I'm aware of the plugs from sinclair, but what are any other ways to get an accurate chamber measurement for brass trimming purposes?..other than book spec
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options for measuring chamber?
- Thread starter rw496
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Well, Sinclair does make those chamber/neck length gages, which evidently work pretty well, so those would be my first choice for you.
Me personally?
I just let my necks grow out past 2.015" (SAAMI max for the .308Win) on my Savage LE2b and then I measure the mouths after sizing and whatnot, for diameter. I'll chamber a case and then see if I'm getting any pinching at the mouth's edge. You have to be careful when measuring things, as one needs to be precise, but as long as you're not getting any pinching, you should be fine.
For example, with my LE2b, I can let the necks grow to the tune of an case length of 2.019"-2.020". I stop at 2.019" and call it a day, but that's a good deal above book maximum, is the point, however I know that I'm safe, because I've carefully measured things.
Others might not be so careful and should then stick with the Sinclair doohickeys.
Chris
The ultimate way is to take cast of the chamber (Cerasafe) and measure that but it's pretty overkill.
Personally, I don't feel a need to measure the chamber's "case length". I just set my trimmer to max length and trim according to that. I don't trim to minimum length because I like having my necks longer and I use a Forster 3-in-1 cutter to trim, chamfer, debur all at once, meaning I trim the cases every time I load.
IMHO on a 308 trimming is almost a waste of time, no one on SH can shoot the .010 difference in length between 2.005 and 2.015, but on a barrel burner cal like 243 trimming back .010 from the end of the chamber will help that tube last longer, it's not a accuracy measurement but a safety/longevity tool.
A 300WM can burn through a throat somewhat quickly, so you might want to go a few clicks below the SAAMI maximum, if you believe that it matters. I shoot a TRG-42 in 338LM and I go a few ticks past the minimum with nary a problem.
As long as you're not getting gas blow-by on your necks, or shoulders, you should be good. If you don't want to trim down to book minimums on a regular basis, then split the distance between min/max and call it a day.
Chris
I make a slice down the neck of an easy chambering, FLS'd case.
Then I cut most of the neck off.
Seat a bullet backwards into what's left of the neck.
Slip the bit of cutoff neck onto bullet.
Chamber the dummy round, the cutoff neck will be pushed down along the bullet.
Measure casehead-to-cutoff neck.
Repeat a few times until you're satisfied your measurement is consistent.
Trim brass back at least .005" shorter than your measurement.
My Savage 308 measured ~2.045"
Then I cut most of the neck off.
Seat a bullet backwards into what's left of the neck.
Slip the bit of cutoff neck onto bullet.
Chamber the dummy round, the cutoff neck will be pushed down along the bullet.
Measure casehead-to-cutoff neck.
Repeat a few times until you're satisfied your measurement is consistent.
Trim brass back at least .005" shorter than your measurement.
My Savage 308 measured ~2.045"
What is the benefit of trimming the case back to either the minimum or maximum length for your chamber? Besides being able to chamber the round of course, I am not new to reloading. Does a longer case length prevent throat wear in a magnum load? Thanks.
The main benefit is you know that it hasn't grown enough to crimp the bullet and cause an overpressure situation or a stuck case. I've never noticed a difference in accuracy after trimming neck length, but I haven't specifically tested it. Logically, it doesn't seem like it would matter much.
This is over my level of expertise, but in the sticky by Tres Mon he seemed to place importance on it and cited good bullet support and proper tension and that there could be a loss in accuracy among other things..seems like others don't think having it exact is too critical
A real simple way measure the full chamber length is to go buy one of those scratch filling crayons. They're a real hard waxy substance. Take a loaded round and make a crayon mark on the bullet extending 1/4" or so from the case mouth edge, forward. Width isn't all that important, just make sure it's as thick as, and level with the case neck.
Chamber the round and remove it. You will see a clear "ledge formed where the wax was pushed back by the second shoulder in the chamber. Measure from the case head to this "ledge" and you have the full chamber length to the second shoulder (where the freebore begins). Run a mop through the bore to make sure that any small bits of wax are removed although they won't damage anything.
Chamber the round and remove it. You will see a clear "ledge formed where the wax was pushed back by the second shoulder in the chamber. Measure from the case head to this "ledge" and you have the full chamber length to the second shoulder (where the freebore begins). Run a mop through the bore to make sure that any small bits of wax are removed although they won't damage anything.
Rcbs precision mic, or hornady lock and load oal gauges( must use hornady modified case, seperate tool).
