working out a 20 Grendel reamer specs

[msalm]

So I'm trying to spec out a reamer for a 20 Grendel (bolt action) and wondering about neck clearances, length and free bore. I picked up a 20 ppc bushing FL die and sized down several Lapua and Starline brass. Lapua ends up at .234" and Starline .232" loaded diameter with a 39 gr Blitzking. I'm building a light carry gun on a Howa mini 7.62 rifle, 11tw Mullerworks barrel. Probably a 23-24" barrel, .560's muzzle diameter. BIB's 40gr are on the menu for this one and I'm told they have a short freebore and to spec the reamer zero freebore. OK, so that's settled, except what neck diameter and do I shorten the OAL on the case since the brass seems to shorten up considerably with sizing down operations. I was thinking of 10-20 thou shorter neck on the reamer and if it's too short I can trim to proper length. Still plenty of neck to seat a bullet and keep the throat back closer to the bullet.

I guess it might be relative, but has anyone noted OAL changes when sizing 6 PPC down to 200 PPC? Do you keep the same trim to length of the parent cartridge or will the necked down version end up shorter to some extent?

As for neck diameter I was thinking .2375 or just a .238 neck, really don't want to turn necks on these little buggers but maybe its a good idea??.

What say you?

 

[Tommie]

I just went through the reamer design process with a different .20 caliber wildcat that’ll shoot 39-40 grain bullets. Got several opinions on freebore. Decided upon 20 thousandths. Gives a little wiggle room for bullet jump (if needed) while allowing for future throat wear. Have no idea if the theory will prove successful but maybe that’ll give you somewhere to start.

 

[msalm]

Thanks for that, what are you using for neck clearance?

 

[Evan]

That's a pretty thick neck, but could be just fine. Based on your measurements I'd go 238.

My 20VT loads measure .231 to .232 and I've got a .234 neck chamber. No problems but it feels slightly worrisome on the clearance.

 

[Tommie]

Thanks for that, what are you using for neck clearance?

The build isn’t completed. Still waiting for that long-awaited call from the smith. After neck turning some formed cases, it looks like it’ll have .003 total clearance. If that proves to be too tight after a marathon PD session I can always take a little more brass off.

 

[Rtheurer]

would there be any reason not to use 22 PPC Brass as the parent case?

 

[JASmith]

Contact Dave Manson at Manson Reamers. — he has a good 20 Grendel reamer design. There are two different freebore options. The reamer designs were made for my 20 Grendel.

It is a no-turn design for a driect neck-down from the 6.5.

 

[msalm]

Contact Dave Manson at Manson Reamers. — he has a good 20 Grendel reamer design. There are two different freebore options. The reamer designs were made for my 20 Grendel.

It is a no-turn design for a driect neck-down from the 6.5.

JASmith, I did in fact find your print on-line. I did talk to Manson and got the reply of ‘nothing on file’. I sent them a copy of the print with some changes based on my measurements. The print I found had something around .242 nd and that seemed too generous.

Care to share any experience with the cartridge?

 

[Ledd Slinger]

For a no turn chamber, I would also recommend starting with a 22PPC parent case and basing the reamer design on cases necked down from it. Norma 6PPC cases would also be better as they only have 0.011" thick neck walls straight from the factory.

0.015" thick neck walls is way too thick on a 20 cal in my opinion. I run 0.0145" neck walls in my large magnum custom chambers. 20 cal varmint rifles down around 0.012".

 

[msalm]

For a no turn chamber, I would also recommend starting with a 22PPC parent case and basing the reamer design on cases necked down from it. Norma 6PPC cases would also be better as they only have 0.011" thick neck walls straight from the factory.

0.015" thick neck walls is way too thick on a 20 cal in my opinion. I run 0.0145" neck walls in my large magnum custom chambers. 20 cal varmint rifles down around 0.012".

I understand where you're coming from, I just don't care for the fireforming needed with blowing the shoulder forward .070".... Maybe I'll bite the bullet and order a .234" neck and plan on a light turning of the necks. This will be a very low volume affair, 50-100pcs should be all I'll ever need. It will be a small 22-23" barrel .5's muzzle diameter barrel on a howa mini action...well under 6lbs bare. Just looking for a handy little truck/calling rifle. A light compact 2.5-8x or even 2-7X scope will be plenty for what I'm looking to do.

