How do I accurately measure case neck length?

[Cassidy]

I am trying to set my case neck length so I can trim to a consistent neck length for each case (6.5x47). How do I accurately measure (what instrument, etc) from the case shoulder-neck junction to the end of the case neck, recognizing the shoulder-neck junction curvature may introduce error. My intent is to be sure I have the same length neck in all cases and can set a specific dimension between the end of the case neck and the end of the chamber case neck based on my reamer drawing (so I can trim back the case neck end to try to avoid the carbon ring; not sure what this dimension should be).

 

[CatShooter]

How much accuracy do you want - the shoulder/neck junction is NOT a defined place that you can put a micrometer on. It is a round place... You will do well to be within +/- 0.05"

 

[rmist]

Why aren't you measuring base to neck length? That's the only measurement I've ever used to trim cases. Measure them all and use the shortest case as your reference and trim a couple thou off that one as long as it's within your chamber specs. I'll post that "most" will trim .010" shorter than the chamber dimension overall length.
Does that help?

 

[LHSmith]

To minimize carbon ring build-up, keep cases with-in 0.005" of the chamber length, which should be verified by using a gauge such as Sinclair's Chamber Length Space Gauges (just because the reamer is spec'd at a dimension does not necessarily mean that is what you have in your chamber). Forget about measuring neck length. Just adjust your sizer dies to give ~ 0.002-0.003" bolt nose clearance (headspace) and you're GTG.

 

[Brians356]

About the only way I can think of to literally make sure all the necks are the same length (if that's really what you're after) is to use that Little Crow Gunworks "WFT" case trimmer that indexes on the shoulder:

http://www.accurateshooter.com/gear-reviews/worlds-finest-trimmer-power-case-trimmer/

However, the upshot of that will be a new thread - "How do I make sure all my cases are the same length at the shoulder?"

 

[BoydAllen]

If you have a gauge to measure shoulder to head, and size all your cases so that that measurement is the same, you can then trim them all so that they have the same case mouth to head measurement, and know that your necks are of identical length.

 

[delivery_boy]

If you have a gauge to measure shoulder to head, and size all your cases so that that measurement is the same, you can then trim them all so that they have the same case mouth to head measurement, and know that your necks are of identical length.

I agree, I simply run the cases through the body or f/l die bumping the shoulders back to a uniform length then trim in the Wilson trimmer. Not much point making all the necks identical if the cases are all different lengths IMHO

Delivery_boy

 

[Cassidy]

All my cases - the batch I'm working on - are now FL sized (Neil Jones) so that headspace on all of them is <0.001 (which is what I want). For the next step in this process I am planning to use my Littlecrow neck trimmer to trim the necks to a very consistent length (so they are all within about 0.002 of each other (if I can technically do this - I think I can with the Littlecrow neck trimmer). However, I need to figure out the length to trim the case neck to. My understanding is there is a division of opinion of how close the case neck end should be from the chamber case neck end. Some say about 0.025 so the case neck end stays clear of the carbon ring buildup (seems to me the carbon will likely form anywhere in the chamber where the case neck isn't, but I may be wrong), and others say to bring the case neck end to within 0.002 or maybe 0.005 of the chamber case neck end (which seems OK to me if there is no carbon ring in the chamber (there isn't) and to also prevent carbon ring buildup which can result in more pressure and vertical outliers. Either way, I've got to figure out how to measure the distance (which instrument) from the case shoulder-neck junction to the case neck end, and compare this with the corresponding measurement in the chamber. Not sure how to do this.

 

[LHSmith]

Case length is the ONLY dimension to be concerned with and compare to actual chamber dimensions. Regular use of Iosso will keep the carbon ring in check.

 

[Cassidy]

I use Iosso on a brass brush and turn it on a 90 degree angle attachment to my electric drill. It amazed me how many times I had to use the brass brush plus Iosso this way to get the carbon ring out - maybe 12-14 times. But the carbon ring is now out.

 

[Cassidy]

LHS - how do you directly accurately measure overall case length. I don't think my caliper will be that accurate.

 

[LHSmith]

I use a chinese made digital caliper as offered by Sinclair. I have it checked against quality Mititoyo's and gage blocks and it's always been on the money. Also I use a Davidson Seating Depth Base , P/N's SDC 0001 thru 0004 attached to the calipers when measuring cases to be used in competition. IMHO +/- 0.001" in case length variation will NOT show up on target (Short Range BR).

 

[Cassidy]

LH - thanks for the info. My view of Jack Neary's video on this website indicates that 0.002-0.003 variation from base to mouth does make a difference as you indicated; he like to keep it within 0.001.

 

[LHSmith]

The Neary seminars on YouTube are a treasure trove of excellent info on short range accuracy. It's like a favorite movie, everytime you watch the video, you learn something new.......especially as you get more trigger time applying that knowledge.

 

[swampshooter]

Why would this only apply to "short range" accuracy?

