How much bump is safe?

[Texas Solo]

My bolt closure is tight, even with factory Fed GMM 168.
I sized and trimmed new Hornady brass and set the seating depth at -.005" off the lands. It's also tight.
Next I bumped the shoulder .002" and it's only slightly better, so I think I found the issue.
Question is how much bump is acceptable? .004 or .006?

 

[Straightshooter1]

My bolt closure is tight, even with factory Fed GMM 168.
I sized and trimmed new Hornady brass and set the seating depth at -.005" off the lands. It's also tight.
Next I bumped the shoulder .002" and it's only slightly better, so I think I found the issue.
Question is how much bump is acceptable? .004 or .006?

I'd take that case you bumped .002" and make a .001 adjustment and see if it then chambers better. If not, I'd do another .001 until it's not tight (unless you want a little tightness). That would be the setting I'd use then on, because after firing, you shouldn't having to bump .004 - 006.

 

[LHSmith]

Did you measure the datum to head dimension on the factory brass and compare it to what your chamber dimension is? There probably was quite a bit of clearance yet proved to be safe and still fired. I bump (fired cases) 0.002" in competition and 0.003" for hunting.

 

[williepete]

here ya go

 

[K22]

In my opinion, .005" is too close to the lands because variations in ogive and measurement methods can sent you into the lands when you think you are not there.

Assuming you are measuring "bump" correctly, a .002" bump should be sufficient to provide trouble free chambering from a sizing standpoint. You can try a .003 bump, but I suspect that won't solve the problem because it lies somewhere else.

The fact that factory ammo chambers tightly, tells me that something is going on with the rifle. Either a rough chamber, a headspace issue, or an extractor issue that resists accepting the rim of the case. This needs to be evaluated by a professional, i.e., rifle smith.

 

[Bill Norris]

I found in some rifles .002 will not let the bolt close quite as easy as I like. On those I bump the shoulders back .001 at a time until I get the feel I want which is not to feel much pressure at all upon bolt handle dropping down. Normally .003 to .004 at the most will be fine.

 

[Greyfox]

The problem is more likely the base rather than headspace. A bump of .002 will almost always correct the headspace. Borrow a small base die or a ring die and try that on one. Also you might try checking the feel with the firing pin assembly removed.

Rick
YMMV

 

[K22]

I found in some rifles .002 will not let the bolt close quite as easy as I like. On those I bump the shoulders back .001 at a time until I get the feel I want which is not to feel much pressure at all upon bolt handle dropping down. Normally .003 to .004 at the most will be fine.

If you're not doing it, check the size case with the firing pin assembly removed. This will give you a much better feel and assessment of chambering.

Also, place a piece of scotch tape on the end of the rim and trim with an exactor knife so no tape is hanging over the rim. Chamber the case, if it chambers without any or very little resistance, you may be bumping too much.

 

[Ccrider]

It all depends on where you are measuring bump from. Your contact point between the neck and shoulder will not always be at the shoulder. It can be further up, closer to the neck. .002 from the last place that is touching will be plenty.

Some dies size differently also.

 

[Texas Solo]

Thanks guys. I'll have to try more bump.
At the .002 that I have, it IS "slightly" better, but still tight. Add tape to the base and it won't close.

 

[Bill Norris]

It all depends on where you are measuring bump from. Your contact point between the neck and shoulder will not always be at the shoulder. It can be further up, closer to the neck. .002 from the last place that is touching will be plenty.

Some dies size differently also.

Right I understand the comparator shoulder and die shoulder may not be exactly on the same angle.

 

[LHSmith]

If you're not doing it, check the size case with the firing pin assembly removed. This will give you a much better feel and assessment of chambering.

+1 IMHO it makes a huge difference in feel.

 

[Dusty Stevens]

Are you doing this testing with a bullet in the case?

 

[Texas Solo]

Are you doing this testing with a bullet in the case?

No on my Hornady brass

 

[Field_2_Fork]

Possibly a tight neck chamber? Are you able to turn a neck on a case and see if it's any better?

 

[Screamer]

The problem is more likely the base rather than headspace. A bump of .002 will almost always correct the headspace. Borrow a small base die or a ring die and try that on one. Also you might try checking the feel with the firing pin assembly removed.

Rick
YMMV

The problem is more likely the base rather than headspace. A bump of .002 will almost always correct the headspace. Borrow a small base die or a ring die and try that on one. Also you might try checking the feel with the firing pin assembly removed.

Rick
YMMV

I had a CZ 527 in .223. The chamber in that rifle was tighter not shorter than my remington .223. I went to a small base die & it solved tight chambering.

 

[Texas Solo]

Already using a SB die

 

[Texas Solo]

Possibly a tight neck chamber? Are you able to turn a neck on a case and see if it's any better?

Don't have the tools

 

[DShortt]

Take a black marker and completely cover the case and let dry. Chamber and extract the case. There will be markings that will show where the case is tight in the chamber.

 

[Coyotefurharvester]

What type firearm and what brand sb die ?