14 replies to this topic

[.40AET]

I checked the FAQ's and could not find any information. Not to say that it is not there. I just bought a Lee FCD for .40. I would like to set up the final bullet crimp to a known good diameter. How much crimp is necessary to get good, dependable, ignition? Thanks very much.
Kirk

[Sixgun]

The easiest way to determine this is to: 1) measure the diameter of the bullets you are using. 2) measure the case wall thickness at 4 spots around the case mouth. Add these 4 measurements together, and divide by 2. 3) add the measurement in step 1 with the measurement in step 2 together. That will give you the diameter that you need.

Hope that helps.

Ray C.

[David Olhasso]

My method is not too scientific. First I use an undersize sizing die (LEE undersize or Redding) which insures that the case wall holds the bullet and NOT the crimp. With the FCD I insure that the bell from the powder die is removed. I then adjust the FCD till I remove the "squareness" off the brass lips. Essentially, all I am doing is crimping the brass enough to avoid any feeding problems.

[TBF]

Bullet dia. + 2x brass thickness - .001 or .002.

Works for me.

Travis F.

[warpspeed]

I remember reading BE one time saying the crimp die for an autoloading pistol cartridge is not a crimp, but a remvoing of the bell created by the powder drop.

Bullet diameter + 2 time wall thickness of brass is usually 0.420" depending on brass.

I adjust the crimp die down until the case is strait again and I cannot feel the lip at the top.

[Erik Warren]

Somewhere around .422" but the better method is to keep cranking down the crimp die a little bit until the mouth flare is gone and the round passes the case gauge.

[Rufus The Bum]

I use .418 exclusively and it works fine.

[ChuckS]

The word from Brian:


Brian on Crimping

[warpspeed]

Rufus,

That sound tight. If you pulled the bullert, what does look like ?

[2cats]

I'm totally down with "crimp" = bell removal; no more. However, I just got some Starline 9mm to help trouble shoot the set back problem I described in another thread. It looks considerably thicker than either my used Federal or Winchester - around 0.012 - 0.013". If we simply apply the bullet diameter plus twice the thickness of the brass, we get 0.3555" + 0.012" + 0.013" = 0.3805", more than the SAAMI max.

So I've got to assume in some cases, like this one (no pun intended), that we have to add the "- 0.001 to 0.002" or "-0.002 to 0.004" parts to this equation, which gets us down around 0.377".

[TDean]

.418" here also.
But make sure you're measuring at the extreme edge of the case (not .010 from the edge).

[Rufus The Bum]

Rufus,

That sound tight. If you pulled the bullert, what does look like ?

I have never had to pull any bullets, .418 is what Benny Hill recommended to me long ago and that is just what I have went with. It might be a bit more than needed, but I like a good, solid crimp. With .418 I have never seen ANY signs of pressure or drop in accuracy. I think factory is somewhere around .418-.421

[kevin c]

Rufus,

That sound tight. If you pulled the bullert, what does look like ?

I'm with WS here, at least for jacketed bullets.

I've heard that if you pull a loaded round and you see that the case mouth leaves a ring on the bullet, the crimp is too tight, and may alter accuracy by compressing and then separating the jacket from the bullet core.

[Rufus The Bum]

Rufus,

That sound tight. If you pulled the bullert, what does look like ?

I'm with WS here, at least for jacketed bullets.

I've heard that if you pull a loaded round and you see that the case mouth leaves a ring on the bullet, the crimp is too tight, and may alter accuracy by compressing and then separating the jacket from the bullet core.

I'm not saying a .418 crimp is the ideal crimp, but in my gun with a .418 crimp I get sub 1" groups at 20 yards, so I have not lost any accuracy OR seen any signs of pressure. By all means use a "looser" crimp if you feel the need, there probably is no difference that I can see, but I'm not a fizzicyst, just a redneck

[.40AET]

Thanks for all of the information. I appreciate everyones advice.
Kirk