Full Length Resize vs Controlled Full Length Resize

[cgseanp1]

Trying to wrap my head around this.. have been watching Erik Cortana youtube videos and was watching his F/L resize last night. He was demonstrating how to bump the shoulder back and additional .002".

Is this additional .002 shoulder bump more than a factory 308 cartridge would have? I assume a F/L resize die would it set it back to the standard measurements, so why is it necessary to bump it back even more?

Will a factory gun (in my case, MRAD) have any trouble chambering a round that was just full length resized without additional .002, or is this for custom guns with tight chambers?

Thank You!

I just noticed that Forster sells a 308 Win NM which automatically bumps shoulder .003" for target rifles.

Back to my original question, should someone with a factory gun just use a standard F/L and not be concerned with the additional setback, or should you always go straight to the extra setback of the shoulder?

[QED]

No, the precision reloading method is to bump the shoulder back from the fire formed size in your rifle's chamber. For precision loads, you want to bump the shoulder back .001" for bolt guns and 003" for an AR. You need a comparator (e.g., Hornady) and good micrometer. I also use the redding competition shell holder sets to control the amount of shoulder bump.

[cgseanp1]

No, the precision reloading method is to bump the shoulder back from the fire formed size in your rifle's chamber. For precision loads, you want to bump the shoulder back .001" for bolt guns and 003" for an AR. You need a comparator (e.g., Hornady) and good micrometer. I also use the redding competition shell holder sets to control the amount of shoulder bump.

[tabascoz28]

All chambers are different. I'm cheap so I used a deprimed .40 case to measure the middle of the datum line of my deprimed 308, before and after. Some dies can bump, other do too much and some don't do at all.

I ruined a bunch of 338LM cases (found at the range) cause I was bumping .010. now I bump .002. (On most of the brass a case head separation line was forming.)

[tabascoz28]

My lee 308 die didn't bump at all after camed over. Bought some redding bump shellholders. Others have shaved down their shellholders for a custom bump.

[QED]

I can't speak to the Forster marketing copy but continual excess sizing creates a real risk of case head separation. For precision rifle and benchrest shooting, the current best practice is to do minimal full length resizing or about .001" bump. Ammo for semi-autos such as ARs should be bumped about .003" to ensure reliable feeding.

[pacrat]

cgseanp1

[1] ... I just noticed that Forster sells a 308 Win NM which automatically bumps shoulder .003" for target rifles.

[2] ... Back to my original question, should someone with a factory gun just use a standard F/L and not be concerned with the additional setback, or should you always go straight to the extra setback of the shoulder?

[1] ... Translates directly to plain English as "BOVINE EXCREMENT SALES PITCH".

[2] ... Answer not as simple as question suggests.

Terms such as "headspace" and "bump" are relative to the measurements of individual chambers. There are NO ONE SIZE FITS ALL solutions to answer your questions.

Same goes for "OAL" and "SEATING DEPTH" terms. Rifles are like Wimmen. They are all different, and each has its own set of personal preferences, and dimensions.

If your goal is to craft best possible accurate rounds that reliably cycle in your MRAD. Without going Bat Ch!t Crazy Overboard on DoDads and WhatNots. Follow Tabasco's advice.

Take a few cases fireformed in YOUR RIFLE. Before any resizing is done. Using calipers and a pistol case inverted on neck to determine base dimension, FOR YOUR RIFLE. Set your FL sizing die to shorten that BASE dim. by .001 to .002".

FYI ..... Never rely on factory ammo, for ANY PRECISE MEASUREMENTS. Measure 10 different makers FACTORY ammo. And you will get at least 7 different dimensions. FACTORY ammo is typically made "ever so slightly" under SAAMI spec dimensions. That is to guarantee that it will fit and function, in the plethora of variations in factory rifle chambers.

[Donny1]

I just noticed that Forster sells a 308 Win NM which automatically bumps shoulder .003" for target rifles.

Bumps it from where? Wherever it currently measures? Those are fancy stuff so I'm curious.

I have LEE Dies in .223, .308. If you adjust them the way they say, touching shell holder then another 1/4 turn give or take, you will be bumping the shoulder a lot and it will work in anything. Start with the die backed just away from the shell holder and work in until you get the bump you need.

[ar15barrels]

Trying to wrap my head around this.. have been watching Erik Cortana youtube videos and was watching his F/L resize last night.
He was demonstrating how to bump the shoulder back and additional .002".

Is this additional .002 shoulder bump more than a factory 308 cartridge would have?

It should be 0.002" from a case fired in the specific chamber that he is sizing the brass for.

Depending on the length of the chamber, that could mean that the case is longer or shorter than the SAAMI standard.

[QED]

It should be 0.002" from a case fired in the specific chamber that he is sizing the brass for.

Depending on the length of the chamber, that could mean that the case is longer or shorter than the SAAMI standard.

.001" for bolt guns. Works OK for load testing in a 6mm creedmoor RPR and 204R in a bone stock savage varmint gun:

[ar15barrels]

.001" for bolt guns.

As long as you don't mind camming the bolt closed on an occasional tight cartridge, 0.001" is fine too.
Your groups would be exactly the same with 0.002" of shoulder bump though so why bother?

[QED]

As long as you don't mind camming the bolt closed on an occasional tight cartridge, 0.001" is fine too.
Your groups would be exactly the same with 0.002" of shoulder bump though so why bother?

I measure my cases post sizing so .001" doesn't result in tight cartridges. This is a game of precision, both in loading and shooting. Sure you can build in more margin, but then you should probably bump .005" for everything to ensure that rounds always fit in everything. No thanks.

[ar15barrels]

I measure my cases post sizing so .001" doesn't result in tight cartridges. This is a game of precision, both in loading and shooting. Sure you can build in more margin, but then you should probably bump .005" for everything to ensure that rounds always fit in everything. No thanks.

Size a few cases an extra 0.001" and do a blind accuracy test.
Report back.

[QED]

Size a few cases an extra 0.001" and do a blind accuracy test.
Report back.

Do what you want. That's what I do. If you can control dimensions well, then control them more tightly. If you can't then do whatever. Tightening controllable tolerances is always a good thing.

[ar15barrels]

Do what you want. That's what I do.
If you can control dimensions well, then control them more tightly.

Since you said you measure the case shoulder lengths after sizing each case, what's your SD?
Post your raw data.
It must be in an excel sheet since you are so sure of what you are doing.
What method are you using to set the shoulders all the same length?
Are you stopping a shellholder hard against the die to eliminate press frame stretch or are so sizing with air between the shellholder and the die?