My chamber length is

M

macv

Guest
1.782. This was established by useing the Sinclair chamber length guage. The chamber belongs to a Sav. 223 Rem. The instructions say that once you get your chamber lgth., then deduct .024. Now, that puts me at 1.758. Most reloading manuals show a lgth. of 1.760 for this case. Why can I not let my cases grow more so in length since I know that 1.782 is what I have to work with. Let's say maybe up to 1.772 before trimming. I feel that I would still be safe. Am I missing something here? What would I have to gain by useing a longer length case.
 
Error in measurement

The following is based on conclusions I made after inspecting a set of these gauges.

The chamber length tool you describe gets you an approximate chamber length. Since the diameter of the spud is not the same diameter as you neck on the chamber and the edge on the spud is "broken" and there is a 45 degree ramp at the end of the neck--the tool actually measures a chamber length longer than the actual chamber is. maybe that is why the instructions tell you to trim at least .024 from what you get with the tool.


Jim
 
Jim, very interesting. I am going to have to mic the spud and see excactly what the dia. is. It makes sense as to what you are saying. More info is needed. maybe I can find out who makes this guage and have a talk with them and get the full picture on their tool. I have followed their instructions from day one, but I just got to wondering about it the other day and this is the reason that I posted the question. Maybe someone will know for sure what the real answer is. However, yours is a very good one. Thank you.
 
macv ...

Safety First! This should give you a good idea on how to proceed.

Chamber Length Safety Zone

Q: How many thousandths shy of actual chamber length does one establish as a safety zone, before assigning a trim "from" length, once measurements have established a rifle's true chamber length? Art

Mike Bryant

A: I use .010" for each increment. For instance, if the chamber length is 1.570" from the base to the end of the neck on the chamber, then the maximum case length would be 1.560" with a trim length of 1.550". Don't let the cases get over 1.560" and you'll be in good shape.

Jackie Schmidt

A; I use a .010" window. 6mmPPC chambers have been shortened to 1.510". Since shooters fire cases to expand them, the cases come out close to 1.500". I trim them back to 1.490." :)
 
OK, but how does one find the actual chamber length. This is the reason I bought the tool. Other than making a cast of your chamber, what is another way to get the actual measurement. :confused:
 
Even if you trimmed your cases to 1.770" you're only gaining 10 thou in case length, which for this application is next to nothing. Seating a bullet that much farther out doesn't increase case capacity, especially if your loads are at or near the rifling already. That 10 thou also isn't going to improve the neck's grip on the bullet enough to matter either.

If the chamber was WAY long say 1.79" you could get away with not trimming your cases for a long time. Otherwise it's interesting to talk about at best and of no practical importance that I can see. However there's lots I can't see, so....
 
Well, if the Sinclair tool is accurate, and the measurement I got of 1.782, that means that I won't have to trim every couple of firings, or more. Don't know how long it would take to get the cases to get to that length. Never tried it. But, if there is no advantage to haveing a longer case, or the longest that your chamber will accept, then I guess it's a mute point. Better to be safe than sorry. And safety is my first concern. But if one is ignorant in what he is doing, you just as well through safety out the door. I guess this is one reason we all ask questions. At least it was mine. Thank you.
 
If you FL size and your sizing die is properly adjusted you shouldn't need to trim that often unless your chamber is way oversized.
 
macv ...

macv said:
OK, but how does one find the actual chamber length. Other than making a cast of your chamber, what is another way to get the actual measurement?
Click to expand...

The easiest way? Get a print of the reamer that cut it. It will be right there on the drawing. See example below.:)
 

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  • 308win Drawing.xls
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I've been using the Sinclair chamber length gauges for a good many years now and find the readings to be very accurate. One of my factory chambers for a 223 Rem. also shows a chamber length of 1.782", and I find that most factory chambers are as much as .020" to .030" longer than max case length/ must be a lawyer/liability thing. When I spec my own reamers I request a chamber length .010" longer than max case length, and that becomes my trim to length, not the loading manual one size fits all " trim .010" shorter than max case length".
 
Measuring

f d shuster said:
I've been using the Sinclair chamber length gauges for a good many years now and find the readings to be very accurate. One of my factory chambers for a 223 Rem. also shows a chamber length of 1.782", and I find that most factory chambers are as much as .020" to .030" longer than max case length/ must be a lawyer/liability thing. When I spec my own reamers I request a chamber length .010" longer than max case length, and that becomes my trim to length, not the loading manual one size fits all " trim .010" shorter than max case length".
Click to expand...

