.008 Bump Required to Smoothly Chamber Round??

6mm ARC

Sounds suspect in its own to have die probs/risk

I never heard of it, but I live under a rock and am a dinosaur by today's standards

Idk if its a SAAMI cartridge

Following

I had a similar issue with 3 barrels i had made for some 35 whelen i was building. I finally got a small based die for a 30-06...cut it off and only used the bottom 2/3 to reside the bottom of the whele. Solved the problem. I now small base size first, then bump shoulder back .002 from the fired measurements...chambers so nice. Im on 6 reloads after starting the small base die. Extraction is much better also. I had clickers before the small based dies.

General RE LEE said:

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?

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I would try using a black felt marker on your resized case around the .2" datum mark above the case base and also around the neck/shoulder area. Then chamber the brass a few times until you feel resistance, followed by inspection of the blackened areas to see where contact is being made in your chamber. This should confirm if the base area of the brass is making contact before the shoulder.

You should absolutely remove the Primer before measuring, the Primer is not guaranteed to dimple the same exact height every time.

I encourage you to carefully strip your bolt of the the firing pin and extractor. When the stripped bolt is forward it should drop freely. Put a fired case in the chamber and check to see if the bolt falls on its own. If it doesn't, bump the shoulder .002" from its fired length, wipe the case and try again. If the case is too long, push it back another .002" and try again. The bolt should fall on its own. When you get to the bolt falling on its own, grab a new case and back the die off .001". The new case should come out .001" longer. See if the bolt drops on it. If so, that's your shoulder bump amount. If not, then the previous case is your shoulder bump. Don't just take .002" off of a fired case measurement, it isn't necessarily an accurate depiction of your chamber.

If that method doesn't work, I'd have to guess that you're not annealing and that your brass has hardened to the point its not fully sizing down. OR your resizing die isn't sizing the base far enough.

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.

EDIT: This post wasn't meant to be an Ad to sell brass. I have one of those in the classifieds. The 6.5 Grendel Brass is all converted to 6 ARC. I can only seem to find about 199 of the once fired. I'm not sure what happened to the rest of the brass. It's lost in the sauce.

Did you strip the bolt by removing the firing pin before trying the fit in the chamber?

Since you have 1500 rounds on it, has this always been an issue? Did it just start? Did it start after a certain number of firings?

Agree with others, likely a die/chamber issue. Try marking the cartridge at .200 line and shoulder area. Cycle it once and you should identify where the problem lies.

Sdvldog1371 said:

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.

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What do you want for the starline 6.5 grendel ?

If everything thing else checks out, then I would check the base of the case, it might not be getting sized until you screw the die down to .008 shoulder bump.

I would assume it's a case issue. I believe Peterson talked about a bulge issue with the 6 arc brass. But I would also double check your trim length and if that's in check get a small base die to bring everything back in spec.

I might be interested in the 6.5 Grendel brass if 7mm 08 doesn't get it.

General RE LEE said:

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?

Click to expand...

Shoulder bump is always talked about etc., but it's not the only dimension that matters hence the "full length sizing" statement. I have a similar situation and if I was just checking my shoulder bump it would not make sense. Fired once, fired annealed and sized cases all measure out the same in my comparator, even between different comparator bodies. This is a 22 GT and alpha brass and chambers flawlessly so far with 1600 plus rounds.
The measurement I get that is getting sized is at the case body and shoulder junction, in other words setting the case taper back ever so slightly. A fired case diameter at body shoulder junction is .462" while a sized case is .458". This is with Forester dies in an ancient rock chucker with #3 shell holder bottomed out and camming over.

Sdvldog1371 said:

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.

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I am interested in your 6mm ARC brass. Please let me know what you want for it. Thanks