.20BR case forming & twist rates.

[Alycidon]

Hi guys,

I am presently trying to form my 20BR cases.

Taking Lapua brass I have trued the primer pockets and cleaned up the inside of the flash holes fine. I am using a new Redding 77666 full length bush die to form the cases but have hit a snag.

I have adjusted the die in the press to just touch when the case is fully raised. I have also adjusted the primer pin to project no more than about 3 mm. First bush in was .248, this would only size down to about 50 thou
(1.5mm) from the shoulder. I have played around with the setting even removing the primer pin completly to allow the case to rise further to no effect. The neck is only coming just over halfway up the bush. Second bush in was .237, same result, only resizes down to 50 thou from shoulder.

My smith intends to turn the necks internally on a lathe as opposed to externally using a K&N tool but somehow I need to get that extra 50 thou resized. Anyone any idea on why I cannot get the case high enough?, my smith would always prefer to make a die but has humoured me using Redding and Wilson products. I suppose taking 50 thou off the bottom of the die would help.

Second point,

I am intending to use Berger 50 grainers as my first choice, optimum twist rate everywhere I have read for this pill is 1 in 9. Last week I came accross a well respected target shooter who could not get the bullet to stabalise through 1 in 9 and finsihed up at just under 1 in 8 with great results. Anyone any experiance of this?, at present my ordered barrels are 1 in 9.

Thanks for your help.

A.

[17VLD]

Most sizing bushings have a radius in them, thats why the last .050"
is not sized completely.I use a 22BR fl die to bring the 6BR brass down first then the 20BR full length die to get it to 20BR then I trim to 1.520"
My 20BR is a 12 twist and it shoots the Berger 50 at my altitude
just fine, sea level may be another story.I am sure the 9 twist will work with the 50 even at sea level no worries on that.Perhaps your friend needs to
get his bore scoped or cleaned he may have a burr or some other problem that is tearing the jacket?? Good luck and keep us posted on your results.
Matt

[Alycidon]

The twist rate problem is sorted, my friend was getting confused with his 22.243 Middlestead, 1 in 9 is the optimum twist for the 50 grain in .20.

I did look at the radius but it looks about 10 thou less than the area not reduced on the neck. May be the problem though.

A

[scootertrash]

A Redding bushing will only size ~ 3/16". (.1875)
17VLD gave a good method to size, using a F/L die.

You also mentioned prepping the Lapua brass by reaming the primer pocket and deburring flash holes. Typically, most folks don't touch Lapua flash holes. Their quality is that good, however I did read of a batch getting out that did have a burr.

If you must deburr flash holes on Lapua, it takes a smaller deburing tool. Many feel the smaller flash holes of the Lapua, contributes greatly to the efficiency and accuracy.If you made the hole larger, you have taken away this advantage.

Mike

[Alycidon]

Hi Mike,

I do use a small tool on the inside of the flash hole entering the case from the bullet end, it sometakes takes off a spec or two of brass sometimes not. Just piece of mind I suppose. Tool is similar to that shown on page 28 of the Sinclair cataloge, just takes a twist or two with the fingers.

It has been recommended to me that I take 10 thou off the case holder to allow it to move further up to the die rather than machine the bottom of the die but I will do some more digging on 17VLD 's meathod

Thanks for your help.

A

[GLWenzl]

Hmmm, now I know how I ended up with them darn doughnuts .... Thanks guys!