 rifles borrowed the straight wall cylinder chamber profile of the FG42 chamber as one method of maintaining a proper chamber seal on the M16, since the rifle begins to cycle while there is still considerable chamber pressure. Otherwise one would get a face full of gas were the chamber to retain the tapered profile, and the cartridge were dislodged while still under pressure.
The taper built into the 5.56 or 223 case assures proper feeding and chambering. Returning the cartridge to the proper dimensions is very important for these functions.
The transformation of a tapered case to a straight walled, cylinder profile, while being extracted under pressure will definitely deform the case and likely increase case head to shoulder length over nominal chamber length.
It is just prudent to full length resize the cases.
The taper built into the 5.56 or 223 case assures proper feeding and chambering. Returning the cartridge to the proper dimensions is very important for these functions.
The transformation of a tapered case to a straight walled, cylinder profile, while being extracted under pressure will definitely deform the case and likely increase case head to shoulder length over nominal chamber length.
It is just prudent to full length resize the cases.
Lots of info here, not sure about some of it.
I know my fired cases fit in my AR, but I also know my AR can close the bolt on a +0.002" case. Somewhere around +0.005", it will not. This is due to action closing weakness. A bolt gun will cycle long cases all day long!
That said, under the right conditions an AR will slam fire. Because of this, I don't want my gun forcing the case in the chamber and possibly slam firing out of battery.
Not really an AR concern, but many semi-auto actions are weak, causing the case to stretch beyond a nominal dimension during firing and needing shortening.
Also, AR cycling is weak as was said above, so for reliability, I want it to be slightly short for the chamber to feed.
I know my fired cases fit in my AR, but I also know my AR can close the bolt on a +0.002" case. Somewhere around +0.005", it will not. This is due to action closing weakness. A bolt gun will cycle long cases all day long!
That said, under the right conditions an AR will slam fire. Because of this, I don't want my gun forcing the case in the chamber and possibly slam firing out of battery.
Not really an AR concern, but many semi-auto actions are weak, causing the case to stretch beyond a nominal dimension during firing and needing shortening.
Also, AR cycling is weak as was said above, so for reliability, I want it to be slightly short for the chamber to feed.