Trimming to chamber length

[scyzer]

Hi all,

I'm absolutely green to reloading, hence, I've been trying to read up as much as I can (so as not to do something catastrophic).

I had a quick question about case trimming that I wasn't able to find a conclusive answer to.

I've bought some new .223 brass that I've full length sized to -0.002" headspace, checked a few samples for chambering issues, uniformed the primer pockets and deburred the flash holes.

As I moved onto case trimming, I've discovered (through the use of a Sinclair gauge) that my factory chamber is significantly longer than the resized brass (1.794" chamber vs 1.755" cartridge length on average).

Now, I've read a bit of conflicting advice that states that I should either:

- Not trim at all until I get closer to -0.010" from chamber length (which I'm assuming is unlikely to ever happen within case life), in order to start bridging the gap and prevent carbon ring build up

- Trim all to a reasonable minimum case length (out of the batch of brass) in order to insure consistency between rounds

- Let the brass grow but just square up the necks (which is rather difficult on my Wilson trimmer as I'll need to make individual adjustments for each case)

Any advice would be much appreciated!

Cheers,

Collin

 

[SheepDog]

Collin,
New brass is normally short in most of it's lengths compared to chambers. When you fire one of your reloads the brass will expand to fill the chamber in all directions. The shoulder will once again be moved forward robbing some brass near the base to do it. Once soft brass has expanded it gets harder. If you continue to move the shoulder back that .039" each time you size your case you will have case failure very fast. It will tear just above the base in what is called a case head separation. Although it isn't always catastrophic it has the potential to be very bad. I suggest that you reset your sizing die to just kiss the shoulder of a fired case. If you mark the case with soot from a candle flame or put a thin coat of machinist's Prussian Blue or a magic marker to color the shoulder of your case and the adjust your backed out die down until it just leaves a mark (or a clean stripe) on the shoulder. Lock it in at that position for full length sizing.
If you were to trim your cases (and yes they will grow and need to be trimmed) at the full length of your chamber and your case expanded .002 to .003" that would put your case neck into a position of pinching the bullet and making it harder to let the bullet go down the bore. It could drastically raise chamber pressures. So that is why the "trim to" length is listed as .010" under the maximum length. Now if you know and have measured the chamber length you can be safe making the cases a few thousandths of an inch shorter than your measured chamber. Just enough that you don't run the risk of pinching the neck. Some of my brass is trimmed a couple of thousandths longer than listed maximum because the chambers are that much longer than the standards. A couple of my guns have to be trimmed to under the trim to length because they are close chambers. You size and trim your cases to fit your rifle as long as you don't let someone else use them in a different gun. It is very rare to find two guns with similar chambers - that is why new brass and factory ammo is always close to the minimum size - anyone can shoot it in most any gun.

I wouldn't worry about trimming your cases until they are within .005" of your chamber length. The uneven mouth will not likely be a bid deal and the cases are likely to need trimming after 5 or so firings.

Hey! Great question! Enjoy the journey...
Paul

 

[RonAKA]

Colin, welcome to reloading. You will find there are lots of issues to deal with that are not clear cut!

At the end of the day, I don't think case length is a big factor in accuracy, unless they are too long and start to crimp the bullet when you chamber the cartridge.

The .223 Rem SAAMI spec calls for a maximum cartridge length of 1.760" and a minimum of 1.730". The minimum chamber is to be 1.772 minimum with a +.015 for tolerance. So, your 1.794 measurement seems a little suspicious as it is beyond SAAMI spec.

My thoughts would be to square up your brass which will likely take 0.001 or so off them, and then trim to 1.760" when they get there.

 

[scyzer]

Collin,
If you continue to move the shoulder back that .039" each time you size your case you will have case failure very fast. It will tear just above the base in what is called a case head separation. Although it isn't always catastrophic it has the potential to be very bad. I suggest that you reset your sizing die to just kiss the shoulder of a fired case. If you mark the case with soot from a candle flame or put a thin coat of machinist's Prussian Blue or a magic marker to color the shoulder of your case and the adjust your backed out die down until it just leaves a mark (or a clean stripe) on the shoulder. Lock it in at that position for full length sizing.

Thanks Paul! I've set the FL sizing die to set the headspace back around 0.002", based on my Wilson micrometer measurements on once fired brass that I subsequently resized.

Colin, welcome to reloading. You will find there are lots of issues to deal with that are not clear cut!

At the end of the day, I don't think case length is a big factor in accuracy, unless they are too long and start to crimp the bullet when you chamber the cartridge.

The .223 Rem SAAMI spec calls for a maximum cartridge length of 1.760" and a minimum of 1.730". The minimum chamber is to be 1.772 minimum with a +.015 for tolerance. So, your 1.794 measurement seems a little suspicious as it is beyond SAAMI spec.

