Heavy bolt lift at low charges with 6BR

[gambleone]

Lapua Brass. I tried to repeat the marks in sharpie again and could not, I don’t think it’s an issue. How would the extractor do that anyway?
Powder measurements are accurate to the grain, being measured on an fx-120i.
Primers are fine but I have never had primers be an indicator of pressure in this action.

When you said you were getting extractor marks, I took it to mean bolt wipe on case head, which could be caused by a tight base after firing.

 

[foxguy]

Any idea how much your die is supposed to size down the base? Alex wheelers video is very informative, but he doesn’t mention how much tolerance at the base you should have. My .0005 seems tight, and I am ready to contact harrels for a die that fits better, but I want to make sure that this small tolerance is something that should be addressed.

Patruck825,

My Harrell's die is reducing my brass .0015 at the 200 line of the Brass.

You have mentioned that the problem mostly went away after taking .002 off of your shell holder. That leads me to believe that you weren't getting the shoulder pushed back as much as you were thinking. How are you measuring your headspace reduction after sizing and with what?

 

[Patruck825]

Patruck825,

My Harrell's die is reducing my brass .0015 at the 200 line of the Brass.

You have mentioned that the problem mostly went away after taking .002 off of your shell holder. That leads me to believe that you weren't getting the shoulder pushed back as much as you were thinking. How are you measuring your headspace reduction after sizing and with what?

Headspace reduction should be correct, measuring it with the Hornady headspace gauge and calipers, bumped the shoulders exactly like Alex wheeler does in his video on sizing brass. Sized it to fit in the action with slight finger pressure and then bumped it another 2 thou. Bolt drops with gravity on the sized case.

 

[Patruck825]

When you said you were getting extractor marks, I took it to mean bolt wipe on case head, which could be caused by a tight base after firing.

No bolt wipe, I meant ejector marks, not extractor, sorry. It’s a mechanical ejector and had a little square from the slot in the bolt where it goes.

 

[hogpatrol]

Are you sizing the new brass BEFORE the first firing? Maybe you got a bad lot of brass. If you haven't, I'd try sizing ten pieces of new brass and see how that works.

 

[Patruck825]

Are you sizing the new brass BEFORE the first firing? Maybe you got a bad lot of brass. If you haven't, I'd try sizing ten pieces of new brass and see how that works.

Yes, I always size my brass before firing, new or otherwise.

 

[hogpatrol]

Yes, I always size my brass before firing, new or otherwise.

Ok, just trying to eliminate another factor.

 

[Patruck825]

I just sent some fired cases out this morning to Harrell’s to have them make me a die. Even if the die isn’t the total cause of the issue, as a PRS rifle, .0005 does not seem like enough room to prevent issues moving forward. This rifle will see nasty conditions often.

 

[nmjwolf]

I just sent some fired cases out this morning to Harrell’s to have them make me a die. Even if the die isn’t the total cause of the issue, as a PRS rifle, .0005 does not seem like enough room to prevent issues moving forward. This rifle will see nasty conditions often.

You can use a small base 308 die and see if the goes away. I had a dasher chambered rifle with the .200 dimension at 470 and have to run my brass through the small base die to avoid clickers...PITA but works.

 

[Patruck825]

You can use a small base 308 die and see if the goes away. I had a dasher chambered rifle with the .200 dimension at 470 and have to run my brass through the small base die to avoid clickers...PITA but works.

Thats a great idea, and i think i have a RCBS small base 308 die at home. Question is, how much does the small base die resize the brass? Obviously i dont want too much room. How much is considered not optimal?

 

[nmjwolf]

Thats a great idea, and i think i have a RCBS small base 308 die at home. Question is, how much does the small base die resize the brass? Obviously i dont want too much room. How much is considered not optimal?

It will be fine and it should size it enough -- I use the same process in my steel gun.
Shot this dope test at 1k with brass sized using 308 small base and then harrels D4. (it was a calm morning)

 

[Patruck825]

It will be fine and it should size it enough -- I use the same process in my steel gun.
Shot this dope test at 1k with brass sized using 308 small base and then harrels D4. (it was a calm morning)View attachment 1053945

That’ll do!! Looks like I’ll be able to size this brass and test it this weekend if not sooner. I’ll report back.

