I know this has been discussed hundreds of times I just want to get everyone's opinion . I been reloading awhile and been just reloading to Sammi specs. Recently I been reading a lot about more things to do to get better accuracy. I just ordered a oal gauge and a comparator to try and get closer to the lands and measure the ogive. My question is how consistent does the trim length need to be? Most of my brass is 1.752 to 1.756. I have some brass that is 1.745 to 1.749 but that is separate. Will the difference in thousands affect the accuracy or bullet seating? Thanks
case trim length
- Thread starter Aceroc
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Do you have a multi-thousand dollar custom rifle? Do you shoot at over 600 yards? A no to either question means: it just doesn't matter.
At some point you will have to trim the cases, as bottleneck cases to grow (unless you have the shoulder and case head in tight contact with the chamber and breech), so you can trim them all fairly exactly with any good trimmer.
Case length does not effect bullet seating, as that is determined by the distance from the seating stem to the shell plate. You may find a few thousandths difference, based on variations in pressure you use on the press handle and any variations between the seating stem and the bullet (the better the match between the two, the better the consistency and less run-out).
At some point you will have to trim the cases, as bottleneck cases to grow (unless you have the shoulder and case head in tight contact with the chamber and breech), so you can trim them all fairly exactly with any good trimmer.
Case length does not effect bullet seating, as that is determined by the distance from the seating stem to the shell plate. You may find a few thousandths difference, based on variations in pressure you use on the press handle and any variations between the seating stem and the bullet (the better the match between the two, the better the consistency and less run-out).
345 DeSoto
Member
What caliber are you loading for?
stubbicatt
Member
My $.02
Trim length can affect the buildup of a carbon ring at the end of the chamber just before the leade portion of the barrel. This carbon ring can constrict passage of the bullet into the rifling both affecting accuracy and creating a pressure problem. First order of business is removing the carbon buildup (if it exists), and then trimming the case necks to fit your chamber.
In order to determine trim length for your chamber, Sinclair sells little plugs that can help you. To use the little plugs, cut a case neck on a sacrificial case and chamber the case with the plug seated in it. You now know your chamber neck length dimension.
The trim to length, by my way of seeing it, is the chamber length determined by the Sinclair plug, minus .003" to .005"
This will prevent future formation of that carbon ring which is the goal of this exercise.
Hope this helps a little bit.
Trim length can affect the buildup of a carbon ring at the end of the chamber just before the leade portion of the barrel. This carbon ring can constrict passage of the bullet into the rifling both affecting accuracy and creating a pressure problem. First order of business is removing the carbon buildup (if it exists), and then trimming the case necks to fit your chamber.
In order to determine trim length for your chamber, Sinclair sells little plugs that can help you. To use the little plugs, cut a case neck on a sacrificial case and chamber the case with the plug seated in it. You now know your chamber neck length dimension.
The trim to length, by my way of seeing it, is the chamber length determined by the Sinclair plug, minus .003" to .005"
This will prevent future formation of that carbon ring which is the goal of this exercise.
Hope this helps a little bit.
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243winxb
Member
presicion target rifles
I keep my 243 win brass at SAAMI maximum for the target rifle. This may require trimming about every 2 or 3 loadings when it goes a few thousands over. I have measured the chamber length and it showed i have a "safety zone" that will allow a slightly longer maximum trim length. Neck tension/bullet pull would be different between short and long trim lengths. Trying to reach the rifling by seating long is not always a good thing with a factory rifle. Start with the bullets base, full diameter, at the neck/shoulder junction. Adjust OAL to fit chamber and magazine.
spitballer
Member
Presumably this is for a .223. I simply trim my cases to 1.75" when they get to 1.76". Just how much effect trim length has on accuracy is open to debate; cases that are trimmed shorter could conceivably allow more blow-by if the bullet is some distance off the lands. Slop in this area can be reduced by ordering an undersized neck with your next barrel change, but you'll have to keep a close eye on brass thickness if you go this route.
moxie
Member
They don't all need to be the same, and if you reload and shoot a lot they won't be.
Just measure each case after sizing. If they are longer than 1.76, as noted above, trim to 1.75. If shorter just leave them alone. They are good too.
Just measure each case after sizing. If they are longer than 1.76, as noted above, trim to 1.75. If shorter just leave them alone. They are good too.
