I'm a little new to reloading, question is, will there be a big difference in accuracy when trim length varies by three to six thousands? My .308 brass (winchester) I trim to 2.008,but some of them are short at 2.004. I'm reloading for a Bergara B14 Hmr and have been getting groups under half moa at 100yds consistently,but sometimes the group will open to just over one moa,could that be from the variation in case length or is it just me not doing my part behind the rifle.
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Trimming
- Thread starter Spring1A
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I was using a Lyman universal, but it started to just peen the case mouth,so I went and got a Hornady cam lock (I know cheap beer) but it seems to be OK,within a thousands or so. I do full length resize and have thought about just neck sizing, but have not bought the die for that. All reloading I do is on RCBS rock chucker.
No matter on that. By looking at it, it seems that the rear shaft can lock in. I assume that the trimming end stays stationary? If that’s the case, I would think setting up the trimmer with your longest case and never adjusting afterwards should yield more consistent trim length if your base to shoulder measurements are + / - one thou. As far as opening of groups, that could be a number of things. You could test with the shortest brass vs the longest but if the base to shoulder dimensions are about the same I couldn’t imagine .004 less of neck causing good groups to really open up. Varying neck tension and / or powder charges for sure.
Yes the rear shaft or the shaft that holds the case is definitely solid,I found a sized case at 2.008 and set the trimmer to that, all long cases I trimmed came out just fine. I will mark the shorter cases and see if there is a change at POI. As far as base to shoulder, the measurements are all within a thousandth on the loaded cartridges, even the resized emptys are the same. Which is one of the reasons if have not bought a neck sizing die. Powder charge all the same, I old school trickle every one O.C.D. I guess. I shoot five shot groups, first thee shots are always good, its usually four and five that gets me. Pisses me off something fierce. So along with checking those shorter cases for POI, I'll have to try and keep that perfect group anxiety in check. Hard to accept that I probably am the weak link. Never wrong you know, just ask the wife!
No worries. It sounds like your methods are good. I suppose if you keep having issues regarding OAL after trim, maybe check out a trimmer that utilizes the shoulder of the sized brass. I have no experience with the trimmer you have so I could be half talking out the ass. If it shoots it shoots haha.
Maybe see if any of the training videos here help you out with shots 4 and 5.
Maybe see if any of the training videos here help you out with shots 4 and 5.
I don't trim my 308 brass until it gets to 2.025, I wouldn't worry about it
You can buy replacement cutters for the trimmer.
I got tired of doing mine manually and bought their little brass smith trimmer.
I love it.
.004 is nothing. Shoot it, let it grow, and trim it to 2.008. Worry about other things.
Thought about tracking down a replacement cutting head for the Lyman, but didn't due to availability of anything for reloading. The Hornady requires their own shell holder, so I checked my local stores to no avail. Went online,nothing except for one on ebay, wait for it... $69! I drilled the hole in an extra rcbs holder a little larger and it works great. If someone would have told me a Hornady number 1 shell holder would go for $69... Holy shit!
.006 case length variation will not double group size. The most likely cause is the shooter.
Do NOT buy a neck sizing die, you would be wasting your money.
Do NOT buy a neck sizing die, you would be wasting your money.
Consider this:
- Why is trim length important? Primarily because varying neck length will vary the force of friction from the case acting against the surface of the bullet, which impacts the overall force holding the bullet in. Other key variables impacting this force are the neck tension which varies the force of the case pressing against the bullet's surface, and the coefficient of friction inside the neck (how "sticky" or rough the surface is) - which is why some of us use neck lube to make this variable more consistent.
- Why is neck tension important? Varying neck tension will cause ES/SDs to open up - sometimes pretty dramatically. I consider consistent neck tension to be one of the important things to keep consistent.
So, am I saying that those .004" differences matter? Nope, not really.
Why?
- The force holding the bullet in place is related to the coefficient of friction (lube, no lube, carbon, etc) x force pressing against the bullet surface (neck tension) x the length of the neck x diameter of the bullet (constant)
- On a .308, the neck is about 170 thousandths, give or take.
- That means that those 4 thousandths are only varying the force holding the bullet in by about 2.3%.
To put this in perspective. When I seat bullets for my 300 PRC (same diameter, longer neck), I look for a seating force of between 40 and 50 pounds. That's a 20-25% variation. That little 2.3% would be getting lost in that variability AND if you use an arbor press with a force gauge to seat, you'll know if the seating force falls outside whatever arbitrary values you set for the boundaries. I just mark those rounds with an X using a Sharpie and don't use them for anything important. With my process, it's about 1 out of every 10-15.
Thanks for the input! The neck sizing talk on here seems 50\50. While FL resizing only bumps the shoulder back one or two thousands, it doesn't seem necessary to buy neck dies. Agreed the opening of the group is shooter related. Need some work on the ZEN throughout the course of fire.
Makes sense, thanks!
This better explains my original post, as my thought process seemed to think, longer or shorter case length would hold the bullet differently. I just wasn't sure where the tipping point might be. I don't have a force guage, just kinda go by feel. I have noticed on occasion that seating felt a little stiffer than others, in the future I'll set those aside. Again thanks! All very useful information
On a second note that YouTube channel really helped with recoil control, I found myself with a death grip on the gun, not even close to on target after I broke the shot, thanks to the guys here as well. I read a post about the 15 pound weight, in relation to how much force to apply to the grip.
As a new reloader, I know you're getting bombarded with "you should do this" and "you should do that" and have to make decisions on which directions make the most sense. It's hard to know which advice should be prioritized.
With that said, I would say that one of the biggest jumps I made in getting more consistent ammo was moving to an arbor press with a force gauge, which in turn led to other relatively minor changes (like using a mandrel and neck lube). Dollar for dollar, collectively these changes were the most effective I made. On top of that, I get better concentricity out of the seating dies used with the arbor press. Lastly, the arbor press is portable. When tuning for seating depth, I can load all the rounds long, take the press to the range, and make adjustments while there. It saves a trip back later to validate.
You're probably not quite at the point where I'd say this is something you should do now - better to get your process down and be as consistent as possible. But when you start reloading for a second caliber, you could consider it at that point (since you need to buy another seating die anyway).
If I don't get SDs 6ish or under, I'm not happy (my 6 BRA gets in the 4s, but then that cartridge is just freakish in many respects).
K&M Arbor Press with force kit: ~$150
LW Wilson Seating Dies: Equal or less than standard seating dies
Mandrel + Die: ~$40 + ~$20 to $40 per mandrel, depending on type
Graphite Neck Lube: Immaterial
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