Starting Loads 105 Scenar and Varget 6mmBR

[Flouncer]

I found older posts and was going to resurrect them, but the pink warning came up and recommended a new thread. So...... New PacNor Barrel, 8 twist, 4 groove (!). I am going to shoot two boxes of factory Lapua 105 ammo, then build with those cases and 100 NIB Lapua cases, Varget, CCI primers, and Lapua 105s. The Hodgon site shows 26.0 as starting load for Varget, and 29.0 as compressed. Yet 30.0 grains is shown typically herein. And I haven't seen the word compressed here either. I guess I am going the long way to asking if I can skip around 20-30 shots building from 26.0 to 29.0 when I hope to end up at 29-30.0 grains. Is starting at 26.0 a waste of time or the safe way to proceed ? Maybe start at 28.0 ?? Thanks !!

 

[Forum Boss]

What's the freebore on your chamber. I have a PacNor three groove and my match load is 30.3 Varget with CCI 450s, about .012 in the lands. That's with an 0.85 freebore. Many chambers are made now with a .100-.110 freebore, so you can seat longer and use slightly more powder.

Suggest you start at 28.5 and work up. Watch for ejector marks.

The Scenars should work both in and out of the lands, but you may have to adjust your loads. Chrono your load development. Make sure you can get a repeatable measurement to first contact with the lands before you try seating well into lands with a hot charge.

 

[Flouncer]

Thank you Boss for your reply.

"What's the freebore on your chamber." -That is a great question. Let's see how I do here. If we mean the distance between the .2435 diameter of the leade and the .2310 diameter of the bore where the rifling starts, then we subtract dimensions shown of 1.9165 and 1.6778 and get 0.2387-inch. These data are from the JGS print # 1262. I can and will measure this but this is what I believe the reamer print shows. My first 20 or 40 rounds will be the factory Lapua so I will have a good known safe dimensional base and charge to start with. The 105 Scenar round chambers freely and without any mark or scuff on the bullet.

Help me out here please. If a chamber has a 0.1 freebore instead of a 0.24 or a 0.80 freebore, doesn't that mean the distance between the breech face and the engagement of the rifling is less, not greater ? And doesn't that warrant less powder ?

Last question. I have always used Federal LR match primers prior to this SR cartridge. In one of my conversations with Sierra technicians, they said the Federal are softer primers, with more heat or kick, so they can be a two way safety valve in load development. They generate hotter loads sooner, and they show signs of distress sooner. Irregardless, I have always used the inception of primer flattening as a warning and backed off. So now I have harder, hotter CCI450 primers, and a Mauser bolt with the "claw" extractor. My knowledge of other actions is nil. The extractor is the little push-pull rod which serves the same function. I haven't ever seen any marks from my ejector on any of my loads, regardless of cartridge. And I have worked a relatively unknown area using RL-17 and 8x57 with 200gr MK to exceed published loaded velocities. All without primer flattening. Maybe I play too safe, because I haven't seen any marks on any case bases, ever, or had a sticky bolt with any load that I threw and shot. I feel kind of blind here.

Edit: The last question is in my case which should occur first; primer change, ejector marks or sticky bolt ?

Maybe it's a good learning experience for all of us to go over these fundamental but critical process and procedures. Thanks again. I get to shoot finally this PM after work.

 

[Killshot]

Mark,
Those aren't the source measurements for the Freebore. Look at your print again, subtract element "U" from element "V" and the result is Freebore. It is usually in the area of .085" to .175" if I remember what Kiff told me. More FB equals longer to the lands.

Some other guys will have to weigh in on pressure signs. I had my bolt firing pin hole bushed and the ejector removed by Gre-Tan.....what's a pressure sign?

Have fun tonight. These 6s make little bitty groups.

 

[Flouncer]

From the print:

1.6778-1.5838 = 0.094-inch.

I see this now from the drawing. Why didn't I see this before ?? 8)

I'll worry about what exactly to do with it when I reload. Right now it's factory ammo from a long ways away at $2 a piece.

I didn't get to shoot yet, fixing shaved off sprinkler heads and cleaning the garage, still. I don't care that much for Dilman anyways. It's a PITA to shoot there if you are going to run a patch or set a chrono. Manana at Folsom, break of day, full tank of gas, thermos of black coffee, brand new stick, and out the door at 6 AM. Life is good. I'll catch daybreak over the hills, hopefully the wind flags aren't sticking straight out.