General case length and trimming questions

R

RileyMartin

New member
Hi all,

I'm still new to reloading and looking to refine my case trimming technique. I'm reloading 30-06 for my M1 Garand and was hoping someone could help with answering some general questions.

1) Can I prolong the life of the case by trimming less, and trim to the MAX case length of 2.494" rather than the Trim-To Length of 2.484"?

2) Can I get more accuracy by trimming to the MAX case length of 2.494" so the ogive of the bullet sits 0.010 further into the free bore?

3) I use a Tri Way trimmer to trim my brass and the case length varies with each case a little to a lot depending on the starting length of a given case. To what decimal place do I need to match my cases in case length to produce the best groups?

Thanks.
 
RileyMartin said:
Hi all,

I'm still new to reloading and looking to refine my case trimming technique. I'm reloading 30-06 for my M1 Garand and was hoping someone could help with answering some general questions.

1) Can I prolong the life of the case by trimming less, and trim to the MAX case length of 2.494" rather than the Trim-To Length of 2.484"?

2) Can I get more accuracy by trimming to the MAX case length of 2.494" so the ogive of the bullet sits 0.010 further into the free bore?

3) I use a Tri Way trimmer to trim my brass and the case length varies with each case a little to a lot depending on the starting length of a given case. To what decimal place do I need to match my cases in case length to produce the best groups?

Thanks.
Click to expand...
1. No
2. Maybe
3. Triway locates off the shoulder of the case, which is better accuracy wise as that is how the rifle will see the cartridge. You will see variation in OAL but as long as it's in spec shouldnt adversely effect accuracy.

Sent from my SM-G950U using Tapatalk
 
No , it best all around the trim mid way 2.484 - 2.494 scale to 2.489 find your chamber length an size you cases for your Garand using a full length die for .003 case headspace bolt face to datum. I trim every time , it's not even a trim after a while , it seems to be more of a clean up once you trim each time. Accuracy is making everything consistent , case length , powder charge and bullets seated to the same ogive measurement. Are you shooting a 150 gr match bullet.
 
I have a dedicated Wilson set up for each cartridge I shoot. I use the power adapter and trim after each firing between the annealing and priming stage the get a ride on the Wilson sometimes a little comes off sometimes nothing but they all get that ride. Consistent ammo combined with consistent form make for consistent groups if that is your goal
 
Riley,

In the day of plentiful government ammunition for matches, a lot of 30 Cal competitors who rolled their own with government cases actually trimmed them -0.020" below specified minimum with the idea their military chambers would give them only about four reloadings out of full-length resized military cases before the pressure ring started to thin unacceptably and they had to retire it. The short trim let them do just one trimming to last the life of the case that way. As long as they didn't crimp into a cannelure it didn't affect bullet jump. They won matches doing it.

The exact bullet hold will have a small effect on accuracy that a benchrest competitor might be able to distinguish and appreciate, but it is less commonly noticeable the Garand. My match Garand shot 10 shots into 0.7" at 100 yards right after I fit it up, but in those days I didn't know much about brass prep. Might I have reduced that to 0.65" if I did? Maybe.

The reason for the trim-to lengths is so manufacturers can have a target trim length of ±0.010" to play with. The military spec is narrower than SAAMI, being 2.4790"-2.4940, so a 0.0150" span with a middle value of 2.4865". In your shoes, assuming you intend to size just enough for function so that your cases last a good deal longer than four loadings, I would make that military minimum the target and not trim again until it came out of the resizing die over 2.494". Ignore the variation.

As Dallasb pointed out, the 30-06 case (and other rimless bottleneck cartridge cases) actually headspace by case shoulder contact with the chamber shoulder, so having the neck the same length from the shoulder forward is more important to bullet jump consistency than the shoulder-to-case mouth measurement is anyway.

As an aside, case shoulder-to-head measurement is most important for smooth feeding and should be at least -0.002" shorter than the case measures as-fired, but needn't be more than -0.003" shorter, regardless of the actual size of your chamber. Such minimal resizing will preserve the brass life a lot in your gun. It just can't be guaranteed to fit or not to jam in someone else's gun if they have a tighter chamber than you do. This is one of the advantages of reloading; sizing to fit just your gun.
 
having the neck the same length from the shoulder forward is more important to bullet jump consistency than the shoulder-to-case mouth measurement is anyway.
Click to expand...

I have to think on this one for a bit. I measure my rounds by measuring from the case head to a datum on the bullet. The shoulder is what stops the case from moving forward in the chamber. If the cases are sized correctly and uniformly with no springback then the distance from the datum on the ogive of the bullet to the datum on the case shoulder as well as the distance from the case head to the datum on the bullet ogive should always be the same regardless of neck length. Neck length only affects how much of the bullet is being grabbed by the neck.