My thoughts would be to square up your brass which will likely take 0.001 or so off them, and then trim to 1.760" when they get there.

Much appreciated! I've actually used three separate cartridges with the Sinclair tool and took repeated measurements as when I initially saw the 1.794", I couldn't believe it myself! All measurements came to roughly 1.793"-1.794" using my mitutoyo digital calipers. It was a factory Tikka T3X Varmint barrel if you were curious.

With regards to trimming to 1.760" (when it gets there), I think that might be the best approach as I doubt I'll ever bridge the 35 thou gap enough and don't want to end up with horribly disparate case lengths in the interim (if they grow at different speeds).

Now, when it comes to squaring up the brass, will I just need to fiddle with Wilson micrometer for each cartridge (to insure I take the minimum amount off)?

Thanks again for all the help and insight!

 

[ireload2]

Chamber lengths can be all over the place. I have checked 100 year old metric military chambers on Steyr Mannlichers that are a full 1mm (.040") over the length of the drawing for the cartridge. For the Dutch 6.5X53R case the specification usually quoted is 2.110. If you find an original Dutch drawing the number converts to 2.112. However I have 4 chambers that measure 2.150.
If I form brass I will make it to the exact length of the chamber. When it is fired it will get shorter. When it is FL sized it will get longer and I will normally trim it .005 shorter than the chamber. If it is neck sized I will trim it only about .002 short.
For cases that start off short I like them to be square but I let them grow until they are almost chamber length. That helps avoid a lot of work doing worthless trimming. If the cases get ragged or out of square I will trim a minimal amount. If it is for ammo that has to be crimped then I make all the cases a standard length that works well with the crimping die.
If your cases do not fire form fully on the first shot they may change lengths a little with the second and third shots. So as long as the case is not too long don't get in a big hurry to trim unless they are uneven and out of square. I spend a lot of time on my brass but I try to avoid trimming if I can. However you cannot get careless load an over length case in some rifles or you might raise the pressures due to a constricted neck.
The 6.5 Jap Arisaka chamber has no step at the end of the case mouth. It only has a long tapering funnel to the origin of the rifling. It would be possible to wedge a long case into that kind of chamber.

 

[Richard Jones]

I cannot remember ever encountering a barrel that didn't have a longer-than-SAAMI neck dimension. Factory, custom, doesn't matter, they've all been long. Not saying they don't exist.

I used to worry about such things and would trim every firing back to SAAMI spec, if there was a spec, but no more. For my usage, the imperceptible difference in neck tension is well, imperceptible. I get the safety factor and do trim if necessary, but it ain't very often.........

Squaring up the case mouth is maybe an added benefit to trimming, but even that, for my use, is not noticeable on target. If it's really noticeable, then sure, I'll fix it. Maybe a BR guy can chime in here.......

 

[Wjesswheel]

Colin, welcome to reloading. You will find there are lots of issues to deal with that are not clear cut!

At the end of the day, I don't think case length is a big factor in accuracy, unless they are too long and start to crimp the bullet when you chamber the cartridge.

The .223 Rem SAAMI spec calls for a maximum cartridge length of 1.760" and a minimum of 1.730". The minimum chamber is to be 1.772 minimum with a +.015 for tolerance. So, your 1.794 measurement seems a little suspicious as it is beyond SAAMI spec.

My thoughts would be to square up your brass which will likely take 0.001 or so off them, and then trim to 1.760" when they get there.

Iam wondering about that crimp your talking about, was running my case length at max salami 2.015 to protect my throat. Kinda of a newbie here and was testing loads as I got to my max powder load of 45.0 grains of varget then started getting casesthat look like this, the one on the right. No other pressure signs other then the damage on the case mouth and huge groupsand significantly more recoil. Was trying to find that magical upper node everyone talks about. Was trimming 2.015 on 308 ( the 45.0 load)and they were growing to 2.019 to 2.020. Was wondering if the case on the right is from the pinching you are talking about. My pet load of 42.6 is on the left trimmed at 2.015 it only grows 002. It's a savage ftr.

 

[RonAKA]

Iam wondering about that crimp your talking about, was running my case length at max salami 2.015 to protect my throat.

I have not experienced it, but it is reported that a case which is too long will increase pressure. I presume the thinking is that the case runs out of room in the neck and gets crimped into the bullet.

 

[BillPa]

I am wondering about that crimp your talking about

A chamber cast of a 25-06 chamber and a stick of brass

They're not perfectly aligned but you can see where the end of the case would be in relationship to the neck portion of the chamber. If the case(neck) is too long it would try to enter the smaller diameter of the freebore portion of the chamber and tend to crimp the neck on the bullet. The problem, when fired the neck wouldn't be able to expand to release a bullet sending pressures skyward.

