Objective crimp measurement

[Jarhead]

Hi All,

I have read quite a few websites looking for the correct crimp tension on a 6.5 Creedmoor round.

Most authors line up 4-5 rounds with progressively tighter crimps- and state that the middle one is good.

I am hoping to find a less "Goldilocks" approach to this.

Is there a measurement of crimp? If yes- how is it measured and what should the value be?

The reason for the question is I have 50 odd large rifle primer brass cases. All of my others are small rifle primer. I will keep reloading the SR primer for accuracy in my Tikka T3, and will reload the LR primer cases back to SAAMI spec and put them in my "Rainy Day" Box. I want to crimp the rounds as they may be in there for some time and might get bounced around.

[in2anity]

Jarhead, what makes you sure you need any crimp at all? Do you have your own personal data proving it brings your groups in?

[SCJ429]

Have to agree with In2, if you are looking for accuracy then do not apply a crimp. If you are going to throw your rounds around, then use more neck tension. You cannot move a bullet with 10 thou neck tension easily, you would need to hammer the tip of the bullet to get it to more. Try removing a projectile from a case with your bullet puller with this sort of tension, it takes a fair bit of effort.

[in2anity]

FWIW, I'm a fan of the Lee Collet dies, potentially with an undersized mandrel (when the situation demands higher neck-tension). Then when my lockup/extraction is starting to cry, I use the Forster Bushing Bump Neck die (with the desired neck-tension bushing).

[Jarhead]

in2anity,

I am not chasing accuracy- but reliability. My thinking goes back the the early 90's. On a training exercise. I opened a box of ammo to find it was about 30 years old. I still remember looking at the LC 61 headstamp. The ammo was older than me! It had red sealant and crimps on both bullet and primer.

I was thinking- prepare for lots of misfires today. I spread the word to the range coaches and reviewed with them what to do when it happens. That 30+year old ammo made me eat my words. Not a one misfire all day.

I am glad you & SCJ responded as you did. It made me did deeper. I always assumed that the crimp and sealant were to keep moisture out of the power. The sealant does that on its own. The primer crimp is there to stop the primer coming out of an automatic when ejecting- they can jam the gun. The bullet crimp is there only when a test batch of ammo fails the pull test due to insufficient neck tension. The batch is run through a bullet crimper and tested again.

So you guys are right- get the neck tension right and call it a day- bullet crimps are a fix for poor quality earlier in the loading process.

[SCJ429]

I recently shot some rimfire ammo from the 80's and not a single misfire. Ammo stores really well so I wouldn't worry about stuff you may not shoot for a while.

The Army is not worried about accurate ammo, just ammo that is reliable and will go off even in the most challenging conditions.

[TassieTiger]

Marksman has previously posted videos showing that the most accurate neck tension is one where it’s just on the edge of being able to be hand / finger moved...or looser.
Tighter neck tensions become harder to get consistent with normal dies...

[Oldbloke]

Marksman has previously posted videos showing that the most accurate neck tension is one where it’s just on the edge of being able to be hand / finger moved...or looser.
Tighter neck tensions become harder to get consistent with normal dies...

I've heard that elsewhere. You dont need a lot.

[in2anity]

I've heard of fullbore shooters "soft-seating" I think they call it. Neck tension is so low, the act of closing the bolt seats the bullet on the lands. Bit of a problem when some old geezer falls over on the mound and there's a cease fire - opening the bolt spills powder all through your action. But to me that says a lot about neck tension with respect to accuracy.

[in2anity]

As I sit here, loading my rounds for Saturday, pondering upon life’s existential questions, I had a thought, which I feel obliged to share.

Jarhead, if you do end up going down the “light neck tension” route, be sure to check your rounds are not seating deeper as a result of feeding from the magazine. That has led me on goose chases in the past.

[Jarhead]

Thanks in2anity,

I am not pursuing that path yet- am next going to explore seating on the lands for better accuracy. I single load when shooting precision long range anyway.......

But I found elsewhere the answer to my initial question.......

A tight crimp would have an outside diameter 5 thousandths of an inch smaller than the OD of the neck.

[in2anity]

Good luck with it Jarhead, keep us posted.

I must say your groups are already impressive - gotta love the 6.5! Some of my service buds swear by the Swede. At Service distances/targets/stances, they basically never have to touch their windage, even with a decent crosswind. The Swede seems to just keep plugging them right in there. Maybe I'll get one, one day. I'm on the 303 wagon right now - and she's shooting better than I can.

As I said, single-feeding fullbore guys soft-seat on the lands. You just need work up to it from mild, to be safe.

[marksman]

l think a smooth clean release of the bullet is paramount to precision, l even give the inside of my case necks a polish when match prepping yea l know
l do not want to see any scratches on the bullet when or if l pull it from the case
l like to say around 2 thou is good or as Tassie said when you cant push or pull the bullet in or out of the case
if you are jumping a bullet l have found a very light lee factory crimp is ideal but some rifles have better accuracy with more tension

what l have found difficult to be able to do this is the the neck thicknesses are all over the shop so that one will be ok and not move in the case but the next will move because of less neck material, the fix is to neck turn or use lee collet dies as the will even out your neck brass with use

it really is pretty important as well as being concentric, what l believe anyway