??Having to bump shoulders on new brass??

[GAnderson]

Hopefully I can explain what is happening well enough for someone to be able to answer a couple of questions so here goes. A friend of mine just got his 6mm Remington back from gunsmith with new chambered barrel. In order for new brass to chamber he has to bump the shoulder a couple of thousandths....this is what the gunsmith told him to do when he called and inquired about the issue. The casings work fine after this and also after being fired from there on out. We can only assume that the reamer used by the smith was a very tight spec reamer....??? Can anyone confirm that this is "OK" or did the smith short cut the chamber a couple of thousandths? Second dilemma, some new cases will chamber without bumping the shoulder but after loading them, they will then not chamber...bullets are well off of the lands and the neck diameter still has .002 clearance. We pull the bullet, bump the shoulder and load the cartridge again and it will then chamber...??? Any thoughts or answers? Thanks in advance on your replies and hopefully answers to these questions.
Gene

 

[CatShooter]

Hopefully I can explain what is happening well enough for someone to be able to answer a couple of questions so here goes. A friend of mine just got his 6mm Remington back from gunsmith with new chambered barrel. In order for new brass to chamber he has to bump the shoulder a couple of thousandths....this is what the gunsmith told him to do when he called and inquired about the issue. The casings work fine after this and also after being fired from there on out. We can only assume that the reamer used by the smith was a very tight spec reamer....??? Can anyone confirm that this is "OK" or did the smith short cut the chamber a couple of thousandths? Second dilemma, some new cases will chamber without bumping the shoulder but after loading them, they will then not chamber...bullets are well off of the lands and the neck diameter still has .002 clearance. We pull the bullet, bump the shoulder and load the cartridge again and it will then chamber...??? Any thoughts or answers? Thanks in advance on your replies and hopefully answers to these questions.
Gene

You have a minimum, or slightelyy shorter chamber.

It is no problem, and I wish all my chambers were that way.

Just run your new cases through the bump die and shoot them.

They will last long, because the worst time for a case is the first firing - that is when case stretch is the most - and when your cases are that close on the first firing, then you are off to a good start.

 

[fredhorace77]

Well i guess it depends on if you're happy with it that way and is it done the way you wanted it. I specifically order my chambers done so that any factory ammo will work. If you ordered a so called "tight chamber" this is what he tried to give you. If you ordered a sammi spec. chamber then see if factory ammo will work. if it will not id send it back

 

[gunsandgunsmithing]

First, determine that where the interference is. It could be radially. Just use a marker or smoke an empty case, the chamber it. Then carefully extract the case. It should confirm where the interference is occurring. Sometimes brass runs a tad on the big side of spec...and some headspace gauges are a tad small, but both still within spec. Either way, I wouldn't consider it a problem on my own personal guns, but should be a simple fix for your smith if you choose to have him look at it.

 

[NorCalMikie]

Every one of my rigs has a "short or snug" chamber as far as headspace goes. Shoot factory ammo? Never happen. My brass gets worked less and lasts a loooong time. Bump the shoulder as needed and no working the brass any more than needed.

 

[jo191145]

A tight chamber makes happy brass.

As for your second dilemma.
Are you using a standard seating die? Many seating dies have a roll crimp feature. They are not meant to be screwed in until they hit the shell holder.
Try to put too much of a roll crimp on a non cannelured bullet and you can bulge the case body just below the shoulders making chambering difficult if not impossible .
Doesn't explain why it works the second time around but,,,,,,,,,

 

[jonbearman]

I think when he pulls the bullets he is stretching the interference out again. Size a couple cases and measure the inside diameter to see how much neck tension you have.The bullets should seat with little effort and if the expander isnt expanding it enough when you seat it the body shoulder junction can buckle slightly if the seater body is too close to the shell plate. Back it out a turn and see if it helps.

 

[GAnderson]

Thanks to all for the replies....I believe the smith did use a tight spec reamer as he deals in a lot of custom rifle smithing and benchrest rifles....my friend just did not know if this was a "good" thing. I agree that it is way better on/for the brass and with all of your reply's supporting this issue I think he will be happy with that. The only thing that has us stumped is when we do find a piece of new brass that does chamber without bumping the shoulder first...it will not chamber when the cartridge is loaded and the bullet seated.....I was thinking along the same lines of jo191145's post regarding the seating die maybe bulging the shoulder just enough that it won't chamber....after we pull the bullet then and bump the shoulder it will chamber with no problems....it has to be in the seater die and/or the adjustment of it. Thank you all again because this will relieve him of a lot of anxiety that something is "wrong".

Gene

 

[BoydAllen]

I see no reason for your rifle to be headspaced so short. Despite what others have written, While I like minimum headspace, setting up a rifle with the headspace so short that a normal die and shell holder cannot size the brass to fit is not a good idea. I suggest that you may want to do some measuring to see where the interference is occurring. Blacking the case with a marker may also be of help to see where it is rubbing. If you have a standard factory FL die, the rifle should be chambered so that the die can be adjusted so that when fired brass is sized that it chambers in a satisfactory manner. If your smith has produced a chamber that does not allow this, and it was not by prior agreement, then he needs to fix it.

