Any way to tell if your case necks are too wide for the throat on your rifle?

[LoonWulf]

So ive just started messing with the 6-284 i picked up last week.
First set of loads clocked well above expected velocity and I got "stop here NOW" class pressure signs before reaching the end of my 5grn ladder.

Thats never happend to me before.

I was using 95gr pulled btsps, IMR 7828, and Necked down Nosler 6.5-284 brass (ive had some issue with nosler brass in my 06, but this stuff seems good, very consistent).
The only thing that deviates from "recommend spec" are the necks are .275, where as the cartridge drawing show the 6-284 at .267 at smallest. The guy i bought the rifle from was shooting resized .284 brass in it before this, and didnt mention an issue (dosent mean there wasnt, I didnt actually ask).

bullets dont fall into the spent cases like they do some of my factory rifles (say remington?) but they also slide in with light finger pressure, which is how my two custom gun guns are, and a little less than spent shells from my new .250AI.

I also pushed a few dummies into the chamber with my cleaning rod to see if i could feel any resistance, and there isnt any unless i dont totally take the .257 size bump (i have a .257 neck sizer im using as an intermediate step) out of the necks.

Also accuracy was horrible, but that could have been the fact it was POURING on me when i was testing this.

So heres the question Is there any definitive way to tell if the neck thickness is an issue without a chamber cast? I have some cerrosafe but its packed away and a pain to dig out now that it is.

 

[edwardware]

You now have a handful of fired brass. . . get thee hence and measure it! The neck of the fired brass is probably ~0.001 smaller than the chamber neck due to spring back.

Based on your description of bullets sliding gently into fired necks, I'll bet you're fine, but you certainly don't have generous clearance.

 

[ants]

So ive just started messing with the 6-284 i picked up last week.
First set of loads clocked well above expected velocity
and I got "stop here NOW" class pressure signs before reaching the end of my 5grn ladder.

This is very important! I have a Howa with the same issue.

I did the cerrosafe in the chamber and got the actual dimensions.
My Howa chamber is narrow at the neck and the throat is short.
This jams the bullet, so pressure shoots way up fast.
I reamed the necks and load the OAL a bit shorter now.
I can work up to full load much more easily.
Another fix would be reaming the chamber itself, but
I like the idea of starting with a tight chamber that will loosen up later.

If your cerrosafe is packed away, my humble advice is to take the time to find it.
Hefty pressure signs are not to be ignored, a chamber cast avoids guesswork.

 

[243winxb]

i dont totally take the .257 size bump out of the necks.

What if you try to size the fat neck by closing the bolt? Then take measurements of the swaged down neck.

But this may jam the action or get a stuck case? I have not done it.



Best to look for the cerrosafe.

 

[Walkalong]

bullets dont fall into the spent cases like they do some of my factory rifles (say remington?) but they also slide in with light finger pressure, which is how my two custom gun guns are, and a little less than spent shells from my new .250AI.

All of the cases? Maybe not?

Anyway, that awfully tight with no room for error. Gotta check the neck diameter of the gun and then ensure ALL loaded rounds are under that. Cerrosafe is easy to use

 

[Blue68f100]

Short leads and/or free bore will cause you issues if your bullet is jamming into the lands. I had this show up on a new barrel for my AR. I used a reamer that only had 0.025" free bore. When I started checking my chamber for bullet jump with the different bullets I use, I had several that were going to be a problem. Like 0.035" jammed into the lands. I ended up using a special reamer to lengthen the free bore. Problem solved. Would not hurt to check if you have the Hornady Gauge.

 

[LoonWulf]

Thanks guys.

I measured the spent cases .278-.279

Since ive never even thought about 243winxbs idea of using the chamber to size the neck of a case figgured id try it. Big claw extractor and a dead blow, figgured getting a case actually stuck stuck, was unlikely.

Used a fired un sized case, expanded with .257 die ending up with a .286 neck, then sized back down in the 6mm die till i could cam the bolt closed....did that a few times and measured the shinny spot .282

Kinda cool to mess with this stuff!

Ill break out the cerrosafe next time im on the other side of the island, but for now im pretty confident that i can continue to mess with loads, but ill stay lower, and ill switch to a known bullet till im a bit more comfortable.

Sorry forgot to mention that im .04 back from the lands, and at 2.81, .006 long of tested data.

 

[LoonWulf]

went out today with a ladder of 100grn hornady sps, and retumbo. I used the last of my 7828 on the last batch of ammo.
started at hogdons min and went to max, zero issues.

I still ordered neck turning stuff (never messed with it and always wanted to see if it made a difference), and ill check my chamber this week, but so far so good.

 

[243winxb]

Have you checked the twist rate in the barrel and matched it to the bullet length/RPM.
http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Berger has one also. http://www.bergerbullets.com/twist-rate-calculator/

 

[LoonWulf]

Yeah, its a 1-10. Does fine with anything upto 100grns in non VLD form according to the calcs. My 1-10 6x47 does ok up to 100grns also, but choked on the 95VLDs.

Something else I noticed last night after going through everything again, is that my cases have about 3gr less water capacity then quickloads thinks they should. While i dont use quickloads as my only data source if i can find ANY published data, I do use it as a piece of information when assessing the safety and reliability of my load recipe.
So after updating QLs water capacity, my velocity was VERY close to what i got in my first outing, and pressure was about 8K over what it was supposed to be.
When i referenced it against the data i used as a baseline (hodgdons), It looks like my cases at 64gr of water have a lower volume than standard.

 

[243winxb]

The 90 gr hpbt match Bergers did well in my 243 Win. With a 1-10 .

Your velocity/RPMs should be higher, better for the longer/heavier bullets.

 

[LoonWulf]

Yeah, According to bergers stability calc my 6-284s dead center the "marginal" range. I may try them, but I was given a couple hundred of these 95grn pulls i wanna mess with a bit more before i do