I think...maybe. I am going to the range and shoot a few and think about this
 
It does not hurt to know the length of the chamber from the shoulder to the bolt face and from the end of the throat (from the beginning of the rifling) to the bolt face. After that there is clearance, most believe the case has head space and there are a very few that know the case does not have head space and the difference in length between the chamber from the shoulder to the bolt face and the length of the case from the shoulder to the case head is called clearance. ME? I off set the length of the chamber from the shoulder to the bolt face with the length of the case from the shoulder of the case to the case head. The difference in the two lengths is clearance.

F. Guffey
 
Hounddawg,

Rimless bottleneck cases headspace (seat) on the shoulder of the chamber during firing. We know this because cases grow by stretching at the pressure ring of the case. If the case did not first go forward, the shoulder would blow out instead because it is thinner, softer annealed brass and would be the place of least resistance for pressure to expand.

Mainly, the firing pin pushes the cartridge forward. When the primer ignites there is some assistance from it because it tries to back out of the primer pocket, flowing around the extended firing pin nose. Both forces act to push the cartridge forward until its case shoulder meets the chamber shoulder. At that moment, bullet jump is determined by how close the part of the bullet ogive that will make the first contact with the rifling leade is allowed to get. That is controlled by the case shoulder's contact with the chamber shoulder.

So, if you want to control bullet jump, you look at the distance from the case shoulder datum to the part of the ogive that meets the throat leade (the ogive has no datum; you just measure it as close to the land-contacting portion as you can and be consistent). I made a comparator that does this directly, using my chamber reamer to both size the shoulder and to cut the hole in the measuring plunger so it contacts the bullet where the actual chamber would. The measurement I get is arbitrary, but consistent, so you can see relative changes and replicate a reference load with it.

There are two problems that become apparent with that measurement. While it does eliminate from the measurement the variations in shoulder distance from the head that occur with resizing, the fact is the seating die depends on the head location to control how deeply it seats the bullet. Also, the ram at the end of the seating die's stem usually contacts the bullet higher up than the gauge does, and bullets can vary a couple thousandths in how far the throat contacting portion of the ogive is from the seating die contacting portion. As a result, I wind up finding up to about 0.003" of variation when measuring with my comparator. What you can do, though, is sort the rounds by that variation and seat the long ones deeper by the correct amount to make them match the shorter ones. I can't say I've objectively measured such small variation mattering to group size, but when looking for variation in loading I like to try out loads that eliminate every variation I can and to compare their performance to less carefully assembled "production" rounds to see if I've made a measurable performance difference, and that's how I came to design that comparator.

You can also make that same measurement without the comparator I made. You just make separate measurements with a case and a bullet comparator of each cartridge and compare the difference from one round to the next. The smallest differences can then be matched by adjusting and applying the seating die to the longer ones until their readings match. The only difference from my direct comparator design is it takes two measurements and some arithmetic rather than making a direct measurement on a dial. But you could certainly invest the time with one batch to see if it makes any discernable difference to your groups.
 
1) Can I prolong the life of the case by trimming less, and trim to the MAX case length of 2.494" rather than the Trim-To Length of 2.484"?
Click to expand...

no.

2) Can I get more accuracy by trimming to the MAX case length of 2.494" so the ogive of the bullet sits 0.010 further into the free bore?
Click to expand...

no. It doesn't work that way.

3..To what decimal place do I need to match my cases in case length to produce the best groups?
Click to expand...

No one can tell you that. Because there is no magic number that will produce the best groups. Every rifle is slightly different.

Before we get into the esoterica of loading "to the ogive", which, I don't do.., lets look at a few basics.

1) Why is there a max case length?? (for .30-06, 2.494")
2) Why is there a trim-to length? (2.484")
3) Why is there a max overall loaded length (COAL)? (3.340")

1) Max case length is set to what it is, so that the case does NOT extend into the barrel too far. We don't want the case mouth extending beyond the chamber because beyond the chamber the barrel is too small in diameter to allow the case mouth to expand and release the bullet normally. The chamber has the clearance needed to allow that to happen, the bore (including the throat) does not. Without the needed clearance (room for the case mouth to expand and let go of the bullet) pressure goes up (and maybe WAY up) and this is a bad thing.

2) Trim to length is an arbitrary number, usually set 0.01" shorter than max case length. (some cartridges use 0.005"). The point is to trim the case back short enough so that when it stretches during firing, it does not exceed the max case length. Cases stretch when fired, and usually stretch the most on the first firing. Trimming 0.01" back, usually means several firings are possible before the case has stretched back out to max allowed length, and needs trimming again. It's done that way so you shouldn't need to trim your brass after each firing.

