Reply With QuoteI have My 6mm BR Norma Trimmer set at 1.5555”. Works great. Brass does grow.
I know I post allot. Part of aging and being very serious about competition shooting. Please if I am getting on any ones nerves let me know and Ill slow down.
This question is for the 6BR-Norma shooters. I will fire-form a few rounds this week. Not many just enough to play with on the reloading bench. But before I get there I am curios regarding the growth of 6BR Brass. Will new brass pull back or will it grow. I am fire forming Alpha and Norma brass.
As you know we are having a good discussion on trimming and neck turning tools but that whole purpose is this!
1) Should I trim the case to shorter than C.I.P spec of 1.5998425 ( round up 3 significant digits) to 1.560 and take trim off .005 off to 1.555 for case growth?
2) Or do I leave it expecting it will PULL BACK a few thousandths?
Yes I could do a few short and leave a few long but hey you guys have been there for me so much What Do You Say?
Thanks
Larry
I have My 6mm BR Norma Trimmer set at 1.5555”. Works great. Brass does grow.
I would put good money that the brass will do just fine on first firing. After fire forming then resize to your desired length. Like above, mine are trimmed to around 1.555". They will grow a bit over time. Depends on the brass and how hot you run them.
I've never used Norma or Alpha brass, but Lapua brass will grow slow. It will typically take 10 firings or more before it needs trimmed. I usually trim after fireform to shortest case in the bunch to make them all the same length. There is some wiggle room because the chamber length is 1.580".
"As long as there's lead in the air....there's still hope.."
I’m not an expert on reamers but the 6 br and ackley’s I’ve dealt with are 1.570 from bolt face to case mouth, I trim mine to 1.555. One time fired 6 br cases occasionally get shorter prior to growing in length, I think that’s due to radial expansion first and how hard they are hit.
Heres some additional information on 6 br.
https://www.accurateshooter.com/cartridge-guides/6mmbr/
I mainly shoot Norma brass. It's not unrealistic to have new brass shrink during forming.Originally Posted by South Prairie jim
The weakest and thinner brass gets pulled first.....Now comes the real problem. How close
is your FL die. If your over sizing your brass, especially in neck / shoulder area, then trim
to length, the next firing will repeat it's pulling in and shortening of the brass where at a
point, it does not seem trimming is needed. A lot will have to do with how the cases are
annealed, or how hard they get if you don't.....On the other side of the coin and over sizing,
besides pulling brass at the shoulder junction, the case, pulls on it's length, although not as
much, but will cause catastrophic head failure earlier. Best I can tell ya', and what I do with a
new chamber and FL die is to, chamber cast both, then hone the FL die where needed. The top
tooling will come close in the BR world because all numbers have become standard over the
years among competitors and the gunsmiths that specialize in that area. Some set ups are so
close that the guys' are just doing a shoulder bump......Bottom line is.....Don't oversize your
brass.
Keeping my bad Karma intact since 1952
Great points and well said my friend. Matching dies to the chamber is one of the first steps for me, I mainly stick with Harrell’s or Wilson and both provide excellent customer service.
I should add that I’ve had much better brass life while not using dies that incorporate the expander ball system therefore not pulling the necks upwards while ensuring radial sizing around .002 at the .200 line and similar at the case shoulder junction.
Interesting stuff pointed out on the reamer and my brain as feeble as it is went into OT. In fact I called Pacific Gauge and Tooling to confirm my thoughts as they provide the 6BR reamer to Criterion for their Savage Pre-fit.
Now that my brain i working again...As confirmed reamers almost always have 0.010 added for assurance that when the case is inserted in the chamber it only sits on the shoulder and not the case neck. Thus with CIP COL being 1.560 indeed chambers would be ~1.570 bolt to neck head.
With that in mind it will always be safe to trim cases to maximum CIP specs. In fact no need to trim unless they exceed 1.570 for the 6BR-Norma.
Although initial trimming to 1.555 maybe ok heres a thought. Heavier inherently longer 6BR bullets, (105-108 grain with a 1/8 twist) it may be better to trim incrementally and let the target tell you what the optimal trim length. All while also working neck tension. I say this as the more metal surrounding the bullet the squarer the bullet before released. Especially if your target is saying for your round it likes shooting "loose" bullets.
Moreover this could also explain why some bench guys are now into the lands. Imagine the stability of the bullet if its being held firm(er) in the case with more metal and then held into the lands. To me thats a much more stable than jumping. Where as you have only the case holding the bullet before the jump.
Again the target will tell.
Larry
1.5598 is the cartridge not the reamer, as far as i know JGS or PTG machine the majority of the reamers made in the USA the Benchrest guys use at 1.570 and varying freebore (which is a different aspect) depending on application, Criterion 1-8 twist 6 br barrel I had was cut at a .093 freebore which is plenty for 105 class vld, I started shooting Berger 108 a little later when the throat eroded a bit and that shot 3in 10 shot groups at 600 yards with regularity.
Trimming a case even .020 short will not effect accuracy.
When I was shooting a Savage for 600 & 1000 yard benchrest my setup was as follows.
Small shank model 12 action
28 in Criterion 1-8 twist bull barrel .100 at the muzzle .093 FB
Rifle basic trigger set very light
bolt lift done by my smith
SSS Dog Tracker stock
Sightron 10-50x 60 scope
Lapua brass, no turning, no annealing
Harrrls B-1 fl die
bushing iirc was .003 under a loaded round neck OD
Varget powder
107 smk at 30.1
108 Berger at 29.7 ish
Br-4 primers
Loaded on a tuned beam scale, the whole set up shot amazingly well and the one thing I discovered was that the less I messed the better it shot.