Sunray
Member
The key to consistently good ammo is consistency in all the bits. As daft as that sounds. Trimming the cases so they're all the same is the easiest thing to do. However, as mentioned, if it's for a hunting rifle, it's not going to make a whole lot of difference.
I follow Moxie's methods. Trim when too long after resized and decapped. Leave alone when in that typical 0.010 window. Saves a lot of trimming by the way as I can measure with calipers and make a trim and no trim pile much faster than I can trim everything. Use this on all my rifles, all are hunting rifles except for one, so I don't bother going all snipercentral on my brass prep as I have not seen it make much difference when I tried.
rskent
Member
I think it's faster to just trim them all. Assuming your trimmer is already set up. For me running them through the trimmer takes less time than measuring them.
I check the first few trimmed cases to check the setup. After that I just trim them. If the cutter cuts them they needed trimming. If the cutter doesn't cut them
they didn't need trimming. Either way, there done.
I check the first few trimmed cases to check the setup. After that I just trim them. If the cutter cuts them they needed trimming. If the cutter doesn't cut them
they didn't need trimming. Either way, there done.
FROGO207
Member
The only advantage to trimming them all to a specific length is realized IF you are going to crimp the bullets in. Then there is more consistency in the bullet pull on release. Nothing I own will require removal of that carbon ring to improve accuracy either. 
I am a bit lazy at times and if I pick up a piece of brass rather than measure it then trim it is easier to just trim them all with the Lee length trimmer chucked into a cheap drill press. YMMV
I am a bit lazy at times and if I pick up a piece of brass rather than measure it then trim it is easier to just trim them all with the Lee length trimmer chucked into a cheap drill press. YMMV
FROGO207
Member
Double post sorry.
Yetiman
Member
Stubbicat said:
My $.02
Trim length can affect the buildup of a carbon ring at the end of the chamber just before the leade portion of the barrel. This carbon ring can constrict passage of the bullet into the rifling both affecting accuracy and creating a pressure problem. First order of business is removing the carbon buildup (if it exists), and then trimming the case necks to fit your chamber.
In order to determine trim length for your chamber, Sinclair sells little plugs that can help you. To use the little plugs, cut a case neck on a sacrificial case and chamber the case with the plug seated in it. You now know your chamber neck length dimension.
The trim to length, by my way of seeing it, is the chamber length determined by the Sinclair plug, minus .003" to .005"
This will prevent future formation of that carbon ring which is the goal of this exercise.
Hope this helps a little bit.
This is exactly what I use and do. I don't think you will see a noticeable difference in accuracy for your use, but it is the best way to prevent carbon build up and to prevent chamber deterioration that can come from always using short brass.
My $.02
Trim length can affect the buildup of a carbon ring at the end of the chamber just before the leade portion of the barrel. This carbon ring can constrict passage of the bullet into the rifling both affecting accuracy and creating a pressure problem. First order of business is removing the carbon buildup (if it exists), and then trimming the case necks to fit your chamber.
In order to determine trim length for your chamber, Sinclair sells little plugs that can help you. To use the little plugs, cut a case neck on a sacrificial case and chamber the case with the plug seated in it. You now know your chamber neck length dimension.
The trim to length, by my way of seeing it, is the chamber length determined by the Sinclair plug, minus .003" to .005"
This will prevent future formation of that carbon ring which is the goal of this exercise.
Hope this helps a little bit.
This is exactly what I use and do. I don't think you will see a noticeable difference in accuracy for your use, but it is the best way to prevent carbon build up and to prevent chamber deterioration that can come from always using short brass.
spitballer
Member
There doesn't seem to be much argument about consistency being the key to accuracy, and I tend to sweat details like this, too. My main concern is cases that are smooshed out so long that they start curling up against the bottom of the bore and cause pressure spikes. I first noticed this several years ago: I couldn't figure out why my nice clean chamfers were curled up after firing until I measured OAL of the cases and realized that they needed trimming. I've always been a bolt fan and I don't know a lot about autoloaders, but I suspect that trim length is very important for autoloaders because it determines, in part, where the crimp is going to be. I may be speculating here, but I suspect that understanding and mastering crimps is going to greatly contribute to the accuracy of an autoloader if this is what you're using. Others may know more about this.
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