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How crucial is trimming brass to exact OAL?

Shadow_Warrior

Shadow_Warrior

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Minuteman
Jul 14, 2004
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Tulsa Ok
Ok I usually trim my Lapua .308 brass every firing to 2.005".
I just measured 10-12 newly fired cases that measure from 2.007 to 2.009".
Will this affect accuracy or should I trim to length every firing?
 
Re: How crucial is trimming brass to exact OAL?

I trim my brass once to 2.00 may trim next lot to 1.995. When it grows after firing you should be able to bump the shoulder back. Bring the lenght back to your trimmed lenght or close. I've done this over 5-6 firings and everything has been ok so far.
 
Re: How crucial is trimming brass to exact OAL?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KHOOKS</div><div class="ubbcode-body">I trim my brass once to 2.00 may trim next lot to 1.95. When it grows after firing you should be able to bump the shoulder back. Bring the lenght back to your trimmed lenght or close. I've done this over 5-6 firings and everything has been ok so far.
</div></div>

I hope you meant 1.995..... But either way if they are all the same it will make no difference what so ever.
 
Re: How crucial is trimming brass to exact OAL?

If your cases are too long, the front of the lips can "seal" the bullet in the collet on the end of the chamber, causing more pressure.
Especially dangerous in semi-auto.
 
Re: How crucial is trimming brass to exact OAL?

While everyone has their own opinion. I trim brass for my bolt rifle to fit the chamber. Loads for this rifle are all labeled and kept seperate from other rounds of the same name / designation.

I measure the chamber length then trim to -.005" The brass for my bolt gun is trimmed to 2.035" The chamber length of the brass to case mouth is 2.040" This keeps the throat from getting burned quiet so bad.

The gas gun gets trimmed to SAAMI spec.
 
Re: How crucial is trimming brass to exact OAL?

Hey Victor. Could you explain your trimming procedure a little more. What kind of bolt gun are you usting and whats the best way to measure chamber length?
 
Re: How crucial is trimming brass to exact OAL?

Here you go...

How I make a chamber length dummy round.

Use an empty case that has been fired in the chamber for which you want to check. Do not size it. Do NOT prime or put powder in it...! Use a Dremel tool ( A cut off, or grooving tool in a lathe would be a better and easier way. But not everyone has a lathe in their garage. ) and carefully use an abrasive wheel to slice off a ring about 1/3 to 1/2 way down the case neck from the mouth. (This can be varied. The ring is just a marker. But the smaller it is, the harder it is to handle.) Deburr both the case mouth and the ring you have just removed. You can either use a standard deburring tool or a piece of fine grit emery cloth wrapped around a small dowel. Do not over deburr / chamfer the original case mouth. If it's square that's a good thing. Square case mouths hold against the edge of the chamber step better. It also makes it easier to measure the length with hand tools. Just barely break the corners. Seat a long bullet (I use a 190 SMK for most 30 cal stuff) in the case that has been cut off. Then work the ring that you cut off down onto the bullet. Remember to keep the original end up. ( Mostly so it's square.) Not the end where the cut was made. Leave .100" or so space between the ring and the case. Place this round in the chamber and CLOSE the bolt to the battery position, ready to fire. If the bolt closes very easy it may not have been long enough to work. I usually have to smack the bolt handle with my hand. But not too hard. Measure the case length before you chamber it to be sure the ring is actually pushing back as it is pushed against the step in the chamber. Bingo... Measure your "perfect" max case length and you have it. I usually measure it 4 or 5 times and average it. I keep the cases about 5 or .010" shorter than the max length from the average I got. If you trim much shorter than that it will cause the throat to erode quicker from the gas as the bullet is fired.
 
Re: How crucial is trimming brass to exact OAL?

Hold on? Help me out here?
Am I hearing that if I trim 3 cases as follows: 2.015, 2.010, 2.005, and give them the exact powder charge of say 24 grs. of 4064, and an OAL (base of cartridge to tip of bullet) of 2.800; they will shoot differently?

If so, then case length is as important as OAL, to accuracy??
 
Re: How crucial is trimming brass to exact OAL?

CONSISTANCY is important. Just trim them all the same length. Or seperate the case length and shoot those in seperate groups.

The key to it all is the consistancy within the lots. If you have varying neck tension, whether by work hardened brass or longer case necks, you will have groups open up.

I'm not talking big differences in groups size. (Maybe .030 to .060" in 5 shot groups at 100 yards). But a truly competitive shooter can see small differences in his groups size.

(My benchrest roots are showing again.)

I trim to chamber length on my cases to save barrel / throat wear.
 
Re: How crucial is trimming brass to exact OAL?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Wil</div><div class="ubbcode-body">consistency is key... much to that </div></div>

Didn't I already cover this??
 
Re: How crucial is trimming brass to exact OAL?

Well Im all about making my barrel last longer so Ill definitely give this a try. Unfortunately the 47gr of varget isnt helping this situation. Ill be backing this load down anyway. They shoot great but the brass and barrel are taking a beating.
 
Re: How crucial is trimming brass to exact OAL?

thats a great idea to find the chamber size. i wondered about that myself. i am new to reloading. when i go thru brass for sorting, i measure it. at this point in my reloading process, anything over max gets trimmed to min, anything under max gets loaded. nice thing is once my trimmer is set, its pretty much set. i do check each case type that i use, but its pretty much gtg.

that said not knowing the exact specs on my chamber leaves me at a disadvantage. i hope that as long as i am below max i am ok, but i will check now and be sure. i have also heard of guys making a mold of the chamber to get specs
 
Re: How crucial is trimming brass to exact OAL?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mussman</div><div class="ubbcode-body">Ok I usually trim my Lapua .308 brass every firing to 2.005".
I just measured 10-12 newly fired cases that measure from 2.007 to 2.009".
Will this affect accuracy or should I trim to length every firing? </div></div>

No, it won't.
 
