Does anyone else have this issue? Sometimes when trimming cases I notice the case lengths will vary. I use several trimmers, a Little crow gun works trimmer, a Lyman electric and Frankford Arsenal. Sometimes they vary up to 4 thousands. 2 of the trimmers spaces off the shoulder and the Lyman odd the rimmed case. I have annealed the cases before sizing most of the time, but happen with both ways. .I have noticed this with all these trimmers Any help? Also what is acceptable case length variations for long distant shooting.
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Varying lengths when trimming cases ???
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I almost never trim cases but when I do, .002 variance is accepted. .004 is a little higher but I don’t think it’s the end of the world.
If you haven’t done so already and want to know how case length variances impact your load, I’d make two test samples of 10 rounds where everything is identical except case oal then fire them over a chrono or LabRadar to see if you notice any material differences in the MV metrics as well as group size.
That should give you the info you need to determine if your case trim length variances are material or not
If you haven’t done so already and want to know how case length variances impact your load, I’d make two test samples of 10 rounds where everything is identical except case oal then fire them over a chrono or LabRadar to see if you notice any material differences in the MV metrics as well as group size.
That should give you the info you need to determine if your case trim length variances are material or not
I use a Giraud Tri-Way on my .308 cases, which like those trimmers you've mentioned, it indexes off of the shoulder. What I've found to get consistent case lengths is two things. 1. I must have consistent head space, which I get when sizing and bumping the shoulders (after annealing and cleaning). 2. When I'm trimming, I try to have as consistent pressure as possible, as the amount being trimmed is affected in thousandths of an inch by the mount of pressure applied. So, for example, if you have headspaces that varies by .001, it's easy enough to get a +/- .002 just by a variance in pressure when trimming.
For the most part, since the trimming is off of the shoulder, I don't worry too much about case length when trimming this way as what's more important to me is getting the length between the shoulder and the case mouth consistent. Indexing off the shoulder does a very good job at this.
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Almost impossible to bump every shoulder to the exact bump on every case. Way too many factors influence this.
You're right. That's why "exact" really isn't in my vocabulary. Rather, I think in terms of tolerances. And for shoulder bump, I'm after +/- .0005, which I come very close to. What's helped me do that is I anneal after every firing and when I size (bump the shoulder) the dwell time really helps in reducing inconsistency. Like I leave the case fully in the die for 5-8 seconds before lifting the die from the case.
That's what I was thinking the issue is, as the Little Crow trimmer is spacing off the shoulder, most cases come out fine, but a handful come out a little off. I think you verified my thought.
Wow, I'm trimming pretty often, almost every other firing. What are you doing to keep the neck growth at a minimum.
I am full length sizing, bumping the shoulder around .002. For my 800 yd plus guns I take a few more steps to maintain consistency. I anneal, resize .002 give or take, trim, clean primer pockets and flash holes, flash holes get cut just once and neck turn if necessary. Just trying to figure out where the variance is coming from when I trim, most all come out within a .001.
Nothing in particular. My loads are relatively mild, I bump .002-.003 on the shoulders and use lake city brass in my 308 and 5.56 rifles, except my Mk11 mod 0; that takes Federal commercial brass and I do have to trim one out of 10 or so. I also buy thousands of 1x fired brass for all my rifles so im not even close to having to use 2x fired brass. I ordered a bunch of new lapua brass for my AXMC 6.5 and 300 Norma barrels but haven’t received it yet. Wondering what sort of trimming they will require.
What brass are you using? Have you looked into a Henderson Precision trimmer?
I am using Hornady, Lake City, Remington and Star Line brass. I will take a look at the Henderson trimmer. I wanted to know where the trim variance was coming from, the die n not bumping the shoulder correctly? Case spring back? Something to do with the trimmer? I though maybe some of you out there ran across this and had some suggestions.
How do your loads perform as is (ie with the variances)?
I suggested the Henderson as it’s designed for high volume trimming. You may still see some variance, similar to what you see now for the reasons stated by other posters. IMO, it’s nothing to worry about.
A few thousandths here and there on neck length will make little difference. Consider an example of a 308 round.
- Neck tension is what holds the bullet in place, and you want consistent neck tension.
- Neck tension is fundamentally caused by friction.
- Friction is a function of area, coefficient of friction (essentially how rough a surface is), and force against the area.
