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Old January 10, 2007, 03:55 PM   #1
Daniel BOON
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small base dies

I have heard that small base dies are needed to reload a semi-auto centerfire rifle; I have a remington 742 (243)that I haven't given up on yet, and was wondering if I should use small base dies;
can anyone give me a clear picture of what small base dies are used for? thank you for any input you may have. Daniel
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Old January 10, 2007, 04:04 PM   #2
Peter M. Eick
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Small base are needed for guns that have to have the brass sized all the way back to SAAMI minimum specs.

I need small base dies for my M1A Supermatch. Conventional dies will make rounds that the bolt does not completely close and I have to reach up and whap the op-rod to close the bolt. With the small base dies I don't need to do this.

If I were in your shoes, I would use a conventional set of dies from RCBS and if you have a similar problem I would write/call RCBS and trade them for small base dies if needed. Why overwork your brass until you need to.

As a side note, my National Match M1A does not need the small base dies, but I loaded all 308 ammo with them because you cannot be sure which rifle it will be fired out of.
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Old January 10, 2007, 05:09 PM   #3
Daniel BOON
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mission from god

with this particular 742, you never know which problem will rear its ugly head, or when.
sometimes the bolt will close, sometimes it won't. but it won't hurt to try. and yes I use rcbs/hornady dies. thank you for your input.
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Old January 10, 2007, 05:17 PM   #4
TimRB
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Small base dies only make the cartridge base smaller than normal dies (duh). Have you confirmed that the bolt is not failing to close because the brass is too long? That would be a cartridge headspace problem.

Tim
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Old January 10, 2007, 07:37 PM   #5
Unclenick
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The terminology is confusing and inconsistent. If you read Denton Bramwell or some other authors, the “base” is the back end of the casehead; the part that includes the rim and the headstamp and the mouth of the primer pocket. Clearly no die can size these parts if they are securely below the level of the shell holder.

So, I called RCBS and chatted with them for a bit. In their terminology, the base is the part of the casehead that lies forward of the extractor groove in a rimless case. It is the point where the .470” diameter datum is taken on the .308 case, and apparently includes the junction between the casehead and web where the pressure ring forms, though I had some trouble getting clear information on that point. In any event, this is the back end of the taper of the sidewalls, and perhaps that is where the name comes from? The base of the conical section that taper defines?

According to RCBS, their small base die should be set up about an eighth of a turn further than contact with the shell holder, and at that position will narrow what they call the “base” very slightly (exactly how slightly wasn’t given). This is to ensure easy loading and extraction. The die will also set the shoulder back about 0.002” more than a standard full-length seating die does, thus shortening the headspace by that much. Between that narrowed casehead portion and the shortened headspace, they have pretty well guaranteed a fit. They recommend the small base dies for both autoloaders and lever action guns and pump guns. Basically, anything that either has to strip a magazine fast or has to take a cartridge from an angled carrier.

Incidentally, if you have feed problems with an RCBS small base die, you can return it to them along with five un-resized, fired cases. They will measure the cases and adjust the die to accommodate your chamber, so long as that chamber’s dimensions are still consistent with safe practice. If their case measurements indicate your chamber to be outside safe dimensional limits, they will inform you that it needs to be corrected. That’s a good service to know is available. I suspect Redding or other small-base die makers would provide a similar service, but you would have to ask?

The dimensional numbers from the RCBS tech come to within what my experience with dies has been. Due to spring-back, many cases don’t return fully to their original size in a standard sizing die. In .30-06, with the relatively stiff Lake City military brass, fired in a chamber that was almost 0.007” over minimum, it would return to about .004” over minimum on the first run through a standard sizing die, and a second stroke into the sizing die allowed to rest for five seconds would bring it out about 0.002” over minimum. A small base die should get you that extra .002” on the first try, and take it to SAMMI “0.0” on a second resizing with rest. At least, in theory.

Nick
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Last edited by Unclenick; January 10, 2007 at 11:20 PM.
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Old January 10, 2007, 08:45 PM   #6
ammo.crafter
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have the same gun in .06 and have been using small base dies for a very longtime. Perfect function.
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Old January 11, 2007, 08:08 AM   #7
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Unclenick,thats some good info.Daniel Boon,I would send the dies+brass in and have them sized to match your chamber.That would help with your brass life and maybe accuracy as well as possible safety(less chance of head-case seperation)..Timrb,That is a good point as well IMO.Also,,Maybe he is seating the bullets and crimping them to far out(maybe bumping into the rifling)and keeping the bolt from closing consistently.just a thought
Oh and Daniel BOON,As far as I know ,Most semi-auto's(like my ar15 in 223)don't need small base dies.Not experienced with the other rifles and calbers though so I could be wrong.

Daniel Boon,Have you checked a chambered round to see if it is slightly touching the rifling??It could be enough to keep your bolt from closing consistently.I would also double check your case length(likeTimrb mentioned)to see if its to long.
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Old January 11, 2007, 06:35 PM   #8
jdmick
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Been using regular FL RCBS dies for an old 740 -06 and a newer 7400 .243 (both autoloaders) with no malfunctions.
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Old January 11, 2007, 09:29 PM   #9
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I've been shooting semi-autos all of my life, and I've never useed a small base die. Not even in my Brownings.

RCBS is the only company that makes them. If they were needed, wouldn't Redding, Lyman, C-H, Dillon, Bonanza etc make them also??
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Old January 11, 2007, 09:51 PM   #10
Peter M. Eick
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I think you need a unique set of circumstances to make the small base dies necessary.

1) A semi auto or lever/slide action without the primary camming action of a bolt action.

2) a minimum dimension or "match" chamber.

I have both of those in my M1A Supermatch. Small base dies work well in it. I believe that there are not a lot of different vendors making them because not many folks are in that boat.

By the same logic, why does Lee make "U" dies when no one else does or the Lee Factory Crimp die or the Redding Profile Crimp Dies or even the Lyman "M" dies.

Each company has its specialties it plays in.
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Old January 12, 2007, 02:21 PM   #11
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I think patents might play a role,I don't know
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Old January 12, 2007, 03:34 PM   #12
Daniel BOON
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742:remington's curse upon mankind

well guys and gals........heres the scoop so far;
I think there are several problems with this rifle, the big problem is it will not load from the magazine. the bolt doesn't seem to close enuff to let the firing pin hit the primer.
take the mag out, and its the same thing; put an empty mag in, and drop a round into the chamber, and it works like its suppose too, with reloads, and factory;
when this project began, I trimmed the brass just a hair, then bumped the shoulder back, that didn't seem to change anything;
is it un ethical to shine it up real fine, then take it to the gun show and sell it for 225$
I value everybody's opinion, and I sure do thank all of you;
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