# Small Base die question



## Mojo1 (Sep 8, 2007)

I have a couple of questions for all you reloading guru's out there. I'm going to start to reload 7mm Mag and .223 for my rifles. I have gotten both calibers in small base dies since I own both bolt and semi- auto rifles in those. 

1. Will it hurt to fire shells that are resized with SB dies in a bolt action, I heard somewhere its not recommended to do it?

2. Do I need to crimp those? If so can you give me a short explanation of how to set up the die to do it?


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## Frisco Pete (Sep 22, 2007)

Small Base dies are intended to resize the case back to factory specifications. Standard dies normally leave the case just a bit oversize from factory spec. However this works fine in most rifles and extends case life because the brass isn't 'worked' so much. Work-hardening is the result of the case being stretched and resized. SB dies make it stretch a bit more each time, but if the chamber requires it, then, that is life and everything is okay.

Ammunition resized with SB dies will work just like factory ammo in any rifle and will not hurt the gun whether bolt or semi.

You didn't mention what rifles you are loading for, but the only 7mm Rem Mags that might need SB dies are the Browning BAR series. Their chambers are often quite tight. As for other Brownings like the BLR, I don't know. You don't need them with bolt-action rifles, but obviously don't want a whole separate set of dies just for them, so you work with what you got.

The most common .223 semi-auto is the AR15 series. With these I have never found it necessary to use SB dies. The 5.56 NATO chamber (or derivative thereof) common to all of the AR15s from about every manufacturer is not tight at all, so a case FL resized with a standard .223 Rem die normally wouldn't give any problems. An actually .223 Remington-spec chamber has less leade for the bullet than a 5.56 NATO chamber, but this doesn't affect resizing. So the general consensus among experienced AR15 reloaders is that SB dies are unnecessary for .223/5.56 AR15s despite what some die makers tell you. But if you already have SB dies and are loading for an AR-type, then it won't hurt anything except perhaps brass life.

Crimping is somewhat controversial. Certainly the bolt guns need no crimp, but the autoloaders, particularly the 7mm Mag, _may_ need it to keep bullets from being set back in the case. I _heavily_ recommend using a light crimp in a separate step from bullet seating and using a *Lee Factory Crimp* die to do it. These are relatively cheap and the best of the type _by far_. You don't necessarily have to have a cannelured bullet with this die. Just read the die instructions with your seating die and set the die to NOT crimp. The Lee FCD will have it's own unique instructions.

One more thing that you should be aware of when loading for the 7mm Remington Mag. Because this round is intended to headspace on the belt, rather than the shoulder (_like an '06 for example_) rifle makers tend to let the chamber be a bit generous in shoulder-to-belt dimensions. _To a degree_ this is not unusual or even bad. A slight amount of headspace "slop" is common with typical factory rifles and brass. Factories tend to ream chambers at the long end of accepted headspace, because the typical bolt-action .30-06 has to chamber dozens of brands of ammo, both American and foreign. Unfortunately for the reloader, rifles chambered for belted cases often show even more slop. The belt theoretically controls headspace, so chambers are often cut more tolerantly, and ammo varies more widely. Sadly it has been my experience that the 7mm Rem Mag is one of the worst offenders in this, with chambers varying all over the place, from tight to loose. The result is that the brass is stretched along its length from the belt to the shoulder upon firing (_pressure forces the case to conform to the chamber dimensions at that time_). Slop in this dimension stretches the brass and thins it just above the belt because that is where the case walls go from thick to thin. After a certain amount of reloadings, the brass is so thin here that the case head separates from the case body. You want to catch that before it happens, obviously!!!!

To aid brass life it is common for Belted Magnum reloaders to carefully adjust the FL die to have the brass sized just enough to headspace on the shoulder (_like a non-belted round_). This is great if you have only one bolt-action 7mm Mag, but the problem _could_ be that the semi-auto 7/Mag may have different chamber specs.
So to set this caliber up correctly for both, you will have to find out which chamber is tighter in this dimension, and the way to do that is to use a *RCBS Precision Mic Cartridge Headspace Tool* for the 7mm Remington Magnum. This micrometer cartridge headspace tool will enable you to set up full length sizing dies for the precise amount of shoulder bump you wish. Precision Mic gages are initially calibrated on a once-fired case, and the micrometer will read shoulder set back variation from initial set-up. 
If you can't find it locally, then try Sinclair International http://www.sinclairintl.com/product/11239/Case-Gauges-Headspace-Tools or other internet reloading tool suppliers.

It is probable that brass life in the 7mm Rem Mag will be much shorter than other non-belted calibers, especially loading for two of them; so watch carefully for case-head separation just above the belt. 3 reloadings is probably about all you can get on an average, depending on the gun - so keep track and examine fired cases carefully.

Another thing to watch for is large variations in reloading data for the 7mm Rem Mag - just because of the aforementioned reason. In my experience this caliber has one of the largest ranges of "maximums" I have ever seen. So try to get data for the powder/bullet weight you choose from as many sources as possible, and average the maximums out to get a better idea of a goal. Work up carefully for all rifles. No need to try to get too hot, especially with an autoloader in the mix.

If you want to know one of the technical reasons behind the new non-belted Short Mags (WSM etc.) it is to reduce the above issues and still retain the performance of the belted case they are similar to in capacity. 
But you got what you got, and lots of reloaders make things work quite well with the 7mm Remmy Mag, so go forth... armed with knowledge... :lol:


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## Mojo1 (Sep 8, 2007)

Thanks for the info! Your right on, I have a BAR 7mm mag that I'm loading for, I'll keep the brass thinning issue in mind, most of mine is once fired stuff I saved. I loaded 12 test rounds the other day to try out soon. 
I knew they head spaced off the belt but didn't know all the other info about chamber diameters.

I'm planning on loading some premium bullet loads for my 223's, they will be used it a bolt action and an AR, I'm going to use the cheap stuff that I buy to plink with. I may go buy a FL sizer die for each then I'll have the whole set for each.


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## wyogoob (Sep 7, 2007)

Frisco, thanks for the info, especially about crimping. I'm pretty weak on crimping.

I do the small base die thing for .223. I only have semi-auto .223s. I have pumps and a few semi-autos in .243, 7mm-08, 308, 30-06, 35 Remington, .270, geeze others too I guess, and have experimented with small base dies some. I found some rifles, especially the older tubular magazine pumps won't cycle rounds other than minimum length. And then others, like the modern Remington pump rifles, it's not a big deal. Like Frisco said case thinning is a problem, especially in 30-06 and .270. RCBS says 0.002" growth with each firing. I seen 0.003" many times. 

So I have got some RCBS X-dies to help on case life. I only have to trim once, 0.020" I think. I'm in the experimental stage with them at the moment, trying to use them in place of the small base dies. Some people think their all hype. I don't know yet.


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## Mojo1 (Sep 8, 2007)

You guys have more experience than me with them. I loaded 12 for the Mag to try out. I took 4 of them and loaded her up and hand cycled them thru, they worked fine like that, but the proof is when I fire 4 in a row.


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