Factory crimp or not???

attila787 · August 17, 2009, 12:18 PM

I'm a little confused I see some people factory crimping their cases and others that don't. I will be shooing both from a bolt and semi-auto (.308) should I crimp my cases????

Can you guys tell me the why and why not when it comes to crimping your cases.

**Unclenick** · August 17, 2009, 12:32 PM

Crimping makes it harder to dislodge or move the bullet if you drop the ammo on the ground or if it is slammed up a loading ramp fast. I have never had any problems with non-crimped match bullets in gas guns in .30-06, .308 Win, or .233 Remington in Garands, M1A's, or AR's, and I've shot more than just a few rounds through these devices. For lubricated swaged lead bullets, that is another matter. Then a crimp is essential as they move in the case necks too easily.

What you will find, if you examine the ammunition, is that rapid chamber will actually set a case shoulder back a little. And while a loading ramp can push a bullet back a little, the sudden stop in the chamber can also pull it a little, like an inertial bullet puller. Chamber and extract a few rounds, measuring the bullet ogive-to-case head location before and after to see where these forces wind up balancing in your gun. Also do it with singly loaded rounds as well as magazine fed to learn if there is a difference.

Crimping also increases start pressure at ignition. In some guns and ammunition component combinations, this helps accuracy and muzzle velocity consistency. In some it makes things worse, so you actually are going to have to try it and see how your ammo shoots with it at the ranges you are interested in? Sometimes it helps, sometimes it hinders.

Also, be aware their are two kinds of Lee Factory Crimp dies. The kind Lee makes for rifle rounds crimps the necks and bullets inward with a collet. The kind they make for handguns applies normal roll crimps to revolver ammunition and normal taper crimps to semi-auto ammunition, but in addition have a carbide sizing ring that makes sure the finished round is withing SAAMI specifications for OD as the cartridge is run in and out of the die. This squeezes some lead bullets too much, but others like it just fine. It's a good way to guarantee easy chamber fit, but at to its effect on accuracy, again, you just have to try it with your ammo.

QBall45 · August 17, 2009, 03:11 PM

I crimp everything I shoot. 45ACP LSWC and 223 rem in an AR. I use Lee's factory crimp die for both.

For me its a consistancy thing. I like to have ammo that has a consistant start pressure. It seems for me for improve accuracy.

Like you have found some guys crimp and some do not. You will need to find what works for you.

With handgun loads some amount of crimp is necessary to remove the bell/flair that you put in with your expander die. In rifle loads some guys say that the case neck tension is enough.

Try it for yourself and you be the judge.

Slamfire · August 17, 2009, 04:08 PM

This is what the Lee Factory Crimp die will do to 6.5 SMK bullets. And you won't know it till you pull the bullet.

I have shot at least 15,000 rounds of match bullets through my M1a, never crimped a one, and nothing bad ever happened.

Maybe if you have a Vulcan cannon, that shoots 5,000 rounds per minute, you might worry about ramming speeds dislodging a bullet.

steve4102 · August 17, 2009, 09:43 PM

This is from the experts at Sierra.

Neck Tension

When we stop to consider the vigorous (read, downright violent) chambering cycle a loaded round endures in a Service Rifle, it becomes pretty clear it suffers abuse that would never happen in a bolt-action. This is simply the nature of the beast. It needs to be dealt with since there is no way around it.

There are two distinctly different forces that need to be considered: those that force the bullet deeper into the case, and those that pull it out of the case. When the round is stripped from the magazine and launched up the feed ramp, any resistance encountered by the bullet risks having it set back deeper into the case. Due to the abrupt stop the cartridge makes when the shoulder slams to a halt against the chamber, inertia dictates that the bullet will continue to move forward. This is exactly the same principle a kinetic bullet puller operates on, and it works within a chamber as well. Some years ago, we decided to examine this phenomenon more closely. During tests here at Sierra’s range, we chambered a variety of factory Match ammunition in an AR-15 rifle. This ammunition was from one of the most popular brands in use today, loaded with Sierra’s 69 grain MatchKing bullet. To conduct the test, we chambered individual rounds by inserting them into the magazines and manually releasing the bolt. We then repeated the tests by loading two rounds into the magazine, chambering and firing the first, and then extracting and measuring the second round. This eliminated any potential variation caused by the difference between a bolt that had been released from an open position (first round in the magazine) and those subsequent rounds that were chambered by the normal semi-automatic operation of the rifle. Measuring the rounds before chambering and then re-measuring after they were carefully extracted resulted in an average increase of three thousandths (0.003") of forward bullet movement. Some individual rounds showed up to seven thousandths (0.007") movement. Please bear in mind that these results were with factory ammunition, normally having a higher bullet pull than handloaded ammunition.
To counteract this tendency, the semi-auto shooter is left with basically two options: applying a crimp or increasing neck tension.

30Cal · August 19, 2009, 12:51 PM

If your OALs don't change by more than a handfull of thousandths after you chamber, then crimp is not necessary.

I crimp revolver and leveraction handloads. That's it. I shoot primarily M1A/M1/AR15.

Alleykat · August 19, 2009, 08:00 PM

Unless you roll crimp into a cannelure, your crimping isn't going to have any effect on keeping the bullet from setting back or moving forward.

steve4102 · August 20, 2009, 09:15 AM

Quote:

Unless you roll crimp into a cannelure, your crimping isn't going to have any effect on keeping the bullet from setting back or moving forward.

Have you tested this theory?

I've done a little testing with crimped vs non-crimped vs increasing neck tension in my BAR and Mini-30. In all cased the crimped bullets(non-cannelure) held better than the non-crimped and also better than the one with excessive neck tension. Accuracy with the excessive neck tension was not so good while the accuracy of the crimped rounds was very good, better than the non-crimped.

