Crimping

Muir

Well-Known Member
Interested, what was the title of that book?

Thanks!
Damned if I can recall off the top of my head. I'll need to paw through my library to find it. Something like "North American Varmint Hunting" or the similar. I remember being quite smug about my discovery and having my coals peed on when I found this guy writing, "...for the finest accuracy, lightly flare the case mouth before seating your bullet....."

It's hard to re invent the wheel.~Muir
 

Muir

Well-Known Member
A lot of factory ammo is crimped
If it was of no benefit the accountants would have deleted that process

Try it
You may be converted
You don’t need to mark the brass to get it to work
A lot of factory ammo is crimped, indeed. That's where Lee got the name "Factory Crimp Die" for their product. Any mark on the case mouth often comes with once fired factory brass and usually is ironed out by sizing or trimming. I ignore it and carry on.~Muir
 

Muir

Well-Known Member
Thanks, it may drop my ES even more so will give it a shot
Seriously. At worst it will be of no benefit. I have been doing it for so long, with so many different cartridges, that I don't even question it: I just do it. In some of the tests I've done comparing same LOT brass, loaded at the same time, on the same equipment -but leaving half uncrimped, the crimped rounds had 30% lower ES/SD over 20 shot strings of each.

MTLEADFARMER and I were at a sports center in the city and the manager of the firearms and reloading department was explaining some erratic grouping he was getting from his 300 WM and asking our opinions. When he drew a typical group on a piece of paper we simultaneously said "Crimp". I doubt he ever tried it despite 75 years of hard core reloading experience standing in front of him suggesting it. MTLF is a skilled reloader and long range marksman who also doesn't consider a load fully developed unless it has been fired crimped. We came upon crimping and it's benefits independently but have compared notes and found our results mirrored each others. If you ever watched this man shoot, and was then told that every round he fired was FL resized and crimped, you wouldn't hesitate to try it.~Muir
 

Muir

Well-Known Member
The short version: Crimping provides a uniform "pull weight" for release of the bullet. The amount of pressure needed to release the bullet in an individual cartridge, sets the burn rate for that charge of powder. (To prove the opposite, seat a bullet over a charge in an unsized case and shoot it) If all other aspects of the case prep and charging /seating are well attended to and uniform, the ES and SD will most likely fall.

Will crimping make a round more accurate? Absolutely not. It will at best, make the interior ballistics uniform which is not synonymous with accuracy. There are too many other variables to deal with once the bullet leaves the case.~Muir
 

hendrix's rifle

Well-Known Member
The short version: Crimping provides a uniform "pull weight" for release of the bullet. The amount of pressure needed to release the bullet in an individual cartridge, sets the burn rate for that charge of powder. (To prove the opposite, seat a bullet over a charge in an unsized case and shoot it) If all other aspects of the case prep and charging /seating are well attended to and uniform, the ES and SD will most likely fall.

Will crimping make a round more accurate? Absolutely not. It will at best, make the interior ballistics uniform which is not synonymous with accuracy. There are too many other variables to deal with once the bullet leaves the case.~Muir
Perfect, layman's terms lol. Cheers for that, got myself some hornady custom grade dies with the built in crimper, loaded some up so will see how they shoot tomorrow!
 

Muir

Well-Known Member
Perfect, layman's terms lol. Cheers for that, got myself some hornady custom grade dies with the built in crimper, loaded some up so will see how they shoot tomorrow!
I hope they work well for you but please don't judge the benefits of crimping by the use of the built in crimp feature. The inexpensive Lee factory crimp die is the proper way to do it. If you do use the built in feature, seat all to depth first, then back out the seater stem and reset the dies to crimp. That will optimize a less than ideal system.~Muir
 

Dr.T.

Well-Known Member
The short version: Crimping provides a uniform "pull weight" for release of the bullet. The amount of pressure needed to release the bullet in an individual cartridge, sets the burn rate for that charge of powder. (To prove the opposite, seat a bullet over a charge in an unsized case and shoot it) If all other aspects of the case prep and charging /seating are well attended to and uniform, the ES and SD will most likely fall.

