How to measure neck diameter in chamber.

[Ryeguy]

What’s the best way to confirm you have the correct clearance for loaded round to release bullet inside chamber?
I’m trying to figure out if I need to neck turn my ADG brass. Loaded round is .2920, freshly fired is .2950… 3thou neck clearance, if I’m doing it correctly.. Starting load development on a 6.5 Saum with high ES/SD and curious if this is my problem? Anyone have any better suggestions to measure/check neck clearance?
Thanks

 

[ruby76]

Can you slide a bullet into a fired case?

 

[milo-2]

Brass when fired, expands, then contracts, .003" growth IMO seems fine, it is growing at least .004", maybe more. Take a pic of the carbon ring on the neck of the brass, the closer it is to the shoulder may help us determine the actual close off point of a fired rd.

Not trying to be negative, shoot it some more, new barrels act funny, and break in can be different in brands-barrels, some it is a one shot process, others a circus.

 

[Dmagna]

Take a fired case and see if you can slide a bullet into it. If yes, then you are good. If no either get different brass or turn the necks

 

[Ryeguy]

Can you slide a bullet into a fired case?

With a little pressure. It sure doesn’t drop in. I guess I haven’t tried right after I’ve shot. I did take the measurement right after I shot.

 

[Ryeguy]

Take a fired case and see if you can slide a bullet into it. If yes, then you are good. If no either get different brass or turn the necks

Should i be checking this after I get home or directly after it’s shot? I understand it might spring back smaller the longer the wait. Also should the bullet **** near drop in? I’ve checked this after a couple hours after shot and I have to finagle it a bit. Guess it’s hard to explain the amount of pressure it takes. Maybe I’ll turn 10 down 1-2thou and see if anything improves?

 

[Ryeguy]

Brass when fired, expands, then contracts, .003" growth IMO seems fine, it is growing at least .004", maybe more. Take a pic of the carbon ring on the neck of the brass, the closer it is to the shoulder may help us determine the actual close off point of a fired rd.

Not trying to be negative, shoot it some more, new barrels act funny, and break in can be different in brands-barrels, some it is a one shot process, others a circus.

Ok I’ll get a pic this weekend when I shoot.
Thanks

 

[Mikecr]

Loaded round is .2920, freshly fired is .2950…

Bullets will obviously drop through the area expanded (as measured).
That they might not drop through donut thickness is meaningless.

I believe you have plenty of clearance, and that creating more clearance could increase your SD further..

 

[milo-2]

Should i be checking this after I get home or directly after it's shot? I understand it might spring back smaller the longer the wait. Also should the bullet **** near drop in? I've checked this after a couple hours after shot and I have to finagle it a bit. Guess it's hard to explain the amount of pressure it takes. Maybe I'll turn 10 down 1-2thou and see if anything improves?

I wouldn't turn any brass until you know. You could open another can of worms by doing so. One is too much clearance results in carbon ring ring factory.
If this is a custom chamber, the smith will know the specs of the reamer used, could be a simple phone call-email.

Here is a pic of Alpha 6.5x47 brass necked down to 6mm, new chamber. A bullet will not go back in the case w/o force.
Yet if you look at the carbon ring on the necks, they are sealing off 2/3 of the way down, which IMO means that I am fine. If that ring was close to the case mouth, I'd be concerned.

 

[milo-2]

talking to myself, lol

 

[Rodbolt]

Nice to have a cast of chamber. So simple.

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[Ryeguy]

I wouldn't turn any brass until you know. You could open another can of worms by doing so. One is too much clearance results in carbon ring ring factory.
If this is a custom chamber, the smith will know the specs of the reamer used, could be a simple phone call-email.

Here is a pic of Alpha 6.5x47 brass necked down to 6mm, new chamber. A bullet will not go back in the case w/o force.
Yet if you look at the carbon ring on the necks, they are sealing off 2/3 of the way down, which IMO means that I am fine. If that ring was close to the case mouth, I'd be concerned.
View attachment 580310

From memory mine likes about like this. Never thought that’s the “seal off” point. If it’s close to mouth that means too little clearance, if it’s at the shoulder it means too loose? Makes sense.

 

[Mikecr]

Quick neck sealing is desirable. Consider the hole through which gases leave the case, and potential benefit of that hole being the same, at the same timing, every shot. IMO, a perfect setup seals immediately, causing no carbon soot on the outside of necks.
Diametric neck clearance is a contributor to carbon sooting, but so is chamber end clearance, attributes of bullet engraving, neck thickness/hardness, and overall pressure curve amplitude & timing.
With this, a sooting rule of thumb for neck clearance would often be precarious.

The notion that bullets should drop freely into fired necks stands without rational basis.
I have one chamber set at 1/2thou neck clearance. From this, bullets do not drop into fired necks. They have to be seated with a die,, so I don't size these necks at all,, and never need to anneal them.
Everything about it works just fine, and it allows me to dismiss a good bit of reloading folklores.

 

[Varmint Hunter]

A rule of thumb is that cartridge brass necks will spring back (inward) about .001" after firing, thus allowing the case to be easily removed from the chamber.
With that in mind, I'd say that you have about .004" of clearance in the neck. More than that would be less desirable IMO.