 

[SRM]

I built a .20 ppc with Lapua .220 r brass. .232” neck chamber and had to neck turn for a .013” neck. Pretty sure a .235” neck would work for no turn.
Pick a good parent case. Bigger the neck, the thicker it gets goin down in size. The more you blow them out, the shorter they get.
Fun stuff isn’t it?!!

The best part of my experience is once trimmed, and formed, they didn’t grow any . Lost count on firings.

 

[SRM]

I did try some Norma brass, 22 ppc, as the necks were a thou thinner and didn’t have to turn but the base dimensions were out of wack. 200 pieces in the lathe, what a pain that was. Still messing with them.

 

[JASmith]

JASmith, I did in fact find your print on-line. I did talk to Manson and got the reply of ‘nothing on file’. I sent them a copy of the print with some changes based on my measurements. The print I found had something around .242 nd and that seemed too generous.

Care to share any experience with the cartridge?

Cartridge worked fine with better accuracy than I can shoot.

Starting with. 224 diameter case and fire-forming may be easier than having to do the intermediate forming needed to get to a .204 neck from a .264” neck.

The second reamer drawing shortened the freebore a bit to better work with the lighter bullets but still do well with the 55 and heavier pills.

The neck diameter allows for the increased brass thickness one gets when necking down. Starting with a 6mm or .224 caliber parent will allow for a smaller chamber neck diameter.

 

[msalm]

I didn’t bother with bushing dies, I used 6ppc and 22ppc Hornady FL sizers with the expander removes. Easy forming in 3 steps with the last one being the 20 PPC bushing FL die. I made a couple bushings out of O1 steel and will need to make a smaller one when I decide where I’ll end up on neck thickness/ chamber dimensions.

 

[riflewoman]

I’m not sure I’d neck from 6.5 to 20 or even 22 without neck turning. Brass being brass it is very likely you’ll have significant and uneven thickening of the neck. This doesn’t mean you’ll need to make them thinner, but they will need cleaning up.

 

[JASmith]

I can’t dispute the need to turn necks for ultimate accuracy.

What I do know is that I got excellent accuracy with my no-turn necks. For me “excellent” is anything better than 0.75 moa. My stuff did that well.

Nonetheless, I now advise folks to start woth 22 cal brass to neck down or 6mm as alternate. Fire forming may be needed when the donor brass is not Grendel, but is probably less of a hassle than the added steps to go all the way down to .20 from .264 caliber.

 

[msalm]

I’ve sized down a half dozen of two different brand 6.5 Grendel Starline and Lapua. 6 and 22 ppc Hornady FL sizers with expanders removed, and the third pass with a Redding 20 ppc bushing FL die. All went well with no lost cases and case mouths were pretty even. I think this will work just fine whether I decide to turn or not. Honestly I’d rather just load and shoot so we’ll see.

Thanks for all the info and suggestions.

 

[Ledd Slinger]

This thread woke up my 20 cal bug and it bit me again

So I went out to the shop and made this 20 PPC round from Norma 6PPC USA brass. Bullet is a Sierra 39gr BK. Outside neck diameter on the loaded round is .228" which means my neck walls are right at about .012" thick. Perfect.

Just ordered a Whidden 22 PPC Bushing FL sizer with .226" bushing (already have .224" bushing on hand). Gonna make a few more rounds when the die gets here to get a custom reamer built that is specd for a .232" no-turn neck. Then I will have a Wilson blank seater die custom made with my reamer. Should work out pretty good

 

[msalm]

That'd be what I'm looking at, only a .070" longer shoulder ... Funny, I have more types and calibers of brass in the loading room than I even remember, BUT that's one case I do not have a single one of. I have plenty of Grendel, a few boxes of 6BR, 222, 222 Mag, 223, 22 Hornet, 250 Savage, XC, Creed, 6mm, 243, 27 Lapua....the list goes on...but no ppc brass. Going to have to stick to the Grendel based 20 cal and neck em down. 40gr BIB's at 3900 to MAYBE 4000 is my hope, but whatever it runs out of a 23" 11tw barrel will be fine.

 

[Ledd Slinger]

You should be able to easily hit 4K with a 40gr bullet, and then some. Especially since you will have significantly more case capacity than the standard 20 PPC.

I might twist the barrel to try the 50gr Bergers and take it long.