To crimp or not to crimp?

[j8064]

Whoa, seems I've lit the fuse of a "resident reloading expert".

Frankly, I'll continue my due diligence of safe reloading in the future. That means understanding and knowing the reloaded rounds I build are safe and will perform as expected. That also includes what crimps and types that are necessary for the rounds I build.

I'll continue to base my reloading practices on the round, propellant, bullet, primer and the firearm in which my reload is intended.

Y'all can reload any way you want. But if you do not undersatand and employ fundamental safe reloading practices, please never fire any of your reloads near me, my family or my friends.

Beyond that...

 

[Traveler]

My 9mm and 45 Auto get the crimp recommended by the reloading manual. (Lee factory crimp die made my 9mm life better)

 

[Bikebreath]

My 9mm and 45 Auto get the crimp recommended by the reloading manual. (Lee factory crimp die made my 9mm life better)

I do a Lee Factory Crimp on my 9mm and 45ACP. They are the only two I load these days.

 

[mopar92]

I reload using a Lee turret with clean used brass. I have reloaded for maybe three years. I hear some people say crimping hurts accuracy on pistol ammo?

Crimping does hurt accuracy. The act of crimping places mechanical stress on the projectile and the cartridge casing deforming it and causing a variance in how the round contacts the rifling in the barrel so it does produce a (VERY) slight negative effect on accuracy.

Now for the benefits of crimping, it assures quality control and helps the beginning reloader have a reliable way of maintaining COAL, helps prevent (but does not eliminate) the chance of bullet setback which can create an overpressure situation and destroy/harm the firearm/you. It also helps to prevent "in magazine" bullet setback. On some harder recoiling semi autos the jostling of the rounds in the magazine can set back the bullet before it is even chambered again creating a dangerous condition. There's also the rare cartridge seperation that can have a bullet seat in the chamber and the casing get ejected (most common with frangible ammo) that can leave unburnt, uncontained powder in the chamber.
On revolvers bullet jump is a known preventable malfunction that occurs when an uncrimped or lightly/improperly crimped bullet jumps forward in the cylinder and wedges against the frame tying up the gun and generally needing a gunsmith or experienced owner to fix.

The above all applies to rifles also and US Mil Spec ammo is all crimped for reliabilty and protection from the elements.

TL;DR Crimp ammo for safety and an enjoyable experience.

 

[Uncle Duke]

Here's a good read from Sierra on many of the considerations and differences inherent to service rifle reloading.

Sierra indicates clearly that Seated Bullets can and will move, either through encountering sufficient mechanical resistance upon chambering, or through inertia generated by the sudden cessation of rapid forward motion. How much force is required in either instance? I don't know. The lab might know or be able to measure or replicate the exact forces required to make it happen. I can't say. I'm not smart enough to be able to know. What I can know is that in lieu of being as smart as the lab folks, I will accept the test results of an accredited industry source. Because what I can also know is what my non-accredited thinking tells me.

Ever use the thumb test and have a bullet move? Well, "enough" force was applied in this instance. I think it safe to assume that we'd all likely agree that that's a potential problem if I can move a bullet using only the force I can generate with my hand. Bullet didn't move? Not "enough" force was applied. That's good! Good enough? Well....I hope so. But have I replicated chambering forces? Maybe. Maybe not.

Ever put a cartridge in an inertia bullet puller, strike the hammer and the bullet doesn't move? Then strike it harder and out comes the bullet from the case completely? Had it move somewhere in between fully seated and fully removed? Again, one unknown measure of inertia was insufficient to move the bullet at all. A second unknown measure of inertia (I hit it "harder") removed the bullet from the cartridge case entirely. A third unknown measure ( I hit it "somewhere in between") meant a degree of forward movement somewhere between the two mentioned extremes.

Just a couple of examples to help me in my mind to visualize what can occur with bullet movement given sufficient levels of either mechanical resistance or inertia.

Make your own judgments. Me, I know what mine are. I don't want seated bullets moving. Not in semi-autos. Not in lever actions. Not in bolt guns. Not in revolvers. Not in any firearm. As Sierra mentions with service rifle specifically, and alludes to generally, each action type presents its own set of specific challenges and considerations.

Degraded accuracy with a mechanical crimp? No doubt in my mind there's an element of that. I know that with certainty because when loaded both ways, the target produces results I can clearly see. Also no doubt in my mind that an AR isn't a bench rifle, at least not to me. And if it is, I'm not and never will be good enough to take the left nut as opposed to the right nut off a gnat with an AR, even if the precision potential was there in an AR for me to be able to do so. YMMV, but that's not primarily what I need in an AR. Me, I'll accept that small level of trade off. And where I won't, the AR won't be my first choice for precision. All things considered, and for me and my purposes, there's much to be said for concepts I think of as plenty accurate and plenty precise enough.

The information below is worth the read generally. One man's opinion.

http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm

 

[Biggfoot44]

I'll make the statement that all (conventional) pistol rounds need some amount of crimp, if only little more than removing the flare. Some situations only need very light, some medium, some heavy.

Crimp per se is only one portion of overall bullet resistance, case neck tension is the other factor. All pistol rounds need bullet resistance for several reasons : Prevent bullet jump from recoil. Prevent being pushed in in feeding in bottomfeeders. Provide for complete and consistant powder ignition.

And a properly designed and seated pistol bullet will NOT be damaged by s suitable crimp. A proper pistol bullet will have a canalure or a crimp groove. ( Think of knurled swaged bullets as having a canalure over the entire bearing surface.)

