.008 Bump Required to Smoothly Chamber Round??

[Stonyman88]

Interesting recent development loading my 6mm ARC Howa bolt action. If I bump shoulder .002", bolt is difficult to close. Virgin brass shoulder is .008" back from a fired case and chambers easily. I kept lowering my FL die in increments till case chambers smoothly, which is right about .006-.008" shoulder bump. Cases are not growing more than .003" when bumping shoulder back this much, which is interesting.

I've never had a chamber that needed more than .002" shoulder bump to smoothly chamber a case.

• Rifle has 1500 rounds on it
• Carbon ring removed in throat
• Bullet seated to jump .060
• Using .350 Hornady comparator and a fired case
• Loads are within Hornady load data and no over pressure
• Hornady 3x fired brass

I'm stumped. Any suggestions?

Did you check the dia. just below the shoulder? before and after you FL sized the brass? I've seen that cause a round not to seat with out pressure if at all, Know your not rookie, just wonder, I bump all mine with just a shoulder bump die then check the dia. of the case. Sure like to know what you find out.

 

[xsn10s]

If I bump shoulder .002 and knock the primer out, it's hard to close bolt. Hmmm

Measure the case head diameter. You can blackout the case in that area with a marker to check for rubbing too. My guess is your bumping the shoulder but not sizing the casehead. So the casehead can even increase in diameter since the die isn't sizing at that time.

 

[243winxb]

bolt is difficult to close

The area marked in red, is not being sized. If it was being sized, the trim length would become longer.

On firing, trim length gets shorter, as the case body expands outward.

Less of a problem when chamber & die are a close match.

 

[Dean2]

If I bump shoulder .002 and knock the primer out, it's hard to close bolt. Hmmm

So already been asked but did not see an answer, or I missed it. Does the fired brass go back into the chamber smoothly, prior to any sizing, depriming or other alterations. It should, and if it does, it means your sizing die is causing the problem. The sizing die is making something wider than it should be because your .008 bump that only grows your brass length .003 has to be going somewhere.

 

[ottobounds]

Not to hijack the OP but I have 2 bags of unopened Starline 6.5 Grendel that I won't be using. Message me if interested.

 

[dk17hmr]

Are you sure it's the shoulder hanging up and not the body of the case? Have you tried any other dies? Also I'm not sure how much it could effect it as I havent tested it but have you tried punching out the primer before zeroing your calipers? I use a Lee universal decapper for that step.

 

[General RE LEE]

By the by, I have probably 200 pieces of once fired hornady 6 arc brass I'd let go for next to nothing. I also have a bunch of starline 6.5 grendel, most of which hasn't been used. I went to Alpha munitions as soon as they released it.

PM sent on the 6ARC brass

 

[General RE LEE]

So already been asked but did not see an answer, or I missed it. Does the fired brass go back into the chamber smoothly, prior to any sizing, depriming or other alterations. It should, and if it does, it means your sizing die is causing the problem. The sizing die is making something wider than it should be because your .008 bump that only grows your brass length .003 has to be going somewhere.

I failed to mention, fire case is as difficult to close bolt as sized case.

 

[Dean2]

I failed to mention, fire case is as difficult to close bolt as sized case.

Something is definitely not right and it sounds like the brass. A fired case should be perfectly formed to your chamber, and on cooling they shrink slightly from their max size on firing. There is no way proper fired brass, that wasn't an over pressure load, right out of the gun should be hard to chamber. Was it hard to extract as well?

Hornady brass has never been known as long life, top quality brass, so 3 firings may be the issue. I would try 10 pieces of virgin brass. Load 5 with a min listed load and 5 with the load you are now using, test the fit of the once fired brass in the gun after firing. Do the 5 min loads fit different than the 5 with your current load, and are some or all different than your 3x fired brass.

 

[Nuclear Worker]

Interesting recent development loading my 6mm ARC Howa bolt action. If I bump shoulder .002", bolt is difficult to close. Virgin brass shoulder is .008" back from a fired case and chambers easily. I kept lowering my FL die in increments till case chambers smoothly, which is right about .006-.008" shoulder bump. Cases are not growing more than .003" when bumping shoulder back this much, which is interesting.

I've never had a chamber that needed more than .002" shoulder bump to smoothly chamber a case.

• Rifle has 1500 rounds on it
• Carbon ring removed in throat
• Bullet seated to jump .060
• Using .350 Hornady comparator and a fired case
• Loads are within Hornady load data and no over pressure
• Hornady 3x fired brass

I'm stumped. Any suggestions?

I would be interested in the 6.5 Grendel brass

 

[Mike Matteson]

Following and Interesting!

 

[6MMike]

Interesting recent development loading my 6mm ARC Howa bolt action. If I bump shoulder .002", bolt is difficult to close. Virgin brass shoulder is .008" back from a fired case and chambers easily. I kept lowering my FL die in increments till case chambers smoothly, which is right about .006-.008" shoulder bump. Cases are not growing more than .003" when bumping shoulder back this much, which is interesting.

I've never had a chamber that needed more than .002" shoulder bump to smoothly chamber a case.

• Rifle has 1500 rounds on it
• Carbon ring removed in throat
• Bullet seated to jump .060
• Using .350 Hornady comparator and a fired case
• Loads are within Hornady load data and no over pressure
• Hornady 3x fired brass

I'm stumped. Any suggestions?

Do you anneal your brass?

 

[Rosebud]

I'm not a fan of Hornadys brass, their bullets are good to go, brass not so much. If you can find Lapua 6.5 Grendel brass it's easy to resize to the 6 Arc. Much better brass. JMO

 

[BrentM]

I measure a fired case with spent primer installed. I zero out my calipers and then measure a case after its been through FL die and primer has been removed.

You need to pop that primer. False reading.