August 17, 2009, 12:18 PM	#1
attila787 Senior Member Join Date: May 7, 2007 Posts: 259	Factory crimp or not??? I'm a little confused I see some people factory crimping their cases and others that don't. I will be shooing both from a bolt and semi-auto (.308) should I crimp my cases???? Can you guys tell me the why and why not when it comes to crimping your cases.

August 17, 2009, 12:32 PM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Crimping makes it harder to dislodge or move the bullet if you drop the ammo on the ground or if it is slammed up a loading ramp fast. I have never had any problems with non-crimped match bullets in gas guns in .30-06, .308 Win, or .233 Remington in Garands, M1A's, or AR's, and I've shot more than just a few rounds through these devices. For lubricated swaged lead bullets, that is another matter. Then a crimp is essential as they move in the case necks too easily. What you will find, if you examine the ammunition, is that rapid chamber will actually set a case shoulder back a little. And while a loading ramp can push a bullet back a little, the sudden stop in the chamber can also pull it a little, like an inertial bullet puller. Chamber and extract a few rounds, measuring the bullet ogive-to-case head location before and after to see where these forces wind up balancing in your gun. Also do it with singly loaded rounds as well as magazine fed to learn if there is a difference. Crimping also increases start pressure at ignition. In some guns and ammunition component combinations, this helps accuracy and muzzle velocity consistency. In some it makes things worse, so you actually are going to have to try it and see how your ammo shoots with it at the ranges you are interested in? Sometimes it helps, sometimes it hinders. Also, be aware their are two kinds of Lee Factory Crimp dies. The kind Lee makes for rifle rounds crimps the necks and bullets inward with a collet. The kind they make for handguns applies normal roll crimps to revolver ammunition and normal taper crimps to semi-auto ammunition, but in addition have a carbide sizing ring that makes sure the finished round is withing SAAMI specifications for OD as the cartridge is run in and out of the die. This squeezes some lead bullets too much, but others like it just fine. It's a good way to guarantee easy chamber fit, but at to its effect on accuracy, again, you just have to try it with your ammo. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

August 17, 2009, 03:11 PM	#3
QBall45 Senior Member Join Date: April 5, 2008 Location: South Central Minnesota Posts: 584	I crimp everything I shoot. 45ACP LSWC and 223 rem in an AR. I use Lee's factory crimp die for both. For me its a consistancy thing. I like to have ammo that has a consistant start pressure. It seems for me for improve accuracy. Like you have found some guys crimp and some do not. You will need to find what works for you. With handgun loads some amount of crimp is necessary to remove the bell/flair that you put in with your expander die. In rifle loads some guys say that the case neck tension is enough. Try it for yourself and you be the judge.

August 17, 2009, 04:08 PM	#4
Slamfire Senior Member Join Date: May 27, 2007 Posts: 5,261	This is what the Lee Factory Crimp die will do to 6.5 SMK bullets. And you won't know it till you pull the bullet. I have shot at least 15,000 rounds of match bullets through my M1a, never crimped a one, and nothing bad ever happened. Maybe if you have a Vulcan cannon, that shoots 5,000 rounds per minute, you might worry about ramming speeds dislodging a bullet.

August 17, 2009, 09:43 PM	#5
steve4102 Senior Member Join Date: December 23, 2005 Location: Minnesota Posts: 2,955	This is from the experts at Sierra. Neck Tension When we stop to consider the vigorous (read, downright violent) chambering cycle a loaded round endures in a Service Rifle, it becomes pretty clear it suffers abuse that would never happen in a bolt-action. This is simply the nature of the beast. It needs to be dealt with since there is no way around it. There are two distinctly different forces that need to be considered: those that force the bullet deeper into the case, and those that pull it out of the case. When the round is stripped from the magazine and launched up the feed ramp, any resistance encountered by the bullet risks having it set back deeper into the case. Due to the abrupt stop the cartridge makes when the shoulder slams to a halt against the chamber, inertia dictates that the bullet will continue to move forward. This is exactly the same principle a kinetic bullet puller operates on, and it works within a chamber as well. Some years ago, we decided to examine this phenomenon more closely. During tests here at Sierra’s range, we chambered a variety of factory Match ammunition in an AR-15 rifle. This ammunition was from one of the most popular brands in use today, loaded with Sierra’s 69 grain MatchKing bullet. To conduct the test, we chambered individual rounds by inserting them into the magazines and manually releasing the bolt. We then repeated the tests by loading two rounds into the magazine, chambering and firing the first, and then extracting and measuring the second round. This eliminated any potential variation caused by the difference between a bolt that had been released from an open position (first round in the magazine) and those subsequent rounds that were chambered by the normal semi-automatic operation of the rifle. Measuring the rounds before chambering and then re-measuring after they were carefully extracted resulted in an average increase of three thousandths (0.003") of forward bullet movement. Some individual rounds showed up to seven thousandths (0.007") movement. Please bear in mind that these results were with factory ammunition, normally having a higher bullet pull than handloaded ammunition. To counteract this tendency, the semi-auto shooter is left with basically two options: applying a crimp or increasing neck tension.

August 19, 2009, 12:51 PM	#6
30Cal Senior Member Join Date: December 3, 2002 Posts: 1,264	If your OALs don't change by more than a handfull of thousandths after you chamber, then crimp is not necessary. I crimp revolver and leveraction handloads. That's it. I shoot primarily M1A/M1/AR15.

August 19, 2009, 08:00 PM	#7
Alleykat Junior member Join Date: July 26, 2007 Posts: 3,668	Unless you roll crimp into a cannelure, your crimping isn't going to have any effect on keeping the bullet from setting back or moving forward.