Plated bullets can potentially be tricky. Ideally you would be achieving most of your bullet resistance through case neck tension, and only a light crimp. *In Theory* the crimp will damage the plated bullet. In my occasional experience with them, I used moderte roll crimp, and my accuracy was within what I would have expected with jacketed from that gun ( iirc 1.25in @ 25yd) , so any bullet damage wasn't a limiting factor. ( Can vary with bullet, wall thickness, expander dia, etc )

 

[StickShaker]

I'm new to reloading but I have experience working with metals. I'm experimenting with crimps at the moment because I really don't want them unless it's necessary. I feel that unless there is cannelure, a taper crimp can't provide any extra hold unless you crimp heavily and deform the bullet. Even then, there is a possibility that you can make the bullet looser because of the springback differences between lead (very slight) and a thin brass tube (quite a bit). I feel the real holding power comes with the proper inside neck diameter vs. bullet and the hardness of the brass.

I loaded up some very light .38 Special target loads with no roll crimp using 4 different bullet styles, two without cannelures and two with. I noticed with the (new to me) once fired brass, that there was still a little bit of roll crimp left over which made me bell more than I wanted to because it was shaving copper plating on one bullet style and lead on the others. An inside chamfer on the case mouth took care of that problem but it's one less step if I can get by with no crimp. I drew a sharpie line at the bullet/case junction and will see if there is any movement after each shot.

 

[ras_oscar]

I am at the trying stuff phase of the learning curve to produce better quality ammo. I have tried plated,lead,and now jacketed. The learning process has been fun so far.

Plated bullets have a thinner copper coating over the core than jacketed. That's why you can't do a heavy crimp, it could cut the jacket. I do a light crimp on all my rounds. FYI, I only reload pistol calibers, not rifle.

 

[alucard0822]

I'll make the statement that all (conventional) pistol rounds need some amount of crimp, if only little more than removing the flare. Some situations only need very light, some medium, some heavy.

Crimp per se is only one portion of overall bullet resistance, case neck tension is the other factor. All pistol rounds need bullet resistance for several reasons : Prevent bullet jump from recoil. Prevent being pushed in in feeding in bottomfeeders. Provide for complete and consistant powder ignition.

And a properly designed and seated pistol bullet will NOT be damaged by s suitable crimp. A proper pistol bullet will have a canalure or a crimp groove. ( Think of knurled swaged bullets as having a canalure over the entire bearing surface.)

Plated bullets can potentially be tricky. Ideally you would be achieving most of your bullet resistance through case neck tension, and only a light crimp. *In Theory* the crimp will damage the plated bullet. In my occasional experience with them, I used moderte roll crimp, and my accuracy was within what I would have expected with jacketed from that gun ( iirc 1.25in @ 25yd) , so any bullet damage wasn't a limiting factor. ( Can vary with bullet, wall thickness, expander dia, etc )

This, the ideal powder and charge will vary depending on the caliber/handgun and the use, same with a crimp. For light to moderate FMJ loads in service caliber autos I use just enough to remove the flare and give a small amount of resistance, using a factory crimp die that also post sizes to ensure good feeding. For heavier Jacketed loads with a cannalure I will crimp a little tighter, Magnum revolver loads, especially with hardcast get a heavy crimp, also seems to give more consistent velocities with the case full of slow powder, and keeps bullets from pulling with heavy recoil. Being Plated tend to be limited to 1200ish FPS, no real need for anything more than a light to moderate crimp.

 

[Magnumite]

Experience has taught me heavy roll crimps work on light and heavy loads. The pull force of the bullet in the case (force required to get it moving) allows pressure to build in a consistent manner, enhancing accuracy. One less variable when building a load. I have seen positive results on the chrono and on targets. I also crimp rifle rounds if a cannular or groove is on the bullets. Heavy with the Lee Collet Crimp Die if available. That is how many, not all, factory rounds are crimped. Again, pull weight.

As read here there are several approaches to crimp. I don't see any discrepencies in the loaders applications except for not crimping handgun rounds... bad juujuu, again, in my experience. Unless in is shooting single shots. YMMV

 

[marc357]

I loaded some ammo for the AR, with no crimp, just to see. Measured OAL. Put one in the mag and let the bolt slam home, chambering a round. Extracted round and measured again.

It was longer.... the sudden stop caused the bullet to slip forward. Repeated with five more rounds. Same same.

Re-seated bullets and crimped them... and will continue to crimp them.

Doesn't have to be a hard crimp in the AR, but it does need it.

If you chamber a round and the bullet doesn't stay put, no matter rifle, pistol, tank gun, howitzer.... it doesn't have enough crimp.

 

[Pinecone]

Pistol rounds have to have some sort of crimp to remove the flare. For semi auto, I taper crimp or factory crimp (Lee FCD). I don't load much revolver, but do roll crimp them.

If you crimp with a lead bullet, the case mouth can dig into the lead. Not a big deal. If you crimp a jacketed bullet that does not have a cannelure for crimping, you will put massive stresses on the bullet and deform the shape. But some rifle bullets (and most revolver caliber jacketed pistol bullets) have a cannelure, so you can crimp those without an issue.

One way that crimping degrades accuracy is that it makes the bullet pull force vary. Because the hardness of teh brass of each case can be slightly different.

 

[marc357]

I give rifle ammo a light taper crimp when using bullets with no cannelure, doesn't deform the bullet. It's a fine line, between just enough and too much.

 

[Magnumite]

Figures...
Using a consistent crimp on ammunition should yield consistent pull weight. Sure, brass thickness, maker, alloy, even work hardening from the number of times reloaded and shot make a difference. Differences in pull weight also occur when not using a crimp from all the above listed factors. Same variables, different technique.