Question for reloading gurus

[buckshotshorty]

Simple question ...I've been reloading since 1972 but don't have the answer for this one:

Does increasing crimp increase pressure?

 

[MJFlores]

Yes, I believe so. Anything causing the bullet extra effort to leave the case allows ignition of powder to build, increasing pressure. Tight necks also increase pressure, although a lot of this may not even show in fired cases and primers.

 

[colt_saa]

Not by enough to be meaningful

 

[Cmax]

What type of round? Are you talking roll or taper crimp?

 

[Rule3]

No not really. In revolvers it prevents bullet creep.

Neck tension is what holds the bullet in the case until enough pressure is achieved. In semi autos the tension prevents set back, a taper crimp only removes the flair if there is any.

Take a rifle round like an 223/556 No crimp is needed. Only crimp in semi autos to prevent the bullet from moving in the mag. In a bolt action there is no need to crimp.

In a 44 Mag with a big lead bullet, you crimp in the cannelure to prevent it from moving forward from the recoil of the other rounds,

 

[fredj338]

A heavy roll crimp can bump pressures a bit, taper, not so much.

 

[scooter123]

I read somewhere that the maximum force required to free a bullet from a crimp is approximately 100 lbs. Going back about 40 years to my college Engineering Statics course work indicates that this force is dependent to a large extent on the diameter, so guessing here that 100 lbs. was probably for a 50 BMG. With 1/2 the diameter and 1/2 the circumference a 25 caliber rifle bullet will peak out with a pull force of 50 lbs.

Now, the required pressure to exert that level of force will be equal to the Force divided by the Area. With a circle the Area is (1/2 Dia) squared time PI, or 1/4D^2 x 3.14159. For that 0.25 diameter rifle bullet that area will work out to 0.049 inch^2. So, 50/.049 = 1018.6 psi. What this means is that the pressure induced by a firm rifle crimp will only require something around 1000 psi to get the bullet moving.

While that isn't a lot of pressure a recent experience when I forgot to crimp some 223 ammunition loaded with CFE223 reveals that some powders do need a bit of help with a rapid pressure rise in order to get a good clean burn going. So, while a crimp may not actually contribute to the peak pressure produced during the complete firing cycle I do believe that a crimp can be an essential element in producing a clean shooting and accurate round of ammunition. Currently the two powders that I consider a crimp to be absolutely essential with are the CFE223 as mentioned and H110, a Handgun Magnum Powder.

 

[venomballistics]

Probably good for a few hundred PSI.
the greater effect is uniform PSI

 

[Rule3]

The biggest handgun caliber I load (as to pressure) is the 460 SW Magnum

The maximum pressure of that round is 65,000 PSI I wonder how much of that is due to crimping the mouth into a perforated crimp line on a XTP FMJ bullet?

 

[Krell1]

I read somewhere that the maximum force required to free a bullet from a crimp is approximately 100 lbs. Going back about 40 years to my college Engineering Statics course work indicates that this force is dependent to a large extent on the diameter, so guessing here that 100 lbs. was probably for a 50 BMG. With 1/2 the diameter and 1/2 the circumference a 50 caliber rifle bullet will peak out with a pull force of 50 lbs.

Now, the required pressure to exert that level of force will be equal to the Force divided by the Area. With a circle the Area is (1/2 Dia) squared time PI, or 1/4D^2 x 3.14159. For that 0.25 diameter rifle bullet that area will work out to 0.049 inch^2. So, 50/.049 = 1018.6 psi. What this means is that the pressure induced by a firm rifle crimp will only require something around 1000 psi to get the bullet moving.

While that isn't a lot of pressure a recent experience when I forgot to crimp some 223 ammunition loaded with CFE223 reveals that some powders do need a bit of help with a rapid pressure rise in order to get a good clean burn going. So, while a crimp may not actually contribute to the peak pressure produced during the complete firing cycle I do believe that a crimp can be an essential element in producing a clean shooting and accurate round of ammunition. Currently the two powders that I consider a crimp to be absolutely essential with are the CFE223 as mentioned and H110, a Handgun Magnum Powder.

What he said.........and some of that was WAY over my head.

 

[rck281]

I always thought that the bullet starting to engrave the rifiling and the rotational inertia were major contributors to peak pressure.

 

[planojack]

I have noted definite evidence of increased pressure with heavier crimps. I had obvious elevated pressure in a handgun load. I pulled the bullets and belled the cases and reseated the same bullets with a different crimp. The pressure signs went away.

 

[Ole Joe Clark]

When the powder ignites the first thing that happens is the case swells to fit the chamber and releases the bullet. Any increase in pressure because of a crimp is only for about 1/10 of a second or so. No increase in pressure to amount to anything. Hatcher's Notebook covers this sort of stuff in detail.

 

[rwsmith]

Slow powders...

When the powder ignites the first thing that happens is the case swells to fit the chamber and releases the bullet. Any increase in pressure because of a crimp is only for about 1/10 of a second or so. No increase in pressure to amount to anything. Hatcher's Notebook covers this sort of stuff in detail.

People that use slow powders with heavy bullets think that this little bit enables a more complete burn of the powder. I'd guess that a heavy roll crimp in a cannelure would hold a bullet in place for a few microseconds for this to happen since comparatively the time from ignition until the bullet leaves the barrel is not much more that that.

Some of us are starting to call taper crimping 'debelling' since all it really does is remove the bell on the case mouth. For a taper crimp to make a difference in holding power at all, it would have to deform the bullet, which is counterproductive.

 

[Nevada Ed]

Yes but still within specs........

A very heavy crimp in the 38 snub nose with a lead bullet can
bring out top FPS and pressures.

I always back off the crimp with jacketed bullets to prevent bullet damage that may effect maximum accuracy.

 

[mikld]

Nope, reread posts number two and number three...

 

[JBnTx]

How much crimp is too much crimp?

My revolver loads have a noticeable roll inward, but don't dig into the bullet.

My 454 Casull loads have a ring indented into the top of the crimp. No bullet creep when firing.

 

[DWalt]

I doubt if any pressure increase would be significant. Maybe someone will want to chrono the MV differences between two exactly identical loads, but with and without crimping.

 

[leathermech]

From my perspective, pressure is relative. That is, it's relative to how close you are to "over pressure".

Safety: If you're in the middle of the published load range, I agree with most everybody here. But if you've worked up to the very edge of safe pressure, I think adding a heavy roll crimp might push you past safe.

Performance: I will say, without reservation, crimp matters on the target with my 44 loads at 100 yards but doesn't matter a bit to my 38 Special on a practical course.

 

[Nemo288]

"What this means is that the pressure induced by a firm rifle crimp will only require something around 1000 psi to get the bullet moving."

Which is why there is a problem of the primer starting the bullet moving before the powder is ignited properly.
This can show up when you use a magnum primer when it's not needed.
Some hard core riflemen have even used pistol primers to try and get around this in the pursuit of ultimate accuracy.

I only use the minimum crimp necessary in any application.
The only time I roll completely into the cannelure is with top magnum revolver loads.
Take a look at some commercial ammo for lever rifles or revolvers.
They also use the least crimp they can get away with.
Not sure what their philosophy is for this but it's what I have observed in the few rounds I have bought (mostly 444 and 44 Special).

===
Nemo