Bumping shoulders too far back?

[timelinex]

I usually bump shoulders back .002". However with my AX338, I have to bump back a full .006" untill there is 'acceptable' resistance on bolt close. Bumping back .004" results in a VERY harsh close. Now, its not effecting accuracy or anything like that. But I'm just wondering whats going on? I thought it's standard to only bump a maximum of .003".

Also, not sure if these means anything but it might. My chamber was too tight to fit any 1x fired brass (even the 1x NT brass from grafs). I would size it, and no matter how far I push the shoulder back it wouldn't chamber without serious force.

On the other hand, new lapua brass and 'properly' bumped fired brass works just fine (already on the 4th firing on a batch).

What gives?

 

[Milo 2.5]

What tool are you using to measure the bump? Sinclair # 749-011-478SV would be the only one I'd use, uses shoulder angle and not just neck diameter. I think your numbers are skewed, no matter how hard you hammer the case, it can't outgrow your chamber?

I'd say you have tight chamber, reason 1x fired stuff wont fit, it's the base of the case not going in, not shoulder length, a small base die may help, but doubt it's made. Use a caliper and confirm diameters of said brass.

 

[918v]

If you are feeling resistance after bumping the shoulder .002" then maybe you are measuring shoulder bump wrong or the neck is too long and is binding at the end of the chamber? You need to find where the binding is: do you have drag marks on the casehead? Is the case mouth getting pinched? Let us know.

 

[timelinex]

So I have 'done it all' sort of speak to try to figure this out when it happened originally. I tried to sharpy an entire case, and there was no marks. I have measured the trim to length with the Sinclair tool and I have a far way to go before worrying about trimming.

Lastly, I have measured bump successfully on all my other cartridges and even my last 338, so I know I'm measuring it right. I use a shoulder bump measuring tool specifically designed for this purpose, I don't remember the manufacturer off the top of my head but I can look it up of its important.

Anyways, im starting to think maybe the resistance isn't coming from the shoulders but rather the bottom of the case, since it's a 'tight' chamber. So what I'm saying is maybe by lowering the die I am sizing more of the base, just enough to prevent resistance. The side effect is that I'm bumping the shoulders more as well.

Does that sound like a reasonable reason?

 

[Cigarcop]

I would measure the base and see what one is new or once fired and see what it is after bumping your shoulder .002.....
I bet your die isn't sizing down enough until your at the point where your pushing your shoulders too far.

 

[Milo 2.5]

So I have 'done it all' sort of speak to try to figure this out when it happened originally. I tried to sharpy an entire case, and there was no marks. I have measured the trim to length with the Sinclair tool and I have a far way to go before worrying about trimming.

Lastly, I have measured bump successfully on all my other cartridges and even my last 338, so I know I'm measuring it right. I use a shoulder bump measuring tool specifically designed for this purpose, I don't remember the manufacturer off the top of my head but I can look it up of its important.

Anyways, im starting to think maybe the resistance isn't coming from the shoulders but rather the bottom of the case, since it's a 'tight' chamber. So what I'm saying is maybe by lowering the die I am sizing more of the base, just enough to prevent resistance. The side effect is that I'm bumping the shoulders more as well.

Does that sound like a reasonable reason?

Yes
Does anyone make a sb die for the lapua? I've had this issue, but usually after a re-barrel, cases from old wont fit in new chamber?

 

[timelinex]

I would measure the base and see what one is new or once fired and see what it is after bumping your shoulder .002.....
I bet your die isn't sizing down enough until your at the point where your pushing your shoulders too far.

So what do I do... Isn't over sizing bad for not just brass life but also accuracy?

 

[Milo 2.5]

So what do I do... Isn't over sizing bad for not just brass life but also accuracy?

You need to figure out where it's hanging up, bumping your shoulders back .006 more than once will surely result in case head separation, on 4 time fired brass it should be showing signs by now, not good.

 

[Milo 2.5]

You can make yourself a base die as I call it, buy another fl sizer, have the shoulder cut off by a smith or machine shop, and trim .005 off the bottom of the die, then size the base of case. BUT you need to know if this is it.

 

[timelinex]

You need to figure out where it's hanging up, bumping your shoulders back .006 more than once will surely result in case head separation, on 4 time fired brass it should be showing signs by now, not good.

Everything looks good on my end from the outside. I will cut one in half and see.

 

[peaceatwar]

Honestly, I would try a different die there are a lot of reamers out there and its possible your chamber was cut with a much different reamer than your die was.

 

[KYpatriot]

Make sure you don't have high primers.

 

[Milo 2.5]

Honestly, I would try a different die there are a lot of reamers out there and its possible your chamber was cut with a much different reamer than your die was.

Let's hope so!

