Trim length, does it make a difference in accuracy???

[Raptor]

A quick question for all you BR and accuracy guys. So does the actual "Trimmed length" actually make a difference in your accuracy??? As an example, say your trim length is supposed to be 2.510 and you have a mix of cases that are at 2.50 and 2.48 to 2.513. will this have any affect on accuracy?? Assuming none of them are over MAX length. The reason I am asking is I borrowed a power trimmer and noticed that my cases seem to vary in length... Thanks guys!!!

 

[bucweet]

I am not a bench rest caliber shooter
That being said from my experience .Yes
Like a lot of inexperienced reloaders I had someone tell me to do my own test, I reloaded some different length brass against all brass trimmed to the same length several different times and better grouping and less random flyers

 

[Raptor]

That is interesting. I get unexplained flyers once in a while and it drives me crazy!! I wonder if it could be something like this?? How close do they have to be?? Hell .005 is less than the thickness of a sheet of paper!!! I could see it they are too long and causing a pressure spike but just couple of thousands one way or the other is hard to wrap my head around.... Thanks for the reply!! Any one else??

 

[Gargoyle]

Daggum Lee trimmer case length gauge and shell holder for $5 on a cordless drill and you're golden.

 

[BartsBullets]

I don’t believe you can shoot the difference. I think it’s important that they aren’t too long and that they are square.

Bart

 

[Raptor]

I don’t believe you can shoot the difference. I think it’s important that they aren’t too long and that they are square.

Bart

That has always been my thoughts on it too. I read a comment on one of the other sights where a gentleman had said that it "Will" affect your accuracy if the case length varied. Like you, I could see it if the case was "To long" but not being .005 or so one way or the other off of the recommended trim length. So, I thought it would be a good topic for discussion with some of you guys who are accuracy oriented to shoot small groups and or BR shooters. I do most of my shooting long range banging steel. Thanks for the reply!!

 

[BartsBullets]

That has always been my thoughts on it too. I read a comment on one of the other sights where a gentleman had said that it "Will" affect your accuracy if the case length varied. Like you, I could see it if the case was "To long" but not being .005 or so one way or the other off of the recommended trim length. So, I thought it would be a good topic for discussion with some of you guys who are accuracy oriented to shoot small groups and or BR shooters. I do most of my shooting long range banging steel. Thanks for the reply!!

FWIW…my brass length varies about .002. I won the 3 Gun at the NBRSA Nationals and just won the Tack Driver. So pretty sure it will be ok.

Bart

 

[Ned Ludd]

Some trimmers index from the shoulder, meaning neck length should be very consistent. However, one may notice some overall case length variance when using this type of trimmer, even though neck length is very uniform. Using a trimmer that indexes from the base of the case can provide very consistent case overall length values, but one may find some variance in neck length when using a trimmer of this type, even though case overall length is very uniform. I've used both types and that is what I have noticed over the years. I cannot reliably state that either system provided better precision in my hands. If there was a difference, I could not shoot it. I don't find that too surprising as having +/-.001" or so variance in bullet bearing surface engagement in the case neck is likely a very small source of error, especially as compared to other larger potential sources of error in the reloading and shooting process.

There is no "perfect" system for trimming cases. We try to make them as consistent as possible using whatever system we have available to us. If minor case length variance caused via some specific trimmer system is worrisome, one can always pick out a few cases at either end of the case length range and test them side-by-side to determine whether they can really shoot the difference. Alternatively, one can just hit the easy button and save themselves some time and reloading components by following Bart's advice above, which is backed up by winning performance.

 

[Bill Norris]

FWIW…my brass length varies about .002. I won the 3 Gun at the NBRSA Nationals and just won the Tack Driver. So pretty sure it will be ok.

Bart

Great job Bart !!! I have looked at case length variances in the past with B R rifles and never saw a difference in group size. Recently looked at it again with my 30BR B R rifle with the same conclusion.

 

[Chaotik]

I have been under the impression, perhaps mistakenly, that variation in overall length due to differences in neck length could produce differences in neck tension (assuming that the amount of % partial neck sizing has an impact on overall neck tension).

 

[mikecr]

Trimming too short can make a difference to SD, as it affects gas blow-back between neck & chamber.
You can see by eye the excess fouling on ejected rounds from trimming too short.
This is not universal as it depends on other things too, but ideally you want necks to seal as consistently as possible.
Given this, I don't trim until within 5thou of chamber end. I don't go by book either, but measure chamber end.

It makes no difference to neck tension compared to all the bigger things that do.

 

[BartsBullets]

Trimming too short can make a difference to SD, as it affects gas blow-back between neck & chamber.
You can see by eye the excess fouling on ejected rounds from trimming too short.
This is not universal as it depends on other things too, but ideally you want necks to seal as consistently as possible.
Given this, I don't trim until within 5thou of chamber end. I don't go by book either, but measure chamber end.

It makes no difference to neck tension compared to all the bigger things that do.

When you do trim your cases back (from the chambers end) how many thousands do you shoot for?

Bart

 

[dgeesaman]

Decimal points matter. In your original post you floated the idea that .03” length variance is the amount in question, but then the subject changed to .002” or .003” variance.

.03 is a lot when precision is the goal. That could easily be 15% of the total bullet seating depth in the neck. That’s excessive variation in overall neck tension.

For me, I want less than .01” total variance and most of my brass is about .005” difference. Even using my newest fanciest shoulder-indexing trimmer I have .002” total variance. I do believe that when it’s down to a few thou your neck tension will be dominated by other variables.

