300 WM. Crimp or not to crimp?

[Calvin45]

I doubt that you need to crimp.

I do crimp loads for one of my 300 win mags though. I had trouble getting the 181g hammers to stay put with a compressed load of H1000 but it was super consistent and accurate even with the crimp so that's what I do.

I also crimp loads for my 358 STA cause it kicks like a mule!

The hammers don't have a ton of bearing surface so that actually makes a ton of sense. With "normal" bullets even the most compressed loads I've done have never caused bullets to creep out of the case over time. But nonetheless, in cartridges intended to be fed from a magazine, in heavy recoiling rifles, using compressed loads, crimping seems more sensible.

And as for the short neck of the 300 win, it has never caused me a moments trouble, there have been no load issues that wouldn't have been solved with a longer neck in my experience with the round. It's probably my favourite cartridge. All the supposed negatives of that short neck seem academic at best.

 

[MagnumManiac]

Ok, I'll bite. Reduce neck tension??? What am I misunderstanding here?

Misunderstanding???
It's quite simple, the amount of case neck that is rolled into the cannelure and, the portion just behind it are no longer bearing on the bullet.
Also, a very heavy crimp may/can cause the entire neck to come away from the bullet a smidge, say 1 10,000th of an inch reducing tension.

It is easily measured with a micrometer that reads to the fourth decimal place.

Cheers.

P. S.
Factory ammo is crimped because it raises start pressure and they KNOW this causes low ES with faster powders they generally use to save costs. This is why factory ammo works across a wide range of firearms.

 

[Mram10us]

Misunderstanding???
It's quite simple, the amount of case neck that is rolled into the cannelure and, the portion just behind it are no longer bearing on the bullet.
Also, a very heavy crimp may/can cause the entire neck to come away from the bullet a smidge, say 1 10,000th of an inch reducing tension.

It is easily measured with a micrometer that reads to the fourth decimal place.

Cheers.

P. S.
Factory ammo is crimped because it raises start pressure and they KNOW this causes low ES with faster powders they generally use to save costs. This is why factory ammo works across a wide range of firearms.

It doesn't make sense that crimping the neck into the brass would reduce neck tension. You go from having a smooth inner neck for the bullet to align with, to having the neck material crimped into the bullet surface. I disagree that it reduces neck tension to crimp, but will do more research.

 

[mwkelso]

@MagnumManiac
Just for my understanding, your knowledge is that crimping reduces neck tension. Is this because there is less bearing surface between the brass and bullet?
If so, is there a point where a heavy enough crimp would increase neck tension rather than reduce it?
Thanks in advance.

 

[Mram10us]

According to rcbs, crimping is used to keep the bullets from moving, while in the magazine, of heavy recoil cartridges. To me, that means, it increases the neck tension so the bullet doesn't move.

 

[MagnumManiac]

I'll explain it differently.
Neck tension is totally different AND separate from crimping.
Crimping is ONLY a means of holding a bullet in place from impact, it does not increase neck tension. Neck tension, or interference, is governed by the amount of springback in the brass neck, nothing more.
ANY bullet movement reduces neck tension instantly, even if crimped.
An example, many late 19th century cartridges were crimped AND neck tension was set just prior to the crimp, which was done in one operation where a set of plier type crimp, either vertical or horizontal were forced into the neck around the cannelure.
This pressure was enough that neck tension was lost, in other words, it reduced the neck tension by displacing brass in the neck so that the bullets were held ONLY by the crimp. They would actually wobble in the neck, but not fall into the case or out of it.

Cheers.

