Getting rid of M Die flare

[7br]

I am having my XP100 in 7br rebarreled. I am playing with the new barrel to see if my loaded cast rounds will chamber and they will not. The new barrel has a .310 neck. If I use the M Die to flare the mouth, the dies will only iron out the flare to .311 and the rounds will not chamber completely. If I don't flare with the M Die, I scrape lead. Any suggestions?

[DAFzipper]

Lee factory crimp die? They work for me.

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[ryanmattes]

Second the FCD. A super light taper crimp should fix you right up.

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[leadhead 500]

What diameter are you turning your case necks to, also have you done a chamber cast to make sure that it is a .310 neck? You need to have 1.5 to 2 thousand clearance for the bullet to release properly

[mdi]

"Factory Crimp Die"? Which one? The Collet crimp? Post crimping sizing die? Collet crimp does not taper crimp. Too often some just think FCD without knowing what cartridge is being crimped (7BR is a bottle necked cartridge https://www.google.com/search?q=7+BR...-2owQGDPZZnPfM )...

I would try just a flare and not use an M die...

[onelight]

The factory crimp die for bottle neck cases is a collet crimp die.

[PositiveCaster]

The factory crimp die for bottle neck cases is a collet crimp die.

Lee FCDs won’t iron out the “flair” left by the M die, they crimp the case mouth. What might work for the OP is a Lee Collet neck sizing die without the mandrel - if they made one for the uncommon 7mm BR. Or he could polish down the M die stem to reduce the diameter of the flair.




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[SSGOldfart]

Second the FCD. A super light taper crimp should fix you right up.

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Yep same here

[1hole]

You are probably lucky, tight chambers are usually an aid to accuracy.

If your present crimper only sizes down to .311, it's too large. But, your bolt action single shot handgun shouldn't need crimps!

I use Lyman's M dies (two-diameter neck plus mouth flare) expanders for everything; they provide straighter necks than ball expanders and that flair helps funnel bullets straight into the bore.

My factory chambers are so loose that I seldom even use a rifle crimper but when I do it's a Lee collet crimper and then only enough to let the ammo chamber well because I think the remaining M flare helps center the case mouth in the chamber neck and that helps align bullets going into the bore.

I wonder if your cast bullets are oversize. Suggest you try a round made exactly the same way but with a jacketed bullet and see how that works.

If .284" jacketed ammo also binds, "paint" some bullets and necks with a dark Dri-Erase felt-tip marker (blue or black) from Walmart's school supplies; then you can immediately see where your ammo is too tight in the chamber.

[porthos]

deep chamfer inside the neck with a taper reamer

[Silvercreek Farmer]

Try backing off the M die a bit. I only expand the neck enough to get around 1/2-3/4 of the gas check to sit in the neck before seating.

[BK7saum]

I use the lee FCD to remove M die expansion on 300 BLK cases. I only expand to the start of the step to just get the gas check to seat. I never have expanded case necks beyond that point. Most will chamber as is because neck is only 0.001"-0.002" over bullet diameter.

[JM7.7x58]

Use your sizing die to just touch the mouth of your case. If care is taken to set the height correctly it should just iron out the flare. I’ve done this when using the Lee RGB seating dies that aren’t designed to crimp.

[bedbugbilly]

I don't load that cartridge but try what JM7.7x58 suggests. Have done that on several bottlenecks.

I use the Lee FCD collet crimp dies on all of my bottlenecks/cast. You can adjust the die to adjust the degree of crimp. I also use Lyman M dies on all of my bottlenecks so am familiar with them. Follow the advice given also on backing the M die off a tad. l

As mentioned though - even you remove the flare - and are we talking the flare at the case mouth or the actual neck expansion done by the M die? - if you iron out the actual flare at the case mouth, is the expanded neck the correct OD dimension the will work in your chamber?

[JonB_in_Glencoe]

the dies will only iron out the flare to .311 and the rounds will not chamber completely

What Dies?
also, neck diameter spec is .315 if your new chamber is .310 you will probably need to use smaller diameter boolits.

[dtknowles]

Try backing off the M die a bit. I only expand the neck enough to get around 1/2-3/4 of the gas check to sit in the neck before seating.

I sort of second this idea but for it to work you need to make sure your brass is all trimmed to the same length. On my 30 BR Long. The brass will not even go into the seater if the flare is too much. It is one of those inline seaters that have a sleeve that holds the bullet and the neck in alignment that is pushed into the seating die. If I have a case that is a little long it won't seat the bullet because the flare is to great and if I have a case that is a little short then I might shave lead because I don't have enough flare. I need only a tiny flare because of the inline seater. I don't crimp, I don't use or have a crimp die. The flare is still there when the round is done. I do get a little resistance when chambering the round but no pressure signs. I am also seating for a little jam into the rifling so resistance is expected.

Tim