How much to bump shoulders on 6br?

[zanemoseley]

So I've got Lapua 6br brass being shot in a factory Savage chamber. So far I've neck sized only so far. The brass has been fired twice and I shot some today that would be the third firing. The bolt is getting hard to close.

I used a Hornady Headspace Comparator tool with the #C insert. I'm measuring between 1.1380" - 1.1395" with the most common being 1.1385". How far back should I bump the shoulders? I was thinking maybe 1.1365" if I can adjust that precisely. What do you guys think. The ammo is shooting great but the bolt gets stuck closing.

 

[Rsadams]

Normally about 1-2 thousands is all you need on a bolt action and 3-4 for an automatic...

 

[Rdlningcltchdmpr]

So I've got Lapua 6br brass being shot in a factory Savage chamber. So far I've neck sized only so far. The brass has been fired twice and I shot some today that would be the third firing. The bolt is getting hard to close.

I used a Hornady Headspace Comparator tool with the #C insert. I'm measuring between 1.1380" - 1.1395" with the most common being 1.1385". How far back should I bump the shoulders? I was thinking maybe 1.1365" if I can adjust that precisely. What do you guys think. The ammo is shooting great but the bolt gets stuck closing.

Two points,#1, take the firing pin out of the bolt so you can feel when the bolt close's with no resistance or very very little. That is the # you should size to. #2, check virgin brass so you have a clear understanding of what the difference is .

 

[Falfan2017]

If you take your firing pin out like the above post you can feel when it’s not touching anymore. Than I give it another 1k. Usually ends up being bumped back 2.5-3k. Some people like a light crush. I don’t. Seems more consistent if none of them crush

 

[rwj]

Might want to also remove the ejector along with the firing pin from the bolt...

 

[JFrank]

Sneak up on your bump, might take a Match or two’ chambering freely is the key.
I’m around .0025 fwiw

 

[joshb]

1.136 is what you seem to need. Sneak up on it. When you get it, keep measuring the cases as they come out. Some may spring back more than others. I don’t like getting to the range and finding a few that are too tight to close the bolt easily. These days, I measure them all. Then, just to be sure, I cycle them all thru the gun with the firing pin out. I hate pulling rounds apart!

 

[ShootDots]

Even though the 6mmBR is a case with a small powder capacity, it does operate at high pressure. With cases that operate at 60+thousand p.s.i., I want the case to "absorb" some of that "instant pressure" before the case fills the chamber walls and the bullet has at least started into the lands. In those high pressure cases, I like right at 3 thousandths shoulder bump. I find that using 3 thousandths bump, and NOT operating at the top node, brass extraction from the chamber is easy and primer pockets really last indefinitely! Bumping that far does not seem to ill effect accuracy in the least..

 

[cw308]

My case headspace is .001 - .002 no more or less , I first used the Go Gauge with shims to find my chamber length from bolt face to datum line , matched that length with my RCBS Precision Mic , can do the same with a comparator. Then test my sizing with a stripped bolt . I have a Rem. 700 the bolt is east to strip but I'm not so sure the Savage bolt is easy to strip and it has that floating bolt face. Your headspace has to be accurate or your seating measurement will be off .

 

[zanemoseley]

Thanks for the advice guys. I set my die tonight at 1.1365" which should be about a .0015" - .002" shoulder bump.

 

[fatelvis]

I was always under the impression that your largest measured fired casing represents the closest measurement of your chamber. Considering that, I always try to bump the shoulders .001”-.002” using that measurement.

 

[cw308]

fatelvis
The best way I found to find my chamber length was to use Go Gauge , for my 308 the gauge is 1.630 and by adding shims to my bolt face I found my bolt face to datum or shoulder was 1.632 . I had a chamber that would cause my cases to get shorter from expansion , once some of the sxpntion was removed the case would chamber also lengthen giving me my .001 to .002 if I only neck sized my cases would be around .004 . Best way using the gauge is with a stripped bolt for finding case headspace and ogive measurements .

 

[Lefty Trigger]

Running .002 on my Lapua brass and it seems happy there.

 

[BenPerfected]

Normally about 1-2 thousands is all you need on a bolt action and 3-4 for an automatic...

With my bolt actions, the shoulder bump on my 6 Dasher brass is 3-4. No issues with 3-4 and 2 is tight on about 10-20% of my 1-2 loaded rounds. It could be because of not enough lube, of maybe it is related to annealing. I decided to stop screwing with 1-2 when 3-4 closes like butter.
Ben

 

[robert8904]

So I've got Lapua 6br brass being shot in a factory Savage chamber. So far I've neck sized only so far. The brass has been fired twice and I shot some today that would be the third firing. The bolt is getting hard to close.

I used a Hornady Headspace Comparator tool with the #C insert. I'm measuring between 1.1380" - 1.1395" with the most common being 1.1385". How far back should I bump the shoulders? I was thinking maybe 1.1365" if I can adjust that precisely. What do you guys think. The ammo is shooting great but the bolt gets stuck closing.

That seems like a lot of variance in those datum lengths. Did you de-prime the fired brass before measuring?

 

[Rsadams]

With my bolt actions, the shoulder bump on my 6 Dasher brass is 3-4. No issues with 3-4 and 2 is tight on about 10-20% of my 1-2 loaded rounds. It could be because of not enough lube, of maybe it is related to annealing. I decided to stop screwing with 1-2 when 3-4 closes like butter.
Ben

I do about 2-2.5 myself I would rather be certain the bolt shuts when you really need it to... Because of many different variables in brass it's hard to get them all exactly the same , that extra thousands helps to be sure there's no problems...

 

[Texas10]

When measuring your spent brass before sizing, put an OAL gage on one blade of your caliper and Headspace comparator on the other. This will remove the error caused by primer protrusion.

I use the #B comparator because it touches about midway down the shoulder. The #C comparator measures more towards the shoulder/body corner. Try both and see which one gives the most consistent measurement.

Are you annealing? After three cycles the brass is fairly work hardened, and you'll notice it in sizing and seating pressure. The shoulder bump will tend to spring back inconsistently, and show in your measurements. When sizing after annealing, you'll have to adjust the die as the shoulder will move more. Be prepared to creep up on your preferred length. I used to anneal every three cycles, now however I anneal every cycle after seeing the results on paper.

I keep two pieces of brass as Standards, one that is max chamber length (stiff bolt closure), and one that is .002 shorter. Both are labeled with date and dimension and used to verify any new measuring tool, or anytime I am questioning what the heck I'm doing, like when having a senior moment while switching from one caliber to another on the loading bench and I grab the wrong insert. Should I ever have to pull and re-install the barrel, these will be very helpful returning to original headspace.

Sizing back .001 to .002 is plenty for most loads, maybe more if your load is on the hot side. Your brass life will be the deciding factor.

 

[mikehotel]

Easy way:

I size back .001-.002 from 2nd fired brass, with the primer removed. BTW, I anneal after each firing YMMV

 

[B23]

I bump 1-2 thou but only once the case has reached its max chamber length and there is zero headspace. Arbitrarily bumping the shoulder back before the case has reached zero headspace can result in having much more headspace than you think.

 

[Delfuego]

Measure the base of a fired and sized cases. Could be the dies/chamber, rather than the shoulder bump.