Inconsistent Shoulder Bump

[Justin L.]

Hi!

A buddy of mine is loading some .300 WSM cases for a Sako A7. The cases he was loading were only once fired in the gun, and he set up his die to bump the shoulder .002”. He was measuring the shoulders and some were going to the .002” bump he wanted, others were .004”-.005”. He has no idea why they are different, any ideas on why this could be?


A little more info, he was using the expander ball in the die at first when he noticed the inconsistency and then removed it, as he was going to use an expander mandrel after, but even after removing the expander ball, he was still getting different readings on the cases.

If you need any more info, just let me know and I will get the specs from my buddy. Thanks all!

 

[rijndael]

Does he anneal brass?

Is he measuring the brass before sizing and after? Is it possible some of his brass is not fully formed making him think it was over bumped?

 

[mfendley]

Has he tested the 1X fired case in his chamber to see if the shoulder needs to be bumped? As rijndael said above, he could be measuring differences that is not due to the sizing die.

 

[Coyotefurharvester]

Lube on the shoulder, brass not fully formed, die not set properly, brand of brass( mixing brands will be inconsistent) some brands suck. Comparator not clean.

 

[Bronsin]

Run the case up in the die and hold for a 3 count, then lower the ram until case is out and repeat once more. That fixed all my shoulder bumping problems. It also fixed my neck tension variance. Those WSM cases are thicker than hell, you may have to hold it longer.

 

[jepp2]

He was measuring the shoulders and some were going to the .002” bump he wanted, others were .004”-.005”

What was the as fired (prior to sizing) case head to datum measurements? And what was the prior to initial firing measurement? Frequently the case isn't full chamber size after the first firing.

 

[K22]

All the previous responses plus:

Why is he bumping to .002? Do the cases need this amount of bump at this point?

Virgin cases usually need to be fire formed before there is a need to bump the shoulder.

Try full sizing with zero bump and see if the case chamber without resistance. Just make sure you are not extruding (lengthening the case). Take measurements "as fired" with spent primers removed then measure after sizing.

Check the consistency of your measuring method, do you get repeatable results, i.e., measure five cases then remeasure to see if you get the same measurements.

 

[rsbhunter]

I have found that if I remove the fired primer ( not resizing) I get a more consistent base to ogive measurement than before. If the primer has even an minute raised portion from catering, your initial measurement won't be consistent. Worth checking , I noticed this measuring multiple fired cases...rsbhunter

 

[Bill Norris]

As mentioned above some cases won't be fully formed with one firing. Inconsistencies will show up when bumping.

 

[cdgaydos]

Is the die set for the press to cam over?
I found it hard to get consistent shoulder set back by screwing the sizing die in/out. It works OK, but sometimes it is not consistent.

As others have mentioned, don’t rush the stroke… count to 3-5 with the case in the die.

What really made it better for me was Redding competition shell holders. Set the press to cam over on one and select the one that gives the set back you want. (I still count to 3-5 and don’t rush it though).

Good luck

 

[bks22345]

I have gotten the most consistency by decapping, resize/shoulder bump, and necking in 3 separate steps. I use Redding competition dies that allow me to do this. I also use imperial or hornady wax, and I lightly wax the whole case body. I have tried other lubricants like alpha’s liquid case lube; it works on some cases but not others. Wax works on everything and I have found if it’s uniformly lubed I get uniform results. You have to be careful if you are using a combination die because the wax can get into the neck area and cause dents. With a body die I haven’t found this to be an issue. I am not a fan of caming over on my press. I use a forester coax press and the die really doesn’t come in contact with the press. I spend the few extra dollars for the forester die holders and once you have them adjusted, they stay that way. I haven’t loaded 308 in about 6 months. I slipped the body due in earlier this week and my shoulders bumped exactly where they were 6 months ago.

 

[searcher]

He should measure all of his fired cases after that first firing and find the LONGEST one. Brass doesn't grow in length after being fired - so that one case will show him that either he has blown that longest case to the chamber max - or there is still more to go. Only after seeing at least three or four cases (all being the longest) become the same "longest" length - would I assume that is a viable measurement off which to bump the shoulder. I'd first see that this has been achieved. Without the expander ball interfering, it is likely (short of having excess lube on the necks) that he is measuring the short pieces that haven't fully extended, then measuring them again after sizing and wondering why they didn't bump. They just won't until they have reached the same length of his longer brass - for which he probably set up the bump for. Brass will seldom blow the shoulders all the way forward on one firing. Two ways to speed it up are to anneal the cases between firings - and to reduce the load and seat the bullets long (Touching the lands), which has the effect of supporting the case against the bolt so the pressure can focus on blowing the shoulder forward. His primary focus should be on watching for the longest cases to ascertain full shoulder blowout and understand that the shorter cases just won't bump properly till they are ALL blown out. If he is getting inconsistent bump on his longest cases, I'm thinking they are not fully blown out. Without annealing, some brass does weird stuff - some spring back more than others, but not usually more than .001"-.002" Hope this helps.

 

[Jetpilot]

I get variations depending on how much lube I use, I think some of the excess lube builds up in the die as well so I start off with correct bump but after a dozen the numbers start to drift. Keep your die clean and don't use much lube, especially nothing on the neck. Be sure you shell holder or base plate is clean as well and clean your case before measuring with gauge\calipers else it builds up in there as well. Others have mentioned good practices like annealing and trying different stokes on your press.