I was oringally taught that after a reletively solid load firing, the brass has expanded to the chamber dimensions . Now having discussed the topic with several wildcat reloaders it seems some cartridges need 2 or even 3 firings before truly matching chamber dimensions. In your experience, how many firings on wildcat fireformed ronds, how many firings do you go through before bumping the shoulder back?
how many firings on wildcat fireform rounds before bumping shoulder?
- Thread starter Winny94
- Start date
Dusty Stevens
Shiner
When they stop growing and get tight. Checking with a stripped and greased bolt you can size them and see if you feel the shoulder. Some cases take 2-3 firings, some just one. The harder you hit them while forming the less they last in the end too.
Spot on.
Depends on the changes taking place in the forming, annealed condition, forming load. And assuming you're managing head spacing along the way.
I consider all cartridges wildcats until local formed, and count on 3 firings before moving to load development with them.
Shoulder bumping is usually required at 5-8 firings, and from then onward.
I don't just slam brass with high pressure loads for the sake of forming. Instead I run a moderate load to get it done.
I consider all cartridges wildcats until local formed, and count on 3 firings before moving to load development with them.
Shoulder bumping is usually required at 5-8 firings, and from then onward.
I don't just slam brass with high pressure loads for the sake of forming. Instead I run a moderate load to get it done.
NorCalMikie
Gold $$ Contributor
Don't rush it. It'll show up in time.
I just got thru forming 100 cases for a 6.5 wc. As it was a new barrel, I loaded them up, to break in barrel and get round count up. Using a false shoulder and 3 grs less than my normal load, I got pretty consistent base to datum measurements that were 3-5 thou less than chamber spec. The new 40* shoulders weren't quite as sharp as I hoped for, but not bad for 1st firing.
This case doesn't have much taper, but that's where the real variance showed up, at shoulder & mid case diameter.
The second firing cleaned everything up nicely, as far as consistent measurements. I have good data from my previous barrel cut with same reamer, so load work-up should be easy, if the Texas temperature cools off.
I have had some FF loads shooting lights out on initial firing, then driving me crazy on second, 3rd is the charm.
This case doesn't have much taper, but that's where the real variance showed up, at shoulder & mid case diameter.
The second firing cleaned everything up nicely, as far as consistent measurements. I have good data from my previous barrel cut with same reamer, so load work-up should be easy, if the Texas temperature cools off.
I have had some FF loads shooting lights out on initial firing, then driving me crazy on second, 3rd is the charm.
I had 5-7 shots through 250 pieces of .243AI brass without ever having had to bump a shoulder or trim a neck and they hadn't even gotten snug on bolt close yet. By the time I got there the barrel was done for match use. I didn't hit them very hard on the fire-forming shot, 39.5gr of powder. The full house match loads ran about 6 grains hotter. Never a case split and that was with Hornady brass.
According to Ackley, "a good stiff load and moderate to heavy bullet" to FF form the case in one operation. The major advantages of the Ackley Improved design was to significantly lessen case growth (brass migration towards the neck) and have the ability to over charge the case and achieve higher velocities without ejection issues.
I have yet to buy an AI chambered barrel, but after reading the following it'll be my next purchase https://1s18w12tqveh1xfywp1ulx42-wpengine.netdna-ssl.com/wp-content/uploads/GunDigestPOAckley.pdf
I have yet to buy an AI chambered barrel, but after reading the following it'll be my next purchase https://1s18w12tqveh1xfywp1ulx42-wpengine.netdna-ssl.com/wp-content/uploads/GunDigestPOAckley.pdf
searcher
Gold $$ Contributor
If the bullet is not jambed and you run a light load - it can take many firings to even get the brass to properly fill the chamber without still maintaining excessive shoulder clearance. A moderate load with a jambed bullet will get you to where you want to be much more quickly in my experience.
Simple
If your fired brass chambers easily, you don't need to strip the bolt, then no shoulder bump.
When fired brass chambers tight then bump the shoulder .001 in a bolt gun.
