6mm arc Encore issues???

[Savage 35]

Guys, I'm just not sure. I've been loading my own for about 20 years and this has me stumped. I've been loading the 90 tac tx for bolt gun pressure according to Barnes load data. Starline brass, Trimmed 1.48", cci 400, LVR, TAC, and 2520 powder, and bullet .050 off the lands, which is 2.34". Barnes shows 2.238". I'm not surprised at this being a single shot vs AR mag length. This barrel is 26", 1-7.5 twist. Barnes data is 24", 1-7.5 twist.Starting at minimum and working up. Velocity is ~150-200 fps slower than listed, not concerned yet. Brass lengthens .005 even with starting loads???? I get primer to crater at 1.5 grains below maximum??? It's only a ~3 grain difference start to max. I drop down 1 grain below max and switch to cci450. Work my way up to starting load and that is a 20fps increase over the 400 primer???All cases grew .005 just above the web, but extract and go back in the chamber fine??? I took the extractor out and dropped a new case in the chamber and it goes below flush .008??? I don't have a no go to check with and I don't have a way of checking brass. What would be your next step?
Sorry for being long winded again.
Thanks for your help
Jamie

 

[SJB358]

Jamie, I will go against the grain of others, but if your charges are not getting book speeds, I add more powder. The book and manuals are guides, but their data is good for velocity. There are so many variables of lots of powder, along with primer temps, that I don't sweat going over max book charges if I have a trustworthy chronograph. Chances are, if your charges are that low, any marks on the primer, and other minor growth related to other signs aren't worth much. I'd increase charges .5 grain at a time until you are in the velocity zone, shown in the book. With your long barrel you shouldn't have any issue meeting their speeds. I use 450's in my 22 and 6 ARC's as well, for the extra fire on ball powders, maybe not needed, but it works for me. Primer cratering on SRP's is usually a sloppy pin in a slightly too large of a pin hole that allows the pin some slop upon ignition and can be mostly ignored as well. I wouldn't sweat worrying about brass if you are that low in velocity. Get your speeds up and see what happens.

 

[Savage 35]

Jamie, I will go against the grain of others, but if your charges are not getting book speeds, I add more powder. The book and manuals are guides, but their data is good for velocity. There are so many variables of lots of powder, along with primer temps, that I don't sweat going over max book charges if I have a trustworthy chronograph. Chances are, if your charges are that low, any marks on the primer, and other minor growth related to other signs aren't worth much. I'd increase charges .5 grain at a time until you are in the velocity zone, shown in the book. With your long barrel you shouldn't have any issue meeting their speeds. I use 450's in my 22 and 6 ARC's as well, for the extra fire on ball powders, maybe not needed, but it works for me. Primer cratering on SRP's is usually a sloppy pin in a slightly too large of a pin hole that allows the pin some slop upon ignition and can be mostly ignored as well. I wouldn't sweat worrying about brass if you are that low in velocity. Get your speeds up and see what happens.

The only issue is with the cratered primer cases, it locked up the gun where I had to really wrestle with it to get it open.

 

[RL338]

Barnes list Hornady brass in their data which has more internal volume than Starline. Starline brass I use is the heaviest in a given caliber.
The brass you tested is it new or has it been fired. I fire my brass before serious load work up.
If you had to wrestle it open , you beyond the safe limit. Break action rifle I load for , I don’t push them to bolt rifle pressure.

 

[Savage 35]

Barnes list Hornady brass in their data which has more internal volume than Starline. Starline brass I use is the heaviest in a given caliber.
The brass you tested is it new or has it been fired. I fire my brass before serious load work up.
If you had to wrestle it open , you beyond the safe limit. Break action rifle I load for , I don’t push them to bolt rifle pressure.

It is new. It only locks up because of the primer crater. After open, the brass falls out no problem. I was just measuring as best I could with new brass and once fired in this situation. The shoulder appears to be moving .010 forward. It still extracts and goes back in just fine. New brass sets.~ 008 below flush in the chamber and the fired brass is flush to ~.002 proud.

 

[Savage 35]

Also, it does this, without the primer crater(shoulder moving forward), at starting bolt gun load. Which is .7 grains below max of gas gun load.

 

[Savage 35]

Sorry, I thought with the Thompson center encore, being able to handle a 300wm, it should be able to handle bolt gun loads 6mm arc???

 

[3 Meter Para Bellum]

I'm not sure I am understanding the symtoms exactly, but could there be a headspace issue here?

 

[Savage 35]

That's what I'm thinking. I didn't want to say it until I heard other opinions. My friends howa I'm loading for is getting roughly the velocity in the load data with a 22" barrel and no brass or primer issues. Starting at the same loads I'm ~150-200 fps slower with a 26" barrel. His brass(same as mine) grows~ .002 in length and~.002 diameter above the web at max loads. Where mine is growing ~.008 in length and ~.005 above the web. It's telling me it's a chamber issue, but I'm not familiar enough to say so.
Jamie

 

[Savage 35]

That's what I'm thinking. I didn't want to say it until I heard other opinions. My friends howa I'm loading for is getting roughly the velocity in the load data with a 22" barrel and no brass or primer issues. Starting at the same loads I'm ~150-200 fps slower with a 26" barrel. His brass(same as mine) grows~ .002 in length and~.002 diameter above the web at max loads. Where mine is growing ~.008 in length and ~.005 above the web. It's telling me it's a chamber issue, but I'm not familiar enough to say so.
Jamie

Mine is growing this much at starting loads.

 

[SJB358]

I’d neck the brass up to 25 and create a false shoulder. That way headspace is a non issue.

 

[Savage 35]

Thanks for that. I'll try and see. I used to do that 25 years ago in a 35 remington contender
Jamie

 

[jimbires]

new brass does grow . most times it takes a few cycles to get it fully expanded . new brass also has a slower velocity . I think this is due to the expansion of the case absorbing some of the energy . with the action getting tight , do not add more powder at this time . you can try the false shoulder , as Scotty mentioned , this will help with brass life , and case expansion in the right area . cratered primers could be a lose firing pin , as Scotty mentioned , or maybe due to the brass cases being excessively short . once the brass has been fired a couple times , and getting a little tight to close the action , adjust the die to just push the shoulder back about .002" - .003" . this will size the case to your chamber specs . after you get the brass fitting properly , try working the load up again . if you have questions on creating a false shoulder , or sizing the brass to your chamber specs , just ask , we can get you going in the right direction .

you only need to create the false shoulder on the initial firing . after that , I neck size until the cases start to get tight , then I adjust my full length die to just bump the shoulder .

sizing the cases to fit your chamber will make up for a chamber that might be a touch out of spec , or at the big side of the spec .

 

[RL338]

I’ve never seen cratered primers in my break actions just flatten with new brass. I figured it was from the ignition of the charge backing the primer out slightly due to the extra headspace of the new brass. Then the brass under pressure expands to fill the chamber causing the primer to look flatten.