Trimming tips?

[Mike Matteson]

I find that there is more variance (higher SD) with consistent but higher clearance, than there is with reasonable trim length variances (provided tight clearance). It's one of those deals where consistency in itself does not win over a better plan.
The better plan on my part is to prevent gas from getting between neck and chamber, which would add neck sealing variance, affecting SD.

I fully agree. I not saying to trim the case way back. I did at one time, and let them grow to where they were to long. Then trim again. So my brass were all different lengths. I hadn't realize that is was causing me problem or possible problem. Now on my Peterson brass (New case right out of the box) they varied several thousands overall length. So I used the shortest dimension, and cut my brass to that length for consistency. (5). The other is I cut my brass for thickness. So they have to be on the money to start with in length. They won't go into the chamber until that done. I still have to fireform them. I'll see what the growth is. Anneal them and size them, Check and see what I have then. What kind of growth I have to the shoulder, and overall length. I only have 3 cases fired presently. The neck area is still tight. so I'll have cut another 1/2thousand off the neck. I'll be at .0125 instead of .013. If that doesn't work, I may reduce to .012 or send the reamer to reshape it. I think where I missed it at was the .243 is really .2435.

 

[Straight Shooter]

Mikecr, I agree with you that I want my trim lengths as long as possible because I have run into the same thing that AZshooter has. Quite a gap between neck and chamber end. I never knew that before I had the borescope.

 

[Mikecr]

A lot of people think that for turning necks, they should be trimmed first, for a consistent stop on the turning tool.
Alot of people assume that trimming to the shortest in the box is a consistent and good thing.
Neither is true.

Necks should be turned when new. But at that point the neck-shoulder junctions are not consistent, so you should not employ a set & forget setting. You should apply a visual/hand touching of cutter to neck-shoulder junction. It's not a critical cut there (as long as you don't go crazy with it). It's just a mitigation of donuts.

Also, necks typically pull back with fire forming. This, because improving of shoulders to any slightly higher angle will pull necks back.
So if you had already trimmed to desired clearance, then with fire forming the clearance will open beyond desired.
You can instead measure your chamber length, log it, measure your new cases, and with any that are too long (or leaving the pack), toss them.
Then after fully fire forming brass to stable, consider if trimming is needed yet, or ever.
Why would you want to toss cases that are different in length than the others? Because they're different in other ways too. Just do it,, brass is cheaper than bad reloading.
If all new cases are long for your chamber, then trim to around 5thou short of chamber end (allowing for excess headspace), keeping in mind that this clearance will likely grow on 1st firing.

So why would trim length variance not be a priority concern?
Because a hair length one way or another of neck comes nowhere near the tension variances you will have -no matter what.
It's totally lost in the noise.
It's more important to get close on chamber end clearance, to keep that sooty gas from getting between necks and chamber.
A far bigger affect.

 

[Mike Matteson]

Mike, I don't have any way around it, except cut all my cases to the same length to start with. Other wises my necks cutting would be at a different point every time. So setting the length comes first, then cutting the thickness is next. Otherwise the cut for thickness would stop at different places. (either short of the shoulder or into the shoulder) Not good in my estimation nor correct either. I can't do much about the difference in case length either, that's the way they came to me. Then cut for thickness. setting up the stops is the most importance thing I believe. So all the cases, are the same length to start with, and you are not cutting into the shoulder, or short of the shoulder each time.
I hearing what you are saying, but how do you cutting for thickness and stop at the same place at the shoulder each time if the case length is different each time? That would take a huge amount of time, to change the stops each and every time. I do agree that the neck length would change at the time of fireforming them. The neck get shorter and the case gets longer at the shoulder at the same time, I believe. Possibly the case would stay at the overall length, just changing where the shoulder length is at. I can't make the case grow to start with.
Do I agree on where the end of the case should be at, but if the case isn't long enough to start with, there not much I can do.
I hear you, and I understand what you are saying. I am not cutting the length much. A few thousand at the most. The cases varied from 2.5185 to 2.525 which is the correct length. Very few that I measured were at the 2.525 length.
I have comparators to check the length at the shoulder. I haven't taken any measurement at this point in time as what is happening, but I will. I'll get the dimension before and afterwards. I am also will set up check the length in my chamber too. I do chart all the info too.