I don't see any advantage to trimming to any specific length, as long as all the cases are the same. The key is to have the same bullet pull force. A case that is .002" longer may have a miniscule amount more, but, as long as all of them are the same then it doesn't really matter. After all the 6 Dasher has a very short neck and does really well.
As a person that really dislikes trimming I would trim to the minimum (and sometimes a few thousands shorter) so that I could shoot and reload more without having to trim again. The issue that came from this is that aside from not all case necks growing the same it also left a buildup in the front of the chamber so that as cases grew closer to max it was crimping the bullet in the case as the bolt closed.
Yep. It’s called a carbon ring. The shorter the case neck, the more room for it to form.
Without dropping names, perhaps the most recognized rifle builder with 41 world records builds suggests that trimming br brass .020 short causes zero issues with accuracy. If you clean your rifle often, carbon ring should not be a problem either.
For competition reloads, I run My cases through the full length trimmer every time, for consistency. The 6BR cases always need at least a little taken off. The 6mmBRA cases, after the first trimming, don’t grow as much, and the cutter doesn’t touch them as often.
As with MOST reamers, ground to about .020 LONGER than MAX trim length. Know THAT before you even think about trimming.
First firing, case OAL should be shorter. Sizing? Depends on the type of die you use.
Precision Bushing Bump Dies won't let the case grow so no trimming needed for a LOOONG time.
If they start getting snug on extraction, a body die size brings them back to workable.
Got Lapua and Norma BR brass with 20 to 25 firings, resizes and still no trimming needed.
All with mid range loads so they last with no primer pocket issues. Aneal as needed, maybe every 3 or 4 firings to keep the brass easy to move when resizing.
Oz never gave nothing to the Tin Man, that he didn't already have.
Quite true, and another reason I chamber cast all new chambers. I want to know what the reamer cut.
JGS did my last several reamers, and a good + or - .001" of the reamer spec sheet. Of course these were
customs, and not off the shelf SAMMI's SAMMI reamers will cut long so all manufactured ammo fits the
one chamber.
Keeping my bad Karma intact since 1952
This is why I use chamber length gauges. On factory chambers I set trim length based on actual chamber depth not SAAMI. I've found some chambers upwards of .040" longer than SAAMI specs. Safely extending trim length helps minimize carbon rings as there's less area for it to accumulate.
I wouldn't think those of you running top brand barrels to run into this.
Glad you guys are here for a discussion keeps me digging. I think Fuj has very sound answer and thats make a chamber cast for Competition rigs. Wish I had one now as it could of provided answers to my thread on Alpha cases not liking my rifle.
What brand? Sinclair?
If all you need to see is length of neck area and throat of chamber then you can do what the cast bullet folks call a 'pound cast'. Lead slug slightly bigger and longer than neck/throat. Place it in the chamber and pound on it with a brass drift (covered in tape) until the slug is all the way in. Then tap it back out from the muzzle. Makes a perfect impression of the neck/throat for measuring different dimensions and the lead doesn't damage anything. Use something like sizing lube and it works easier.
Doing a chamber cast won't tell you much if you can't measure from the bolt face. I use a chamber length gauge, which is a case with a shortened neck and a flat face plug inserted. The plug has a lip that is neck diameter, and will push back into the case when chambered. Measure the case and that's you total length.
"As long as there's lead in the air....there's still hope.."
Fred I was thinking of a cast for other measurements.
Also Fred here is what a guy does that doesnt have a lathe. Bottomline it is what poor Iowegian engineers do with a young family for a chamber length gauge. I made one one for my .22-250 Rem and this rifle a 12BVSS when it wore a .22-250 factory barrel.
I took a 1/4 dowel spooled it up in my hand held electric drill chuck (poor Iowegian mans lathe) and sanded down the diameter with 120 paper. Once I got near .230 drill time was over. It took me quite a few pieces of dowel to get it just right and so it would fit snuggly in the neck of .22-250 case. Once its fit seemed okay I cut the neck off the SACRIFICIAL CASE with a Dremel tool while the dowel was inserted.
The dowel was then cut too 1.25 inches long. The dowel was then inserted into another new case SACRIFICIAL CASE (no primer, powder and Winchester I think). If the neck was not snug a gentle sqeeze with pliars firmed it up. The neck piece fitted on the end of the dowel stopped in the barrel where the mouth case mouth would stop. As you slowly closed the bolt the free end of the dowel pushed back into the new case. I would carefully remove it and take 5 measurements and figure the average. That would give me my trim length. I suppose I could make another one for the 6mm and I should as I also have a 6mm Remington hunting rifle.
Heres a secret I learned with the Iowegian inside case length gauge. There is no messing with neck tension to get a good measurement or squeezing the neck with pliers. Just put the dowel with the case neck on it in some water overnight and it will swell enough to press against the inside of the new rifle case neck. The wet dowel seemed to stick better also. If you use a pencil sharpener and put a point on the end of the dowel without the case neck mounted, it will go into the sacrificial case easily.
I got the idea after I bought my first Hornandy OAL Gauge and watching the shaft move in tube slot.
Trimming a case is pretty basic stuff, no reason to make it more complicated than necessary, the reamer print should be close enough trim a case .015-.020 short of.
Yes. NOE also makes them but they are understaffed right now so ship times are delayed.
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