Everyone thank you for your help so far.

 

[Patruck825]

I’m not sure how much this helps, but this is the reamer used in my barrel.

Can anyone better at this than me tell me anything meaningful from this?
It looks like my chamber is 1.4 thou tighter than the reamer says it should be. Print says .4714 at the .200 line but my fired brass shows .4700

Headspace I’m not sure what to make of it. It says 1.1670 min and 1.1770 max, but both my chamber and my go gauge are 1.1595, the go gauge plus a single piece of cellophane tape would not close.

View attachment 1053984

 

[Patruck825]

Fooling with my press I’ve observed something else that has me concerned. It’s a Hornady single stage with those quick change bushings.

When the press reaches the top of its stroke during sizing I can see a gap between the shell holder and die that increases. There’s no way you can force the die down as far as you should with this slack.

I have been debating buying a co ax for years, but this just might push me over the edge. Not to get off topic, but does the coax exhibit this slack upon sizing?

 

[rwj]

Fooling with my press I’ve observed something else that has me concerned. It’s a Hornady single stage with those quick change bushings.

When the press reaches the top of its stroke during sizing I can see a gap between the shell holder and die that increases. There’s no way you can force the die down as far as you should with this slack.

I have been debating buying a co ax for years, but this just might push me over the edge. Not to get off topic, but does the coax exhibit this slack upon sizing?

Why can’t the die be lowered to compensate for the bushing slack?

 

[Patruck825]

Why can’t the die be lowered to compensate for the bushing slack?

I don’t think you should have to apply that much pressure to a press handle, it would also bump the shoulder too much.

 

[rwj]

I don’t think you should have to apply that much pressure to a press handle, it would also bump the shoulder too much.

There are some very knowledgeable members on this forum and I hope they correct this input if incorrect. Based on the info provided, the chamber is closest to the minimum dimensions (perhaps slightly undersized) and not a good match with the sizing die.

 

[hogpatrol]

I’m not sure how much this helps, but this is the reamer used in my barrel.

Can anyone better at this than me tell me anything meaningful from this?
It looks like my chamber is 14 thou tighter than the reamer says it should be. Print says .4714 at the .200 line but my fired brass shows .4700

Headspace I’m not sure what to make of it. It says 1.1670 min and 1.1770 max, but both my chamber and my go gauge are 1.1595, the go gauge plus a single piece of cellophane tape would not close.
View attachment 1053996
View attachment 1053984

.4714 minus .41700 is .0014 or fourteen ten thousandths of an inch not fourteen thousandths. Put another way, it's1.4 thousandths.
How are you arriving at the headspace gauge measurements?

 

[Patruck825]

.4714 minus .41700 is .0014 or fourteen ten thousandths of an inch not fourteen thousandths. Put another way, it's1.4 thousandths.
How are you arriving at the headspace gauge measurements?

thanks for the catch, i corrected the post.

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.

 

[Patruck825]

Hey that's identical to my chamber.

I have been having a b!tch of a time getting it to shoot with a certain lot of Lapua brass that I bought 500 pieces of.
I measured the thickness at the neck and it's .0135 thick. add that to my .2435 bullet. yeah. crowded.

I finally am on the right track with full power loads and no pressure signs.

Add up your total neck thickness and your bullet at the p-ring, and subtract your chambre neck of .271, then divide by 2. I bet you that number is pretty small. I bet you that number is less than 1 thousands of an inch.

Don't buy into the lie of fitted necks or no clearance necks.....it's a lie it's a lie, it's a lie.
The brass has to expand and relax but if it has NO room to expand, when it relaxes it's going to get trapped when the chambre relaxes.
M->

Interesting, I only have calipers but my brass measures 0.0125 to 0.013
Would this cause the ejector marks and heavy bolt lift though? I do have some residue on some of my case necks after firing that I normally don’t.
The things shoots very accurately though, so no complaints there.