Ill take stupid questions for $500 alex!

[RichardCranium]

Okay so I have a Bergara HMR. 308 and have just recently been reloading so I'm chalk full of stupid questions but this one is mainly confusion. I see a lot of people talking about how fire formed rounds out of your rifle are best but then they say trim the neck. If after I fire my round my case oal is 2.015 and I'm supposed to trim to 2.005 wouldn't that defeat the fire forming to my exact rifle? Obviously I am resizing my cases but still curious if trimming to 2.005 is best or leave closer to 2.015. With how close im seating to the lands im not getting much bullet seat at the trim length. .015 counts im guessing. What are your thoughts?

 

[supercorndogs]

How much bullet do you have in the neck?

 

[hlee]

Yeah, what he said... Pictures could help too. I read somewhere that you should get at least one bullet diameter’s worth of seating depth, not including the boat tail. So, a flat base 308 bullet should be 0.308“ into the case. I can’t remember where I read it, and I’m not confident that it’s gospel, but id still be a bit leery of loads that have less than that much contact between the case and the bullet.

Fire forming is to get the diameter of the cartridge to be close to that of your chamber. You will also be pushing out the shoulder of the cartridge to better fit your chamber. You need to trim the neck, or it will eventually grow into the rifling and can dangerously spike pressure.

 

[RichardCranium]

.266 of bearing surface and .412 would include bearing surface and boat tail.

 

[RichardCranium]

Yeah, what he said... Pictures could help too. I read somewhere that you should get at least one bullet diameter’s worth of seating depth, not including the boat tail. So, a flat base 308 bullet should be 0.308“ into the case. I can’t remember where I read it, and I’m not confident that it’s gospel, but id still be a bit leery of loads that have less than that much contact between the case and the bullet.

Fire forming is to get the diameter of the cartridge to be close to that of your chamber. You will also be pushing out the shoulder of the cartridge to better fit your chamber. You need to trim the neck, or it will eventually grow into the rifling and can dangerously spike pressure.

I've read that same thing about seating depth matching the bullet diameter which drives the confusion.

 

[supercorndogs]

I think you will be fine. I don't think it will make any difference. I don't trim mine until they get over 2.015. That is just the maximum sami trim length. Your chamber will accept brass longer than that. The trim doesn't have much to do with sizing other than, brass tends to grow a lot when the shoulder is getting pushed back a lot. Fire forming is about the shoulder and body. The trim length doesn't really have anything to do with it.

 

[RichardCranium]

I think you will be fine. I don't think it will make any difference. I don't trim mine until they get over 2.015. That is just the maximum sami trim length. Your chamber will accept brass longer than that. The trim doesn't have much to do with sizing other than, brass tends to grow a lot when the shoulder is getting pushed back a lot. Fire forming is about the shoulder and body. The trim length doesn't really have anything to do with it.

So my question to that is if fire forming is for the shoulder and body doesn't that get resized when you full length resize? Again this may be a stupid question but I really dont know.

 

[supercorndogs]

Some what. You shouldn't be pushing your shoulders back to SAMI numbers. You should bump your shoulder back .001-.004 on fired brass, that chambers with some resistance. Sometimes you end up with a die and chamber that don't jive well, and with that much bump the body doest get sized enough and you get cases the chamber and extract hard.

 

[918v]

I have measured a dozen or more 308 factory chambers and they are about 2.050” long, so trimming to 2.005” is not necessary. You can let them grow longer if you want. Check your chamber.

But loading that close to the lands in a factory rifle is kinda dumb.

 

[RichardCranium]

I have measured a dozen or more 308 factory chambers and they are about 2.050” long, so trimming to 2.005” is not necessary. You can let them grow longer if you want. Check your chamber.

But loading that close to the lands in a factory rifle is kinda dumb.

Why is that kinda dumb?

 

[918v]

Why is that kinda dumb?

Because you’re prolly past mag length and barely in the neck.

 

[918v]

And you will not improve accuracy over what you can get at normal coals.

 

[RichardCranium]

And you will not improve accuracy over what you can get at normal coals.

My mag still feeds I checked that but the part about accuracy, is that due to lack of bullet seating or for some reason factory rifles just dont benifit from being closer to the lands?

 

[Fig]

I'm not sure what the standard is, but when I say I'm "fireforming", it is not merely the first firing from virgin brass.
If I post here about my "fireforming" I am taking the brass of one caliber, and using dies to get it close to a wildcat caliber for which there is no production brass, and then finishing it off by exploding it into my breach so that the brass balloons up to fill any space left over and becomes brass for that cartridge. Depending on how radical it is we often use fast, shotgun powder and cram Cream of Wheat into the neck, because a bullet would cause the expansion to be too violent.

What you're really talking about is just shooting virgin .308 brass. That's not fireforming, and if you want to talk neck sizing you're in the wrong place, because I'm sure there are very few here who believe in it. Just about everyone FL sizes every time, in which case your brass is not conforming exactly to your chamber, but we have found that doesn't really matter, or at least is doesn't matter outside the bench rest world where you're shooting for tiny groups. Even then it may not matter...

FL size and don't worry about it one bit.

 

[Jcrios014]

I'm not sure what the standard is, but when I say I'm "fireforming", it is not merely the first firing from virgin brass.
If I post here about my "fireforming" I am taking the brass of one caliber, and using dies to get it close to a wildcat caliber for which there is no production brass, and then finishing it off by exploding it into my breach so that the brass balloons up to fill any space left over and becomes brass for that cartridge. Depending on how radical it is we often use fast, shotgun powder and cram Cream of Wheat into the neck, because a bullet would cause the expansion to be too violent.

What you're really talking about is just shooting virgin .308 brass. That's not fireforming, and if you want to talk neck sizing you're in the wrong place, because I'm sure there are very few here who believe in it. Just about everyone FL sizes every time, in which case your brass is not conforming exactly to your chamber, but we have found that doesn't really matter, or at least is doesn't matter outside the bench rest world where you're shooting for tiny groups. Even then it may not matter...

FL size and don't worry about it one bit.

This

 

[918v]

is that due to lack of bullet seating or for some reason factory rifles just dont benifit from being closer to the lands?

For one thing, with so little of the bullet in the neck you are reducing bullet pull which affects combustion. This is offset somewhat by the bullet being so close to the lands, until the lands erode. Then you run into ES/SD problems. Some people will tell you they can overcome this by increasing neck tension. But why all these gymnastics when seating to normal coals will give you equal if not better accuracy? There are more than one magic powder/bullet coal combinations. You just have to find them.

Remember this is a factory rifle not a benchrest rig. You don’t need to be so close to the lands to get the accuracy.

 

[Doom]

Factory chambers typically have more freebore than SAAMI minimum spec. As previously noted it can lead to bullet seating issues. A 168 SMK touching the lands in my REM 700 leaves only the boattail in the case.

That bullet seated to 2.800 or 2.820 is 1/2 MOA, and that’s probably about .100” jump.

One thing to note on OAL of case is fired case will be shorter than resized case. Uniformity of length is more important for consistancy than any specific length.

 

[Ugly_Duck]

I just love the title