Trimming Question

[Ryan3344]

Hi,

I am prepping some once fired Hornady brass for a Tikka T3X in 6.5 CM. I just FL resized using a Hornady custom die to bump the shoulder 0.002, and then checked them all through a Lyman headspace gauge. 11/30 brass processed are coming in just slightly too long, (at the neck, not HS), about 0.001 to 0.003 over spec.

I have measured the chamber of the rifle at 2.9480, and am reloading to max COAL at 2.8250, so I have a jump to lands of 0.1230. I understand the value of trimming cases to all being uniform as it pertains to accuracy, but I am wondering if there any safety concerns reloading and shooting that brass without trimming it, since there is such a jump to lands. I can't imagine the case mouth being compressed in the lands and not expanding to allow the bullet to release, but want to hear the opinions of other with much more experience than myself. Are there other safety considerations of a slightly too long case neck?

I have a case trimmer on order and intend on trimming cases for uniformity as my ultimate goal in reloading is precision, but for the time being I do not have a trimmer and was hoping to continue my testing. Of course if it isn't safe, it's a no go until the trimmer arrives. Any insight is appreciated, thank you!

 

[WeiserBucks]

You wont jam the case mouth into the lands, but you could exceed the length they'll fit in the chamber before interference. See what I'm saying based on the picture?

 

[wind gypsy]

Hi,

I am prepping some once fired Hornady brass for a Tikka T3X in 6.5 CM. I just FL resized using a Hornady custom die to bump the shoulder 0.002, and then checked them all through a Lyman headspace gauge. 11/30 brass processed are coming in just slightly too long, (at the neck, not HS), about 0.001 to 0.003 over spec.

1 to 3 thou over what spec? SAAMI max brass length? Like the long ones measure 1.921-1.923?

I wouldn't worry about getting each case the exact same length. I just dont think it matters that much as long as it's not wildly off.

As @WeiserBucks said, brass isn't at risk of contacting lands, its at risk of contacting the mouth portion of the chamber. SAAMI 6.5 creedmoor freebore diameter is 0.2645". Neck diameter at the case mouth is 0.2960.

Edit with SAAMI 6.5 Creed chamber dimensions, most are Min dimensions. Shows case mouth (depending on outside chamfer) could run into unwanted contact at 1.925-1.9408" length. Thus, the 1.920" max dimension specified.

 

[MallardSX2]

I always trim to what my Nosler book says it should be. Then I never have to keep up with it. I just make sure they are all trimmed at that amount. +-.001

I would think if you cant have brass flow into the neck area then you could be opening yourself up to some serious overpressure issues. There is probably .010 of open case neck area in a chamber for that brass to flow into. Just guessing though. I am sure someone on here knows.

Length is 2.015 for my .308...

 

[steelheadmike]

Over what spec?

It sounds like you have a comparator. Use it and measure cases before and after sizing. You're looking for 0.002" of shoulder bump. Re-sizing the brass makes it so that the cartridge will fit in your chamber.

After sizing, measure the case length (this is your trim length). Some people like to trim back to the published trim length (me included, or at least close to it and I try to keep all the case lengths consistent).

Case length has nothing to do with the jump to the lands. Jump is controlled by how deep the bullet is seated, not how long the case is.

How did you measure a "chamber length"? Do you mean the COAL using a given bullet when said bullet hits the lands? A better measurement for this is cartidge base to ogive (CBTO). When someone talks about bullet jump, they are measuring CBTO not COAL.

 

[Rugger7622]

I asked this question a couple months back. I've gone to a Sinclair chamber gauge for all my calibers and then trim back .005 from that measurement, if I ever get there. All my chambers have been significantly over the SAMMI trim number. Seems to work, it's always been weird to me that the reloading groups is the most data/measurement group but few know their actual chamber.

 

[S.Clancy]

Hi,

I am prepping some once fired Hornady brass for a Tikka T3X in 6.5 CM. I just FL resized using a Hornady custom die to bump the shoulder 0.002, and then checked them all through a Lyman headspace gauge. 11/30 brass processed are coming in just slightly too long, (at the neck, not HS), about 0.001 to 0.003 over spec.

I have measured the chamber of the rifle at 2.9480, and am reloading to max COAL at 2.8250, so I have a jump to lands of 0.1230. I understand the value of trimming cases to all being uniform as it pertains to accuracy, but I am wondering if there any safety concerns reloading and shooting that brass without trimming it, since there is such a jump to lands. I can't imagine the case mouth being compressed in the lands and not expanding to allow the bullet to release, but want to hear the opinions of other with much more experience than myself. Are there other safety considerations of a slightly too long case neck?

I have a case trimmer on order and intend on trimming cases for uniformity as my ultimate goal in reloading is precision, but for the time being I do not have a trimmer and was hoping to continue my testing. Of course if it isn't safe, it's a no go until the trimmer arrives. Any insight is appreciated, thank you!

