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The question of why trim carbine cases sometimes arises among shooters who reload. It usually goes like: this is just the first reloading, it doesn’t matter; they don’t stretch that much, gee, no, I don’t own a micrometer; or, oh, they are good (substitute your brand) cases that don’t stretch.
I’d be the first to agree trimming is a lot of bother. But as to necessity, it is necessary.
A friend recently gave me a .30 cal green can of once fired range pickup .30 Carbine brass that totaled about 900 cases. They had clearly been fired from 10 or more unknown carbines. They were headstamped WW, RA4, CBC, LC67-72, PS 76, PSD XX, S&B, RA43-53, PMC, PA53, WRA53, LC54, RP, and a couple dozen LC52. The LC52 had 3 different fonts all of which I pitched since I don’t know one Chinese corrosive from Lake City for sure. All in all, factory once fired brass of various makes.
Knowing that factory ammo hovers around 1.280”, I measured a random batch of the fired cases. Fired, they both seemed to shorten and to lengthen ranging from 1.275” to 1.285” in the can. Didn’t seem too bad for length so I decided to experiment.
1) All cases were lubricated and full length resized with a carbide die set. Measuring some as I went along, the FLR process would take a case of 1.275” and make it into 1.292” length in one check. Another case check had a 1.285” case turn into a 1.294” case by FLR. Way long.
2) All cases were mouth expanded just enough to start a Remington FMJRN 110 bullet and primed in the process. EVERY single case was eyeballed to make sure the primers were even or under the head. This bullet ready case length is what matters after FLR, expanding, and priming.
3) At this point, the non-trimmers would say the cases are ready for powder and a bullet.
4) I pulled out and measured the length of random 20 cases. They measured:
75% of the cases exceeded the maximum allowable case length of 1.290”. 100% exceeded the sometimes given trim to length of 1.285”. 100% exceeded the factory range of 1.280” for new ammo. 100% exceeded my 1.280-1.282” suggestion to match factory ammo.
Three of the 20 would not have fit into any chamber within the normal headspace range. The hammer would have dropped on an unlocked bolt on those. Two of them were a jam fit into a field reject chamber.
So that’s why I suggest trimming every reloading, even new cases and even the special favorites some folks use.
Thank you Steve. I have been telling my friend who got me into reloading that .30 carbine cases should be trimmed EVERY time they are reloaded, but he insists they don't. If you don't mind, i am going to print your write-up and let him read it. Hopefully, he will see the light and start trimming. Again, thank you.
Just another old man's opinion and comparing methods with you. Not a flame in any way or manner.
My once fired cases are always trimmed to 1.286" after resizing and expanding. That way I am starting with cases of a uniform length. After the first loading all cartridges are boxed, labeled and kept segregated for the rest of their life. That way I know how many time a case has been loaded.
I have 50 LC54 cases that I just loaded for the 5th time. Of those 50 less than 10 were a snug fit in my calipers set at 1.288". This, of course, is after resizing and expanding. So, only .002" stretch after 5 resizings. I'm sure if it was mixed brass the stretching would have varied more.
I just purchased a number of R-P once fired cases so it will be interesting to see what I find. I'm sure they are not all of the same lot.
I measure before priming. If the case needs trimming how can you do this if it's primed? The fact being that if your primer isn't at least flush, preferably slightly below flush, you're wrong already. If you had a high primer then somehow trimmed to 1.280" what would you have when the bolt face finished seating the primer? Hopefully, just excessive headspace and not a slam fire.
I would think that any case under the max. length of 1.290", after resizing and expanding, would be ok to load. I'd suggest resizing, expanding then checking that case length. If they do not exceed 1.290" they should be good to go.
I also feel that a variation of .010" between trim and max. case length is too much for a cartridge that headspaces on it's case mouth. A 1.280" case in a chamber that specs just under "Field" seems awfully short. That's why I use the Lyman 1.286" data.
And yes, I too have found factory cases considerably shorter than 1.286".