My advice, stick to the published min-max trim lengths unless you have the means to "accurately" measure it.
Bill

 

[savagedasher]

I trim mine .005 shorter then reamer print .
I do the cases every time I anneal .
My trimmer has a 3 way cutter .
Larry

 

[Wjesswheel]

A chamber cast of a 25-06 chamber and a stick of brass

They're not perfectly aligned but you can see where the end of the case would be in relationship to the neck portion of the chamber. If the case(neck) is too long it would try to enter the smaller diameter of the freebore portion of the chamber and tend to crimp the neck on the bullet. The problem, when fired the neck wouldn't be able to expand to release a bullet sending pressures skyward.

My advice, stick to the published min-max trim lengths unless you have the means to "accurately" measure it.
Bill

A chamber cast of a 25-06 chamber and a stick of brass

They're not perfectly aligned but you can see where the end of the case would be in relationship to the neck portion of the chamber. If the case(neck) is too long it would try to enter the smaller diameter of the freebore portion of the chamber and tend to crimp the neck on the bullet. The problem, when fired the neck wouldn't be able to expand to release a bullet sending pressures skyward.

My advice, stick to the published min-max trim lengths unless you have the means to "accurately" measure it.
Bill

I just checked my hornady book your correct 2.010 is max trim length. I made a cheat sheet or load card up that I have on my loading bench where I have written 2.005 to 2.015 for trim length. I did start trimming to 2.005 after I saw the pinched cartridge! And have been for awhile.I can measure them accurately, just made the mistake when I copied it over to the load card. I shoot pretty mild loads, try to be as thorough as possible. Thankful nothing catastrophic happened. Thanks for the help.

 

[tenring]

Just remember, brass trimmed short of the chamber length will encourage a carbon ring, which is difficult to remove. I try to keep mine .005" short of the reamer diagram length.

 

[savagedasher]

Why would someone let the carbon ring to happen in the first place ?
Larry

 

[500Stroker]

I trim mine .005 shorter then reamer print .
I do the cases every time I anneal .
My trimmer has a 3 way cutter .
Larry

Larry, just curious, what brand 3 way trimmer do you use?
Sorry to get off topic, but inquiring minds want to know.
Thanks

 

[savagedasher]

Larry, just curious, what brand 3 way trimmer do you use?
Sorry to get off topic, but inquiring minds wont to know.
Thanks

Rcbs but I had a tool grind shop change the angle for the inside of the neck . Larry

 

[ireload2]

The reamer drawing is a piece of paper. It is not necessarily what is on your reamer or your chamber.
The only real item your case touches if the chamber of your barrel.

I trim mine .005 shorter then reamer print .
I do the cases every time I anneal .
My trimmer has a 3 way cutter .
Larry

 

[savagedasher]

The reamer drawing is a piece of paper. It is not necessarily what is on your reamer or your chamber.
The only real item your case touches if the chamber of your barrel.

It's the print my reamer was made to . Every thing else does haven checked correct . My dummy chamber is correct .
From what I have seen in the dummy chamber it look fine . Thank go letting me know . Larry

 

[223Randy]

The thing that scares me here is, YOU are "Green to reloading" and if i read this correctly, you measured your chamber length with calipers and got 1.794" and you are thinking of using brass longer then 1.760" which might work, IF the chamber is actually 1.794. I would suggest that you make Darn sure of your measurements before going over 1.760" long.

Just my $0.02
Randy

 

[Zero333]

I let it grow to within 0.015".

I have Winchester 308win brass that's on it's 25th reloading and have not lost a single piece and had to trim it 3 times thus far.

I anneal Winchester brass ever 5th or 6th loading. Lapua brass every 3rd or 4th.

 

[scyzer]

The thing that scares me here is, YOU are "Green to reloading" and if i read this correctly, you measured your chamber length with calipers and got 1.794" and you are thinking of using brass longer then 1.760" which might work, IF the chamber is actually 1.794. I would suggest that you make Darn sure of your measurements before going over 1.760" long.

Just my $0.02
Randy

Hi mate. Appreciate the concern. Again my procedure to get the chamber length was:

1) Get 3 once fired cartridges from my current rifle

2) Deprime, resize to -0.002" headspace

3) Trim down the necks to significantly under SAAMI minimums

4) Insert the Sinclair chamber length gauge (

) and seat the gauge at a rather high level

5) Insert the brass w/gauge into my chamber and close the bolt

6) Carefully remove and measure

7) Repeat with multiple measurements and different brass (removing and reseating the gauge each time)

Let me know what else I could do to be sure of my chamber length.