My philosophy on trimming:

1. If they chamber, it's fine.

2. When they grow enough that some (not all) won't chamber, I trim them all to SAAMI spec, which for 6.5 CM is 1.910". You should get multiple firings before they need trimmed again.

***Chamber after resizing***

 

[wind gypsy]

I always trim to what my Nosler book says it should be. Then I never have to keep up with it. I just make sure they are all trimmed at that amount. +-.001

I would think if you cant have brass flow into the neck area then you could be opening yourself up to some serious overpressure issues. There is probably .010 of open case neck area in a chamber for that brass to flow into. Just guessing though. I am sure someone on here knows.

Length is 2.015 for my .308...

View attachment 898740

Depends on reamer how much the chamber actually has for room but the dimensions shown on the nosler data above is saami max ammo dimension. Commonly called "Trim length" is usually about 10 thou less than that. SAAMI chamber min is about 10 thou longer than SAAMI brass max to the case mouth on 308.

 

[satchamo]

I always just set my trimmer to the trim length listed in the manual and run it all through. If it’s long it’ll trim, if it’s not, nothing happens. It doesn’t matter much from case to case as long as they aren’t long. But that’s on a Frankford prep center.

 

[wind gypsy]

For whatever it's worth, my 4x fired and resized Lapua 6.5 creedmoor brass was all still 4-8 thou below SAAMI max and has never been trimmed. I don't think the 4 thou variance in length amounts to a lick of difference in performance.

I asked this question a couple months back. I've gone to a Sinclair chamber gauge for all my calibers and then trim back .005 from that measurement, if I ever get there. All my chambers have been significantly over the SAMMI trim number. Seems to work, it's always been weird to me that the reloading groups is the most data/measurement group but few know their actual chamber.

Because it doesn't really matter that much. Pretty easy to shoot em until they get close to SAAMI max and then trim 5-10 thou across the lot of brass and repeat. If one is really concerned and has a bore scope available you can look to see just how close the brass is the start of freebore.

 

[crossone]

A Tikka extractor is pretty flimsy. If you get a case stuck in the chamber and break the extractor, you'll wish you had trimmed it. Been there.

 

[Ryan3344]

View attachment 898723

You wont jam the case mouth into the lands, but you could exceed the length they'll fit in the chamber before interference. See what I'm saying based on the picture?

This is very helpful thank you! I have seen these cut away photos before but it didn't click until right now. Disregard anywhere I mentioned the neck hitting the lands, I clearly see I misunderstood. I didn't realize the chamber necked down again after the case mouth, and I was thinking there wouldn't be interference with the neck mouth expanding unless enough brass flowed forward to push the mouth all the way to the lands.

I guess I sort of thought it was a straight pipe from the shoulder taper straight through to the lands.

1 to 3 thou over what spec? SAAMI max brass length? Like the long ones measure 1.921-1.923?

I wouldn't worry about getting each case the exact same length. I just dont think it matters that much as long as it's not wildly off.

As @WeiserBucks said, brass isn't at risk of contacting lands, its at risk of contacting the mouth portion of the chamber. SAAMI 6.5 creedmoor freebore diameter is 0.2645". Neck diameter at the case mouth is 0.2960.

Edit with SAAMI 6.5 Creed chamber dimensions, most are Min dimensions. Shows case mouth (depending on outside chamfer) could run into unwanted contact at 1.925-1.9408" length. Thus, the 1.920" max dimension specified.
View attachment 898761

Yes over the SAAMI max brass length, so those measurements are exactly correct.

I hear you there, I think at this stage in my reloading career there are many other factors that will effect accuracy and need to be accounted for before making sure all the brass lengths are exactly the same. Trimmer is on order though and that's something I'll eventually start doing just for consistency's sake.

Yes I definitely see that now, thank you!

Thanks for the diagram and info. Sounds like if that brass flows and the neck grows another .002 then we could potentially start running into some problems so I think I'll wait for the trimmer.

Over what spec?

It sounds like you have a comparator. Use it and measure cases before and after sizing. You're looking for 0.002" of shoulder bump. Re-sizing the brass makes it so that the cartridge will fit in your chamber.

After sizing, measure the case length (this is your trim length). Some people like to trim back to the published trim length (me included, or at least close to it and I try to keep all the case lengths consistent).

Case length has nothing to do with the jump to the lands. Jump is controlled by how deep the bullet is seated, not how long the case is.

How did you measure a "chamber length"? Do you mean the COAL using a given bullet when said bullet hits the lands? A better measurement for this is cartridge base to ogive (CBTO). When someone talks about bullet jump, they are measuring CBTO not COAL.

Over the maximum brass length stated in the manual at 1.920.

Yes I have comparator, and as mentioned in the original post, that's exactly what I did. I bumped the shoulder back 0.002" but then some of my brass are .002 - .003 over the max of 1.920.

I misunderstood chamber shape and dimensions and thought that the case neck would be free to grow to the lands. But I clearly see now where I was wrong.

