I reload for a hunting rifle to provide context for my question meaning that I'm valuing fast and reliable feeding over tightest bench rest group sizes. That being said, I've always FL resized my brass but have started to get bulging on my 338 win mag cases after only a couple firings just above the belt that create tight or full inability to chamber a round. My thought is bump sizing the cases might reduce the forces and flow of brass vs a full resize thus increasing the life of my cases while possibly (?) increasing accuracy. Any thoughts on that? Secondarily, how far should I bump the shoulders to ensure reliability while balancing the idea of maximizing case life? Thanks
Bump sizing question
- Thread starter hillman23
- Start date
- Status
I haven;t had the issue with my only belted mag cases (.458 Win Mag), but this might be an option for you.
http://www.larrywillis.com/answers.html
http://www.larrywillis.com/
http://www.larrywillis.com/answers.html
http://www.larrywillis.com/
Steve in NC
Member
hillman23,
Bumping the shoulders back further is only going to compound your issue going forward. This is an old issue that has been around for years and is based on the very loose tolerances applied to belted chambers in regard to the .220" nominal headspace dimension. I'm an old long range shooter and I built a jig back in the mid '80s to measure the variation of that .220" dimension. Belts on cases vary a LOT and this is the issue. Cutting a tight chamber and head spacing off from the shoulder helps but eventually you start getting hard extraction or when it gets really bad cases will stick while chambering also. I have a rifle that was built in the '80s that is a 6.5-300 Win Mag that has the belt turned off to get around this very issue. I have a special made collet to hold the brass in a lathe to cut off the belts before fire-forming. But everything is a band-aid to the original issue though.
The only 2 ways to truly fix this issue is to not deal with the belted cases at all... i.e. I now use a wildcat chambering based on the 8x68 metric case which is for all intents and purposes a beltless 300 Win Mag. Or to use the Larry Willis die as Walkalong pointed, to resize that small area in front of the belt that isn't supported by the chamber that any mass produced sizing die will not get down to to properly size no matter what you try to do to fix it.
Being you already own this 338 Mag getting rid of the belt isn't an option. Spend the money and get on the waiting list for one of the Innovative collet dies to deal with this issue. Only other option is to get rid of the brass once it shows signs of expanding in front of the belt. You can cheat a little and use a flat file to literately relief cut that expanded brass section in front of the belt to get a couple more firings out of your cases.
I have access to one of Larry's dies so if you find the waiting list is a long time out and you need cases sized... PM me here and we can make arrangements for you to ship me your cases and I'll size all of them for you to get your through until you receive shipment of this die.
Hope this helps,
Steve
Bumping the shoulders back further is only going to compound your issue going forward. This is an old issue that has been around for years and is based on the very loose tolerances applied to belted chambers in regard to the .220" nominal headspace dimension. I'm an old long range shooter and I built a jig back in the mid '80s to measure the variation of that .220" dimension. Belts on cases vary a LOT and this is the issue. Cutting a tight chamber and head spacing off from the shoulder helps but eventually you start getting hard extraction or when it gets really bad cases will stick while chambering also. I have a rifle that was built in the '80s that is a 6.5-300 Win Mag that has the belt turned off to get around this very issue. I have a special made collet to hold the brass in a lathe to cut off the belts before fire-forming. But everything is a band-aid to the original issue though.
The only 2 ways to truly fix this issue is to not deal with the belted cases at all... i.e. I now use a wildcat chambering based on the 8x68 metric case which is for all intents and purposes a beltless 300 Win Mag. Or to use the Larry Willis die as Walkalong pointed, to resize that small area in front of the belt that isn't supported by the chamber that any mass produced sizing die will not get down to to properly size no matter what you try to do to fix it.
Being you already own this 338 Mag getting rid of the belt isn't an option. Spend the money and get on the waiting list for one of the Innovative collet dies to deal with this issue. Only other option is to get rid of the brass once it shows signs of expanding in front of the belt. You can cheat a little and use a flat file to literately relief cut that expanded brass section in front of the belt to get a couple more firings out of your cases.
I have access to one of Larry's dies so if you find the waiting list is a long time out and you need cases sized... PM me here and we can make arrangements for you to ship me your cases and I'll size all of them for you to get your through until you receive shipment of this die.
Hope this helps,
Steve
Thanks for the info and the incredibly generous offer! I have plenty of good cases to get me through at this point. I’m definitely not a high volume shooter and I expect my current supply to last me for quite some time. I’m very appreciative, Steve.
FLIGHT762
Member
What are you "Bump Sizing" to now? How are you measuring your "Bump Sizing"?
I've reloaded for the 338 Win. Mag, 300 Win. Mag., 300 Weatherby Mag., and 7MM Rem. Mag. I set my die to "Bump" the shoulder minus .002"-.003" for the rifle it's being fired in. I've had very good luck doing this and not sizing off the belt.
I have the Larry Willis Collet Die, but, I've never really had to use it yet.
I use the Hornady & Sinclair bump sizing system to determine case head to shoulder length.
I've reloaded for the 338 Win. Mag, 300 Win. Mag., 300 Weatherby Mag., and 7MM Rem. Mag. I set my die to "Bump" the shoulder minus .002"-.003" for the rifle it's being fired in. I've had very good luck doing this and not sizing off the belt.
I have the Larry Willis Collet Die, but, I've never really had to use it yet.
I use the Hornady & Sinclair bump sizing system to determine case head to shoulder length.
I wasn't bump sizing until today, Flight762. I just got the Hornady Headspace comparator set yesterday so I could measure my fire formed cases against my fully resized cases based on setting up the sizing die according to the manual. It was a highly illuminating experience to discover that my fully sized cases had their shoulders set back .018" compared to their fire formed mates. I set the sizing die up today and sized a batch of cases at -.003" by backing the sizing die up in the press and incrementally screwing it down, sizing, and measuring the case until I got the desired length.
FLIGHT762
Member
Yes, it is an illuminating experience. When you actually see the numbers, you can realize that for years, you have been bumping the case shoulders way too far back. When you set a F/L die up according to the instructions, you are just guessing. Before I knew what I was doing, my 338 Win. Mag cases got two to three sizings before getting a case head separation. I had been setting the shoulders too far back for my rifle's chamber.
A bump gauge of some kind really helps you get to where you need to be.
Blue68f100
Member
You can setup your die the poorboy way. Find a pistol cartridge that will fit over the neck of the round, contacting the shoulder. Then use your calipers to get a measurement, from the base to base. Then run it through your sizing die and compare the 2 readings. This will tell you how far or how little you have moved the shoulder. It's low teck but it works.
- Status