One thing that I have noticed is the variation of case wall thickness, even in brass of the same manufacturer and lot. This can be felt when expanding the case mouth and also when seating the bullet. However, I have not found this to be critical, especially when considering the accuracy potential of the M1 Carbine.
BTW the Chinese LC52 cases are in fact corrosive but you can easily sort them out as they are all Berdan primed.
In honor of my father, Howard C. Ricks. Corporal, Co. E, 2nd Battalion, 20th Marine Engineers, 4th Marine Division. Later renamed Co. B, 4th Pioneer Battalion after Marianna Operation. Service dates February 1943 to October 31, 1945, Combat action: Roi-Namur, Saipan, Tinian and Iwo Jima. His rifle SA 893999 met "Captain Crunch". http://wwiimemorial.com/Registry/pla...oreeID=1841138
Without retyping over and over, my thoughts are in bold in the right spot.
I trim to 1.286" per my old Lyman manual.That is the longest of the various recommended trim to lengths and the only manual that does. Factory unfired ammo runs 1.275-6-7-8-9-1.280-1-2" and rarely more. Other more common trim to lengths are 1.280" and 1.285". The whole issue is cases short enough to allow the bolt to close unimpeded. Factory ammo is usually in that range. The full length resizing process makes the cases way too long. I want nothing interferring with my bolt turning locked. Trimming back into the factory range of 1.280-1.282" is just a couple more turns of the Forester crank. I like that length since it was good enough for the factories.
Let me elaborate on that a little more.
Just another old man's opinion and comparing methods with you. Not a flame in any way or manner.
My once fired cases are always trimmed to 1.286" after resizing and expanding. That way I am starting with cases of a uniform length. After the first loading all cartridges are boxed, labeled and kept segregated for the rest of their life. That way I know how many time a case has been loaded.I have found initial uniformity useless when cases are (A) fired in several carbines and (B) loaded in large batches of mixed cases. If you keep cases separated by just one carbine, it might, just might, make for uniformity, but I doubt that. My batches of 500 cases, 860 in this instance, will be batch loaded, color coded on the head with a magic marker, and shot until the rims are useless or they are lost in the grass etc. The rims are chewed up and the cases thrown away before they ever wear out the body. So I really don't care how many times they are reloaded. I go by case condition. Using a standard load, I already know what the load is because it is a carbine case. Remington 110 FMJ, any small rifle primer, any case, and 15.0 grains of WW296 with a red head. This batch of 860 will get a sky blue head and 14.5 grains WW296. Red-sky blue, that's all I need to know.
I have 50 LC54 cases that I just loaded for the 5th time. Of those 50 less than 10 were a snug fit in my calipers set at 1.288". This, of course, is after resizing and expanding. So, only .002" stretch after 5 resizings. I'm sure if it was mixed brass the stretching would have varied more.I would go crazy keeping track of 50 cases. 500 is a better size batch. Me, kids, and a spouse might burn 300 on a fun summer afternoon. Sorting them by red or sky blue is enough bother. That is one issue. I consider 1.288" way too long to be used in this or that or another carbine at random without knowing their headspace is on the long side. When a carbine if filthy dirty and full of crud, I don't want long cases. Short ones insure function.
I just purchased a number of R-P once fired cases so it will be interesting to see what I find. I'm sure they are not all of the same lot.RP brass is some of the best brass there is. They have tended to not stretch as much as WW or PS or even LC brass. They don't hold up any better or worse, just don't seem to stretch as much. They are also, in years past, shorter from the factory than other brands.
I measure before priming. If the case needs trimming how can you do this if it's primed? The fact being that if your primer isn't at least flush, preferably slightly below flush, you're wrong already. If you had a high primer then somehow trimmed to 1.280" what would you have when the bolt face finished seating the primer? Hopefully, just excessive headspace and not a slam fire.You lost me on this one. I expand a case, prime it as it pulls out of the die, and look at EVERY case against a good overhead light to make sure by both feel seating the primer and by vision with the Mk.1 Mod.0 eyeball that the primers are seated under flush or at worst confirmed with a looking glass to be no less than flush. I do not do high primers. The Forester trimmer doesn't care if a case is primed or not. The head locks into the collet, the pilot goes up the case mouth, and the cutter cuts until the set stop bottoms out on the crank shaft.