Re: How crucial is trimming brass to exact OAL?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: AXEMAN</div><div class="ubbcode-body">That's a great idea to find the chamber size.

That said, not knowing the exact spec's on my chamber leaves me at a disadvantage. I hope that as long as I am below max I am ok, but I will check now and be sure. I have also heard of guys making a mold of the chamber to get spec's. </div></div>
Sinclair makes a simple gauge piece that fits in a shortened case so that the chamber length can be measured.
 
Re: How crucial is trimming brass to exact OAL?

otherwise clipping 50 thou off? has to be .005 not .050
Bill

o<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: NotAGuru &#8853;</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KHOOKS</div><div class="ubbcode-body">I trim my brass once to 2.00 may trim next lot to 1.95. When it grows after firing you should be able to bump the shoulder back. Bring the lenght back to your trimmed lenght or close. I've done this over 5-6 firings and everything has been ok so far.
</div></div>

I hope you meant 1.995..... But either way if they are all the same it will make no difference what so ever. </div></div>
 
Re: How crucial is trimming brass to exact OAL?

Guess i wasnt clear. I meant that cutting them down any extra will make almost no difference. As long as they dont hit in the chamber you will be fine. And yes the more you trim back the more pressure you loose but .005 does not make much of a difference at all if you not hitting in the chamber. Vic knows whats going on listen to him.....
 
Re: How crucial is trimming brass to exact OAL?

+1 for Victor. The guy has been reloading since 1972. Ive learned more from Victor than I could have in 5yrs. He is a plethera of knowledge and well deserved for everyones attention. Im not saying he is the King of reloading but there isnt much that he doesnt know or hasnt tried in the 30+ yrs of reloading.
 
Re: How crucial is trimming brass to exact OAL?

I guess I'll be the odd ball. If I was shooting benchrest, I would probably trim every time just for the peace of mind. Since I don't, I only trim when the case exceeds the maximum OAL. For the matches I shoot, a 0.03-0.06 improvement in my groups isn't worth the added work and wouldn't help me place any higher. That's just me though. You have to determine for yourself if it's worth it.
 
Re: How crucial is trimming brass to exact OAL?

Hey guys, let me explain something. I'm just a retired tool & die maker with a lot of experience. The things I speak of have helped me with MY EQUIPMENT. Yes, I'm a benchrest shooter. So every little bit helps. Or at least it helps me.

To average Joe out pounding steel or tromping through the woods for game with a factory chamber / off the rack rifle, a lot of what I say probably won't make sense.

But I'm no "expert". Just experienced. I try to learn new things all the time to make things better. If something I say sounds outrageous, pay it no heed.
 
Re: How crucial is trimming brass to exact OAL?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Victor N TN</div><div class="ubbcode-body">Hey guys, let me explain something. I'm just a retired tool & die maker with a lot of experience. The things I speak of have helped me with MY EQUIPMENT. Yes, I'm a benchrest shooter. So every little bit helps. Or at least it helps me.

To average Joe out pounding steel or tromping through the woods for game with a factory chamber / off the rack rifle, a lot of what I say probably won't make sense.

But I'm no "expert". Just experienced. I try to learn new things all the time to make things better. If something I say sounds outrageous, pay it no heed. </div></div>

Don't forget that letting the necks grow helps to create a better gas seal and you won't see soot on the necks or shoulders. Less gas blow-by means more velocity down range. Of course, there's a fine line in knowing how long is too long and how short is letting that gas escape out back end (chamber).

I can let my necks grow to 2.820+ COAL in my 10FP LE2b barrel, so 2.815 plus a hair is where I trim to.

Chris
 
Re: How crucial is trimming brass to exact OAL?

same as Chris above,
I trim to .005 less than published and now have a Giraud to its no proplem to check after each reloading that there consistant and the same length
Bill
 
Re: How crucial is trimming brass to exact OAL?

I dont even bother checking to see if the brass needs trimming, I just trim them at every reload on my Gracey trimmer.
 
Re: How crucial is trimming brass to exact OAL?

thanks for the run down victor.sometimes things sound so simple once there spelled out for you.this metod sounds like it makes a lot of sense.
 
Re: How crucial is trimming brass to exact OAL?

You should want your cases to all be the same OAL, they NEED to fit in your chamber. If you trim to SAAMI MAX OAL, unless you had your chamber cut specially (and specially WEIRD) your cases will fit. Trying to trim your brass so you are 'close' to the max case length for your specific chamber is a waste of time.
Trim them consistently, to whichever length you trimmed em to before. I damn sure wouldn't worry about a batch of my cases being 3 or 4 thou short, I'd just trim the long ones to match and be done with it.
 
Re: How crucial is trimming brass to exact OAL?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Schwim</div><div class="ubbcode-body">Like Winchester 69 said, just spend the $7 and get this tool. Measure your chamber length and keep cases trimmed back .005.

http://www.sinclairintl.com/.aspx/pid=32925/Product/Sinclair_Chamber_Length_Gage </div></div>

Stole my thunder..Lol Not that I'm against home projects, but for 6.95 it's done deal.
 
Re: How crucial is trimming brass to exact OAL?



Any time you can make Your Brass more accurately fit YOUR Chamber, your going to support the bullet better during it's Violent entry into the rifling.
 
Re: How crucial is trimming brass to exact OAL?

I've been reloading since 1964 and I just found out about the Sinclair gauge a few years ago. I can't count the hours of wasted time trimming cases that didn't need it. Most chambers are much longer than SAAMI specs. I square up new brass and then do not have to trim for 5 or 6 firings.
 
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