Crimping and cannelures

[sam23]

Hi,
I am just getting into reloading for my rifles. I have a 30-30 lever action and a 270WIN both used for hunting so I have been told that both of these need to be crimped. I have a few questions about the process that hopefully someone can give me a hand with:

1. Do I need to use a cannelured projectile to be able to crimp or can any "straight" projectile be crimped?

2. Does a cannelured bullet crimp itself during the bullet seating stage on the press or do you have to use one of the dedicated crimping dies?

3. I have heard the terms taper and roll crimp used. What is the difference between these and when should each be used? Which does the Lee Factory Crimp die give?

4. Does crimping affect the pressure inside the cartridge when fired to the extent that I need to change the amount/type of powder used?

5. When crimping a cannelured bullet, does the cannelure have to be positioned right on the rim of the brass or does it sit further into the next? I have seen projectiles with multiple cannelures so I don't understand how they work. Do they get a crimp in each cannelure?

Thanks!

 

[dahermit]

I am just getting into reloading for my rifles. I have a 30-30 lever action and a 270WIN both used for hunting so I have been told that both of these need to be crimped. I have a few questions about the process that hopefully someone can give me a hand with:

1. Do I need to use a cannelured projectile to be able to crimp or can any "straight" projectile be crimped?

You only need to crimp the 30-30 with a tubular magazine. No need to crimp the .270.

2. Does a cannelured bullet crimp itself during the bullet seating stage on the press or do you have to use one of the dedicated crimping dies?

You do not have to use a dedicated crimping die. The dies made for the 30-30 will have a crimping feature and can be adjusted to crimp or not.

3. I have heard the terms taper and roll crimp used. What is the difference between these and when should each be used? Which does the Lee Factory Crimp die give?

Neither, the Factory Crimp Die for rifles uses a collet that performs the unique crimp. Taper crimps are normally associated with autoloading handgun cartridges that headspace on the mouth of the case.

4. Does crimping affect the pressure inside the cartridge when fired to the extent that I need to change the amount/type of powder used?

No, but if changing from a load worked-up without a crimp to a crimped load, recheck your group and zero.

5. When crimping a cannelured bullet, does the cannelure have to be positioned right on the rim of the brass or does it sit further into the next?

A good place to put the crimp is in the middle of the cannelure. Small changes in seating depth may be experimented with when looking for best accuracy.

I have seen projectiles with multiple cannelures so I don't understand how they work. Do they get a crimp in each cannelure?

No, use one or the other. The multiple channelures are for the purpose of giving the option of finding optimal seating depth or Cartridge Over All Length (COAL).

 

[TimSr]

Dittos to what dahermit said.

I'll just add that I've never seen a flat nose bullet made 30-30 that did NOT have a cannelure.

Your die that seats the bullet is also the crimping die. It will give you the type crimp you need for a given caliber. Discussions often give the impression that you can choose what type crimp to use, but it's dependent upon your crimp die. Some people purchase an additional unique crimp die, Lee's factory crimp die, but your standard crimp/seating die in your die set will do the job just fine.

The case neck tension is the major factor in holding your bullet in place, especially with bottleneck rifle cartridges.

 

[F. Guffey]

I have seen projectiles with multiple cannelures so I don't understand how they work. Do they get a crimp in each cannelure?

If the bullet has a cannelure and the reloader chooses to crimp the crimp must be applied at the mouth of the case in the canneulure. And then there are the few reloaders that use bullet hold. I want all the bullet hold I can get because there are too many conflicts when using neck tension.

When it comes to crimping I can not miss because I have a machine that applies a canneulure to a bullet that dies not have one. I do not use it but I have one just in case.

F. Guffey

 

[NoSecondBest]

Both the first two answers are spot on....well written. I've been loading for going on 55 years and the answers given are 100% correct. If you have a Lyman 49th Edition loading manual, please read all the info in the manual, not just the "recipes". If you don't have one, get one. I have a lot of loading manuals and none of them are nearly as good as this one in helping a new loader get started. Good luck, be safe, have fun.

 

[sam23]

Thanks guys. If the normal bullet seating die creates a crimp, why does the Lee Ultimate 4 Die set include both the bullet seater and a factory crimp die?

If they call it the "factory" crimp die, is that implying that all rounds that come from the factory are crimped?

If I want to crimp, do all of my cases need to be trimmed to uniform length every time I reload? I was hoping that is a step that I could cut out to save some time.

 

[NoSecondBest]

You really should use cases that are uniform length for best results. That's part of the process I would never skip. I don't trim each time, I check the cases to see if they are fairly uniform and not out of spec. If they are, I trim. If they aren't, I don't. If I'm loading for max accuracy, I always trim. It doesn't take that long and skipping steps in the loading process is never a good idea.

 

[sam23]

I would still measure them often too check they are an acceptable length but I didn't want to trim each time in order to make the brass last longer. I had thought that trimming each time would partly negate the fire-forged advantage and the accuracy that gives.

Most of my shooting is close range hunting so I don't need extreme accuracy. If my case lengths are very slightly different, will the crimping not work or will it still work? I was hoping to use quick change bushings. Can I only use those quick change bushings if I trim the cases every reload? If I didn't trim, would I need to reset the seating die each time? Or will that minor difference not effect it too much for my purpose/expectations?

 

[Unclenick]

Sam23,

Bullets with multiple cannelures are for different seating depths in different cartridges. A good example is 44 Magnum and 44 Special. Both have about the same SAAMI cartridge maximum overall length, but the cases are different lengths. As a result, a bullet to be used in either cartridge needs two cannelures for the two different case lengths to come out with the nearly same overall cartridge length.

Average pressure will go up a little with a crimp. Crimps slightly delay release of the bullet by the case neck, letting the powder build a little more start pressure before it gets the bullet under way. This causes the pressure peak to occur slightly earlier than when you don't use a crimp, so expansion of the powder space by the bullet moving forward is a little less at the peak. With the same amount of gas in slightly less space, the pressure is a little bit higher. If it were much, though, the load manuals would all publish different loads for crimped cases. They don't. So it's not a dangerous increase.

Revolver cartridges and cartridges for tubular magazines in rifles generally need crimping. The former to prevent bullets backing out, the latter prevent them being pushed deeper into a case. Semi-auto pistol cartridges also frequently get at least a light crimp, especially for lubricated lead bullets to prevent recoil and feed ramp contact pushing bullets deeper into the case. In a gun like your 270, unless you are shooting lead bullets, you are unlikely to see any forces that will seat the bullet deeper unless you drop a bullet on its nose, so the crimp is then optional and used only if it improves accuracy.

Test for accuracy improvement at the longest range you want to use the cartridge at. At very long ranges, the slight distortion of the bullet by crimping can have an adverse effect on accuracy, and that's the reason for testing at your longest practical range. You might get an accuracy improvement at 100 yards that has gone away by 300 yards and is worse at 600 yards. Only by testing at your longest range can you see if you are making an overall improvement with it or not.