 

[LawnMM]

Trim a piece to the trim to length and see if it binds. You said you had a long way to go before having to trim, as in its longer than trim length or shorter?

When do you trim? If you size after trimming you can lengthen the neck to the point of interference again.

 

[timelinex]

Trim a piece to the trim to length and see if it binds. You said you had a long way to go before having to trim, as in its longer than trim length or shorter?

When do you trim? If you size after trimming you can lengthen the neck to the point of interference again.

I actually just trimmed this last firing with my Giraud. Actually under trimmed accidently (2.710),so that is not the issue.

 

[dauntedfuture]

I suspect that the shoulder dimensions of your chamber don't quite match that of your sizing die. Remember that you are measuring a .006 reduction to get the bolt to close off an arbitrary point in the "center of the shoulder" in actuality, you might be bumping the center of the shoulder where you measure .006, the front part close to the neck .008 and the portion where the shoulder meets the case body .001 or less.

Are you using a shoulder bump die or a FL die, there is a difference? The shoulder bump die only moves the shoulder back and does not resize any body dimensions. If you are using a shoulder bump of a Neck die, there will be a time when you will have to FL size the brass to get it to "re-fit" in the chamber. As a matter of practice and experience I have noted no advantage to neck sizing brass and in fact I get better accuracy with FL sizing; most high-power LR shooters FL size all their brass for what its worth.

1 X brass fired in a bolt gun should go back into that rifle without much trouble. You might try removing the firing pin assembly to determine if its the case that's causing resistance or the action locking up with the firing mechanism.

You can also try smoking a case to identify where there is an interference issue, there might be a location lower on the body of the case that needs more sizing that is only affected when you adjust the dies down more.

 

[timelinex]

You need to figure out where it's hanging up, bumping your shoulders back .006 more than once will surely result in case head separation, on 4 time fired brass it should be showing signs by now, not good.

This is a cut open 3x fired. Absolutely no signs of case head separation.

 

[Milo 2.5]

I suspect that the shoulder dimensions of your chamber don't quite match that of your sizing die. Remember that you are measuring a .006 reduction to get the bolt to close off an arbitrary point in the "center of the shoulder" in actuality, you might be bumping the center of the shoulder where you measure .006, the front part close to the neck .008 and the portion where the shoulder meets the case body .001 or less.

1 X brass fired in a bolt gun should go back into that rifle without much trouble. You might try removing the firing pin assembly to determine if its the case that's causing resistance or the action locking up with the firing mechanism.

TL,
This guy may be on to something about measurements? Like I said, need to figure out exactly where it's hanging up.

 

[timelinex]

OK,

Here is what is going on! I use a hornady comporator gauge set with the .420 insert which is supposed to cover 338lm. By mile's advice, I tried measuring the bump with a different tool. I used a 45 ACP case which sits literally mm below where the other gauge does. Voila.. Looks like I'm bumping somewhere in between .001" and .002" according to this make shift gauge.

So then, it all makes sense now. No wonder I was still having a bit of a rough bolt close! I just prepped all my damn brass too. Oh well, I guess I'll just live with it till next time around.

The funny thing is those hornady gauges worked just fine on my other rifles brass...

Thanks for all the advice guys.

 

[Squid284]

I have much more faith in the Sinclair bump inserts than going off a datum line insert.

I would try
- a different FL sizing die (Redding?)
- what are your tolerances at the neck like?
- is your chamber or die rough, i.e. leaving marks on the brass after firing? What is the bolt lift and extraction like after firing?
- are you seating bullets into the lands?
- measure every aspect of fired vs unfired cases, this should give you some clues as to what is going on

 

[Milo 2.5]

I have much more faith in the Sinclair bump inserts than going off a datum line insert.

I would try
- a different FL sizing die (Redding?)
- what are your tolerances at the neck like?
- is your chamber or die rough, i.e. leaving marks on the brass after firing? What is the bolt lift and extraction like after firing?
- are you seating bullets into the lands?
- measure every aspect of fired vs unfired cases, this should give you some clues as to what is going on

I do believe, thanks to [MENTION=107777]dauntedfuture[/MENTION], the problem was resolved. TL now just needs to make sure his tight fitting rds don't put a burr on his bolt lugs!

 

[dauntedfuture]

Glad to help. You can also use a paperclip to see if your cases are close to separation. In reality I have not seen it in a bolt gun unless you have mixed range pick up brass in with new stuff. Its quite hard to overwork brass that much in a bolt gun but it can be done. If you were shooting an M1A, that's another story all together as that rifle will stretch the hell out of brass. You usually see a shiny ring on the outside of a case before things come apart and provided you are not shooting a match there is not a real crisis. If you do have a case separation its a good idea to toss that lot of brass.