Heavy bolt lift at low charges with 6BR

[hogpatrol]

My blue box Lapua 6BR brass loaded round, unturned neck is .267. A .271 chamber is ok for that brass. Measure your loaded round and make your calculations from that number.

It’s a pre fit barrel and was tightened onto a go gauge that measures 1.1595, a single piece of tape on the back and it wouldn’t close, which only adds a thou.

What tool did you use to measure the headspace gauge?

 

[Patruck825]

My blue box Lapua 6BR brass loaded round, unturned neck is .267. A .271 chamber is ok for that brass. Measure your loaded round and make your calculations from that number.


What tool did you use to measure the headspace gauge?

a loaded round comes out to about .2685 for me.

I used a Hornady headspace gauge with the 350 insert. I use the same gauge to measure shoulder bump on my cases.

 

[hogpatrol]

a loaded round comes out to about .269 for me.

I used a Hornady headspace gauge with the 350 insert. I use the same gauge to measure shoulder bump on my cases.

You can't accurately measure a headspace gauge or anything else with that tool. It only gives a reference number to work with. The same goes for calipers checking anything. Unless you are checking your loaded rounds with a micrometer that reads in tenths, you are not getting a precise reading.

 

[Patruck825]

You can't accurately measure a headspace gauge or anything else with that tool. It only gives a reference number to work with. The same goes for calipers checking anything. Unless you are checking your loaded rounds with a micrometer that reads in tenths, you are not getting a precise reading.

ill add it to the list of things to get.

 

[Sheldon N]

I run a TL3 and it does seem unusual that you would get heavy bolt lift at those low charges. With the big ejector slot I see marks starting to faintly appear even at moderate charges, then more pronounced ejector marks once heavy bolt lift starts. I use the bolt lift as my primary indicator of where to back off in charge weight.

My first instinct would be to check neck clearance issues, stuff like whether a bullet falls into a fired case without resistance. Also check for a carbon ring in the throat that might impede the bullet.

Base diameter sizing is something to keep track of, and I agree with the comment that you really need a micrometer to measure that accurately. My experience has been that you don't see the base of the case reach full expansion until maybe 3-4 firings on the brass. As far as how much sizing is needed at the base, I've seen clickers and premature heavy bolt lift when I was getting very little sizing on a smaller diameter chamber, but that was 0.0002 (2 ten thousandths) of sizing between fired/sized. Once I get above 0.0005 sizing at the base I've not had any problems with heavy bolt lift or clickers. Sizing 0.001 would be nice, but that does require a pretty tight die. I've done it with a small diameter 308 die, but it also pushed the shoulder forward several thou and made bumping the shoulder problematic. Seems like the top benchrest guys here on the forum size around 0.001 at the base, 0.002 at the base would be a lot and more than I would want. I have a small diameter chamber Dasher with some brass that's got 10 firings and my Harrels D4 die only gives 0.0005 or so of sizing at the base. I sent my brass to Harrels and they picked this die for me.

 

[Patruck825]

My first instinct would be to check neck clearance issues, stuff like whether a bullet falls into a fired case without resistance. Also check for a carbon ring in the throat that might impede the bullet.

So I tested this, and a bullet does not drop freely into the case, it hangs up a little bit where the bearing surface begins after the boat tail, but if If I give it a little tap it will fall in. Some cases easier and some require a little more pressure. Looks like it’s just on the edge of having enough room.

Should I start neck turning my cases?

 

[Sheldon N]

So I tested this, and a bullet does not drop freely into the case, it hangs up a little bit where the bearing surface begins after the boat tail, but if If I give it a little tap it will fall in. Some cases easier and some require a little more pressure. Looks like it’s just on the edge of having enough room.

What do you see in the measurement of neck OD for fired brass, vs measuring the neck OD of loaded rounds? Measuring 5-10 cases to make sure you've got a good sense of the average and any outliers.

 

[Patruck825]

What do you see in the measurement of neck OD for fired brass, vs measuring the neck OD of loaded rounds? Measuring 5-10 cases to make sure you've got a good sense of the average and any outliers.

I am seeing a consistent .2675 on loaded rounds and .2695 on fired brass

 

[hogpatrol]

.0007 per side is not enough in my recent experience. That always gave me heavy boat lift and ejector marks on the base of the brass at reduced charge levels.

M->

How did you arrive at .0007 with a reamer neck of .271?

 

[hogpatrol]

.271-.2695=.0015 ÷2=.00075.
Throw out the point 0 0 0 0 5 because it is absolutely meaningless.
I can breathe on something and make it grow more than that

M->

.271-.2695=.0015 ÷2=.00075.
Let us throw out the .0005 because it is absolutely meaningless.
I can breathe on something and make it grow more than that
....but to be honest I thought his loaded round was .2685 which is a different from what i was thinking. I saw the .2695 and jumped on it wth out thinking.

M->

.271 chamber neck diameter minus .2675 loaded round = .0035 clearance, MORE than enough. The .2695 number is the neck diameter after springback.

 

[Stan Taylor]

I would find a gunsmith to fix the problem the guys on here don't have your problem in there hands to diagnose the problem you are having.

 

[Patruck825]

.271 chamber neck diameter minus .2675 loaded round = .0035 clearance, MORE than enough. The .2695 number is the neck diameter after springback.

This is assuming my chamber neck is actually cut to .271 and not undersized like the rest of it seems to be. Shouldn’t a bullet drop into a fired case with that much room?

 

[shortgrass]

I would find a gunsmith to fix the problem the guys on here don't have your problem in there hands to diagnose the problem you are having.

Aww, come on Stan, anything can be 'fixed' on the interdnet!

 

[hogpatrol]

This is assuming my chamber neck is actually cut to .271 and not undersized like the rest of it seems to be. Shouldn’t a bullet drop into a fired case with that much room?

Sir, There exists a false belief that everyone can install a barrel on a Savage or Remage and just go shoot. At this point the best suggestion I can make is to follow Stan's advice and take it to a good gunsmith to see if he can take some measurements and determine if there is a problem. There are too many posts on this thread, even though they are with good intentions, are incorrect and causing confusion.

 

[rwj]

Scratching my head. Where did you get the figure of .2675 ?

The OP provided the dimension after measuring loaded rounds...

I am seeing a consistent .2675 on loaded rounds and .2695 on fired brass

 

[Patruck825]

Sir, There exists a false belief that everyone can install a barrel on a Savage or Remage and just go shoot.

Having done it in 4 other calibers without a single issue, I would hope I had the simple process figured out by now. I don’t think it is the means of install that is the issue, there is obviously something at play here that would have arose even if it was a shouldered barrel install. A chamber that is too tight, is a chamber that is too tight.

 

[bigstick6017555]

cerrosafe and a micrometer, worked for me several times

 

[hogpatrol]

Just a data point, 6BR .270 neck, Lapua blue box 6BR brass, no turn necks, loaded round .2678-.2685, 2000+ rounds. Did two pd hunts in Texas, 90+ degrees, 600 rounds over three days each time, no hard bolt lifts and still shoots 3/8 to 1/2 minute of PD. YMMV

 

[hogpatrol]

in your experience wilk you get in trouble with brass that has wall thickness of .0135, and a bullet of .2435 ?

M->

What measuring tool are you using? I'm guessing calipers? If so, those measurements may not be correct.

 

[bigstick6017555]

before you turn necks, regardless what brass you use you need to know the chambers neck exact! dimensions. guessing is not the way to go