Trimming - measuring off the base or shoulder?
- Thread starter thefitter
- Start date
Alot of the shortrange benchrest shooters trim off of the shoulder.
You take a chunk of old barrel and run the reamer in just like you would do for making a barrel stub.You then flip the barrel chunk around and run a 3/8 inch drill through the bore.Put a stop collar on an end mill just like a meplat trimmer and you have an instant neck trimmer you can use at the range between relays.
Lynn
P.S. When I size down a picture I will try and post it here.
You take a chunk of old barrel and run the reamer in just like you would do for making a barrel stub.You then flip the barrel chunk around and run a 3/8 inch drill through the bore.Put a stop collar on an end mill just like a meplat trimmer and you have an instant neck trimmer you can use at the range between relays.
Lynn
P.S. When I size down a picture I will try and post it here.
Attachments
Erik Cortina
Team Lapua Brux Borden Captain
What, Tony Boyer trims off of the shoulder? Poor guy, he'll never be competitive that way! ;D
Basic fundamental when reloading? So was seating bullets to reloading book suggested COAL when I didn't know any better!
Outdoorsman said:
Basic fundamental when reloading? So was seating bullets to reloading book suggested COAL when I didn't know any better!
holstil
Silver $$ Contributor
I'm not trying to throw gas on a fire, just been doing some thinking and would like to discuss.
It seems to me that you would want to trim from the shoulder, the neck is what grows and needs trimming. The case should be sized to the chamber. The case will always be the changing factor limited by the chamber wether you resize first, after, anneal or not if you trim from the base or the shoulder. May as well have all the necks the exact same.
Possibly the biggest thing would be to fire the brass through your chamber trim or size then trim. I think that if the brass finished up within .002 or .003 that would be plenty good. I bet it works out closer than that anyway.
On the other hand, if you size then trim from the base you are trusting that the sizing step went exactly as planned to give you the correct body length. If you don't size after firing and before trimming you are trusting that all the brass moved the same when fired. In either case this would justify the shoulder as datum technique where you need either the chamber or the die to hold the body length.
My routine is to set my die so that my fired brass is just a smidge snug in my chamber. Check every piece with firing pin removed as I always have, then trim the necks.
I got me a new tool comming, I'm curious to find out any differences from my previous base as datum setup. This sounds like a case of cat skinning.
Why would anyone trim brass every time? Does your brass move that much? Maybe I'm spoiled shooting 40deg shoulders cause my brass doesn't move in 4 or 5 firings (Lapua).
Thanks for that picture and idea Lynn. I think I'll be making my next trimmers.
Jim
It seems to me that you would want to trim from the shoulder, the neck is what grows and needs trimming. The case should be sized to the chamber. The case will always be the changing factor limited by the chamber wether you resize first, after, anneal or not if you trim from the base or the shoulder. May as well have all the necks the exact same.
Possibly the biggest thing would be to fire the brass through your chamber trim or size then trim. I think that if the brass finished up within .002 or .003 that would be plenty good. I bet it works out closer than that anyway.
On the other hand, if you size then trim from the base you are trusting that the sizing step went exactly as planned to give you the correct body length. If you don't size after firing and before trimming you are trusting that all the brass moved the same when fired. In either case this would justify the shoulder as datum technique where you need either the chamber or the die to hold the body length.
My routine is to set my die so that my fired brass is just a smidge snug in my chamber. Check every piece with firing pin removed as I always have, then trim the necks.
I got me a new tool comming, I'm curious to find out any differences from my previous base as datum setup. This sounds like a case of cat skinning.
Why would anyone trim brass every time? Does your brass move that much? Maybe I'm spoiled shooting 40deg shoulders cause my brass doesn't move in 4 or 5 firings (Lapua).
Thanks for that picture and idea Lynn. I think I'll be making my next trimmers.
Jim
I get a kick out of some of the points usually brought up in discussions like this one. Everyone's looking for loads & loading procedures that contribute to lower ES & Sd numbers, but some of the theories as to what contributes to this are pretty thin IMHO.
Case in point - if consistent neck tension is an important factor in lowering ES, dosen't it follow that consistent neck length is also important? How better to get consistent neck length than by using a trimmer that indexes off the shoulder? IOW, is consistent OAL case length more important than consistent neck length? (or does either really matter?)
