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Match chambers
bolthandle
Member Posts: 1,213 ✭✭
Haven't been here for a while but have a ?????.
When you have a match chamber how many .000 do you remove from the necks (in general) to allow for chambering and bullet release to avoid excessive pressure.
Bolt
When you have a match chamber how many .000 do you remove from the necks (in general) to allow for chambering and bullet release to avoid excessive pressure.
Bolt
Comments
Cast the chamber, or otherwise measure the diameter of the neck area, and than measure the OD of a cartridge neck with a bullet seated.
You want the neck to be a min of .002 smaller than the chamber dimension.
You answered my ???
Bolt
What is unknown is the diameter of the neck area in your chamber. Once that is known than the "how much should I remove from my brass" becomes clear.
Example:
If your neck area is .340 than you can safely use any brass that's thinner than .015 (.308 + .015 + .015 +.002 = .340), however if you have a .330 neck, than you must use brass that is no thicker than .010 in the neck area.
As most 30cal brass tends to be in the .013 to .014 thick, in the first case you might simple turn for a 75% clean-up of the neck, while in the second case you would be required to turn every piece of brass.
Unfortunately these days, there's more to what is referred to as a "Match" chamber in firearms than just the neck diameter. While that may be one of the components of a Match chamber it may not be all of the changes represented by that term.
Chamber reamer makers used to charge additional dollars for 'wildcat' reamers and Match reamers. With the advent of CNC machining and grinding, the significance of these two variations lost a lot. So now when a gunsmith or client orders a reamer that deviates from the SAAMI specifications, the makers usually mark the reamer as being a "Match" reamer. This is supposed to alert the gunsmith to the fact that this reamer has some change(s) in the dimensions.
The general definition of a Match chamber is that all of the cylindrical dimensions have been tightened up from the SAAMI specifications. This includes the body diameters as well as the neck and shoulder diameters. A Match chamber can also have significant deviations in both the diameter and length of the leade and the angle of the throat. Changes in either of these dimensions will have an effect on the process of reloading the cases safely and correctly.
Unless you know that the neck diameter is the only change, you need to cast the chamber and carefully measure the entire chamber and compare it to a SAAMI specification print for that cartridge noting all other changes. If you don't feel confident in this process, you need to see a gunsmith and have them do it.
Best.
Don't "most" match chambers just tighten up the neck area in the chamber while leaving the overall case length the same as the SAAMI specs? Also when this is done dosen't the gunsmith that did this actually stamp the barrel with the actual neck deminsions to avoid someone from trying to chamber a round that is made to SAAMI specs?
For instance, if one was to have a 6.5/284 match chamber wouldn't he want to have a longer throat(leade)when chambering the 140GR SMK etc. to keep from striking the lands? Seating the bullet to deep in the case would reduce case capacity which would effect the performance of the bullet and possibly increase case pressure?
Am I correct on this?
Also I read in another thread something on what rounds would be suitable for a small ring Mauser.
Reason I ask is I have receantly obtained a small ring which is chambered in 6mm Rem. and the chamber has a buldge in the body area of the case on one side, would this be due to a botched up chamber job or pressure from the round?
I feel that it is due to the chamber job but want input from someone else as I want to re-barrel it in the same caliber with a long twist to shoot light bullets, it has a 1/12 twist now.
Do you feel that this chambering is to much for this action being that it is based on the parent case of the 7mm Mauser/257 Roberts?
Bolt
Bolt
"Don't "most" match chambers just tighten up the neck area in the chamber while leaving the overall case length the same as the SAAMI specs?"
That was the common application for a number of years. The term 'Match' has since morphed into covering any number of custom changes in the manufacturing of chamber reamers. For instance, I specify a particular throat angle which is different from the SAAMI specification drawing and my reamer gets marked 'Match' in order to differentiate it from a standard SAAMI spec reamer. Usually, the reamer maker will also stamp the throat angle on the shank so that I don't have to guess or run to the optical comparator to check.
"Also when this is done dosen't the gunsmith that did this actually stamp the barrel with the actual neck deminsions to avoid someone from trying to chamber a round that is made to SAAMI specs?"
That's always been the proper procedure as far as I'm concerned. It sure saves time and effort in situations such as this.
"For instance, if one was to have a 6.5/284 match chamber wouldn't he want to have a longer throat(leade)when chambering the 140GR SMK etc. to keep from striking the lands?"
It depends. In most cases we want a longer throat or leade or both in order to seat the bullets out of the case to maximize the amount of powder space available. However, we usually prefer to have the bullet touching the lands or seated into the lands. This is tested though since there are occasions when bullets seated off the lands are more accurate.
As an explanation, the leade is the cylindrical area just in front of the transition angle in front of the neck. It has been referred to as freebore. The throat is a coned-shaped area in front of the leade which performs the function of a funnel or transition for the bullet from case neck to the lands.
"Seating the bullet to deep in the case would reduce case capacity which would effect the performance of the bullet and possibly increase case pressure?
Am I correct on this?"
Absolutely correct. Not possibly, DOES increase pressure.
"Reason I ask is I have receantly obtained a small ring which is chambered in 6mm Rem. and the chamber has a buldge in the body area of the case on one side, would this be due to a botched up chamber job or pressure from the round?"
Based just on your description, it sounds like a pressure problem. But, without actually putting an eyeball on it, that would be a guess. Long distance diagnostics can be iffy. You really need to see a gunsmith to have this action checked thoroughly.
"I feel that it is due to the chamber job but want input from someone else as I want to re-barrel it in the same caliber with a long twist to shoot light bullets, it has a 1/12 twist now."
This is a hard one also since you haven't told us anything about the receiver except that it's a small ring. Judgements like this should be done hands on in person not guessing from a few words in a written description. The condition of the action is very important as is the manufacturer and model.
"Do you feel that this chambering is to much for this action being that it is based on the parent case of the 7mm Mauser/257 Roberts?"
The reasoning for the 6mm Rem. case is that there is very little work, if any at all, to get it to function in these receivers. In your situation, I think the 6mm Rem. is too much capacity for the light bullets that you want to shoot. Unless you use a real long barrel, there is a significant waste of powder with the light bullets.
I would opt for the new 6mm-6.5 x 47 Lapua which is the 6.5 x 47 Lapua case necked down to 6mm. The cases are superb and the capacity would be nearly perfect for the lighter bullets. A similar case is the older design, 6mm International, which is the 22-250 necked up to take the 6mm bullets. It's also a terrific varmint case due to the powder capacity and shape. These will work in your small ring Mauser as long as the condition of the action is good. More information can be gotten from:
www.6mmBR.com
I think the 6mm Rem. is too much for your action simply because of the propensity for folks to hotrod this cartridge. It has too much capacity.
Best.