6BR Trim Length

[critter_bill]

I shot the 6BR for about 20 years as a 1/14" twist with light bullets but am still fairly new to the 1/8" twist with heavier bullets. Using the Berger Hybrid 105 currently. I realized each chamber differs as do reamers but, on average, what trim to length do you trim your 6BR Lapua brass? I had assumed most would trim to 1.550" or so but just received my Giraud cutter preset to 1.530" on the sample case. Thanks for your input.

 

[DeltaBravo]

Bill,

If it won't go thru a 1.55 gap on my caliper, it's time to trim/chamfer with my PMA trimmer. My setup puts the new length at 1.548. HTH

Dennis

 

[comagutsa]

i trim mine to 1.555

 

[NorCalMikie]

What you REALLY need to do is get an EXACT measurement of YOUR chamber. Write that measurement down and refer to it before you even think of trimming. Sinclair makes plugs just for that. And, they work like a charm. I have/use them on every caliber round I shoot. Never have to guess about trimming or not.
Max trim length on the 6 BR is 1.560. Most chambers are cut longer. Example= My 22,6 and 6.8 BR chambers are 1.580. That leaves a lot of room before I need to even think about trimming.
Depends a lot on the type of dies you use. I use Forster Precision Bushing Bump Dies and most of my BR brass has anywhere between 20 and 30 firings and havn't needed trimming. Some folks have mentioned carbon buildup ahead of the case necks because of the gap. Never ran into that problem. Think before you start trimming. You can't put it back.

 

[critter_bill]

Thanks for the responses and PMs. Although I've been loading since 1987, I have been surprised a couple of times on cartridge length. The first was with a 6BR Rem 40XBR in 1991, I had the Rem cases loaded for a 1.560" length and no-turn neck but when the rifle arrived, it had a .266" neck and 1.520" chamber. It was made to the old Rem specs and not the newer Norma specs.

And, just this year, I bought a couple of 6PPC barrels chambered by my long time gunsmith Dwight Scott in .268 ND that had a chamber length of 1.500" instead of the usual 1.520". I bought these from someone else, unfired, so maybe he didn't know about the short chamber. I am certain that Dwight would have advised the customer of the 1.500" dimension but I had no idea until I managed to get a copy of the reamer drawing.

Guess I'm getting a bit gun shy on new (to me) chambers. I realize you can always trim shorter for safety but then risk the carbon ring buildup in the unfilled neck area. I had one of Sinclair's little plugs in .22 caliber when I began loading for the .223. About time I bought a 6mm.

Thanks again.

 

[Richard Jones]

.......I had one of Sinclair's little plugs in .22 caliber when I began loading for the .223. About time I bought a 6mm.

Thanks again.

or................http://bulletin.accurateshooter.com...-chamber-length-with-home-made-modified-case/

 

[critter_bill]

What you REALLY need to do is get an EXACT measurement of YOUR chamber. Write that measurement down and refer to it before you even think of trimming. Sinclair makes plugs just for that. And, they work like a charm. I have/use them on every caliber round I shoot. Never have to guess about trimming or not.
Max trim length on the 6 BR is 1.560. Most chambers are cut longer. Example= My 22,6 and 6.8 BR chambers are 1.580. That leaves a lot of room before I need to even think about trimming.
Depends a lot on the type of dies you use. I use Forster Precision Bushing Bump Dies and most of my BR brass has anywhere between 20 and 30 firings and havn't needed trimming. Some folks have mentioned carbon buildup ahead of the case necks because of the gap. Never ran into that problem. Think before you start trimming. You can't put it back.

Thanks for the advice. That's why I was asking before cutting. Since all my previous cutters came preset to the normal "nominal" trim to length, I was caught off guard by the shorter length of 1.529. Good advice as in, "measure twice and cut once."

 

[NorCalMikie]

And, keep in mind the type of die you use can effect length. The expander button WILL pull the neck longer with every up stroke. That's where the bushing dies shine. None of that coming into play.

CB:
You mentioned the "short" length case? Load that round just the same as the rest of them. Mark it so you can't miss it. Fire that round and see if there's any difference on the target compared to the other rounds. That should give you results that none of us can prove. May not be THAT critical after all. Less to worry about.

 

[critter_bill]

NCM, I would gladly do that with the short case but he was sacrificed to make the "collar" modified case. I've no experience at long range since I'm limited to 300 yards at the Greenville Gun Club here in SC. I'm primarily a point blank range shooter with 6PPC, 220 Beggs, .223 in 1/14 and 1/8 twists. I recently sold my BAT 308s and returned to the 6BR with a complete set-up that I purchased from a board member here in November. One of my shooting buds that I mentored 11 years ago has been competing in 600 yard matches and is itching to try 1000 with his 6BR. The BAT/NF rig that I purchased had a complete set-up for 6 Dasher as well but I am selling this to my 600 yard shooting buddy so I can focus on the 6BR at 300 yards.

I use Harrell's (and sometimes custom) bushing dies. When I do use Redding bushing dies, I always install the carbide expander to reduce drag. I'm a retired Dimensional Lab Rat (CMM programmer/vision system programmer, etc) and used to measure my cases to death to trouble shoot and, as you said, found most of my runout and case stretch came from dragging the expander back through the sized neck. It was even worse with non-bushing dies which greatly reduced the neck ID.

I had seen the modified case article that Richinva linked, but never thought that I could cut the collar off without distorting it. But, it wasn't so bad. Just took a little gentle filing to remove the brass burrs.

Again, thanks for the tips and advice. We're never too old to learn from others.

 

[NorCalMikie]

I'm a retired Dimensional Lab Rat (CMM programmer/vision system programmer, etc) and used to measure my cases to death to trouble shoot

There's your problem right there. Too busy looking at "details" and not enough trigger time.
Got a shooting buddy that keeps records like you can't believe. Date, time, temp, wind direction, where the Sun is, powder charge, bullet weight, who's at the bench next to him, etc. While he's writing, I'am burning off a couple hundred rounds of .308 out of my M1A. What it boils down to is "Whatever makes you happy in life, go for it and enjoy it". Keep in mind, you're only going around one time (unless you're Shirley MacLane) so enjoy every minute of it. And, life's getting shorter every minute.

And you are 100% correct. We're never too old to learn something new from others.