What advantages does a tight neck chamber have? Can all cartridges benafit?

W

Wheres_Waldo

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I'm wondering what all advantages a tight neck chambered rifle would have over a SAAMI spec chamber of the same cartridge?

Can all cartridges benafit from a recut chamber with a tight neck? Granted everything else on the rifle is up to par?

If not, specificly a 300WM?
 
I think - - -

Gene Beggs might tell you it has no advantage as long as the parent brass has consistent dimensions.

From my view, if brass has a consistent thickness around it's neck, there is little, if anything, to be gained from making it thinner. Making it thinner makes it more fragile. I don't see that as an advantage.
 
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It's about CLEARANCE, not actual neck thickness. You don't want clearance to exceed .002-.004 (depends on the bullet) or you will begin to see accuracy loss.

Some bullets, notably flatbase, are "self-straightening", some like VLD's need more guidance IMO.

The neck tolerance is about guiding the bullet straight into the rifling lands. The neck of the case acts as the vital bushing in achieving this alignment.

Also running close tolerances, like .003 or less, will allow you to resize the neck dozens of times before it splits. For cases with neck clearance of .002 or less it's possible to reload the same case 50-100 times.

al
 
It depends on what the rifle will be used for. Perhaps it's a good idea to step back and look at why saami chambers are cut they way they are. The chamber specs are designed so that any brass you purchase will safely chamber in a given gun. So if you are shooting factory ammo, or want to have the ability to shoot factory ammo, then you are advised to stick with a saami spec chamber, though one can go on the minimum size.

However, if you plan to only run handloads, and have measured the given lot of brass to know what the dimensions of the loaded rounds you might want to have a custom reamer made that will be just a few thousandth's over the dimensions of a loaded round. As mentioned it will aid in the alignment of the cartridge in the chamber and reduce the amount of growth of your brass.

But make sure the rifle is marked as to having a tight neck so you and anyone in the future is aware of the fact it is a tight chambered rifle.
 
"tight neck chambers"

Wheres Waldo: When I have a new barrel chambered, it is alway cut with my spec'd. (pacific) reamer. Ex: recently had a new Hart 1-8 fitted to a Savage in 223 Rem. Planned on using Lapua brass. Loaded neck dia. is .250", so a .253" chamber neck dia. was ordered. using a .248" Redding bushing, so the maximum the case neck is being "worked" is .005". Factory chamber neck diameters for a 223 are .256"/.257", and if sizing with a "conventional" FL sizing die, the neck will be over-squeezed down to around .244", so that brass neck is being "worked" .013". For one of my 6BRs' the chamber neck dia. is .272", Lapua loaded neck dia. is .269", bushing sized down to .267". Again, working the brass a maximum of .005". Guess which brass will have split necks and become work hardened first? None of the brass requires outside neck turning, not one of my favorite pastimes.
 
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Thanks for the comments gents.

The rifle will be used primarily for long range paper punching, and I would like to give it every chance to be as accurate as possible.

Hand-loads are on the agenda, with brass having the necks turned for minimal run-out as of now.

The barrel has only maybe 1000 rnds. left, I've heard a 300 WM digests a barrel in about 3k round count. I'll have to see when the time comes, but am wanting to have a chamber cut with minimal neck clearance.

All sounds good, Maybe I should start work on a barrel reamer. Do i need 2 reamers, including a finishing reamer?
 
Tight necks & reamers

Wheres Waldo: I have no knowledge of a 300WM, so hesitate to comment. Depending on the quality of brass ( for any cartridge), the neck thickness variations that are common ( some as much as .004") would benefit by taking a light cut to remove the "high spots". A good chamber neck dia. for a "no-turn" neck is .003" larger than a loaded round neck dia. Might be a good idea to measure a factory round & use that dimension + .003, then it will always be "safe" to fire factory ammo in the rifle. I always include neck dia. (NK) in the ident engraving on the barrel. All my chambers have been cut with a finishing reamer only: only one purchase required. If I am sure I'll never use that reamer again, it's put up for sale & I can get a return of approx. 70% of my cost. A high quality reamer, like Pacific, will cost around $140, with the floating pilot.
 
f d shuster said:
Wheres Waldo: I have no knowledge of a 300WM, so hesitate to comment. Depending on the quality of brass ( for any cartridge), the neck thickness variations that are common ( some as much as .004") would benefit by taking a light cut to remove the "high spots". A good chamber neck dia. for a "no-turn" neck is .003" larger than a loaded round neck dia. Might be a good idea to measure a factory round & use that dimension + .003, then it will always be "safe" to fire factory ammo in the rifle. I always include neck dia. (NK) in the ident engraving on the barrel. All my chambers have been cut with a finishing reamer only: only one purchase required. If I am sure I'll never use that reamer again, it's put up for sale & I can get a return of approx. 70% of my cost. A high quality reamer, like Pacific, will cost around $140, with the floating pilot.
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Using f d Schuster's numbers, note that if you have .004 neck runout and you add .003 of neck clearance then you are guaranteed .005 or more of inbore cant. Further note that if you do a "cleanup cut" you're only increasing this figure, you cannot reduce it.

al
 
brass problems

alinwa: yes, I agree, if working with the "extreme" you could be creating even more "slop". On top of that, the .004" thickness variation will extend down thru the shoulder and body area of the case. Just one of the many problems when using some of the typical "junk" brass that's out there. Ideally Lapua is the solution: is it available in 300WM? I still believe keeping the chamber neck dia. at a "no-turn" dia., approx. .003" larger than loaded neck dia., is an alternative & "safe" choice. In my opinion, of course.:)
 
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