Im new to reloading so correct me if I'm wrong. I believe the precision mic will help preserve brass life by not overworking your brass. You can take fire formed brass from your weapon and measure it with precision mic compared to sammi specs. Then use the precision mic to help dial your resizing die slightly below fire form specs so your cases arent to short( making the brass have to work harder to fire formed specs). If you trim your cases on the minimum side of saami specs your brass has to stretch to fire formed size. Keeping the stretching to a minimum preserves case life from my understanding. Once again I'm new to the reloading world and i was just reading over the rcbs precision mic and hornady oal gauges.
The precision mic will help identify headspace and bullet seating depth to .001 accuracy from there own description. Read all instructions with the tool to fully understand what I tried to explain.
Im new to reloading so correct me if I'm wrong. I believe the precision mic will help preserve brass life by not overworking your brass. You can take fire formed brass from your weapon and measure it with precision mic compared to sammi specs. Then use the precision mic to help dial your resizing die slightly below fire form specs so your cases arent to short( making the brass have to work harder to fire formed specs). If you trim your cases on the minimum side of saami specs your brass has to stretch to fire formed size. Keeping the stretching to a minimum preserves case life from my understanding. Once again I'm new to the reloading world and i was just reading over the rcbs precision mic and hornady oal gauges.
The precision mic will help identify headspace and bullet seating depth to .001 accuracy from there own description. Read all instructions with the tool to fully understand what I tried to explain.
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You can do pretty much the same thing that the RCBS mic does with a "Sharpie" and some "Kentucky Windage" with your die. Mark up the shoulder of a fired case, back off the sizing die, then start sizing and adjusting the die down a small amount after each time. Look carefully for the first signs of contact with the sharpie mark. Once you see this, if you're real clever, you can add a series of witness marks to the top of the die and calculate how much the die will move down as you move it one increment down. Hint: A full turn of a "14 thread pitch" will move in .0714" Put a small round disk under the depriming rod lock nut that you've divided up with 20 or so equally spaced marks on it's perimiter and you'll move the die in .0035" for each increment.
Once you've set your "bump" just lock the die down and don't look back. If you want a very inexpensive "tool" to measure .308 "headspace" on a cartridge, just use a 40 S&W case. It's so close to the .400" datum dimension that you can use it very effectively for "bumping" shoulders on .308 cases.
If brass life is paramount, don't worry about the bump, consider annealing. That will add tons of life to your brass and almost totally eliminate neck splits.
Save the money you'll spend on the RCBS Mic (a tool which will probably just sit in the box after the first one or two uses) and spend it on something far more useful like ammo
The only *crucial* need in trimming brass is to prevent the caseneck from growing long enough that it begins leading into the freebore of the chamber. If it does, it will pinch down on the bullet, hindering the freedom of the bullet to launch forward. This can cause pretty severe pressure spikes, and can be dangerous. I suspect it would also do nothing good for accuracy.
Also, per Dave Kiff at PTG, the casemouth needs to be at least .005" shy from the end of the chamber, because pressure will stretch the case forward several .001"s during firing.
Personally, I don't believe varying neck length impacts practical accuracy. I've shot many little groups with untrimmed 1x milsurp brass (prior to buying a giraud) whose length varied from 2.010" to 2.035". I suppose that for extreme accuracy applications like benchrest, it might make a tiny difference - but for field shooting conditions, I really don't think it does.
You're dead on about the need for case mouth trimming although I'll toss in a couple of my thoughts.
I trim cases primarily to square up the case mouth. For some reason the darn things don't stretch evenly so I give them a clean-up after each shooting. Since I'm doing this with a lathe type trimmer I might as well trim for length as well as the "squaring up", chamfer, and de-burr which occurs at the same time.
Case length uniformity is necessary if you're crimping the finished rounds. If the bullet for my .223 "AR Food" has a cannelure I crimp. Irregular case lengths make for irregular crimping which can affect accuracy.
The problem with one who's starting out in reloading getting the thought that trimming cases is unnecessary can be problematic. Learn the reasons why one trims a case than then act appropriately. Shoot a "factory" case a couple times and it can get real long, real quick. Once the case has been "stretched" with a couple firings, they don't seem to grow in length as rapidly, especially if trimmed to minimum length. Most standard rifle cases will have failed (neck split, case head separation, loose primer pocket) before they grow back enough to be a problem.
Last thing, the need to trim or lack of need can vary widely from rifle to rifle. If all reamers were exactly the same for a given caliber then there would be a standard answer. As it is, they are all ground to within a range of specifications. Also, depending on amount of use, they wear and chamber dimensions vary from the first chamber to the last one created by the same reamer. Then you get into the realm of custom reamers etc. In short, there is no one answer that fits all circumstances.
Learn the "why" and it will make sense what you need to do with a specific rifle.
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