I think I also used the wrong term here, I suppose what I measured isn't chamber length but would be max COAL. I measured it using a Hornady OAL gauge. Having thought that there wouldn't be any interference with the case neck until the lands, I thought that would be a useful measurement for this discussion, but I see now it is not. I do use CBTO measurements when seating bullets. It seems as though this rifle has a lot of freebore and I intend on playing with seating depths more when I have more experience but for now I am seating the bullets to the manual COAL, using that cartridge to obtain CBTO, and then using CBTO for quality control cartridge to cartridge.

 

[steelheadmike]

This is very helpful thank you! I have seen these cut away photos before but it didn't click until right now. Disregard anywhere I mentioned the neck hitting the lands, I clearly see I misunderstood. I didn't realize the chamber necked down again after the case mouth, and I was thinking there wouldn't be interference with the neck mouth expanding unless enough brass flowed forward to push the mouth all the way to the lands.

I guess I sort of thought it was a straight pipe from the shoulder taper straight through to the lands.



Yes over the SAAMI max brass length, so those measurements are exactly correct.

I hear you there, I think at this stage in my reloading career there are many other factors that will effect accuracy and need to be accounted for before making sure all the brass lengths are exactly the same. Trimmer is on order though and that's something I'll eventually start doing just for consistency's sake.

Yes I definitely see that now, thank you!

Thanks for the diagram and info. Sounds like if that brass flows and the neck grows another .002 then we could potentially start running into some problems so I think I'll wait for the trimmer.



Over the maximum brass length stated in the manual at 1.920.

Yes I have comparator, and as mentioned in the original post, that's exactly what I did. I bumped the shoulder back 0.002" but then some of my brass are .002 - .003 over the max of 1.920.

I misunderstood chamber shape and dimensions and thought that the case neck would be free to grow to the lands. But I clearly see now where I was wrong.

I think I also used the wrong term here, I suppose what I measured isn't chamber length but would be max COAL. I measured it using a Hornady OAL gauge. Having thought that there wouldn't be any interference with the case neck until the lands, I thought that would be a useful measurement for this discussion, but I see now it is not. I do use CBTO measurements when seating bullets. It seems as though this rifle has a lot of freebore and I intend on playing with seating depths more when I have more experience but for now I am seating the bullets to the manual COAL, using that cartridge to obtain CBTO, and then using CBTO for quality control cartridge to cartridge.

Sounds like you're on the right path. I've found that my brass is typically a little over the max case length after sizing but I don't pay too much attention to it because it's going to get trimmed.

 

[wind gypsy]

This is very helpful thank you! I have seen these cut away photos before but it didn't click until right now. Disregard anywhere I mentioned the neck hitting the lands, I clearly see I misunderstood. I didn't realize the chamber necked down again after the case mouth, and I was thinking there wouldn't be interference with the neck mouth expanding unless enough brass flowed forward to push the mouth all the way to the lands.

I guess I sort of thought it was a straight pipe from the shoulder taper straight through to the lands.



Yes over the SAAMI max brass length, so those measurements are exactly correct.

I hear you there, I think at this stage in my reloading career there are many other factors that will effect accuracy and need to be accounted for before making sure all the brass lengths are exactly the same. Trimmer is on order though and that's something I'll eventually start doing just for consistency's sake.

Yes I definitely see that now, thank you!

Thanks for the diagram and info. Sounds like if that brass flows and the neck grows another .002 then we could potentially start running into some problems so I think I'll wait for the trimmer.



Over the maximum brass length stated in the manual at 1.920.

Yes I have comparator, and as mentioned in the original post, that's exactly what I did. I bumped the shoulder back 0.002" but then some of my brass are .002 - .003 over the max of 1.920.

I misunderstood chamber shape and dimensions and thought that the case neck would be free to grow to the lands. But I clearly see now where I was wrong.

I think I also used the wrong term here, I suppose what I measured isn't chamber length but would be max COAL. I measured it using a Hornady OAL gauge. Having thought that there wouldn't be any interference with the case neck until the lands, I thought that would be a useful measurement for this discussion, but I see now it is not. I do use CBTO measurements when seating bullets. It seems as though this rifle has a lot of freebore and I intend on playing with seating depths more when I have more experience but for now I am seating the bullets to the manual COAL, using that cartridge to obtain CBTO, and then using CBTO for quality control cartridge to cartridge.

I've never knowingly pressed my luck on letting brass get too long but I also dont believe it grows substantially in length during the firing process (Someone check me on this). In my mind, most of the forces are expanding the brass outward to the chamber walls which would make it more difficult to also expand forward? If there is lots of space between the brass and the chamber at the shoulder I could see things migrating farther forward possibly?

Anyways, doesn't hurt to wait a bit to trim them down a hair. I wouldn't waste your time trimming every firing or 2 to make them all within a thou though. If youre not overworking brass during the sizing process you should realistically only need to trim once or twice in the brass's lifespan (depending on cartridge and extent of lifespan obviously).