 

[Mram10us]

I thought neck tension was "the amount of tension the brass neck exerts on the bullet, thus increasing the amount of force needed to move that bullet."
Crimping increases the force needed to move the bullet, thus increasing neck tension. I just wanted to say it another way so new guys don't get confused

 

[Deleted member 107796]

As you can see by the responses, crimping still comes under the heading of mystery for those without significant experience with crimping. The WSM line does have short shoulders and my 7wsm is why I started crimping. I saw that there were cases where the neck tension was not enough to prevent the bullet from slipping a bit under force. I crimp for this, my 338wm and a few others when I load cannelured bullets. The result is what our friend, Reloader, quoted here and can be found from other sources... it may or may not help SD and other factors related to precision and accuracy:

"Like I said in my post, I've found crimped loads to produce slightly better accuracy and slightly better SD. The paper and chrono don't lie. You can't knock it until you've tried it.
This link pretty much sums it up:

http://www.accuratereloading.com/crimping.html

My results were very much the same.
There's another link on AR showing the lowered SD values when using the Lee FCD with a 308. Saeed could point you to it.
The fact is Crimping can improve things. May not make every rifle shoot better but, I'd venture to say it will not hurt anything if done properly."

 

[West Calamus]

As you can see by the responses, crimping still comes under the heading of mystery for those without significant experience with crimping. The WSM line does have short shoulders and my 7wsm is why I started crimping. I saw that there were cases where the neck tension was not enough to prevent the bullet from slipping a bit under force. I crimping for this, my 338wm and a few others when I load cannelured bullets. The result is what our friend, Reloader, quoted here and can be found from other sources... it may or may not help SD and other factors related to precision and accuracy:

"Like I said in my post, I've found crimped loads to produce slightly better accuracy and slightly better SD. The paper and chrono don't lie. You can't knock it until you've tried it.
This link pretty much sums it up:

http://www.accuratereloading.com/crimping.html

My results were very much the same.
There's another link on AR showing the lowered SD values when using the Lee FCD with a 308. Saeed could point you to it.
The fact is Crimping can improve things. May not make every rifle shoot better but, I'd venture to say it will not hurt anything if done properly."

Excellent Link Co Guy, interesting

 

[Calvin45]

As you can see by the responses, crimping still comes under the heading of mystery for those without significant experience with crimping. The WSM line does have short shoulders and my 7wsm is why I started crimping. I saw that there were cases where the neck tension was not enough to prevent the bullet from slipping a bit under force. I crimp for this, my 338wm and a few others when I load cannelured bullets. The result is what our friend, Reloader, quoted here and can be found from other sources... it may or may not help SD and other factors related to precision and accuracy:

"Like I said in my post, I've found crimped loads to produce slightly better accuracy and slightly better SD. The paper and chrono don't lie. You can't knock it until you've tried it.
This link pretty much sums it up:

http://www.accuratereloading.com/crimping.html

My results were very much the same.
There's another link on AR showing the lowered SD values when using the Lee FCD with a 308. Saeed could point you to it.
The fact is Crimping can improve things. May not make every rifle shoot better but, I'd venture to say it will not hurt anything if done properly."

One of those things that you just can't know if you don't try, that's the fun of handloading, the experimentation. Even if it proves detrimental or useless you have fun learning for yourself

 

[Muddyboots]

Long time bench guy once told me that crimping for a bolt gun is a solution for a problem you haven't figured out.

 

[mwkelso]

Long time bench guy once told me that crimping for a bolt gun is a solution for a problem you haven't figured out.

Would this be something in your hand load recipe that your rifle doesn't shoot well with? IE: different primer, bullet, powder, etc.?

 

[Deleted member 107796]

Long time bench guy once told me that crimping for a bolt gun is a solution for a problem you haven't figured out.

If it's a solution, it's a solution, regardless of how it came about! For me, it was a solution to a real possible future problem, which was a 7mm bullet slipping under recoil, which I'd never want. With further work on solutions that I haven't figured out, I came up with some incredibly accurate 338wm Barnes TTSX rounds that I also crimp.
I think Calvin45 said it best.

 

[rsmithsr]

it really depends on the brass the dia and how much crimp.
the brass can flex, lifting off the bullet behind the crimp, thus less tension.
unless the use REQUIRES a crimp, do not crimp.

It doesn't make sense that crimping the neck into the brass would reduce neck tension. You go from having a smooth inner neck for the bullet to align with, to having the neck material crimped into the bullet surface. I disagree that it reduces neck tension to crimp, but will do more research.