Questions. Bumping shoulders back.

[phaedra1106]

Yes my chamber is my guide. I'm aware of that my question is can you bump them back to far and if so what are the consequences.

See my first answer.

I bought some New Lapua brass. I'm using one of the new unsized cases as my base line. I full lentgh sized a case fired in the rifle with a normal die set up. The shoulders on the resized brass are set back further than the new Lapua brass. That surprised me the set back is quite noticeable.

Let me see if I have this correct.

You've measured the shoulder datum point on a new unfired Lapua case, that case chambers OK?

You've then took a fire formed case and ran it through a FLS die with a normal shell holder, it's shoulder datum point is shorter than the new case but it won't chamber?

[rox]

my question is can you bump them back to far and if so what are the consequences.

Can you bump too far? Yes you can.

The consequences? Excessive brass stretch during fire & resize cycles (the kind that causes weakening at the web followed eventually by incipient case head separation). In the extreme case you might see light strikes, variable ignition, even misfires.

Even with standard shell holders, not all dies will bottom-out and limit you to SAAMI min dimensions.
And even SAAMI min case-size combined with SAAMI max chamber-size can be setting-up for a *lot* of case stretch.

Dies don't move the shoulder datum a fixed distance, they move it to a fixed point. Your setup should place the case shoulder datum at the point that gives you the desired clearance from the case shoulder datum to the chamber shoulder datum. Since the latter is a fixed value, so is the former. 'Amount of bump/set-back' is moot. It depends where you start from, which is variable.

The same die setup will give you different results with different brass makes, number of firings, whether or not annealed etc, which is where your variable shell-holders can come in handy to avoid having to adjust the die setup when working with different brass.

..

[phaedra1106]

Just a thought, is the rifle def. chambered 6.5x55 Swedish Mauser or is it 6.5x55 Scan?

Drawings for both can be found here,

http://stevespages.com/jpg/cd65x55skan.jpg

http://stevespages.com/jpg/cd65x55swedishmauser.jpg

[Alpha1]

Chambering the cases is not a problem I solved that problem after taking the gunpimps advice.

I can chamber any of the cases I'm working with but I don't intend to necessarily use any of the bumped cases. At the moment I'm just learning about shoulder bumping. Once I have got a full understanding of the process including the pit falls then I'll put that knowledge into practice. This is just the learning curve.

[phaedra1106]

OK, well in that case see my earlier post and limit the amount of headspace to a maximum of 2thou" for any cases you want to load and fire :)

[ovenpaa]

Alpha1 - How are you measuring the amount you are bumping the shoulders back by with regards to the reference case (Lapua)

[Alpha1]

I'm using the Hornady measuring thingy. You can actually use a shell holder. I thought about ordering one of yours do you do them in 6.5x55. As I said my new brass is Lapua unfired. I full lentgh resized some cases that have been fired in the gun then stood them next to the new brass and I was surprised how far the shoulders are set back. There is a noticeable difference between the Lapua and the resized brass. You don't have to measure it it's easy to see. The reloads are set back a noticeable amount. As I said I'm just trying to understand the process at the moment. The way my luck runs I don't want any mishaps.

[Martin]

You appear to be setting the shoulders too far back. Your die is probably screwed in too far and needs to be backed out a little.

However, the resizing process requires accurate measurements to get it right. With experience you can resize by 'feel" as another post has referred to however, you have your measuring tools so I'll assume you will use those for the moment.

First, I suggest you measure a new Lapua case and adopt that measurement as your baseline. Zero your calipers with your case in your headspace gauge. Do this 2 or 3 times to check you are doing it correctly and getting consistency.

Measure one of your cases that you have already resized (the ones that surprise you regarding how far they have been set back) and let us know the variance - it will be a few 'thou I expect.

Secondly, don't get your resizing experience using expensire new brass, try and get some discarded old brass, clean it and use that.

The main objective is to FLS the brass so that the shoulders are set back about 0.002 when fully fire formed (after 2-3 firings).

I would not expect the FLS brass to measure negative when compared to your baseline zero.

Get this right first, then you can refine the process.

Martin

[Alpha1]

I have measured several new Lapua cases to the shoulder and they vary in length. So I picked one and used that as my starting point.
The dies are Redding standard full length dies.Out of curiosity I sized a couple of once fired cases with out the expander ball in place.
The difference in the shoulder set back was quite visible it was a lot. To much for this rifle.

Any way once I got that out of the way I had a play using the rifle as a test bed. I used once fired cases for all my testing they were all trimmed to a uniform length. I settled on the redding .008 competition shell holder.
I have discarded all my old brass and ran all the new lapua through the full length die.

[phaedra1106]

How much headspace was the .008 shell holder giving you when you resized the fire formed brass?