I would think that any case under the max. length of 1.290", after resizing and expanding, would be ok to load. I'd suggest resizing, expanding then checking that case length. If they do not exceed 1.290" they should be good to go.You may think that. I do not think that. I do not agree at all with that idea. I would not even consider using cases that exceed 1.285" and trim mine to always be in the 1.280-1.282" range which again is the upper end of the factory lengths of good quality ammo measured over the years. Maximum cases in a carbine are not a good idea. Feel free to re-read the sticky at the top. Carbines are a minimally functional piece of machinery that need every bit of help to operate, i.e., close the bolt before dropping the hammer. The number one cause of bolts not turning shut are long cases and dirty guns from firing. Keeping the cases at factory new length is a good start to making sure the things actually work.
I also feel that a variation of .010" between trim and max. case length is too much for a cartridge that headspaces on it's case mouth. A 1.280" case in a chamber that specs just under "Field" seems awfully short. That's why I use the Lyman 1.286" data.And the carbine you shoot swallows a field gauge? Or almost swallows a field gauge? Or is that rare unused one that barely closes on a 1.291" GO gauge and is tighter than a knats posterior? Or do you know? Matching factory ammo, LC USGI for one, causes no known problems with a carbine. Long ammo does. Long ammo in a worn to death long headspaced carbine may be a good idea. Long ammo in a short carbine is a problem waiting to happen. Factory standard ammo gets trapped under the extractor in any carbine short of FIELD REJECT and is held there for a good primer strike. That is adequate.
And yes, I too have found factory cases considerably shorter than 1.286".Boxes and cases of boxes have been more in the 1.280" range noted repeatedly. 1.286" would be a really long factory round.
One thing that I have noticed is the variation of case wall thickness, even in brass of the same manufacturer and lot. This can be felt when expanding the case mouth and also when seating the bullet. However, I have not found this to be critical, especially when considering the accuracy potential of the M1 Carbine.OK.
BTW the Chinese LC52 cases are in fact corrosive but you can easily sort them out as they are all Berdan primed.OK.
Let me know your thoughts. Done.
Added: My only interest is safety. Factory length cases are safer than longer cases as a generality. I make ammo for any safely headspaced carbine. And as close to factory length standards as I can make it.
Last edited by .Steve.; 02-28-2010, 07:56 AM.
Reason: 12.282" corrected into 1.282" (a 12" carbine case would be a doozie.)
I do not disagree with anything already said. It is more work than I feel is necessary but I am still learning about 30 Carbine. Case trimming is a necessary evil, but it is my least favorite reloading task.
I measure every case after resizing and expanding. Currently, those over 1.288" get trimmed. Less than 1.288" do not get trimmed. Eventually, I'll machine a fixed gauge to measure this but currently I use a caliper. I use a Lee trimmer and if I remember correctly it trims to around 1.282". When I make my gauge, I may make it less than 1.288".
I find I have to trim virtually all once fired factory cases. The percentage of reloaded cases requiring trimming is much lower than the once fired factory cases. Of course some of the cases requiring trimming after the second or third firing may have been on the longer side before and finally stretched over my limit.
I have not reloaded new cases yet so no info on their length and changes in length when fire/resized. I do have 500 new cases on hand but have enough other cases in service that I do not have to tap into the new cases. I will size measure, and trim if necessary all new cases used.
Segregating cases by number of reloadings is a good idea but I have elected to not do it for the 30 carbine. I have not seen any issues with reloading 30 carbine that tell me that case life is short and the number of reloadings needs tracking. But that may change in the future.
I do keep track of the number of reloadings for my AR-15 rounds (17 Rem, 204 Ruger and 223 Rem). I begin to have issues with cases after 4 or 5 loadings so I need to know when they are reaching the end of their life. With 17 Rem and 223 Rem I can move the cases to bolt rifles, neck size the cases and they last a long time after being retired from AR-15 use.
