Can Undersizing Cause Tight Bolt

[Ccrider]

I have been working up loads for a 6br. I have read where a lot of folks bump the shoulder back .001-.002. When I do this, after firing the round, my boot is noticeably stiff. I am not seeing any other pressure signs.

If I bump the shoulder back .007, the bolt stiffness after firing goes away. I get the same results using a fl die or a shoulder bump die.

My question is whether the stiff bolt from the minimally sized brass is a true pressure sign? I know it could be since in theory, less pressure would be needed to expand the brass enough to seal the chamber.

Thanks

 

[Terry]

A hard bolt open is a sign of excessive pressure in many cases. Make sure the chamber and ammo are clean. Moisture or oil can cause this problem. Try backing off .5 grains of powder.

 

[Toby Bradshaw]

It's possible that your die is not sizing the base of the case until it is run so far into the die that it pushes the shoulder back excessively (and 0.007" is excessive).

Coat a loaded round (0.001-0.002 bump) with Sharpie or Dykem, fire it, extract it, and see where it is rubbing.

 

[Ccrider]

It's possible that your die is not sizing the base of the case until it is run so far into the die that it pushes the shoulder back excessively (and 0.007" is excessive).

Coat a loaded round (0.001-0.002 bump) with Sharpie or Dykem, fire it, extract it, and see where it is rubbing.

Will do.

 

[243winxb]

After you extract the brass , that produces hard bolt lift, try putting it back into the chamber.
If hard to rechamber, its a pressure sign.

 

[Ccrider]

After you extract the brass , that produces hard bolt lift, try putting it back into the chamber.
If hard to rechamber, its a pressure sign.

Will try this also.

 

[Ccrider]

Btw, the load is 31gr Varget, 95 Berger VLDS CCI 450 Primers in an 8tw 21 inch barrel.

 

[Texas10]

Is your full length sizing die actually resizing the case wall near the base? If so, by how much? What barrel are you shooting?

 

[jr600yd]

Tex has a point. Try this. Take a 308 die (or 3006, 243, 260 etc ) remove the decapping stem and size your 6BR case. Measure the base diameter of this case against one you ran thru your 6BR die.

 

[powderbrake]

Btw, the load is 31gr Varget, 95 Berger VLDS CCI 450 Primers in an 8tw 21 inch barrel.

I run an 88 gr at 30.7 gr Varget with no problem, yours is a bit hotter, maybe it's pressure.

I recommend cleaning your chamber after every time you clean the rifle, as leftover cleaning fluids in the chamber can cause hard extraction. I use the Sinclair tools https://www.sinclairintl.com/gun-cl...tools/action-cleaning-tool-kit-prod35492.aspx

I don't measure my brass after sizing, I recommend the Wheeler method of finding the correct sizing of the brass.

 

[johnnyi]

I run an 88 gr at 30.7 gr Varget with no problem, yours is a bit hotter, maybe it's pressure.

I recommend cleaning your chamber after every time you clean the rifle, as leftover cleaning fluids in the chamber can cause hard extraction. I use the Sinclair tools https://www.sinclairintl.com/gun-cl...tools/action-cleaning-tool-kit-prod35492.aspx

I don't measure my brass after sizing, I recommend the Wheeler method of finding the correct sizing of the brass.

This method ensures proper fit into your chamber every time! I share this video a lot with new and even some experienced shooters that ask about extraction or bolt closing issues. @Alex Wheeler did an awesome job with creating this video! I’m sure it’s helped many shooters. He also has another great video about finding your lands.

 

[gunsandgunsmithing]

Was this brass ever fired in a different chamber?

 

[Ccrider]

Was this brass ever fired in a different chamber?

No.

It is aCriterion barrel.

Powderbrake and Johnny, I will try the wheeler method to determine how much to size the case. I don’t think the .002 is sizing the brass enough. Looking at the video, he is sizing more than .002.

I will also check to see how much the FL die is sizing the base.

 

[Ccrider]

What parts do I need to take out of the bolt. The entire pin assembly or will the pin come off?

 

[gunsandgunsmithing]

No.

It is aCriterion barrel.

Powderbrake and Johnny, I will try the wheeler method to determine how much to size the case. I don’t think the .002 is sizing the brass enough. Looking at the video, he is sizing more than .002.

I will also check to see how much the FL die is sizing the base.

IME, pressure is the only thing left. For years, people only neck sized brass from a given chamber and without issue unless it was fired too hot. The only other thing would be if the chamber was tight even with unfired brass.

If the brass had ever been fired in another chamber, it would tend to expand when fired to fit that chamber. If the new chamber is at all tighter, particularly in the web area, you get bolt click. Bolt lift has everything to do with the fired case's dimensions on the way out and little to nothing to do with how it was sized to go in.

 

[NorCalMikie]

You're bumping the shoulders back but not touching the rest of the body. Time for a body die size OR full length. You'll be starting all over again till the next stiff bolt lift.

 

[Ccrider]

Ok. I checked several things.

First the full length die is sizing the base of the case although not very much-.00055.

I took the firing pin out and still had that soft pressure sizing down to .002. At .0035 there is no resistance. So presumably I need to size back to .005 or .006, following Alex’s video. I will give this a spin and see what happens.

 

[powderbrake]

Ok. I checked several things.

First the full length die is sizing the base of the case although not very much-.00055.

I took the firing pin out and still had that soft pressure sizing down to .002. At .0035 there is no resistance. So presumably I need to size back to .005 or .006, following Alex’s video. I will give this a spin and see what happens.

You also have to take out the ejector. If you don't have an ejector holding tool (about $26 at Sinclair) You can cut a small wood dowel to fit the bolt face, and c clamp it to compress the ejector, and then with a small punch, remove the pin holding the ejector. Carefully release the clamp so as to retain the ejector. Remove the ejector and spring. Now you can use the Wheeler method to size to a loose bolt handle drop.

Replace spring, ejector, and pin.

 

[urbanrifleman]

I was never able to run max loads in my Criterion 6BR 1-8 barrel. It would always pressure out much sooner than my other barrels.

 

[Ccrider]

Thanks Powderbrake. I will order the tool.

I was never able to run max loads in my Criterion 6BR 1-8 barrel. It would always pressure out much sooner than my other barrels.

Me thinks this may be my situation.