 

[GAnderson]

To clear up maybe some confusion.....once the new brass has been fired in the chamber it works perfectly after that....after 4-5 firings you will notice just a little bolt stiffness....bump the shoulder again and it works great. We were just scratching our heads over a NEW piece of brass that would chamber first WITHOUT having to bump it first....once we loaded THAT piece it would not chamber....in all likely hood, the seating die is set too low and causing the shoulder to bulge just enough to not chamber.....the bullets are seating very nice and smooth with what feels like the right amount of friction. I just called him and asked if when he pulled the bullet on THAT NEW brass if it would then chamber and he said it would not. He then runs it in the bump die and bumps it about .001 - .002 thou and it will then chamber....he can then load that round and it will chamber just fine....evidently the "bumping" process is doing enough to the brass to offset what the seater die is doing and allowing it to chamber, so it has to be in the seater die adjustment. I am heading his way later today to help him try to set the seater die and see if this fixes it. I think his best bet is to just run all new brass in the bump die first, load them and enjoy shooting....bump the shoulders when they need it after that....

 

[tclaunch]

I found a beautiful old South Bend Heavy 10 16 months ago, and have had a great time learning to chamber barrels. I have found from many barrels now that I prefer to have the "go" gauge to have a slight feel or "presence" on closing the bolt with striker assembly removed. I did a 260 recently and the fired Lapua brass grew .001" after firing, this comparing new to once fired brass. So count me in for the snug headspace, I do prefer this. I feel your friend got a great smith that set him up right!

Seating die bodies set to low are almost always the culprit on chambering issues.

 

[BoydAllen]

If you use a comparitor to compare a GO gauge to new, unfired brass, I think that you will see why I made my comment. There is several thousandths difference, and so for unloaded new brass to require bumping, the chamber would have to be several thousandths under minimum. Also, I think that the thought that the seating die may be set too low is worth looking into.

 

[gsg5pk]

Depend on quality of QC from factory.

 

[CatShooter]

If you use a comparitor to compare a GO gauge to new, unfired brass, I think that you will see why I made my comment. There is several thousandths difference, and so for unloaded new brass to require bumping, the chamber would have to be several thousandths under minimum. Also, I think that the thought that the seating die may be set too low is worth looking into.

With the 6mm Remington...

SAAMI Chamber is Min 1.7767" - Max 1.7867"

SAAMI Case is Min 1.7737" - Max 1.7807"

So it is clear that it is possible to have a minimum chamber and maximum case and have a negative headspace (the case is longer than the chamber, and the fit is tight)... with the 6mm Remington, the case can be 0.004" LONGER than the chamber and still "be in SAAMI spec".

This potential for overlap exists with most centerfire cartridges.

I would prefer a minimum chamber every time.

 

[BoydAllen]

I have no quarrel with minimum, but I have never seen new brass that would not easily chamber in a minimum chamber. Have you?

 

[CatShooter]

I have no quarrel with minimum, but I have never seen new brass that would not easily chamber in a minimum chamber. Have you?

Yes... I had a M-700 257 Roberts that would chamber Remington, but Winchester took a little extra effort.

 

[gunsandgunsmithing]

I have no quarrel with minimum, but I have never seen new brass that would not easily chamber in a minimum chamber. Have you?

Yes, Boyd, I have. I agree that it is rare. But even if the brass is short at the datum, that doesn't mean that it cant be "off" slightly at some other point, such as the radius at the neck/shoulder or the shoulder to body.
All that said, he simply needs to paint the case with a marker to see where the interference is. I haven't seen that yet. Have you? You'e an engineer, right?
As a tool and die maker, I had to deal with engineers who just couldn't see why their blueprint wouldn't work. Sometimes tolerance stacking and real world manufacturing cross paths in a negative way.
Just think about all the tolerances that come ito play here...chamber reamer, chambering, hs guage itself, brass, dies, reamer for dies..etc. The reamers are a big consideration as they are tapered and have specific radii. That applies to the dies BOTH reamers, and the chamber. Oh, and the brass maker....they aren't perfect either. EVERYTHING has tolerances. Catshooter is right...SAAMI specs do sometimes conflict between brass and chamber dimensions. That's not even considering all the other stuff.

 

[Con]

I'm another that's seen it. I've headspaced Savage actions short, but for hunting prefer them to be as per spec with the Go/No-Go guages so I can use factory loads. But a batch of older PMC 243Win factory loads will not chamber almost 60% of the cartridges. Rifle has to just close on the No-Go for them to chamber freely. What do chamber shoot like stink though! Have a Tikka T3 in 243Win that likewise will virtually refuse PPU 243Win factory loads.

Set up a 308Win on the Go being used as a No-Go once, very old Musgrave (Sth African) factory loads all chambered well when nothing else would.
Cheers...
Con

 

[Old Navy]

You have a minimum, or slightelyy shorter chamber.

It is no problem, and I wish all my chambers were that way.

Just run your new cases through the bump die and shoot them.

They will last long, because the worst time for a case is the first firing - that is when case stretch is the most - and when your cases are that close on the first firing, then you are off to a good start.
[/quote] +1

 

[JFrank]

Humm
I hate short anything