There is nothing wrong with erring on the safe side.
As you say, once fired factory cases almost universally need trimming. And frequently a good bit. In that batch of 860 cases, the RP needed the least trimming, the S&B and CBC the most, LC about average consistently, and the WW and PS/PSD cases were all over the place for length but most were near the LC for an average.
After the first factory firing, trimming, and the first reloaded firing, the length seems to settle down and stretch less due to work hardening or some other metal idea. Then trimming is just a way to check, square the case mouth, and make sure none are too long. You may check yours with a micrometer, but I do it with the trimmer. If it cuts the case then the case was long. If it doesn't cut, the case was not too long. There is much less cutting of metal after the first trimming. Often the cases are unsquare and the trimmer just cylinders them evenly. Much less work. This is also why case life isn't much of an issue. The metal stops moving fairly quickly. Loss rate and rim damage takes over. If I loaded 50 cases 20 times a year, I might notice, but loading two sets of 500 twice a year, they last longer in time.
An oddity I noticed was that the CBC cases had three small stakes to crimp in the primers. None of the other rounds had a crimp except one WRA53 case. All the rest were just primer pockets.
If a reloader knows he has a worn long headspace carbine and only shoots that one carbine with his reloads, "longer" trim to lengths make some sense. In reverse, if a reloader knows he has a tight headspaced carbine, "shorter" trim to lengths make sense. But if you don't know what carbine your ammo will go into, factory lengths for a trim to make sense to me. The area between 1.280" and 1.282" is not too short and not too long.
Safety is the only criteria. If a carbine always functions 100%, that is a good sign. If a carbine "occasionally" fails to lock its bolt down and run the slide over the extension lug, that is a VERY bad sign.
My experience has been that case length is the number one predictor of function in a carbine once the machinery has good springs and proper parts.
The one puzzle I have seen with 14.5 grain WW296 and 110 FMJRN loads is a shortening of cases. The expansion of the case cylinder to fill the chamber shortens the cases and the pressure is at a point that does not stretch them from firing. I don't like them to get under 1.280" either.
I size all my cases then measure them. I separate the "need to be" trimmed and "no need to be" trimmed. It seems to save some time rather than try to trim them all. I trim to 1.284".
I do not keep track of times fired for this caliber, all others yes.
I ran accross a half box of LC69 .30 carbine ammo this afternoon. Just for fun, I used my caliper, the [__]_______ looking thing, which I usually call a micrometer, which it isn't.
Measuring from case mouth to the head as close as possible before the head end falls off the side of the beveled edge of the rim was interesting.
The 25 LC69 cases ran from 1.280" to 1.286" with most clustering in the 1.283-4" range. Longer than I expected.
A similiar half box of PS76 ran from 1.275" to 1.285" with most clustering at 1.279-80-81".
That is similiar to LC72 cases I've checked in the past.
It is no wonder the fired cases come out with such a range of lengths. They start out all over the place.
RP commercial clusters in the 1.279-80-81" range from past checks, but much closer toleranced, long to short.
I'm not so sure it means all that much, but I was not impressed with military ammo consistency of length. I do note the trend to stay towards the short end of what is allowable rather than going to the long end. I would suspect some of the PS76 is under length a bit.
I have been collecting components to begin reloading and this is amazing information. Reports like this and the first hand knowledge all together here just can't be found in a single book.
My original post was about the length of factory fired, full length resized, and then mouth expanded carbine cases. With 20 random samples from 860 factory fired cases of at least 15 brands taken from 10+ carbines, none of which were mine, and then processed:
75% of those cases exceeded maximum case length and could not be safely reloaded. Safe reloading practices required trimming prior to reloading.
After that info, there is a discussion of what trim-to length to use and when to trim. There are numerous ideas on that topic. Looking at the variability of factory unfired ammo, considering the range of case lengths noted, a reloader could probably make an arguement for any length between 1.280" and 1.285" and be matching some factory ammo length. Most of the factory unfired cases fall into a range of 1.279-1.284". I think that is a good range to match reloaded ammo to.
