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cessna
07-22-2008, 08:32 AM
Gentlemen:

I want to have a reamer made for a .300 Dakota 1000 yard BR rifle I am building. Please excuse my ignorance, but; I have never had a reamer made before. My gunsmith says to order a finishing reamer and a go gauge. My question is how to dimension the neck diameter.

JGS has some custom .300 Dakota reamers on hand. They sent me a dimensioned drawing of this. I think that it might be better to send them a dummy round so they can cut the throat to my chosen bullet and seating depth. When ordering a reamer, do you suggest sending them a dummy cartridge with the neck turned and them specify how much larger that the neck to make the reamer? I do not want a "no turn neck" chamber. Is there a standard reference number that is ised when making a reamer for a tight neck such as the SAAMI dimension -.002"?


Regards,

Steve Cass
Tucson

mike in co
07-22-2008, 01:18 PM
its best to work with the reamer maker, esp since this is your first.
the neck size is more about the quality of your brass than a specific number plus or minus some existing drawing.

mike in co

Bnhpr
07-22-2008, 03:55 PM
Gentlemen:

I want to have a reamer made for a .300 Dakota 1000 yard BR rifle I am building. Please excuse my ignorance, but; I have never had a reamer made before. My gunsmith says to order a finishing reamer and a go gauge. My question is how to dimension the neck diameter.

JGS has some custom .300 Dakota reamers on hand. They sent me a dimensioned drawing of this. I think that it might be better to send them a dummy round so they can cut the throat to my chosen bullet and seating depth. When ordering a reamer, do you suggest sending them a dummy cartridge with the neck turned and them specify how much larger that the neck to make the reamer? I do not want a "no turn neck" chamber. Is there a standard reference number that is ised when making a reamer for a tight neck such as the SAAMI dimension -.002"?


Regards,

Steve Cass
Tucson

Steve,

When you order a reamer the neck dia and freebore are the critical dimensions you need to decide on before you place the order.

The neck dia will determine your clearance between your brass and the chamber. Most benchresters turn their necks for consistency, so they specify their reamers less that .343" on 30 caliber cartridges. I'm not familiar with your case, so you will have to investigate what works for the Dakota.

I have been using .334 necks on my 30 cal benchrest reamers, with a .331 loaded neck dia., as advised by some really good shooters on this forum.

On freebore, your reamer, barrel twist, and bullet must be matched together.

JGS should help you with that. Start with what bullet you want to shoot. For example, if you want to shoot a 168 matchking, you would probably get a 10 to 12 twist barrel and JGS maybe will say .040" or so freebore (rough guess)

Talk with JGS, I have had good luck with their reamers.

Ben

cessna
07-22-2008, 04:57 PM
Ben,

Thank you for the reply. that is good information and that's what I was looking for. I'll check my dummy cartridges and see how they fit your suggested neck dimensions. I wanted to have .002 - .003 clearance. I assume that that clearance should be from a turned case neck.

As for the freebore, my thoughts are that it would be best to send them dummy rounds with the bullet I want to use (210 gr Bergers) seated to the depth I want. Then I can rely on their experience to determine the freebore.

Regards,

Steve Cass
Tucson

mike in co
07-22-2008, 05:36 PM
Ben,

Thank you for the reply. that is good information and that's what I was looking for. I'll check my dummy cartridges and see how they fit your suggested neck dimensions. I wanted to have .002 - .003 clearance. I assume that that clearance should be from a turned case neck.

As for the freebore, my thoughts are that it would be best to send them dummy rounds with the bullet I want to use (210 gr Bergers) seated to the depth I want. Then I can rely on their experience to determine the freebore.

Regards,

Steve Cass
Tucson

be sure to consider throat wear. you will get some intial in break in, and then little steps as you shoot more. i would start with the bullet a bit short of where you "think" it should be.

mike in co

cessna
07-23-2008, 08:31 AM
Thanks Mike. I hadn't considered that. However, I have been looking at the seating depth.

About the only thing I do not like about the .300 Dakota case is a somewhat short neck. If you want to maximize powder capacity by keeping the boat tail of the bullet within the case neck, there is not a lot of wiggle room for seating depth. So, I was planning on setting my dummy round up with the boat tail encroaching a bit into the case. I plan on using 210 gr Bergers; however, if I want to go to a 180 or 190 I want to be able to reach the lands and still have some grip on the bullet. This is probably a concern with the
.300 WM and others as well.

It looks like you pretty much have to give up a bit of case capacity to promote proper seating and keep the bullet straight. Case in point: if I seat a 210 SMK with the base of the boat tail even with the neck/case junction, the actual the actual neck gripping length is only about 1/8". If I were to use that seating depth for the dummy round and then wanted a .040" leade from that I think that there may be problems. So, it looks like maybe the best bet when making the dummy to send to the reamer maker would be to seat the bullet where you want it and then seat it another .040" deeper to acount for the leade being added back in. Does this make sense?

Regards,

Steve Cass
Tucson

mike in co
07-23-2008, 09:04 AM
most people like to see 1 caliber of neck contact. i have shot 30 cal with as little as .25 or so. what happens to case capacity it you seat the boat tail in the case(below the neck) what to you loose down range ?


mike in co

cessna
07-24-2008, 01:32 PM
Steve,
I have been using .334 necks on my 30 cal benchrest reamers, with a .331 loaded neck dia., as advised by some really good shooters on this forum.
Ben

Ben, the drawing for the reamer for the .300 Dakota that JGS provided shows a neck OD of .340". My dummy round with a seated 210 SMK and unturned brass has a neck diameter of .336". So, my thoughts are that your suggestion of using a .334" chamber neck should work well. I'll turn a case to .331" loaded neck diameter and see if there is enougn brass left to properly tension the bullet.

Regards,

Steve Cass
Tucson

Bnhpr
07-25-2008, 03:53 AM
Ben, the drawing for the reamer for the .300 Dakota that JGS provided shows a neck OD of .340". My dummy round with a seated 210 SMK and unturned brass has a neck diameter of .336". So, my thoughts are that your suggestion of using a .334" chamber neck should work well. I'll turn a case to .331" loaded neck diameter and see if there is enougn brass left to properly tension the bullet.

Regards,

Steve Cass
Tucson

The thicker neck seems to be fine for me, some guys run much thinner. They do well too. Consistency can be achieved either way, but there are a large spread of opinions here on this matter.

I have just been skimming the necks, and my brass is lasting well, but I'm shooting a short .308 win case with shortened Lapua brass and win brass.

I have a 30 br reamer with a .334 neck too.