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I lightly crimp all my 5.56 and 300blk. Ive heard of a lot of people crimping real hard to compensate for a neck tension issue and they end up bulging the shoulder and running into chambering problems. If you're serious about getting every last FPS, getting the absolute smallest SD and tightest groups, run a couple through various levels of crimp and document your results against an uncrimped control.
 
Here is a few pictures of what happens if a round does telescope into the case and it is fired.

upload_2019-4-30_13-3-50.jpeg
upload_2019-4-30_13-4-7.jpeg
upload_2019-4-30_13-4-26.jpeg
upload_2019-4-30_13-4-45.jpeg
 
It is always interesting to see the comments " I always do ... or never ..., and I have yet to have a problem." Reno's post and pics show what can happen when a bullet gets shoved down into a case and someone is shooting top end 5.56 loads. You never have a problem, right up until you do. I will continue with the Lee factory crimp die because I like my AR's. Almost as much as I like my fingers and eyes. :cool:
 
How do you crimp a bullet without the cannelure? Would running a smaller diameter bushing do essentially the same thing if there was no cannelure?
 
How do you crimp a bullet without the cannelure? Would running a smaller diameter bushing do essentially the same thing if there was no cannelure?
It's possible, just not optimal. You end up pressing the case mouth into the jacket. Some could argue jacket deformation will affect your accuracy. Your mileage may vary.
 
It is always interesting to see the comments " I always do ... or never ..., and I have yet to have a problem." Reno's post and pics show what can happen when a bullet gets shoved down into a case and someone is shooting top end 5.56 loads. You never have a problem, right up until you do. I will continue with the Lee factory crimp die because I like my AR's. Almost as much as I like my fingers and eyes. :cool:

The same can happen if you over crimp. One crucial thing is that if you want to crimp is that all of your cases have to be uniform in length. I do know a couple guys that have blown up ARs because a case happened to be over-long and that caused the crimp to be excessive. I think you can "feel" the difference but when you're cranking out hundreds of rounds, you sometimes "zone out" and miss it.

Personally, I used to crimp but got lazy and felt that it didn't make enough of a difference. But now that I have a Frankford Arsenal case trimmer, uniform trimming is a lot easier. I might go back to crimping. Having said that, I have never had a problem while not crimping.
 
If it telescoped that bad that it blew up the gun, he's got a feeding issue or neck tension issue.

Even crimped cases will allow the bullet to be forced back a bit into the case if there's a feeding issue.
It was factory ammo as well if I remember match grade stuff.

It happened a couple of times before the kaboom took place.

Let's say it opened my eyes to how a little problem could result in a big problem really quickly.

With that said.

To each there own on this subject, it's come up over the years many many times.

If you pay close attention to your ammo and gun. It shouldn't be an issue, but like said above, it isn't a problem until it is.

Ball powders help prevent telescoping, as they do a better job filling the entire case, IE the bullet can't travel too far back into the case.

Carry pistols usually have this occur more, especially if you remove and rechamber the top round in the magazine everyday.
 
Should you...

Yeah.

Do most people... no

Why? More consistent release of the bullet from the case this giving more accuracy.

Why would you crimp?
Bullet coming forward during chambering. Manufacturers do it for liability reasons.

Toast lands butter side up or butter side down, do your own experimenting and see which route works for you.
Yes. I always use a slight crimp on my handloads. Believe it or not, when you have your dies set propeely and lightly crimp, your run-out is going to be better. Hence straighter ammo with less tir, produces more accurate ammo/tighter groups.
 
You use a taper crimp. It doesn't cut into the bullet, just gives more of a grip than not crimping.
The Lee factory crimp die is a taper crimp die. They even claim it is effective on cases that aren't uniform in length. I run my brass through the Frankfort Arsenal Trimmer to ensure a max length of 1.755" after sizing.
 
Interesting conversation.
Usually with a bottleneck case, bullet setback does not cause over pressure , COAL getting longer and approaching the lands is what causes over pressure......If a round is worked up to pressure limit .010" off the lands gets set back it only offers more lede . If that same round sets forward and touches land or takes over half of the available lede it will be a big pressure spike .
 
Interesting conversation.
Usually with a bottleneck case, bullet setback does not cause over pressure , COAL getting longer and approaching the lands is what causes over pressure......If a round is worked up to pressure limit .010" off the lands gets set back it only offers more lede . If that same round sets forward and touches land or takes over half of the available lede it will be a big pressure spike .


I think we're talking about a bullet being pushed WAY back into the case. Not just a few thousandths.
 
I think we're talking about a bullet being pushed WAY back into the case. Not just a few thousandths.
I think there has to be a point where its got enough bullet in the case AND enough berring surface in the neck to seal and cause over pressure .....but if you really research it , its not common .
 
Some further examples of bullet set back or telescoping.


Common occurrence with carry guns is rechambered rounds that should be expired.
upload_2019-5-1_11-46-56.jpeg


Common rifle example, this will still chamber, IE it still can go boom!
upload_2019-5-1_11-48-40.jpeg

Lastly, a gotcha picture. Set back too far! :p
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