Case in point - if consistent neck tension is an important factor in lowering ES, dosen't it follow that consistent neck length is also important? How better to get consistent neck length than by using a trimmer that indexes off the shoulder? IOW, is consistent OAL case length more important than consistent neck length? (or does either really matter?)
6BRinNZ
It is a quick and easy method to use without any setting-up.
If you enlarge the picture the stop collar allows you to remove the end mill without changing the setting for easy cleaning out of the chips.If you look really hard you will see two set screws not just one like on a meplat trimmer.The second set screw holds the reamer in place so you can turn the entire body while holding onto the brass.
I believe Stu Harvey at Stu's Precision has been making them for years as well.He is on the guns of the week on this website but I don't know what he charges.
The posted picture in the post above is a 300 Weatherby and a 6 Grendel both made by John Crawford on this forum.He makes alot of benchrest specialty tools.
Lynn
It is a quick and easy method to use without any setting-up.
If you enlarge the picture the stop collar allows you to remove the end mill without changing the setting for easy cleaning out of the chips.If you look really hard you will see two set screws not just one like on a meplat trimmer.The second set screw holds the reamer in place so you can turn the entire body while holding onto the brass.
I believe Stu Harvey at Stu's Precision has been making them for years as well.He is on the guns of the week on this website but I don't know what he charges.
The posted picture in the post above is a 300 Weatherby and a 6 Grendel both made by John Crawford on this forum.He makes alot of benchrest specialty tools.
Lynn
lynn said:
Pull out your copy of Tony Boyer's book The Book of Rifle Accuracy and turn to Chapter 13, CASES, pages 156 & 157, the section entitled Overall Length/Trimming.
As you'll quickly see, Mr Boyer indexes off the base as depicted in the pictures he presents. One showing his case dimensions and where they're measured from and the other, a picture of his Wilson Trimmer, which is set up to trim off the base of the case.
As he mentions in the first sentence, each evening during a match, he checks the overall length of each case. The only way I know of doing that, is taking the measurement off the base, as the picture illustrates and through his own words as he warns/suggests "Watch overall case length" in the last paragraph on page 157.
Erik Cortina
Team Lapua Brux Borden Captain
"Everything from the shoulder back is correct, so the only thing left to check is the length of the neck." -The book of rifle accuracy, page 156
Like I said before, it doesn't matter where you measure from, if your base to shoulder measurement is the same, and the shoulder to case mouth is the same, then base to mouth is also the same!
At that point, it doesn't matter where you measure from.
Like I said before, it doesn't matter where you measure from, if your base to shoulder measurement is the same, and the shoulder to case mouth is the same, then base to mouth is also the same!
At that point, it doesn't matter where you measure from.
Erik Cortina said:
Erik, IF is a contention, a supposition [of an uncertain possibility]. It's like the word ASSUME. And we all know of an experience when an assumption didn't turn out as expected.
I don't measure the base to shoulder dimension of my cases to ensure they're all the same, and I don't measure my cases from the same exact point on the shoulder to the end of the mouth to ensure they're same too, [which is what the statement above implies one must do] to ensure that overall length is the same.
Two measurements would be extremely time consuming. I make one measurement, that I'm certain of, from base to mouth, and I'm sure that's why Mr. Boyer emphasized overall case length in the title of his section on cases.
When I see him at the Nationals in Midland, I'll be sure to ask him why the tool pictured above, didn't find it's way into his book with an explanation on its use.
Erik Cortina
Team Lapua Brux Borden Captain
Outdoorsman said:
It is not an assumption, if your base to shoulder is not the same, then you need to adjust your FL die properly.
I don't measure base to shoulder and then shoulder to mouth everytime!... I have things to do! ;D
I measure base to ogive when I set up the headspace on my FL sizing die, I then set up my Giraud trimmer to trim the appropriate amount, and since the Giraud headspaces off the shoulder, then that's ok. I don't actually measure from the shoulder to the case mouth, the Giraud does (headspace), I simply set the trimmer to where it trims the shortest of my cases. Then, next time I'm ready to trim, I simply anneal the case, then run it in FL die, and then stick it in the Giraud trimmer, which headspaces off the shoulder.