 

[BoydAllen]

Jack knows the dimensions of his reamer's print, and he uses that minus the desired clearance between the end if the neck portion of the chamber, and his cases, to calculate his trim length. If I remember correctly, from the videos, he uses a reamer that has a bolt face to end of neck dimension of 1.525, and trims to 1.490, which gives a nominal gap of .035. If you trim often, and make sure that getting your chamber's neck clean happens every time you clean, you won't have a problem, no matter what the gap. I have been told that for long range, that some shooters have found that their longer bullets, and slower powders may dictate a different approach, keeping the gap to a minimum. Some of this depends on what powder you are using, and to a certain degree, the pressure you load to. I have shot a lot of 133 in my 6PPCs, and have inspected my barrels, from time to time, with a bore scope. None have had a carbon ring, although I have seen some fouling in the corner at the end of the chamber neck. This happens IMO because of the diameter of bore brushes, especially after they have been used a bit, as compared to the diameter of chamber necks, and because their bristles are bent as they enter the freebore part of the chamber. If you trim well back from the end of the chamber neck, as Jack does, any fouling that accumulates in the corner, will not extend back to your case necks, because normal cleaning will remove it in that area. If you want clean corners, you will need to switch brushes to a slightly larger diameter, run it up to the end of the neck, and twist it several times, every time that you clean. For this little chore, I prefer nylon brushes over the bronze ones I normally use, and I may put a little IOSSO on the end to speed things up, makng sure to clean out any abrasive residue from the chamber and the rest of the barrel. In your OP you seem to want to measure your chamber from bolt face to end of neck, and the only tool that is made for this, I would never use, no matter what the manufacturer says. It is made by Sinclair, and if you get one, and use it, be very careful to trim the case neck as the instructions tell you to. In any case, I am never going to put a piece of steel in a case neck, run it into my chamber, and close the bolt. If I were going to do that particular chore, I would have something similar made from brass.

 

[Brians356]

the only tool that is made for this, I would never use, no matter what the manufacturer says. It is made by Sinclair, and if you get one, and use it, be very careful to trim the case neck as the instructions tell you to. In any case, I am never going to put a piece of steel in a case neck, run it into my chamber, and close the bolt. If I were going to do that particular chore, I would have something similar made from brass.

Boyd,

Are you aware of anyone having damaged a chamber using the Sinclair gauge (assuming the case was trimmed as short as instructed)?

I would think it prudent to make sure the edges of the slug are slightly radiused and polished; given that, I see little chance of mishap.

 

[BoydAllen]

I have a rifle that came to me with a barrel (stainless, custom) that has a chamber that, when examined with a bore scope, appears to have one of the tools used with a case that was not sufficiently shortened. The end of the neck part of the chamber is slightly deformed in the shape of the radius that you mentioned, and a ridge of metal, that we removed with a throating reamer, was pushed up slightly above the ID at the rear of the freebore.
For my custom chambers, I have the reamer print. For my factory barrels, I use the SAAMI specification, which may be wrong, but I have not found any advantage, in the calibers that I shoot, to keeping the gap small, so any discrepancy is (to me) unimportant.
Years ago, way before the Neary videos, I used to trim the brass for my tight necked .222 so that it was only .005 shorter than my chamber (at the neck). I used to wonder why my fired cases showed some shiny spots on the ends of their necks, even though I knew that there was some clearance there. Today, I have a better understanding of this area of the chamber and the fit that is best. There are a number of areas where shooters' tendency to think that closer or tighter is better has been proven incorrect. I am not saying that this is always true, but we can sometimes go overboard in that direction.

 

[Brians356]

Fair enough. But doesn't it seem likely that, assuming a Sinclair gauge was what caused the damage, that the case neck was not shortened sufficiently?

My only concern is to be able to leave my necks as long as possible for maximum bullet engagement, allowing me to shoot lightweight varmint bullets and still get them out near the lands (if required) in factory chambers. For this reason I cannot use Nosler brass in 223 Rem - the cases come cut shorter than SAAMI Minimum Case Length. (When they named it "Custom" brass, they weren't kidding.)

 

[CatShooter]

Years ago, way before the Neary videos, I used to trim the brass for my tight necked .222 so that it was only .005 shorter than my chamber (at the neck). I used to wonder why my fired cases showed some shiny spots on the ends of their necks, even though I knew that there was some clearance there. Today, I have a better understanding of this area of the chamber and the fit that is best. There are a number of areas where shooters' tendency to think that closer or tighter is better has been proven incorrect. I am not saying that this is always true, but we can sometimes go overboard in that direction.

I also cut my tight neck 6mmBR to a 0.005" end clearance, and 0.0008" neck clearance (less clearance is more better, right??)

The rifle was accurate, but a real Prima Donna. After a group or two, it would throw bullets out of the group for no apparent reason.

I watched Jack's videos and he said 20 to 25 thou end clearance and 2.5 to 3 thou neck clearance, so I took a chance and recut my cases.

I cleaned the throat well and shot the newly cut cases.... that was the end of the thrown shots - the gun now is a kitten to shoot and load for.

Sinclair has sold a kagillion of those gauges, and I have never heard of problems with them.