Gunsmithing Chamber problem?

T

TNSAF

Private
Minuteman
May 3, 2009
13
0
49
Alberta, Canada
#1
Had a Pacnor barrel installed on my 280 AI. Trimmed all my brass to 2.525". 168 gr sierra hpbt seated .010 off the lands. At first I thought the necks spliting was due to work hardening, but then I noticed the ring around the neck. The neck also has a slight taper on the end starting at the ring. My guess is there is no room for the neck to expand when fired causing a pressure spike and splitting. Any ideas?

img00037-20090703-2009.jpg
 
#4
Re: Chamber problem?

Looks to me like the guy that did the work may have used an extra neck reamer and cut the neck area too much. The cases are splitting because the neck is too large, diameter wise. That ring looks to be the result of two different neck reamers being used.
 
#6
Re: Chamber problem?

Time for a complete chamber cleaning followed by a Cerrosafe chamber cast (Brownells 800=741-0015)

If the chamber meets specs, form brass initially by using the "neck up/down false shoulder" method to ensure proper headspace.

let us know.
 
#9
Re: Chamber problem?

The cases have been fired 6 times.
OD of necks on loaded rounds- .309.5"
OD of necks on fired cases- .316"
This isn't an issue with Pacnor as a local smith chambered the barrel. First time there was to much free bore, alot more than what we discussed at the beginning of the build. I wanted .010 - .020 off the lands when a specific bullet was seated with the boat tail below the neck. Allowing the full neck to grip the bullet aiding in proper alignment. He agreed to fix it right away. Said he would set back the barrel and use a no neck reamer. Not sure if " no neck reamer" is the right name. I've had case necks split before, due to times fired and work hardening. What I haven't seen before was that ring and taper at the case mouth. Not sure if it could be a safety issue or not. If it is causing the necks to split or maybe just a coincidence and the brass has had it. By no means do I have anything bad to say about this gunsmith. Just thought some of you guys might have seen this before. I'll be speaking with him next week as he is away. Thanks
 
#10
Re: Chamber problem?

Do the damned chamber cast. that is the ONLY way you will know what the inside of the chamber looks like and measures out. It is gunsmithing 101 and all the rest is just guessing and a waste of time.
 
#11
Re: Chamber problem?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mr. Humble</div><div class="ubbcode-body">Do the damned chamber cast. that is the ONLY way you will know what the inside of the chamber looks like and measures out. It is gunsmithing 101 and all the rest is just guessing and a waste of time. </div></div>
WOW, Mr. "H".......I guess YOU are the only one that everyone should listen too then. Since you don't think "we" should waste the OP's time with our postings.........
Your screen name says it all.
BTW, since when is asking a question a "waste of time" ?
Later,
LG
 
#12
Re: Chamber problem?

While it's just guessing until you can get a chamber cast made, it sounds like your gunsmith probably used the wrong throating reamer, leading to an overly large diameter at the neck. I don't have the SAAMI specs at hand for the 280 AI, but from what I've found online, it looks like chamber neck diameters of .312 to .315 are common for either turned or unturned brass. If your fired brass is measuring .316, then your throat is probably closer to .317 or .318, depending on just how hard your brass is. Mistakes happen, and hopefully your gunsmith will make it right if this is the case.

- Cameron
 
#13
Re: Chamber problem?

Lumpy, I don't know how many "custom" rifles or weird foreign guns you have dealt with BUT I can tell you that a chamber cast is the only 100% foolproof way to see the inside dimensions of a chamber.
That's why any decent gunsmithing book from the 1800s (when casts were sulphur) to 2009 will tell you to do a cast, let it get to the right temp and then measure it with a very good mike.
Any other suggestions are nothing but guesswork based on "I think" not hard dimensional data.
Sorry if I sound like I know what I'm talking about, but 50 years of fooling with rifles has taught me that a chamber cast is the "gold standard" to diagnose chambers questions.
Maybe if you try it, you'll be sold?
 
#14
Re: Chamber problem?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mr. Humble</div><div class="ubbcode-body">Lumpy, I don't know how many "custom" rifles or weird foreign guns you have dealt with BUT I can tell you that a chamber cast is the only 100% foolproof way to see the inside dimensions of a chamber.
That's why any decent gunsmithing book from the 1800s (when casts were sulphur) to 2009 will tell you to do a cast, let it get to the right temp and then measure it with a very good mike.
Any other suggestions are nothing but guesswork based on "I think" not hard dimensional data.
Sorry if I sound like I know what I'm talking about, but 50 years of fooling with rifles has taught me that a chamber cast is the "gold standard" to diagnose chambers questions.
Maybe if you try it, you'll be sold? </div></div>

Funny thing, you are correct about the chamber cast but...with a neck like that, the ring around it, if he makes a cast it may not come out.
 
#15
Re: Chamber problem?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Cameron Murphy</div><div class="ubbcode-body">While it's just guessing until you can get a chamber cast made, it sounds like your gunsmith probably used the wrong throating reamer, leading to an overly large diameter at the neck. I don't have the SAAMI specs at hand for the 280 AI, but from what I've found online, it looks like chamber neck diameters of .312 to .315 are common for either turned or unturned brass. If your fired brass is measuring .316, then your throat is probably closer to .317 or .318, depending on just how hard your brass is. Mistakes happen, and hopefully your gunsmith will make it right if this is the case.

- Cameron </div></div>

I think that is what I said in the first few posts.
 
#17
Re: Chamber problem?

Maybe this is a dumb question, but seeing the ring around the neck like that and remembering that 2.49x is about the trim length for that case in standard 280 trim is a 2.525 too long with the AI version? Could that be part of the issue.

Just throwing it out there, I don't know what the trim is for the 280 AI. Sometimes the overlooked "simple" question is the answer.
 
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