Armory Sponsor
Posted: 7/20/2013 1:31:04 AM EDT
|
How much can a crimp effect pressure, or the pressure curve?
I read a comment which stated crimping has no effect on pressure, but I can not believe this. I ask because of a blown primer I had with a near max load in which the bullet was crimped unnecessarily. Yes, lots of reasons for blowing a primer but I need to explore this avenue. I have gotten over my paranoia of set back and crimping everything regardless if it had a cannelure or not. Bullets without cannelure received a light kiss of crimp, but no more. Loading test rounds last night, I measured neck OD before/after seating bullets, and all increased by minimum of .002". Other threads stated this level of OD increase indicates good neck tension. Did the push test and chambering test as well, no set back. So how much effect does crimping have on pressue/pressure.curve? |
|
Here is an article by Sierra on crimping. It talks basics mostly referring to the difference between a taper crimp and a roll crimp.
Not one word about over pressure and crimping, not one. http://www.exteriorballistics.com/reloadbasics/crimp.cfm |
http://www.ar15.com/forums/t_6_42/394487_Big_boom_______PICTURES_NOW______Page_2_.html&page=1  My Guess- A Lee Factory Crimp die was used on reloading. The crimp was to deep into the M193 bullet, cutting it almost in half. On firing, bullet separated, leaving an obstruction in the barrel?  High Pressure resulted.. Not soft brass. The primer flowed back into the firing pin hole. The primer would not do this at normal pressures. The case head also flowed back into the ejector hole, another sign of very high pressure. Note that post starts with 1 bullet & ends with a different bullet. Confusing.
|
|
Quoted:
http://www.ar15.com/forums/t_6_42/394487_Big_boom_______PICTURES_NOW______Page_2_.html&page=1 http://i338.photobucket.com/albums/n420/joe1944usa/Firearms%20%20and%20%20Reloading/KABOOM/VeryHighPressure.jpg My Guess- A Lee Factory Crimp die was used on reloading. The crimp was to deep into the M193 bullet, cutting it almost in half. On firing, bullet separated, leaving an obstruction in the barrel? High Pressure resulted.. Not soft brass. The primer flowed back into the firing pin hole. The primer would not do this at normal pressures. The case head also flowed back into the ejector hole, another sign of very high pressure. I doubt the Lee Factory Crimp was the result of this failure. There are incidences with older ammunition where the bullet actually cold welded itself to the case mouth. Firing these rounds sent the bullet and the separated case mouth down the bore at to the target. No KB occurred. |
|
So how much effect does crimping have on pressue/pressure.curve? GI ammo has a bullet pull of 35 to 45 lbs. My testing shows, if the bullet expands the case neck on seating .002" or more, the round will be in the 35 to 45 lb area. What effect annealing has on neck tension, i dont know. Have not tested it. Interesting subject.
|
|
The only way a crimp would raise pressure , is if it was cold welded or so completely over done that , as a result of the over done crimp, the bullet was fubar'ed. I have never seen any such a
beast since it probably won't chamber anyhow. Very doubtful that a crimp could result in a kaboom.. |
|
Quoted:
The only way a crimp would raise pressure , is if it was cold welded or so completely over done that , as a result of the over done crimp, the bullet was fubar'ed. I have never seen any such a beast since it probably won't chamber anyhow. Very doubtful that a crimp could result in a kaboom.. Good point, If a crimp is that extreme it would most likely distort the case so bad it would not chamber or cause the neck to lose tension altogether resulting in extreme set-back and a possible KB. |
|
We do not have access to Pressure testing equipment, but we do have Chronys. With increased pressure there is increased velocity.
