Crimping?

Hakaman · Post by **Hakaman** » Tue Dec 21, 2010 12:59 pm

A topic I submitted to AR-15 forum:

I began shooting in a Service Rifle league this past summer with a RRA NM AR-15. I also started reloading about 1 year ago.
I have my load to a point of very good accuracy: LC brass, Win primers, 24.5g of Varget with a 69g Sierra Match bullet, @ 2.260".
My question is this: Do you crimp your bullets/brass for Service Rifle Competition? Which of course includes rapid fire (semi-auto feeding).
The 69g Sierra, needless to say, does not have a cannelure.
Thanks, Haka

Hakaman · Post by **Hakaman** » Tue Dec 21, 2010 4:44 pm

I guess I have to answer my own question, and I base it on results from another forum, plus this info from Lee.

* Tests demonstrate that even bullets which have no cannelure will shoot more accurately
if crimped in place with the Lee Factory Crimp Die.
LEE FACTORY CRIMP DIE
Factory ammunition is often more accurate and better able to withstand rough handling because
the bullet is firmly crimped in place. A firm crimp improves accuracy because pressure must build
to a higher level before the bullet begins to move. This higher start pressure insures a more uniform
pressure curve and less velocity variation. Even powder selection is less critical.

Until now, handloaders seated the bullet to touch the rifling to achieve similar results.
This is not always possible nor desirable. The Lee Factory Crimp Die is included at no extra charge with
Lee PaceSetter Dies. It's just another added value that only Lee Dies offer.

Post by **Bullseye** » Wed Dec 22, 2010 9:06 am

I had not seen your posting, but I do use the Lee Factory Crimp on my homemade match bullets.

R,
Bullseye

Hakaman · Post by **Hakaman** » Wed Dec 22, 2010 9:12 am

I had not seen your posting, but I do use the Lee Factory Crimp on my homemade match bullets.
R,
Bullseye

No problems, it is sort of a unique question, and I have heard it answered either way. Some of the better shooters in the league refuse to crimp, but I am understanding it can actually be a positive to crimp. I feel more comfortable with a crimp due to possible bullet shifting. Thanks for your reply,
H

Post by **Bullseye** » Wed Dec 22, 2010 9:34 am

My concerns are mostly bullet shifting while feeding up into the chamber. I have some factory match bullets that have struck the ramp while loading and the bullets were dislodged into the casing. Now those rounds sit in the demill pile. But my crimped rounds stay put when fed and I see the same level of accuracy from either style round.

Manually cycling the bolt on the AR during the highpower rapid stages, when dropping into position, is when I saw my greatest failures of this kind - needless to say I'm not a big fan of that rules change, the AR was not designed for cycling the charging handle on a magazine with just two rounds in it. Crimping my bullets and going to the new style (Magpul Gen III longer legged, anti-tilt followers) have remedied this problem for me.

R,
Bullseye

blue68f100 · Post by **blue68f100** » Wed Dec 22, 2010 2:17 pm

I don't shoot competition but my biggest concern would be setback during the cycling or forward shift. Since the bullets do not have the cannalure grove a tapper crimp can be used. I'm not a big fan of the Lee FCD dies. If not setup correctly (too much crush) you actually end up with a loose bullet. So use a minimal amount of crimp tapper or FCD. When I setup my tapper crimp die I use a bullet puller to measure the crimp. You only need 0.001"-0.002" of crimp to hold the bullet tight.

Target shooters prefer to use NO crimp. They want the most even consistent bullet tension they can get. Any crimp die that works from the outside will have a greater degree of inconsistencies. Length and brass thickness plays an important part of this. Just as little as 0.001" variation of thickness will cause it to have less tension on that side. The reason some go to the 10th degree on checking adjusting every thing to have all as identical as possible.

Hakaman · Post by **Hakaman** » Wed Dec 22, 2010 3:35 pm

Target shooters prefer to use NO crimp. They want the most even consistent bullet tension they can get. Any crimp die that works from the outside will have a greater degree of inconsistencies.

According to some people who have tested crimped rounds against non-crimped, say
they actually get more accuracy. Lee Precision says the same thing.
Thanks, Haka

check this out:
http://www.ar15.com/forums/topic.html?b=9&f=14&t=229999

Hakaman · Post by **Hakaman** » Sun Dec 26, 2010 4:47 pm

I guess I'm bored today, but, here are some results of what a Lee factory crimping die for a rifle looks like:
*
*
*
This first photo shows a "solidly" crimped round with a 55gr fmj bullet,
and you can see the intent behind the crimp not to damage the jacketing.
As I was reading the Lee die description, it says the collet style applies pressure horizontally,
so as to not damage the bullet with sharp edges.

*
*
*
I had a bugger of a time removing the 75gr Hornady HPBT with my hammer style bullet remover.
You can see the results of what the Lee factory crimp(collet style) rifle die does to the bullet, and it's jacketing.
This is a heavy crimp and reflects the most pronounced indentation it will cause. I don't know if this would
affect accuracy or not, but several sources, including Lee, say crimping improves accuracy.
It leaves an subtle indentaton, but does not hurt the jacketing.

*
*
*
You be the judge,
Haka

bgreenea3 · Post by **bgreenea3** » Sun Dec 26, 2010 6:42 pm

that is a solid crimp. I woukd back off the adjustment about 2 turns, it looks a bit tight.

I'd load some up with various degrees of crimp take them out and see what groups best in your RRA.

Hakaman · Post by **Hakaman** » Sun Dec 26, 2010 11:41 pm

that is a solid crimp. I woukd back off the adjustment about 2 turns, it looks a bit tight.

I'd load some up with various degrees of crimp take them out and see what groups best in your RRA.

Good idea. I usually don't crimp them that tight, though.
thanks, haka

Post by **Bullseye** » Mon Dec 27, 2010 7:24 am

That little bit of ring won't affect the bullet's flight, it's even and concentric. The truth is in the testimonial on how much harder it was to pull that bullet. It would take considerable more force with a collet style puller too. This is why I use them as the bullet cannot be seated back into the casing in the event of a ramp strike or jam. Your detonation, propellant burn, and pressure are more consistent as the cartridge has to overcome the crimp to release the bullet. When I first looked at the picture my first thought was that it was too heavy of a crimp. Shooting them and comparing the results will determine what is best for your rifle.

R,
Bullseye

blue68f100 · Post by **blue68f100** » Mon Dec 27, 2010 8:30 pm

My first impression is too much crimp. All you need is enough to give you consistant bullet pull/resistance. Does not require a lot to do this. Excessive crimp will can/will increase internal pressures in the round. So look for over pressure indicators when you shoot those. May not be a problem but rather be safe than sorry. I hope those are not near the upper end.....

Hakaman · Post by **Hakaman** » Mon Dec 27, 2010 9:07 pm

I hope those are not near the upper end.....

Sierra 69gr Jacketed HPBT, Hogdon Varget 24.7gr, (23.0 - 26.4 gr), 2.255"

H

charlesb · Post by **charlesb** » Wed Mar 09, 2011 2:58 pm

Hakaman wrote: You be the judge,
Haka

Back in the '60s, aircraft designers were big on the 'wasp waist' design that reduced drag.

Just sayin'...