If I measure base to mouth they are all the same because they are all the same from base to shoulder, which is where the Giraud headspaces from. Do you understand what I mean when I say that it doesn't matter where you measure from as long as every case is the same?
A= base to shoulder (chamber headspace)
B= shoulder to mouth (Giraud headspace)
C= base to mouth
A+B = C
I use A+B because of the nature of my trimmer, you use C because that's how your trimmer works, we are simply skinning a cat different ways, dig?
holstil
Silver $$ Contributor
If you only measure from base to mouth you don't know where the shoulder is within that measurement to the base. You wouldn't know that no matter how you trim. I have to check all my cases after sized to make sure they fit in my chamber properly. I think we agree on every piece of brass not resizing the exact same, mostly due to different amount of firings. Same goes for spring back during firing.
If you are only concerned about the oal fit of the case, base to mouth, then this is a moot point. If you are one that fits the case to shoulder and regulate the neck lengths then I believe the shoulder as datum is better.
In either case the base to mouth will work out consistently the only difference is knowing where the shoulder is.
I got my wft tool last night, It works like a champ so far. I trimmed about 20 cases that had been fired sized checked in my chamber and trimmed. They all worked out to be the same within what I could read on my dial calipers.
We'll see if it continues. I believe it will, this thing is very well built and feels like quality USA made. It is just like what Lynn has pictured but with a bearing. The part or bushing that the shell is held by is press fit into the ID of the bearing and could be substituted with your choice of chambering. The cutter is an end mill that can be adjusted.
Jim
If you are only concerned about the oal fit of the case, base to mouth, then this is a moot point. If you are one that fits the case to shoulder and regulate the neck lengths then I believe the shoulder as datum is better.
In either case the base to mouth will work out consistently the only difference is knowing where the shoulder is.
I got my wft tool last night, It works like a champ so far. I trimmed about 20 cases that had been fired sized checked in my chamber and trimmed. They all worked out to be the same within what I could read on my dial calipers.
We'll see if it continues. I believe it will, this thing is very well built and feels like quality USA made. It is just like what Lynn has pictured but with a bearing. The part or bushing that the shell is held by is press fit into the ID of the bearing and could be substituted with your choice of chambering. The cutter is an end mill that can be adjusted.
Jim
http://www.youtube.com/watch?v=ZOPf5Iva-Oo
http://www.youtube.com/watch?v=7SZWvn68bRU
Here are two videos taken at the super shoot shooting clinic hosted by Jack Neary.If you watch the end of video one and the beginning of video two he talks about case preperation and how he does it.
If your mind isn't closed you will learn alot by listening to what he is actually saying.
Lynn
http://www.youtube.com/watch?v=7SZWvn68bRU
Here are two videos taken at the super shoot shooting clinic hosted by Jack Neary.If you watch the end of video one and the beginning of video two he talks about case preperation and how he does it.
If your mind isn't closed you will learn alot by listening to what he is actually saying.
Lynn
holstil
Silver $$ Contributor
Outdoorsman, thanks for sharing. Those videos are interesting.
I like the part where he is talking about trimming and that how .002 or .003 can really matter if the brass is too long. I learned to not let the brass grow to within .010 of the chamber mouth edge.
I'm going to watch the rest of them now, Jim
I like the part where he is talking about trimming and that how .002 or .003 can really matter if the brass is too long. I learned to not let the brass grow to within .010 of the chamber mouth edge.
I'm going to watch the rest of them now, Jim
Hostil
If you carefully watch then re-watch the first two videos you will hear how many times your cases need to be fired before they are all stable and uniform.
Once they are stable/uniform it doesn't matter which tool you use as they will now all do the same thing regardless of which method is used.
This is the point Erik has been trying to convey.Listen to what Jack has to say about bumping the shoulders and you'll better understand why it doesn't matter which method you use as they will all come out the same.
Lynn
If you carefully watch then re-watch the first two videos you will hear how many times your cases need to be fired before they are all stable and uniform.
Once they are stable/uniform it doesn't matter which tool you use as they will now all do the same thing regardless of which method is used.
This is the point Erik has been trying to convey.Listen to what Jack has to say about bumping the shoulders and you'll better understand why it doesn't matter which method you use as they will all come out the same.
Lynn
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