I do note the info about the Lee fixed trimmer making cases at 1.282". That is the same as what I am happy with in the 1.280"-1.282" range. With different factory lots clustering in the low 1.280's range, fairly close together, a trim to length between 1.280" and 1.285" will most likely be acceptable. My past experience with carbines keeps me to the shorter end of the range.
I cannot suggest that longer trim to lengths be used for screening cases and would not reload cases 1.286" or longer because I don't know whether mine will be used in a loose or in a tightly headspaced carbine.
The Lee trimmer apparently cuts cases to a fixed length. My Forester trimmer gets set with a gauge and then confirmed with the first cases trimmed in a batch. When reloading previously reloaded cases, I put them into the trimmer and crank the handle. None, a little, a lot, depending on the case, metal gets removed. I know that way that none are longer than my trim-to. It is about as easy as measuring. The trimmer does the measuring in one step. But the result is that I reload nothing longer than my trim-to.
Instead of measuring every case after resizing I just trim them all. I have my trimmer set to 1.285 per the Speer Manual #14. Measure a few after trimming just to check the trimmer. This way all brass is the same length.
I use a mixture of new commercial RP and various LC, WCC etc. I have a set of RCBS trim dies that allow a simple pass of the file to trim to length. I check case length frequently with a Starret micrometer. I rarely have to trim anything, very, very rarely. I presume that it is because I don't load to maximum. The powder is lately, WW820 or 2400. I just don't have a lot of case growth. Checking new cases before firing, they are always short and show no growth after firing. I guess the question is: does a reasonably tight headspace and modest loads result in this situation? I'm almost to the point of checking every three loads as it just isn't an issue.
The first firing, whether factory or reload, is when the most dramatic stretching occurs.
The only length that matters is the length after FLR and mouth expanding.
Just fired, just FLR, whatever, make no particular difference.
Normally the FLR die is what makes them longer. They expand the case cylinder when firing, often get shorter or longer or oval, and the FLR die compresses the cylinder and moves the mouth forward 1/100 or 2/100s.
After the first firing, change is a lot less, but not predictable. Many cases will barely stretch and some-a few- from the same batch get long.
The Lee trimmer apparently cuts cases to a fixed length. My Forester trimmer gets set with a gauge and then confirmed with the first cases trimmed in a batch. When reloading previously reloaded cases, I put them into the trimmer and crank the handle. None, a little, a lot, depending on the case, metal gets removed. I know that way that none are longer than my trim-to. It is about as easy as measuring. The trimmer does the measuring in one step. But the result is that I reload nothing longer than my trim-to.
Yes, the Lee trimmer cuts to one length. It is determined by the gauge that screws into the cutter and with a pin that passes through the flash hole and bottoms on the case stud. When it stops cutting, the pin has bottom out. Historically with Lee gauges I have for other cartridges, the variability is plus/minus about 0.001". There may be some variability from gauge to gauge for the same cartridge. I use a modified battery powered screw driver for power but a drill motor works as well.
Not a bad idea using the cutter as the case gauge. I don't because with the Lee, it takes too much time putting the case in the trimmer and then removing it--trimming is my least favorite reloading task. For most cartridges, I machine a "go-no go" gauge from 3/16" aluminum plate that is the maximum length that I want a case to be. Essentially a fixed caliper. If the case fits in the gauge, it does not get trimmed. If it does not fit, the case gets trimmed. I generally err on the short side and cases that marginally fit in the gauge get trimmed anyway. I can measure 50 cases in a New York minute and then trim only the few that need it.
If I start trimming a batch of cases and virtually all of the first 10 or so require trimming, I throw in the towel and trim the all. This occurs usually with brass that is new to me on the first reloading cycle (factory or purchased reloads).
Presently for 30 carbine I do use a caliper, but I set it to my maximum length and lock the blades in place. It then simulates my fixed length gauge. I don't physically measure each case. Eventually, I'll make a new gauge for 30 carbine.
Either way works and the best method is what your comfortable with.
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