Need advice - 243AI Neck Concern

[craigp40]

Guys, I just got my new build, a 243AI with 8 twist Rock. To my surprise, I found that the neck dimension is 0.272". Not a tight neck, but a good bit less than standard. Is there any reason that I wouldn't want this? I'm gonna be using this for field work (tactical comps and hunting). My loaded rounds measure 0.272" so I'm a bit concerned that I have no tolerance for thick brass, powder soot, etc.

Will I even be able to shoot factory 243 Win rounds in a pinch?

 

[PFCSkoug]

Re: Need advice - 243AI Neck Concern

ive never seem a .272 chamber need to be turned if thats your concern.

 

[scotharr]

Re: Need advice - 243AI Neck Concern

You have a .272 chamber and your loaded ammo has a 272 OD? Not good......that is a complete no-go: not even safe. Even if you could shoot it, the tiniest spec of dirt will prevent the round from loading. You sure you got your measurements correct?

For a field gun, you should have at least .003 clearance between chamber and cartridge: .005 would be perfect in my opinion. .006" clearance would be on the high end but still very acceptable. A SAAMI-minimum .276 chamber would be a good fit with your .272OD ammo.

Generally the American brass is thinner and you might get away with a .272 chamber. Lapua, on the other hand, comes out around 273OD unturned. I have a 274 chamber and have to turn the Lapua brass down to .0145 thickness: .002 which is pretty tight for a field gun...little too tight. I recently decided to go with a 275 reamer with .272OD Lapua cartridges. This provides .003" clearance: still tight.

 

[craigp40]

Re: Need advice - 243AI Neck Concern

Let me clarify a bit. This rifle is a switch barrel rig. The original barrel is a 14 twist Shilen with 0.277" neck. The loaded round I shot in the 8 twist barrel was from previous loads for the 14 twist barrel. I would assume there will be no change in the OD of the loaded round for either barrel since I'm using the same sizing die for both. When I measured the neck of the spent shell from the 8 twist barrel, it measured 0.272 as well. Also, I tried to slip a bullet by hand into a spent case and can't even come close to pushing it in.

Scooter, the issues you bring up are exactly what I'm worried about. Is 0.276" the SAAMI min for this chambering? I'm not shooting benchrest, so having zero tolerance isn't something I want. It's looking more like I might be sending this back.

 

[steve123]

Re: Need advice - 243AI Neck Concern

In your situation it would be a good idea to neck turn or at least inside neck ream.If you completely clean the necks it will take approximately 2.5 thou off total.It's an easy one turn process for that small amount of removal.

On many of my rifles throughout the years...

After turning,I have 1.5 thou neck clearance on a loaded round and have never had a single problem,just saying.

Steve

 

[ntexaslongshot]

Re: Need advice - 243AI Neck Concern

as the others have said, you need at least 3-4 thou clearance. if you don't want to turn necks or ream, sent it back. it's just not worth the risk.

you're probably getting a thou or so spring back on your fired case measurement but its still too tight. way to tight if you aren't going to turn the necks.

 

[craigp40]

Re: Need advice - 243AI Neck Concern

Yeah, I really have no desire to turn necks. It will probably go back, but I'm waiting on a response from my gunsmith. he was checking the drawings on the reamer to be certain what the dimensions are.

How do they fix it? Do they just ream out the neck portion a bit more? Or is it an entirely different reamer that requires the whole chamber to be redone? I'm sure I'll get an answer from the smith, but figured it's worth talking about here as well.

 

[scotharr]

Re: Need advice - 243AI Neck Concern

.276 neck is the SAAMI spec and that's what I'd ask for from your gunsmith. He will need to rechamber it: not sure about the details of how much or little extra work this is over a standard chamber job

 

[brand692]

Re: Need advice - 243AI Neck Concern

Craig, if you did not order a 272 neck, I would definitely send that barrel back. Scooter is correct, SAAMI is a 276 neck. While a 272 neck is SAAMI for the 6mm BR Norma, I would consider a 272 neck a "tight neck" in your application, and it would would require neck turning.

If you haven't turned necks before, it, IMHO, is the worst part of prepping brass. For the 6PPC and is part of the reason I no longer own one. Its very time consuming, and really, with the current manufacturing standards of brass, there is no reason to turn necks any longer.

Lots of BR shooters who demanded those tight tolerances are now shooting no turn neck chambers; and with the brass Lapua makes, there is no need to.

I shoot my loads with a .003 clearance on the neck, .0015 on each side.

Tight neck chambers I have had redone had to be set back and re chambered. They weren't set back much, but they were set back.