crimping

[redding]

A querie. am i right in thinking that a crimped round would create more pressure and so a higher velocity?

[dannywayoflife]

When ive experimented with crimped loads over a chrono Ive found MV to be almost identical to the uncrimped. What I have found is with some loads the SD and ES was far better with crimping

[terryh]

Redding,

 

The only round I've 'seriously' crimped i.e. put a cannula on the bullet where I wanted it then crimped into this, was a 22K hornet and it made a big difference in accuracy/consistency, not much in velocity. I would put this down to the small case capacity and not a lot of neck to tension and retain the bullet while the primer does its thing before the powder can do its?

 

I put a slight crimp onto 223/5.56 reloads as they are being used in a straight pull, but to be honest not sure if it's necessary, more of a checks and balance thing?

 

I suppose in theory it could increase velocity? But have no empirical data to show this.

 

T

[Andrew]

When ive experimented with crimped loads over a chrono Ive found MV to be almost identical to the uncrimped. What I have found is with some loads the SD and ES was far better with crimping

 

In my experience this is exactly what occurs.~Andrew

[Guest Stacka]

Why crimp what's the reason behind it

[gbal]

Crimping won't normally add enough neck tension to the bullet to increase release pressure enough to have a measure able increase in velocity,and may act to sightly change the pressure curve.It can make tension more uniform in some brass cases,and this can aid consistency.

 

Stacka, the main purpose of crimping is to increase the grip of the brass case on the bullet,often in pistols and military ammo,sometimes in hunting ammo,where the ammo is magazine loaded,and subject to (repeated) recoil forces-especially in self loaders,which tends to loosen/separate the bullet (a bit like a very small inertia bullet puller). Many military FMJ's and some commecial ammo have a cannelure groove on the bullet,and often pistol dies include the option to apply a cannelure crimp, to retain the bullet until firing.

 

Target shooters tend to the other end of the spectrum,with relatively light neck tension-using bushing dies to control this,and their match bullets have no cannelure.Indeed neck tension is often so light that bullets should not be loaded into the lands,lest they slight grip of the land retains the bullet,and if bolt is opened to withdraw an unfired round,the bullet is retained and powder spilled into the action/trigger-messy! Since target shooters tend to want maximum velocity,and need not seat in lands,this again suggests cannelure/crimping offers no real velocity increase normally.

 

gbal

[Andrew]

Why crimp what's the reason behind it

 

I agree to what gbal has said about bullets shifting but sporting ammunition makers use it for the other reasons mentioned: It does reduce Standard Deviation and Extreme Spread. It is not necessary for the bullet to be held in place- except perhaps for the heaviest recoiling cartridges- but they do it to increase uniformity. I have run many comparisons in Hornet, .,223, 308, and 30-06 and in every single case the SD and ES was reduced: This with 10 and 20 shot strings with the only difference being the application of a crimp. While this did not guarantee accuracy from a particular rifle due to incompatibility of the bullet or powder to the weapon, it did produce more uniform results on the chrono. This can only help, even in a less than accurate load. A recent article in Shooting Times (US) has pointed out the benefits of crimping. Would I crimp a BR load made for a custom chamber? No. But all sporting/target loads from a factory chamber get crimped.

 

I trim and crimp all my loads now, and have Lee make custom Factory Crimp Dies for the odd-ball cartridges I shoot so that i can crimp themas well. I should mention that only the Lee Factory Crimp does a proper job of crimping.~Andrew

[dannywayoflife]

I echo what andrew has written. I crimp my 223 AR ammo as it does get a rough journey from mag to chamber but as Andrew says and I said earlier it seems to improve your ES and SD figures. I don't crimp my 308 ammo as it shoots very very consistently (SD 6 ES 11) as is so just want to shoot now! But it's worth playing with when setting up a load!!

[bradders]

I crimp my 223 AR ammo as it does get a rough journey from mag to chamber

OK just stop it right now.......

[Murph]

I agree to what gbal has said about bullets shifting but sporting ammunition makers use it for the other reasons mentioned: It does reduce Standard Deviation and Extreme Spread. It is not necessary for the bullet to be held in place- except perhaps for the heaviest recoiling cartridges- but they do it to increase uniformity. I have run many comparisons in Hornet, .,223, 308, and 30-06 and in every single case the SD and ES was reduced: This with 10 and 20 shot strings with the only difference being the application of a crimp. While this did not guarantee accuracy from a particular rifle due to incompatibility of the bullet or powder to the weapon, it did produce more uniform results on the chrono. This can only help, even in a less than accurate load. A recent article in Shooting Times (US) has pointed out the benefits of crimping. Would I crimp a BR load made for a custom chamber? No. But all sporting/target loads from a factory chamber get crimped.

 

I trim and crimp all my loads now, and have Lee make custom Factory Crimp Dies for the odd-ball cartridges I shoot so that i can crimp themas well. I should mention that only the Lee Factory Crimp does a proper job of crimping.~Andrew

Plus 1 on this. I found a slight increase in MV-about 25 fps. My understanding of crimping is that it improves accuracy on loads that are seated far from the lands and it definitely improves es and sd. I did a few experiments with different sized crimps from one thou to 10 thou and found that a 6 thou crimp gave me the best results. A lighter crimp actually saw a slight reduction in MV- don't ask me why. On average crimping reduced es and sd by half. One of my loads had an es of 40 fps uncrimped and 22fps crimped with no pressure signs in fairly hot loads.