 

[SSL]

A quick question for all you BR and accuracy guys. So does the actual "Trimmed length" actually make a difference in your accuracy??? As an example, say your trim length is supposed to be 2.510 and you have a mix of cases that are at 2.50 and 2.48 to 2.513. will this have any affect on accuracy?? Assuming none of them are over MAX length. The reason I am asking is I borrowed a power trimmer and noticed that my cases seem to vary in length... Thanks guys!!!

If you are referring to finding a perfect length that shoots best, I doubt it. If you mean keeping all brass the absolute (statistically anyway) same length, I feel 100%, absolutely, positively and without a doubt...maybe.
Look at everything many shooters do to make sure their brass is uniform: Uniform primer pockets, worry about primer seating depth, neck-turn to a uniform thickness (or maybe only just 'skim' turn), custom premium dies, weigh each piece of brass and segregate by weight and maybe even hold late night black magic rituals involving eye of newt and black cats.
Not making fun of those people. I'm not a competitive shooter, but I do obsess about the care and conditioning of my brass. Making sure each case is the same length just makes sense to me. I look for that perfect combination that produces that .000" group too. Besides, I find all that case prep to be therapeutic!

 

[BoydAllen]

On the trimming short thing, Jack Neary had had a 6PPC reamer made with a max case length of 1.525 with the thought that it was so much longer than cases that have been fire formed and trimmed to clean up the shortest at about 1.490 would never grow enough in their useful life to need trimming again. Later he found that trimming often improved his results, which put an end to that plan. On one of his videos he mentioned that with that chamber he still trims to 1.490, which gives him a end of neck to end of chamber neck of .035 which has not hurt his accuracy at all. Bottom line, there is a lot of assuming going on.

 

[BoydAllen]

To the OP, if your trimmer indexes off of the shoulder, IMO that is the best because the case is knocked forward during the firing process so that the shoulder of the case is in contact with the chamber shoulder and having consistent case length from the chamber shoulder is what counts functionally. All of that can be perfect, but sized cases can vary in their shoulder to head length and when they do, the OAL of perfectly trimmed cases (indexed off the shoulder) will vary by that amount. On the other hand if you use a trimmer that indexes off of the head, the case overall lengths can look really consistent but their functional length in the chamber will vary with the head to shoulder dimension. I have both kinds of trimmers, and if my sizing process is producing consistent shoulder to head dimensions then it does not matter which I use. If I was concerned about having too much variation in shoulder to head dimension, I would either have to sort and do separate die adjustments or anneal.

 

[Raptor]

Decimal points matter. In your original post you floated the idea that .03” length variance is the amount in question, but then the subject changed to .002” or .003” variance.

.03 is a lot when precision is the goal. That could easily be 15% of the total bullet seating depth in the neck. That’s excessive variation in overall neck tension.

For me, I want less than .01” total variance and most of my brass is about .005” difference. Even using my newest fanciest shoulder-indexing trimmer I have .002” total variance. I do believe that when it’s down to a few thou your neck tension will be dominated by other variables.

What I was talking about was actually several thousands either side of the "Specified" trim length. plus and minus. So, we could be talking about .005 to .006 in OAL difference. I also seat "My" bullets down to the base of the taper on the bullet to the bottom of the neck so neck tension should not be an issue. Thank you for your thoughts....

 

[Ledd Slinger]

As part of the trimming process, I believe a good even chamfer on the neck is just as important as the neck being square. I like the K&M VLD chamfer tool. Does a really good job of taking the error out of my hand and making a nice even cut all the way around the inside of the neck. I don’t run it very deep tho (maybe .010” or so). Just enough so the bullet base has a nice smooth means of entering the case mouth evenly and unscathed.

 

[BoydAllen]

As part of the trimming process, I believe a good even chamfer on the neck is just as important as the neck being square. I like the K&M VLD chamfer tool. Does a really good job of taking the error out of my hand and making a nice even cut all the way around the inside of the neck. I don’t run it very deep tho (maybe .010” or so). Just enough so the bullet base has a nice smooth means of entering the case mouth evenly and unscathed.

I like K&M's idea of a pilot that extends through the pilot hole, but I think that there angle is a bit steep for the main chamfer. A while back Redding came out with this.

 

[Rocketvapor]

I enjoy these discussions, with comments from expert shooters, on the little nuances of reloading that might make a difference for great shooters, and maybe a little improvement for the rest of us. For reference, the wife and I still get some 9's @ 600. Just a couple fewer of those would be welcome.
I'm shooting 22 Nosler in an AR and new brass comes in pretty consistent @ 1.755" (SAAMI cartridge length is 1.760" - 0.020, chamber is 1.772"). After tumbling, annealing and sizing some grow in length. It seems to take a couple firing before trimming is needed. I'll measure case length with decent calipers and trim anything over 1.600 - 1.602" with the Hornady hand crank trimmer back to 1.600". Anything longer and the lee collet die doesn't size to the absolute end of the neck.
Funny that Lee has shortened the collet on the newer dies to do exactly that.
I deburr and lightly chamfer the neck so the bullet bearing surface (all boat tail bullets) gets seated scratch free.

My FL sizing (body die) is set for about 0.002-0.003" under chamber, and I can easily tell with a fit check. I can bump and find the length that will just chamber (bolt is fully rotated), then another 2 thou.
I don't neck turn as the thickness is pretty uniform.
This is about all I'm set up to do with the brass and think it exceeds my shooting skill.
1.600" trim and I don't see any carbon collecting.