 

[Mikecr]

I hearing what you are saying, but how do you cutting for thickness and stop at the same place at the shoulder each time if the case length is different each time? That would take a huge amount of time, to change the stops each and every time.

If you have a stop on your neck turner, remove it.
You can do this by eye, regardless of neck length:

 

[Mike Matteson]

If you trust your eyes. I'll do some thinking on that. I have order out "Sinclair Chamber Length Gauges for the different calibers I reload for. I didn't have a choice on the chamber gauge for the 6mm. It's tighter chamber one, but not knowing if that will work either. I would have gotten the regular gauge and had the smith turn it down. I am not to far from the Smith, so I can have it turned down more if needed. I have to go there anyway, because he was moving the last time I was there. So he couldn't set up and ream my blank bullet seating die.

P.S. Good looking case.

 

[Straight Shooter]

Mike and Mike, thank you for sharing all your info and ways of thinking. It is very beneficial to us less experienced teloaders.

 

[RidgeTop]

I trim .01 below saami and measure always after cleaning and sizing. I will allow it to grow .003 before another trim and if you use Wilson trimmer you shouldn't have any variation when trimming. Remember to be consistant in cleaning, sizing, trimming, loading and shooting. Also remember to wipe down your brass after sizing to remove the lube used to size.

I use RCBS Case Lube - 2. It washes off with water. No chance of oil contaminating powder or primer.

 

[Lenny Foffa]

I used to trim to the manuals Max Case Length, and their suggested 10/1000 Shorter than that Listed case length, for the 270 Win. Then I purchased the Sinclair Chamber Measuring Gauge, that is seated in a Modified 270 Win Case, where YOU trim the neck bask and insert this gauge. Chamber the case and Gauge assembly. Close the bolt slowly. Extract the case and Gauge. Measuring the length of the case and the inserted gauge, I have learned that my Weatherby Ultralight has a chamber 40/1000 longer than the Listed Max Case Length, and my Win Model 70 Super Grade has a chamber 35/1000 longer than the listed Max Case length. I had been doing lots of trimming for no good reason. My cases all remain between 2.535 and 2.542. Nothing is even close to 2,580 . If and when I see cases grow or stretch to 2.455, then I will trim them back 5/1000 to 2.540. I have seen no pressure signs, no extraction issues and no issues opening or closing the bolt. Just my personal opinion.

 

[QuietTexan]

I hearing what you are saying, but how do you cutting for thickness and stop at the same place at the shoulder each time if the case length is different each time?

Like Mike said you eyeball it. I use the K+M cutter with their recommended cutter based on case shoulder angle, it cuts a wider and shallower band on the shoulder than the standard 50* cutter. I had no issues turning my 243 cases down by eye, they were getting blown out to an AI shoulder and one case held together for 11 firings in a row - no web expansion, no measurable case head stretch, didn't grow enough to need trimming, and there was no apparent thinning in the neck/shoulder area as a result of turning the neck down.

It's one of those things that once you do it once it clicks and you do it 50 more times without really having to worry about it.

I had been doing lots of trimming for no good reason.

That's what pretty much everyone that actually measures a chamber finds out.

And when guys stop trimming compulsively they actually stop introducing variance into their cases by trimming them at varying headspace lengths. If someone trims a case new they've started a self-perpetuating cycle of having to trim every firing until the cases stabilize. Don't trim the first time because there's no need to based on actual chamber length and let the cases go a few firings. It's interesting how so many cases never actually grow to the point they need to be trimmed, and how tight a range cases will stay in when left alone.

 

[Mike Matteson]

When you start out with inconsistent case length, you are inconsistent to start with. Some say that the case aren't growing much either. It's been over the years of reloading, the cases grow. Belted Mag being to worst. Found that only neck sizing stop most that case separation. I now feel that fireforming the belted mags and only bumping the shoulder back a thousand or two would do about the same That's fine, but the cases are still inconsistent. It would be nice to have the necks longer that they should be, and cut back to length of what the chamber is. Most people wouldn't take the time to check and see how there chamber measure out. Now I went through a fair amount of case from a brand new box Peterson Brass (500). Found that there was a 6 thousand differences in the cases lengths. Now I cut back about 10 case to all the same length "consistent" Not inconsistent. Concentricity leads to accuracies. It would very nice if the case length were all the same. I have taken the time to measure out another top of the line of case to see if they vary in length. Some are other calibers, and some are Lapua cases. I do have a new box of Lapua 22-250 New in this location. They varied from 1.8995 to 1.94055. Better than Peterson, but not much. I only did 10 case with Lapua. I did a greater amount of case in Peterson. I do agree fully that the case should be within a thousand or two fitting the chamber. Now I using a tight chamber in this new rifle. I don't have any choice, but reducing my thickness, in the neck. That's what I wanted, and that what I got. In not thinking about different in case length in new cases. No problem right, Wrong. So if I was going to do this again, I would change the reamer some to an try account for this difference in case length to reduce the length in the neck area by a few thousands. Making my chamber a little shorter in the neck length. This being my first time in. having a custom reamer built.
So I'll live by what I have done, and be more careful the next time.

