converting grendel brass to 6mm arc chambering issues

[fifdynutz]

Hi guys, recently I acquired a lot of 90g sierra TGK's for my 6mm arc, trying to perfect a 90g ELDX load i had been working on. I also purchased a 500ct of starline 6.5 grendel brass to convert. in the past i had luck converting grendel brass with my hornady custom grade 6mm arc dies by just simply running them in to the die a few times and trimming. I have since broke that die and bought a new set of the same dies. Now recently with the new brass, new sizing die, and new bullets i cant seem to get the bolt to fully lock when chambering (AR).

If i chamber the brass by itself (converted starline), it will lock, if i seat a bullet at 1.70 o-give (starline) like i have in the past using 6mm arc brass, it will not.

i have to run the bullet WAAY down off the lands to get it to lock, i feel like there is something else at play here. im using 2 different rifle to test the chambering and here are the measurements to the lands

14.5" faxon
-tgk 90 2.360 to lands
-eldx 90 2.223 to lands
-eldx 103 2.368 to lands

16" faxon
-tgk 90 2.352 to lands
-eldx 90 2.216 to lands
-eldx103 2.365 to lands

my test ammo measured out at:
TGK- 2.260
eldx90-2.200
eldx103-2.260

my headspace measurements were as follows

6mm arc brass new- 1.185
6mm arc brass 1x -1.29X
converted startline grendel- 1.205 (new die)
converted 1x hornady grendel- 1.185 (old die)

ive noticed that this new die no matter how far i set it down will only headspace to 1.205, where it appears my old die was seating to 1.185. but this doesnt seem like enough of a difference to not get a bolt lock?


Im about to pull my hair out on this load. any insight or help would be greatly appreciated.

 

[Mike Casselton]

.020 is more than enough to prevent the brass from chambering.

You could take that amount off the top of your shell holder, re-set the die and your problem should go away.

 

[SupressYourself]

To me, if the sized brass chambers without issue, but won't after seating a bullet, thats a bullet problem, like it's seated way into the lands. Perhaps your measurements are a bit off. Do you still have any of the previously loaded ammo to try / compare to?
I would pull out the bolt, remove the ejector, and try chambering by hand. That may give you a better feel for whats happening.

 

[fifdynutz]

To me, if the sized brass chambers without issue, but won't after seating a bullet, thats a bullet problem, like it's seated way into the lands. I would pull out the bolt, remove the ejector, and try chambering by hand. That may give you a better feel for whats happening.

By measurements they shouldn't be in the lands, and it passed a sharpie test. This is where my main confusion lies

 

[spife7980]

If its fine before the bullet either they are seated too long and into the lands (what it sounds like since seating deeper solved it) or they expanding the neck wide enough that its now too wide to enter further.

 

[fifdynutz]

If its fine before the bullet either they are seated too long and into the lands (what it sounds like since seating deeper solved it) or they expanding the neck wide enough that its now too wide to enter further.

Could this expose the necks possibly needing turned?

 

[spife7980]

Could this expose the necks possibly needing turned?

Possibly, yeah.

Get some measurements on the diameters and compare to fired brass or the reamer/print.

 

[Snuby642]

We need a new law halting the use of 6.5g brass in anything other than 6.5g.

You guys are fucking up my stash.

 

[fifdynutz]

We need a new law halting the use of 6.5g brass in anything other than 6.5g.

You guys are fucking up my stash.

find me some 6arc brass and i'll mail you this load of starline lol

 

[fifdynutz]

when i get home i will take some neck measurements and see if that is possibly the hold-up. next step is probably milling the shellholder?

 

[fifdynutz]

can anyone recommend a good neck turner if thats the route i need to go?

 

[jakelly]

If the sized brass chambers fine with a positive bolt lock, then there’s no need to shave your die or shell holder. If the neck OD measures fine, I’d look at seating depth, trim length, and obscure stuff like the rim thickness and web diameter. The problem has to lie in one of those areas. If you do not find it, you need to look again.

 

[B y r o n]

I'm getting totally confused by some of your measurements. You've got measurements to the lands that are actually longer than max. OAL are supposed to be.

If your new die will not size brass down to max headspace dimension then I say it's time to contact the die manufacture.

 

[Snuby642]

This sucks.

One reason I picked 6.5 grendel was it's unpopularity.
Components were overflowing shelves all over town.

Then came 6 arc and messed up my day.