If your fired brass chambers easily, you don't need to strip the bolt, then no shoulder bump.
When fired brass chambers tight then bump the shoulder .001 in a bolt gun.
When you feel resistance closing the bolt it’s time to bump shoulders back
DaveTooley
Gold $$ Contributor
Once the brass starts to get tight in the chamber it has already formed a memory from work hardening at full chamber length. I set up my FL sizing after the second firing so it forms a memory at the shorter length. It allows for expansion as well as contraction. If it can't contract after firing you end up with premature hard bolt lift.
It is like memory, which is set or reset.
When brass yields, as in up-sized during firing, it springs back to a new dimension. Same with down-size yielding. Once cases reach the interference fit where shoulder bumping is needed, they will usually have to be bumped every cycle from that point onward. This, because the brass is then more inclined to go back to where it's been (it's memory) on every successive firing. Same with brass everywhere else.
It makes sense to try & manage the bump to desired head spacing -before setting a memory from interference fit. Then it also makes sense to do this with the case bodies and necks, and custom FL dies that are local chamber associated work to allow consistent extraction.
There is another way to do the same, while BR shooters resist the notion of it.
You can go 'fitted' chamber to new brass dimensions plus no more than 1thou. With this, by never allowing new brass yielding to begin with, larger dimension memory is mitigated.
For case bodies and necks this is easy, especially with low taper case designs.
For shoulders it's a lot more difficult, because of their low and less than fully formed angles (with new brass).
Perhaps you could sneak into perfect memory while forming greatly improved shoulders, 40deg+, and then remove all sizing, all together, from that point onward.
I've already tested this with bodies & necks using a BAT RS action/26wssm Imp. It works great. But 35deg shoulders still require bumping -eventually & onward. Currently using a custom bump die for this.
I do not yet know what shoulder angle could mitigate a need for bumping. Will try either 45 or 60deg with my next chamber(haven't decided), in hopes of removing any need for resizing dies.
I figure minimum sizing is better than maximum sizing, and that zero sizing as load developed, will be better still. True or not, at least I'll learn about this much.
When brass yields, as in up-sized during firing, it springs back to a new dimension. Same with down-size yielding. Once cases reach the interference fit where shoulder bumping is needed, they will usually have to be bumped every cycle from that point onward. This, because the brass is then more inclined to go back to where it's been (it's memory) on every successive firing. Same with brass everywhere else.
It makes sense to try & manage the bump to desired head spacing -before setting a memory from interference fit. Then it also makes sense to do this with the case bodies and necks, and custom FL dies that are local chamber associated work to allow consistent extraction.
There is another way to do the same, while BR shooters resist the notion of it.
You can go 'fitted' chamber to new brass dimensions plus no more than 1thou. With this, by never allowing new brass yielding to begin with, larger dimension memory is mitigated.
For case bodies and necks this is easy, especially with low taper case designs.
For shoulders it's a lot more difficult, because of their low and less than fully formed angles (with new brass).
Perhaps you could sneak into perfect memory while forming greatly improved shoulders, 40deg+, and then remove all sizing, all together, from that point onward.
I've already tested this with bodies & necks using a BAT RS action/26wssm Imp. It works great. But 35deg shoulders still require bumping -eventually & onward. Currently using a custom bump die for this.
I do not yet know what shoulder angle could mitigate a need for bumping. Will try either 45 or 60deg with my next chamber(haven't decided), in hopes of removing any need for resizing dies.
I figure minimum sizing is better than maximum sizing, and that zero sizing as load developed, will be better still. True or not, at least I'll learn about this much.
I'm having to produce cases for my 256 Newton. Using 1x fired .270 brass, trim, neck down then fully re-size. I'm on my 3rd firing and still not feeling any resistance to the brass. I figure one or two more firings and I'll have to go back and bump.
I know I could use 25-06 brass and just size it up but I have 2 25-06's now and NO 270.
I know I could use 25-06 brass and just size it up but I have 2 25-06's now and NO 270.
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