Run some test over the Chrony. Start with a known safe load with no crimp and record velocity. Gradually increase the crimp to it's usable max without distorting the case itself. Record results. My guess is that you will see little to know measurable increase in velocity. Certainly not enough increase that would cause a firearm to "blow-up". No velocity increase = no pressure increase. |
|
Quoted:
We do not have access to Pressure testing equipment, but we do have Chronys. With increased pressure there is increased velocity. Run some test over the Chrony. Start with a known safe load with no crimp and record velocity. Gradually increase the crimp to it's usable max without distorting the case itself. Record results. My guess is that you will see little to know measurable increase in velocity. Certainly not enough increase that would cause a firearm to "blow-up". No velocity increase = no pressure increase. The chronograph only tells what the average pressure down the bore was, not the peak pressure. Since the peak pressure lasts only a very short time it does not have that much affect on the area under the pressure-time curve. |
|
Quoted:
The crimp was to deep into the M193 bullet, cutting it almost in half. On firing, bullet separated, leaving an obstruction in the barrel] You can't heal retardation. Whomever did this should not be allowed near guns or ammunition.... and should be fitted with a foam helmet. 
|
|
Quoted:
More crimp = more pressure. The crimp only has a small part in light to medium-heavy loads, but a heavy crimp on a max load could result in a blown up gun. That's one reason why we work up our loads. I believe rifles are Prof tested at around 130% of max. There is no way in _____ that simply applying a crimp is going to blow up a gun. Can it result in pressure signs like flattened primer, sure. I will even go as far as maybe a blown primer. You have to have some kind of major malfunction or load mistake to blow up a gun. BTW: A Lee FCD for rifle can not produce a substantial over crimp. The collet closes on itself before that can happen. |
|
Quoted: You can't heal retardation. Whomever did this should not be allowed near guns or ammunition.... and should be fitted with a foam helmet. Quoted: Quoted: The crimp was to deep into the M193 bullet, cutting it almost in half. On firing, bullet separated, leaving an obstruction in the barrel] You can't heal retardation. Whomever did this should not be allowed near guns or ammunition.... and should be fitted with a foam helmet. Keep your comments respectful. If you want to call someone a name, don't do it in this forum. dryflash3
|
|
I always try to put numbers to things when thinking about them.
Here's what I was thinking when thinking about this question - let's look at the stresses involved. If it takes approximately 30 lb to pull the bullet out of a case neck, then that equates to approximately 40 lb per linear inch around the perimeter of the case mouth (0.7" linear inches at case mouth). When you fire the cartridge and the pressure begins to build to several thousand psi, you get about several hundred pounds pushing on the bullet (10,000 psi -> 400 lb). This equates to several hundred pounds per linear inch around the perimeter of the case mouth. From the example above, we know this is well in excess of what's required to release the bullet. In fact, it takes less than 1,000 psi to achieve the 40 lb per linear inch required to release the bullet. We also know 10,000 psi is way below the peak pressure. From this we know the bullet has been released from the case mouth long before peak pressure. So, my guess is this - crimping only directly affects the pressure curve during the time it takes to build up to 1,000 psi. The difference in that early time can affect the shape of the pressure curve after the bullet releases but it's effect is very likely to be very small. I do not believe anyone would be able to measure the effect using a commercially available chronograph. This assertion is based upon considerations of the very large number of samples required to detect what I believe would be tiny changes in muzzle velocity. The chronographs and reloads have too much variability to see the difference. |
|
Quoted:
http://www.ar15.com/forums/t_6_42/394487_Big_boom_______PICTURES_NOW______Page_2_.html&page=1 http://i338.photobucket.com/albums/n420/joe1944usa/Firearms%20%20and%20%20Reloading/KABOOM/VeryHighPressure.jpg My Guess- A Lee Factory Crimp die was used on reloading. The crimp was to deep into the M193 bullet, cutting it almost in half. On firing, bullet separated, leaving an obstruction in the barrel? High Pressure resulted.. Not soft brass. The primer flowed back into the firing pin hole. The primer would not do this at normal pressures. The case head also flowed back into the ejector hole, another sign of very high pressure. Note that post starts with 1 bullet & ends with a different bullet. Confusing. You can't over crimp with the lee die... |