 

[fifdynutz]

I'm getting totally confused by some of your measurements. You've got measurements to the lands that are actually longer than max. OAL are supposed to be.

If your new die will not size brass down to max headspace dimension then I say it's time to contact the die manufacture.

my measurements to the lands are using each specified bullet and a hornady modified case/length checker.

my "test load" measurements below those are the OAL my test rounds measured out at. all are shorter, which would state that im not touching the lands with my loaded rounds

 

[fifdynutz]

Checked all my neck measurements, everything is in spec, trim length is good, etc.

I milled a bit off my shell holder, and viola! I have excess control of my headspacing now. Ran it about .002 past my factory 6arc brass spec, loaded a long TGK dummy round and it locks up effortlessly. Seems to be headspacing was the issue from what I can tell

 

[jakelly]

How then was sized brass chambering fine before seating a bullet, but after seating the bolt wouldn’t lock?

 

[fifdynutz]

Maybe it was smashing the brass into the chamber dropping the bolt? And with a bullet in it it has enough rigity to not form to the chamber? Shit idk

 

[B y r o n]

my measurements to the lands are using each specified bullet and a hornady modified case/length checker.

my "test load" measurements below those are the OAL my test rounds measured out at. all are shorter, which would state that im not touching the lands with my loaded rounds

These are two different measurements and cannot be used for comparison. Your measurement to the lands has more to do with headspace. Measurements over max headspace are just that, rounds that won't chamber or require additional force and also generate more chamber pressure and could be dangerous.

 

[fifdynutz]

H

These are two different measurements and cannot be used for comparison. Your measurement to the lands has more to do with headspace. Measurements over max headspace are just that, rounds that won't chamber or require additional force and also generate more chamber pressure and could be dangerous.

How so? Using the tool I'm setting the bullet to the lands, pulling it out, and measuring coal. Then I'm seating the loaded bullet, measuring coal and comparing the 2 to see my distance off the lands. I don't understand how that doesn't make sense, unless I'm explaining it wrong

 

[Cascade Hemi]

H

How so? Using the tool I'm setting the bullet to the lands, pulling it out, and measuring coal. Then I'm seating the loaded bullet, measuring coal and comparing the 2 to see my distance off the lands. I don't understand how that doesn't make sense, unless I'm explaining it wrong

I don't know what he meant but you're only measuring the distance from the shoulder to the lands. The comparator case is a minimum size piece of brass, not your actual chamber length. You need to measure a piece of fired brass and add its additional length to your comparator length.

 

[supercorndogs]

Was your seating die set too low for the longer brass, bubbling the shoulder?

I would be using a fired case to decide how much I need to size my brass, rather than a sami spec. Your brass will last longer.

 

[B y r o n]

H

How so? Using the tool I'm setting the bullet to the lands, pulling it out, and measuring coal. Then I'm seating the loaded bullet, measuring coal and comparing the 2 to see my distance off the lands. I don't understand how that doesn't make sense, unless I'm explaining it wrong

What I meant was when you measure to the lands you get the max length that bullet can be seated and the bolt should be able to close. This measurement is specific to that bullet only as other bullets will have different shapes even when they look similar. Yes you can measure OAL for that bullet/cartridge combination but again that doesn't mean that the same length will work with a different bullet. Trying to compare OAL for different bullet/cartridge combinations would be similar to comparing apples to oranges. Use the same tool you use to measure to the lands on your loaded round and then you will be comparing apples to apples.

I see you already shortened your case holder and can now size your brass properly so the bolt will close. It would be best to store that shell holder with that die set because if you try using another you'll be back in the same fix of not being able to properly size your brass.

 

[Snuby642]

I would be using a fired case to decide how much I need to size my brass, rather than a sami spec. Your brass will last longer.

I went through the whole saami spec OCD thing when I first started. It took my mentors on the hide a long time to beat it out of me.

Don't be me.

I will add to the excellent advice above and say that it will improve your groups as well.

Imho

 

[jakelly]

H

How so? Using the tool I'm setting the bullet to the lands, pulling it out, and measuring coal. Then I'm seating the loaded bullet, measuring coal and comparing the 2 to see my distance off the lands. I don't understand how that doesn't make sense, unless I'm explaining it wrong

First of all stop using COAL length for anything other than magazine constraints, it’s the only place it matters. I think I understand what you were saying earlier, but you are adding layers of confusion. You need to use base to ogive (BTO) and base to datum (BTD) when referencing seating length and headspace respectively.