...~Muir
Hi Muir - out of interest, why would crimping provide a more uniform 'pull weight' (presumably you're referring to neck tension) - aren't you pushing neck inconsistencies towards the inside of the neck, creating more irregular neck tension, as well as providing much higher neck tension? I would have thought that finishing with an expander /mandrel would be the best way to achieve a consistent neck tension, by pushing inconsistencies outwards. (If you neck turn, then I guess the argument is as good either way).

Also, lower next tension tends to be the way to go to achieve very high levels of accuracy, so I'm curious as to why folks would want to go the other way (besides shooting very heavy recoil)?

Clearly it works for some!

Many thanks!
 

Muir

Well-Known Member
Hi Muir - out of interest, why would crimping provide a more uniform 'pull weight' (presumably you're referring to neck tension) - aren't you pushing neck inconsistencies towards the inside of the neck, creating more irregular neck tension, as well as providing much higher neck tension? I would have thought that finishing with an expander /mandrel would be the best way to achieve a consistent neck tension, by pushing inconsistencies outwards. (If you neck turn, then I guess the argument is as good either way).

Also, lower next tension tends to be the way to go to achieve very high levels of accuracy, so I'm curious as to why folks would want to go the other way (besides shooting very heavy recoil)?

Clearly it works for some!

Many thanks!
I need to head to the city. My girl friend is waiting patiently for me to arrive. All I can say for the moment is that it doesn't work as you described. You are thinking external ballistics. This is a matter of internal ballistics. As was pointed out earlier, many factory loads come crimped and it's not to keep the bullet in place.
Gotta go. ~Muir
 

Dr.T.

Well-Known Member
Hi Muir

I figured that neck tension affects internal ballistics (essentially how much pressure builds up before the bullet is released) but I'm curious to hear more!

Also noted re. factory loads being crimped, but on the other hand, I don't know of a single benchrest or F class shooter who crimps (perhaps because match grade does dont usually have a crimp function). Perhaps factory ammo is crimped to make it more robust?

Safe travels!
 

Heym SR20

Well-Known Member
Crimping equals a firm and equal neck tension and keeps firmly held in the case in storage, transport, in your pocket and whilst in the magazine.

Non crimping equals one less job to do but you can end up with little tension on one case and quite a bit on the next. And also risk of bullets moving in case etc.

To get good accuracy you want to build up pressure before the bullet starts to move. You can either seat the bullet long so that it is right on the lands. The Benchrest boys I believe use very little neck tension and seat the bullet extra long so its pushed back by the lands as the bolt is closed - but this would be impractical in the hunting field.

A good crimp has the same effect.
 

Dr.T.

Well-Known Member
Hi Heym

I agree that crimping gives firmer neck tension (you make the neck smaller) which would stand up better to rough handling, but I'm not sure that this translates to more consistent neck tension (as above, you're pushing inconsistencies inwards).

As for whether crimping adds another step, I believe some dies (e.g. some from RCBS) have an in built crimp, which you set by running the die a bit deeper. I haven't used a stand-alone crimp die, and personally wouldn't do so!!

Running very little neck tension and seating the bullet long is 'soft seating' and it can work very well, although I agree that it's not ideal for field use, principally in case you need to eject a live round (same goes for using higher neck tension and a long bullet to get a 'jam'). However, whether you jam or jump a bullet depends more on what the bullet/ chamber combo prefers - plenty of benchrest and F class shooters 'jump' their bullets (probably more common now than jamming) as newer designs (such as Berger hybrids) tend to work better that way (rather than, say a VLD design that tends to prefer a jam).

Running low neck tension is more to do with getting optimal consistency... I'm not talking so loose that you can pull it out with your fingers! Anything more than about 1.5 thou of neck tension is plenty for field purposes.
 

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