|
Quoted:
You can't over crimp with the lee die... Quoted:
Quoted:
http://www.ar15.com/forums/t_6_42/394487_Big_boom_______PICTURES_NOW______Page_2_.html&page=1 http://i338.photobucket.com/albums/n420/joe1944usa/Firearms%20%20and%20%20Reloading/KABOOM/VeryHighPressure.jpg My Guess- A Lee Factory Crimp die was used on reloading. The crimp was to deep into the M193 bullet, cutting it almost in half. On firing, bullet separated, leaving an obstruction in the barrel? High Pressure resulted.. Not soft brass. The primer flowed back into the firing pin hole. The primer would not do this at normal pressures. The case head also flowed back into the ejector hole, another sign of very high pressure. Note that post starts with 1 bullet & ends with a different bullet. Confusing. You can't over crimp with the lee die... Agreed, and as bfoosh has pointed out, if you really overcrimp a roll or taper crimp you have distorted the case so badly it most likely will not chamber. |
|
Quoted:
http://i338.photobucket.com/albums/n420/joe1944usa/LeeFCD.jpg Internet photos using the FCD. I have never used a FCD & never will.  http://i338.photobucket.com/albums/n420/joe1944usa/FirearmsReloading102/LeeFactoryCrimpDie.jpgThen like most naysayers regarding the Lee Factory Crimp die, your comments regarding it use and abuse are actually meaningless. |
|
Quoted:
http://i338.photobucket.com/albums/n420/joe1944usa/LeeFCD.jpg Internet photos using the FCD. I have never used a FCD & never will. http://i338.photobucket.com/albums/n420/joe1944usa/FirearmsReloading102/LeeFactoryCrimpDie.jpgWell... there is proof that even the simplest things can be messed up. I'm sure that if the directions are disregarded, as well as SAMMI specs for the resized case, then you can also produce ammo crimps like that. I'd be willing to bet that those cartridges show pressure signs... from the neck protruding into the throat of the barrel.... as a result of pushing the shoulder way to back, or not trimming them to a correct length Back to the original question... All of this has got me wondering about elevated pressure from the crimp.... or unbeknownst to us ... the problem of "Cold" or pressure welding. I have personally experienced this in a .44 Mag reloaded by myself. While I know that it can wreak havoc on accuracy, has anyone ever seen a graph or chart on pressure increases ? Here is a link to an article that has a form of increased neck pull effecting a known accurate round... http://bulletin.accurateshooter.com/2013/05/ultrasonic-cleaning-case-neck-friction-and-bullet-seating/ |
|
Quoted:
The crimp only has a small part in light to medium-heavy loads, but a heavy crimp on a max load could result in a blown up gun. . No, if the gun blows up, you've done something a lot worse than just a heavy crimp. Keep in mind that guns are tested to 125% to 150% of maximum pressure before leaving the factory. Blowing up your gun means you got into the 175%-200% range. There is simply no way that an extra-heavy crimp is going to do that. |
|
Quoted:
No, if the gun blows up, you've done something a lot worse than just a heavy crimp. Keep in mind that guns are tested to 125% to 150% of maximum pressure before leaving the factory. Blowing up your gun means you got into the 175%-200% range. There is simply no way that an extra-heavy crimp is going to do that. Quoted:
Quoted:
The crimp only has a small part in light to medium-heavy loads, but a heavy crimp on a max load could result in a blown up gun. . No, if the gun blows up, you've done something a lot worse than just a heavy crimp. Keep in mind that guns are tested to 125% to 150% of maximum pressure before leaving the factory. Blowing up your gun means you got into the 175%-200% range. There is simply no way that an extra-heavy crimp is going to do that. Excellent point. |
|
Quoted:
http://i338.photobucket.com/albums/n420/joe1944usa/LeeFCD.jpg Internet photos using the FCD. I have never used a FCD & never will. http://i338.photobucket.com/albums/n420/joe1944usa/FirearmsReloading102/LeeFactoryCrimpDie.jpgThe way the Die works that would be impossible. My guess is that loader used the wrong caliber die. |
|
Quoted:
The way the Die works that would be impossible. My guess is that loader used the wrong caliber die. Quoted:
Quoted:
http://i338.photobucket.com/albums/n420/joe1944usa/LeeFCD.jpg Internet photos using the FCD. I have never used a FCD & never will. http://i338.photobucket.com/albums/n420/joe1944usa/FirearmsReloading102/LeeFactoryCrimpDie.jpgThe way the Die works that would be impossible. My guess is that loader used the wrong caliber die. That or they left trim length way long after resizing. |
Armory Sponsor