 

[WiscGunner]

When you start out with inconsistent case length, you are inconsistent to start with. Some say that the case aren't growing much either. It's been over the years of reloading, the cases grow. Belted Mag being to worst. Found that only neck sizing stop most that case separation. I now feel that fireforming the belted mags and only bumping the shoulder back a thousand or two would do about the same That's fine, but the cases are still inconsistent. It would be nice to have the necks longer that they should be, and cut back to length of what the chamber is. Most people wouldn't take the time to check and see how there chamber measure out. Now I went through a fair amount of case from a brand new box Peterson Brass (500). Found that there was a 6 thousand differences in the cases lengths. Now I cut back about 10 case to all the same length "consistent" Not inconsistent. Concentricity leads to accuracies. It would very nice if the case length were all the same. I have taken the time to measure out another top of the line of case to see if they vary in length. Some are other calibers, and some are Lapua cases. I do have a new box of Lapua 22-250 New in this location. They varied from 1.8995 to 1.94055. Better than Peterson, but not much. I only did 10 case with Lapua. I did a greater amount of case in Peterson. I do agree fully that the case should be within a thousand or two fitting the chamber. Now I using a tight chamber in this new rifle. I don't have any choice, but reducing my thickness, in the neck. That's what I wanted, and that what I got. In not thinking about different in case length in new cases. No problem right, Wrong. So if I was going to do this again, I would change the reamer some to an try account for this difference in case length to reduce the length in the neck area by a few thousands. Making my chamber a little shorter in the neck length. This being my first time in. having a custom reamer built.
So I'll live by what I have done, and be more careful the next time.

I like your thinking on the custom reamer for next time.

For my clarification, you the Lapua measured better than the Peterson? I am dyslexic with number so I can never fully trust my own math. You mention "6 thousand differences in the cases lengths" with Peterson which I read to be .006" but when I subtract 1.8995 from 1.94055 I get .041" with your Lapua numbers. Seems Lapua had almost 7times more variance. What am I misunderstanding?

 

[QuietTexan]

It seems like you're focusing heavily on overall case length and not considering variance in headspace length in new cases. I've measured more than 0.003" variance in lots of Lapua, Peterson, Nosler, Hornady, Norma, Starline, Remington, and ADG. Usually more along the lines of 0.004" over a group of 50-100 cases. Moving a shoulder .002 will change the length of the case, trimming too soon or when new removes material that might be needed to keep the cases longer once the shoulders move forward.

 

[Mike Matteson]

I like your thinking on the custom reamer for next time.

For my clarification, you the Lapua measured better than the Peterson? I am dyslexic with number so I can never fully trust my own math. You mention "6 thousand differences in the cases lengths" with Peterson which I read to be .006" but when I subtract 1.8995 from 1.94055 I get .041" with your Lapua numbers. Seems Lapua had almost 7times more variance. What am I misunderstanding?

Joined the club. I am dyslexic too. No it's .0041 difference. What we are talking about is the length and where the neck ends. Getting withing a thousand or so. The closers the better, and I agree on that. Just getting there is another story. It's been my understand the same length in all your case is needed. this controls the release of the bullet. There are 3 or 4 things coming into play here. You are dealing in case length, neck thickness, neck tension. All being the same in controlling the bullet.
Learning something new all the time. This a great place to be, and you will learn a lot here.
Back to eyeball it. I believe it's hard to see a thousand. Close only counter in Horseshoes, and Hand-grenades. Believe me I pitch a lot of them in Vietnam. (I couldn't stop myself. )

You might put info down in another place to look at and start a log. I have and it's about 30+ pages long now. I did a year ago and it's helps.