- Area is the inner circumference of the neck (.308 x 3.14159) times the length of the neck (~250 thousandths for a 308)
- So... neck tension is directly related to length of the neck.
This is one reason why you want to trim - keep the length consistent means keeping one of the prime variables in neck tension consistent. HOWEVER, think about it... if you're off by, say 2 thousandths out of 250 thousandths, that's less than 1% difference in neck tension on a 308. When I seat rounds, I like to be within 10 lbs of seating pressure. That's 10 lbs out of roughly 40 or 25%!
That ~1% of neck tension difference due to length makes little difference.
I like to keep things within a few thousandths and will trim every 3 or 4 firings, but don't worry about it in between.
I trim every time after sizing my brass, mainly to keep consistency . . . AND, it helps avoid carbon ring issue in the throat . . . or at least extend the time before I really need to remove the carbon ring. But because I anneal after firing, I always have to trim .002-.004 off. A lot depend on your chamber size and/or the die dimensions where it's expanded and reduced by substantial amounts. If you don't anneal, the neck growth tends to me much less. See this. . .
"Further observations:
Case trimming to length: With this particular die set up we needed to trim the annealed cases more often than the un-annealed cases. We used an expander and a shoulder bump of 0.002”. Whenever one of the three cases of a set reached a length of 2.012”, all three were trimmed to 2.006”. Over twenty reloads, we trimmed an average total of 0.0225” from the annealed cases v 0.010” from the unannealed cases. The amount of trimming to length necessary varies with both the amount of shoulder bump and if an expander is being used. An expander tends to draw the neck forward. Many reloaders do not use an expander, and this eliminates this factor. In addition, the more bump, the more brass is extruded forward. Because annealed cases can be sized with excellent accuracy and repeatability, a bump of just 0.001” can work very well in bolt action rifles. This will reduce or even eliminate the need to trim to length."
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I use a Frankford Arsenal case trimmer. A couple things I've noticed:
1. For the most repeatable results (and I mean to within .001") it takes more time than I would like per case because I don't use too much pressure and I make to rotate the case numerous times. And the pressure used should be the same on every case.
2. Once you have the cutting depth set, I wouldn't go putting virgin brass through it or it will cut the shit out of it. WAY past the depth you want. I think this happens because the bottom of the shoulder where it meets the rest of the case body is more rounded. You can see the difference in the roundness of that area between a fired and sized piece of brass and a piece that has never been fired. The fired and sized brass will have a sharper corner on the shoulder. This is the case for my 300WM anyway. Due to the more rounded corner of virgin brass, more case material can be inadvertently pushed into the trimmer causing way too much to be trimmed off. I should point out that this was new PPU brass. Haven't tried any other virgin brass in it.
1. For the most repeatable results (and I mean to within .001") it takes more time than I would like per case because I don't use too much pressure and I make to rotate the case numerous times. And the pressure used should be the same on every case.
2. Once you have the cutting depth set, I wouldn't go putting virgin brass through it or it will cut the shit out of it. WAY past the depth you want. I think this happens because the bottom of the shoulder where it meets the rest of the case body is more rounded. You can see the difference in the roundness of that area between a fired and sized piece of brass and a piece that has never been fired. The fired and sized brass will have a sharper corner on the shoulder. This is the case for my 300WM anyway. Due to the more rounded corner of virgin brass, more case material can be inadvertently pushed into the trimmer causing way too much to be trimmed off. I should point out that this was new PPU brass. Haven't tried any other virgin brass in it.
L E Wilson trimmer....problem solved. They're slow and hand powered , but does the job.......right.... when one gets the hang of it.
I also highly recommend the Wilson method. Like so much in my very short time in precision shooting, you have to choose where you are going to spend your time and money. So many skills to learn and toys to play with; so little time and even less money to do it.
I use a Wilson also for my precision reloading and like how it works. I find it much more accurate than my Giraud although its much slower. It all depends on your purpose and requirements.
I used to use my Wilson and like how accurate it can be for over all case length. But, I prefer a trimmer indexing off the shoulder over one that does so off the base so that I get a more accurate length of the neck.
. . . well, yea . . . I also like a 3-way that saves a huge amount of time.
That's a good point about trimming virgin brass. When the brass is not fire formed, the head space of virgin brass can have a lot of variance, which can result in (as you say) cutting "the shit out of it". Though eventually, it'll grow back.
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