3) COAL = Cartridge Over All Length. AKA Maximum overall length (with bullet). This is measured from the base of the case to the TIP of the bullet.
Not the ogive, the tip. This is the industry standard maximum length of the loaded round in order to work through the actions of ALL the rifles in that chambering. It is also a length that keeps the bullet OFF the rifling (with the standard bullets for that caliber)

In other words, a round at max COAL will work through the magazine, feed into the chamber, and not have a regular bullet jammed into the rifling. IF your rifle doesn't allow that, it is considered defective/out of spec in some ways. Some rifles have shorter throats than others. Some will not take every bullet design loaded to max spec length without jamming the bullet into the rifling. Others can takes rounds longer than max spec length without issue. Some rifles will chamber and shoot rounds too long to work through their magazines. There are lots of possible variations, so industry specs are set to work in "everything". Ammo makers make their ammunition slightly smaller/shorter than max industry specs, just so that it will work in everything.

NO matter which way you use to measure and adjust your seating die, your loaded round will have a certain length, over all. The length of the case neck does not affect this. A .30-06 round loaded to 3.340" over all length is 3.340" no matter if the case is 2.494" or 2.484" long. The ogive is in the same place, relative to the base of the case, and that is what matters for keeping it out of the rifling leade.

Do keep in mind that certain loading methods and techniques which have been found to increase the accuracy of certain rifles do not increase the accuracy of every rifle. Some rifles won't notice the difference. The load that gets sub-moa groups from a benchrest bolt gun, cannot be counted on to give those same groups fired from a military semi auto, pump, or any other type. It might not even deliver that same amount of accuracy in a different benchrest bolt gun.

Every gun is different, at least a little, and while some things are general constants, there are always exceptions, most very minor, some, are ..less so. Extreme variations are rare, but they do happen.
 
"...more accuracy by trimming..." Trimming has nothing whatever to do with accuracy. Neither does case length.
The whole off-the-lands thing is a load tweaking technique and nothing more. It's not done until you have worked up the load. It is a 100% trial and error thing that is different for every rifle. And it's not absolutely necessary.
"...the case length varies..." Something is loose on your trimmer or you're not using it correctly.
"...measuring from the case head to a datum on the bullet..." That's not how the OAL is measured.
"...case headspace..." No such thing. Headspace is a rifle manufacturing tolerance only. Case do not have headspace.
"...trim every time..." Totally unnecessary. Trimming is done on an 'as required' basis only.
 
@ UncleNick

What I was saying is regardless whether you are seating from from the metplat of the bullet or the ogive datum the measurement is based on the distance to the case head. Uneven neck lengths or OAL only effect the amount of bullet gripped by the neck wall. I trim after sizing, cleaning and annealing and use the bullet ogive as my seating datum because that distance is a constant. Distance from the ogive to the metplat will vary according to the die that bullet came from
 
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I get the mid range on trim length and keep it there , I trim every time. Most of the time it's more of a clean up , not much to trim .I try to keep things exact.
 
OP: If you are not resizing, then size first, then trim. Unclenick has the data for how far. That was new to me, now I to have to rethink.

Unclenick: It would seem that you do not need headspace at all. Many shooters swear by the view that you want the bolt to close a bit hard, ie no space in the head space as it were.

While I don't like that, they are not blowing guns up and until I got my quality control down better, I would have some of those close hard as well. No blown cases.
 
I am currently using Hornady 150gr FMJ/BT with Cannelure. My brass is South Korean military brass, KA73, that I’ve fired and swaged.

Thanks for all the info but what are good resources to learn how to implement?

I am currently only doing the basics:

Deprime
Clean
Resize
Inspect
Measure & Trim

I’ve only reloaded the brass two or three times and haven’t needed to anneal yet. I haven’t bought an annealer yet.

Thanks
 
Riley
Sierra has a 150 gr HPBT match bullet no cannelure , military brass is on the thick side less volume so watch your hot loads . Had a Garand once 40 years ago , still kicking myself in the ass for letting it go .

Chris
 
The M1 Garand is an engine, purpose built to run on a certain "grade" of fuel. This is GI ammo and its equivalent factory or handloads matching the GI load specs.

Outside that range, unmodified Garands are known to have issues, and even bent op rods have been said to happen.

Stick with established loads for the Garand and it should be fine.
 
To further my learning on reloading and achieving better accuracy what should I be adding to my reloading process for my M1 Garand?

Thanks in advance for any help and info provided.
 
RileyMartin
I see you deprime first , are you wet tumbling your brass . I'm using the RCBS Precision Mic for checking case headspace ( bolt face to case shoulder datum line ) and seating your bullet from bolt face to ogive measurement. Caliber specific , easy to use and very accurate .
 
I don't do it in that order.

I de-prime, M die the neck, clean, then shoot until I have hit 5 cycles, trim and anneal.

Its a convenient thing. The de-prime has lube on the cases, so I do the M die and that adds stuff to the neck and I get it all cleaned out before I anneal (as much as tumbling does, liquid cleans the inside as well, less smoke, cleaner anneal but I don't care for the time consuming process nor the need to handle liquids into the kitchen and back.

I don't bother to check for the trim (random samples) I just automatically trim and trim them all.

Some grow more than others, they all get set back to the baseline. I may give em a bit extra per Unclenick though its a good reminder as about 5 shootings has some of them up to the max.
 
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