small base die??

[shedhorn]

i just started to reload for my bushmaster predator in 223 556. i went and bought dies every body told me that i have to use small base dies or i will have a slam fire. so i bought the small base dies. i loaded 50 rounds up and went to the range. i noticed that the out side of my cases looked dirty, so i shot some new pmc 223 and they looked clean. my question is because iam using the small base dies it is letting gasses into the chamber? what die should i be using small or regular.

btw the load i was shooting was pmc brass with 24gr of varget with 55gr nosler ballistic tip.

i did use the search it was 50/50 some use small base and some dont. i wanted to ask first hand what you guys think with my set up. thank you

 

[Hummer]

Re: small base die??

Unless you have a custom match chamber I seriously doubt you will need small base dies.

Measure a new unfired round .200" up from rim and then measure a fired case and let us know what you have.

 

[shedhorn]

Re: small base die??

the best i can tell, new .369 fired .372

 

[ChrisGarrett]

Re: small base die??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: shedhorn</div><div class="ubbcode-body">i just started to reload for my bushmaster predator in 223 556. i went and bought dies every body told me that i have to use small base dies or i will have a slam fire. so i bought the small base dies. i loaded 50 rounds up and went to the range. i noticed that the out side of my cases looked dirty, so i shot some new pmc 223 and they looked clean. my question is because iam using the small base dies it is letting gasses into the chamber? what die should i be using small or regular.

btw the load i was shooting was pmc brass with 24gr of varget with 55gr nosler ballistic tip.

i did use the search it was 50/50 some use small base and some dont. i wanted to ask first hand what you guys think with my set up. thank you </div></div>

I bought a small base 223 Redding body die off of here for cheap and use it to bump my shoulders back in conjunction with bushing neck sizing dies.

I shot some of this SB 'sized' brass last month and I was getting soot on the case body, midway down.

There's conflicting info on exactly what a small base sizing die actually sizes.

Some think it exists to give one a 'shorter' front to back measurement, meaning it bumps the shoulders back more than a typical die. I had to grind about .003" off of my body die's bottom, because I couldn't get it to size down enough on my Dillon 550b. That .003" made the difference and headspacing is fine in this regard.

Obviously, this SB body die didn't do the 'front to back' sizing.

Other info I've read, states that a SB sizing die actually compresses the case body, especially near the case head, in more. It's squeezing the width of the case body and not bumping the shoulders back more than a typical die.

I've never seen soot on a case body (necks/shoulders sure) in my 16+ years of reloading.

I'm not too worried about it, as it wasn't a lot of gas blow-by, but I might just start looking for a standard body die.

The way I understand it, is that SB dies are made for loose chambers often found in machineguns. People generally think it's for headspacing concerns, but I think that this die that I have does the opposite and cinches the body more than your typical die.

Sizing wasn't a problem and I didn't come close to sticking one, but I saw a bit more abbrasion near the bottom third, than maybe is typical.

The soot on the body is evidence of this, in my case at least.

Next time, I'll take some before/after measurements and see what I can see.

Chris

 

[shedhorn]

Re: small base die??

SOOT that was the word i was looking for, my small base sized brass is sooty after being fired. i iam going to go and buy a regular die and give it a try. sucks i just got done sizing 400rds... well my 6yr old son did.

after shooting the small base sized brass, can i go back to a regular die?

 

[armorpl8chikn]

Re: small base die??

I have a small base die so that I can use once fired brass from unknown sources in my AR15. I have also used it to size 223 brass before making into 300Whisper, it eliminates a lot of problems. If you always use your own brass then a regular set of dies will probably do fine.

 

[Fuzzball]

Re: small base die??

The sizer is not your 'problem.' Normal sizer dies are about 3 thou larger at the base than SAAMI minimum specifications. Small base dies restore the bases to the minimum.

The size die used will have no direct impact on case blow-by; that only happens when the chamber pressure is low. Some blow-by likely occurs in most rounds after the bullet exits and pressure falls. Most objectionable blow-by probably occurs with light loads that fail to completely force the case hard against the chamber walls.

Since rifle makers know autos have light chambeering force they rarely cut tight chambers in them, that would lead to many failures-to-chamber and many ticked-off customers. Thus, it's very common for conventional sizers to work quite well for autos.

 

[EddieNFL]

Re: small base die??

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> i went and bought dies every body told me that i have to use small base dies or i will have a slam fire.</div></div>

Never heard that one before.

Never tried a SB die. Probably loaded 4K LC once fired (M16) brass last year.

 

[Hummer]

Re: small base die??

Small base dies are misunderstood. I have 57 sets of dies and not one of them is marked SB and for some calibers I have duplicate dies (30.06, 308 primarily as they are the ones I shoot the most). If you carry a caliper to a gun show etc and spot the used dies and I measure the inside of the bases and get dies of various sizes. For instance 30.06 new cases measure .465 on base and I have dies that size .466, .468, .469 and .471. The first three are factory dims. The .471 is a die I polished out to take down SAAMI chamber fired cases which run upwards of .473 as I don’t want to work brass any more than I have to in order to achieve longer case life. OK so I am cheap haha.
First off a SAAMI chamber dimension for .223 Rem calls for .3769 with a tolerance of +.002 so .3769-.3789 is what you are supposed to have for chamber size. So a fired case (after spring back) measuring .372 means your chamber is more than likely .373 so you have a tight base dimension which translates into much longer case life.
Loaded ammo calls for .3759 and .-008 for so theoretically the base dimension could be .3679 min to .3759 thusly your loaded ammo is on the very small end of the tolerance range.

I assume since you are on this forum your rifle has been built as a match rifle and some of the best have very tight chambers as do the bolt rifles I build.
Now the next question is the dies you currently have, please FL size those fired cases (from your rifle) and tell us how much your current dies sizes down the base dimension.