Read my reply above to make sure you understand what you are measuring. The spud does not have a sharp corner--therefore it will NOT measure to the joint of the neck and 45 degree ramp even if the spud diameter was the same as neck diameter. The gauge is ok to use to get an estimate of absolute chamber length-but it does NOT give absolute chamber length. If you have the absolute chamber length-you should have max cases that are .01 shorter than that actual chamber length. Trim length is normally .01 back from that. If you use the gauge set-you should allow a little more than that.

Jim
 
Quick Example of chamber length gauge use

I just made a quick drawing on CAD to illustrate an example of how those gauges work and what error may be encountered versus actual chamber length.

I drew a 30 BR Chamber with a .330 ND and a chamber length of 1.510 inch. The chamber has a 45 degree ramp to the freebore from end of neck. I then arbitrarily used the spud diameter of .325 (as I do not have one of the gauges here in the shop right now). So as not to make it grossly off-I put a .005 break radius on front corner of the spud. That "gauge" in the 30 BR Chamber that is 1.51 long would read the chamber being 1.518 inches long.

Now--for those that have the gauges and say that they accurately measure the chamber length versus giving a relative chamber length, please share the actual dimensions of the gauge with me and I can calculate the error present versus actual chamber length. the closer the spud diameter is to actual chamber neck diameter and the smaller the "break" of the sharp corner-the less error there will be.

This topic interests me because I had a client BR shooter last summer trying to tell me that the 30 BR Chamber I put in his barrel was 1.525 inch long versus the quoted 1.515. He was using one of those gauges. The optical comparator here and at the reamer grinder shop showed the reamer was 1.515 to the corner of the neck and 45 degree chamfer from a 0.0 HS. A piece of barrel chambered with the reamer up to the shoulder junction and measured with precision tools also showed the chamber length to be 1.515. It was of great concern to me as I surely did not want him to be using 1.515 cases!

We all need to be careful with the tools we are using to do measurements and make sure we UNDERSTAND what we are measuring with them and what the error of measurement is.


Jim
 
Jim, I had just checked my chamber plug and mine has sqaure 90 deg. corner. There is no radius at all. I guess that being the case, would it make it just a bit more accurate than if it was a 45 deg. angle ? Or is the chamber in the neck area have a radius. And if so, I can see what you are saying about the plug going a little farther and into that radius area, therefore making your reading a little longer. Am I understanding this correctly?
 
Square corner

If it has an absolute square-sharp corner it will not go in as far as radiused or chamfered. You can estimate how far beyond the absolute chamber end the gauge is measuring by subtracting gauge diameter from neck diameter, then divide by 2. However, heed what the others have replied--t is much better to be safe than to get every last portion of an inch neck length.
 
Just reread your post where you say that the chamber area has a 45 deg. ramp to the free bore. I guess that answered my last ques.
 
When you say subtract plug dia., mine is .251, from case dia., are you referring to a fired case?
 
Find someone with a borescope. It's interesting to actually look at the area under magnification. Make up some 'long' and 'short' cases, cut the web/head section off and slip them onto the end of a chamber guide or arrow shaft or hunk of tubing of some sort.

Take a look.

I know that this is a pita but sometimes a visual inspection is worth a thousand words.

I'm firmly in Jim's camp..... if you don't KNOW!!! Then back 'wayy off. Crimping neck onto bullet is not pleasant.

BTDT


al
 
Subtract plug d from chamber neck d

macv said:
When you say subtract plug dia., mine is .251, from case dia., are you referring to a fired case?
Click to expand...

Case diameter is not neck diameter of chamber--subtract the plug diameter from chamber neck diameter--if you want to estimate that--you can add about .001 or more to fired case diameter.

But---once again I would question what benefit this is going to be.

Al's reply is a good way to do it as well.

Jim
 
Alinwa, guess it would be very interesting to scope. Hope I can get it done. I did not have intentions of stretching out my cases to the very max. length. My question at the beginning of the post was really to find out all that I could on the matter. Just trying to get a little smarter. I will always go to the safe side. But getting to the safe side, means that I have to have all the answers. And there were many giving here. Thank you all for the comments and for being safe minded.
 
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