Crimping continued

[elk hunter]

This is a pulled 7 mm 155 gr FMJ BT from scrubbed ammo, probably was to be used in some clandestine CIA BS. I pulled these because of 2 things the ammo mis-fired every 2-3 rounds and I could easily see the deep crimp. Both are bad ju-ju so out they came. I've been playing with these off and on for the last 2 years and still cant get better than min. of garbage can accuracy at 100 yards. Whats learned by this you wonder, don't use a crimp that heavy and don't crimp unless the slug has a crimp ring. These slugs will probably end up in my lead pot to salvage the lead and the jacket material will end up in landfill. The powder was used for yard fertilizer and the berdan primed cases went into the scrap can. This is the best pic I can supply with my phone camera, this is a perfect example of what you don't want. HTH
elk

[JackEllis]

I'll give everyone a free laugh this morning by exposing my ignorance about crimping.

I *thought* the whole purpose of crimping was to avoid having primers and bullets pop out in gas operated rifles. What's the sense of crimping in a bolt rifle?

I have occasionally had to pull a bullet from a round I assembled incorrectly and it generally takes a considerable amount of force. Even more so with some factory rounds I picked up at the range.

What am I missing here?

[ironhorse1]

Wow! I would call that a excessively deformed bullet. My best guess is that the deformed bullet is no longer properly engaging the rifling.

Rather than engaging along the entire length it is now separated into two separate and rather small areas.

I wonder what other effects there are on the in flight ballistics due to the dent formed by crimping?

irh

[elk hunter]

Wow! I would call that a excessively deformed bullet. My best guess is that the deformed bullet is no longer properly engaging the rifling.

Rather than engaging along the entire length it is now separated into two separate and rather small areas.

I wonder what other effects there are on the in flight ballistics due to the dent formed by crimping?

irh

I guess your wondering if they keyholed, no they didn't they punch a clean round hole. Reduced bearing surface will have a bad effect on lots of things.

[elk hunter]

I'll give everyone a free laugh this morning by exposing my ignorance about crimping.

I *thought* the whole purpose of crimping was to avoid having primers and bullets pop out in gas operated rifles. What's the sense of crimping in a bolt rifle?

I have occasionally had to pull a bullet from a round I assembled incorrectly and it generally takes a considerable amount of force. Even more so with some factory rounds I picked up at the range.

What am I missing here?

Jack, crimps are a needed and necessary thing just not this much or in these types of bullets. Tube feed lever guns, revolvers are in need of a crimp to keep the bullets from moving back or forward but not most other types. A crimp can and does help A LOT when used properly with cast lead bullets in bolt guns with start pressures and that helps a lot with lots of things, things you want.

Just a little thing that might help you next time you want to pull a bullet a tip if you want to call it that. Run that cartridge into a seat die and just bump the slug enough to move it a little bit, not a lot is necessary just a little movement, you might hear a tiny pop or snap sound. Now try your collet bullet puller.

[kcheung2]

I'll give everyone a free laugh this morning by exposing my ignorance about crimping.

I *thought* the whole purpose of crimping was to avoid having primers and bullets pop out in gas operated rifles. What's the sense of crimping in a bolt rifle?

I have occasionally had to pull a bullet from a round I assembled incorrectly and it generally takes a considerable amount of force. Even more so with some factory rounds I picked up at the range.

What am I missing here?

A loosely tensioned projectile will actually pop "in" to the case (aka setback). To visualize the physics, when the gun fires it recoils backwards, but the projectile has inertia to remain stationary until the front of the magazine well pushes the entire round backwards. And to continue with that visualization, the mag well pushes the projectile backwards but due to minimal tension, the case will tend to remain stationary until the back of the projectile pushes against the powder.

The physics apply the same regardless of bolt action or semi. Firing a few times likely won't cause much setback, but do it 9 times (or 29, etc in free states) and that 10th round (or 30th, etc) might exhibit setback if there is insufficient tension. Notice I said tension, not crimping per se. That's because crimping vs not is a Coke vs Pepsi thing, but as long as there is enough tension (either via crimping or proper neck sizing) then it's fine.

Pulling a bullet does take some effort, but setback is pushing the bullet into the case. It actually takes a lot less force to do that. If you want to prove it to yourself, a light tap with a mallet will likely push a projectile into a case.