Full Length Sizing Questions

saskdude99

saskdude99

Regular
Super GunNutz
Rating - 100%
100   0   0
Location
Saskatoon
I was watching a video from a top long range shooter in the US and he said most elite long distance shooters full length resize and bump the shoulder back .020".
Question is how do you measure that distance the shoulder is moved back. Seems kind of subjective when dealing with .020.
 
The number I've heard is more like 0.002". 20 thou setback is asking for early case separation.
To measure that, you need some tools. A Hornady case comparator set will probably be a good start. You're only interested in how much the shoulder of the case moves when you resize it, not the absolute number.
 
OldDude got it right..002 not .020

You need a bump gauge on a caliper - Hornady make one, Wilson and others, a way to mesure accurately the shoulder bump.

There is other ways, such as extended shell holder but you still need to mesure at some point.
Sizing die is backed out from touching the shell holder, then a case sized, bump mesured and slowly the die is screwed in, case sized again and this repeated until desired shoulder bump is reached.

For a hunting load and informal target, I would not bother. Those method are usually for custom chamber but prolong case life if this is a concern. It remove case slop in the chamber but also remove ability to cope with crud of any kind.

Most Sizing dies are made to resize the case to SAMI specs and function in any gun. Like when you buy factory ammo, so they are set up to touch the shell holder at full press ram. They usually overwork the brass in the process, but you are 100 % sure they will work in your gun and your buddy’s gun.

Up to you to see if it is of any benefit for your purpose. You do not specify if this is for a bolt gun or semi. Semi need more bump, in the range of .004

9F4AA45D-5FBD-44A8-BD0B-0BD44CD234DF.jpeg
 

Attachments

  • 9F4AA45D-5FBD-44A8-BD0B-0BD44CD234DF.jpeg
    9F4AA45D-5FBD-44A8-BD0B-0BD44CD234DF.jpeg
    13 KB · Views: 479
Last edited:
Definitely won't be 0.020", that's way too much. 0.002" is a popular number.

My Whidden die set contains a full length sizing die that also has a bushing for fine-tuning the neck diameter. Plus it includes a micrometer seating die with a spring-loaded pre-load sleeve to align everything leading up to the seat. And to your question, it includes a shoulder bump gauge like the one shown in Janeau's photo, but cut precisely to match the sizing die.
 
I haven't seen the video the OP is writing about.

I'm thinking the LR shooter making the video has a chamber cut with a custom reamer, right on minimum spec and likely a sizing die cut with the same reamer or another custom reamer that is extremely close.

At the very least the neck dimensions will be very close, to help keep the cartridge from tilting in the chamber.

The .002 shoulder set back would help keep the rear of the case against the bolt face, which would also elimnate any tilt in the chamber.

I had a 308 Palma Match chambered rifle that I had to do the same thing, just to chamber the cartridge and achieve consistent accuracy

I had a partial chamber made up so that I could measure the OAL from the shoulder to the base of the cartridge
 
If you can remove the firing pin assembly just size the case enough so the bolt will drop closed with little to no resistance. You may feel the spring pressure of the ejector though. I crowd the tight end of no resistance for target rifles and the loose end for hunting rifles. Works great. The sweet spot would measure around a thou or two.

One caveat is that if extraction of a fired case is stiff near the top of the bolt throw then you’re not getting enough sizing at the base. You’d have to turn your die in a bit more to avoid the issue, if it’s important to you that is. It all depends on how well your die matches your chamber. I’ve rarely had problems with SAAMI chambers though.
 
Last edited:
You can get you base line measurement from your fired brass, and bump back. As stated above, this is easy to do and measure for.

I am doing it that way, and it is working out great for me. Is it the only thing, no, but it all adds up.

Mine is a hunting rifle, but built on a defiance action with a proof barrel. Have it shooting out to 1200 yards now, and plan to see what I can do out to 1500 yards for the fun of it, still using a hunting round. Shooting 6.5 PRC. No I will not be shooting at game that far out, but it is nice to know what limits you can personally attain.
 
wallz said:
You can get you base line measurement from your fired brass, and bump back. As stated above, this is easy to do and measure for.

I am doing it that way, and it is working out great for me. Is it the only thing, no, but it all adds up.

Mine is a hunting rifle, but built on a defiance action with a proof barrel. Have it shooting out to 1200 yards now, and plan to see what I can do out to 1500 yards for the fun of it, still using a hunting round. Shooting 6.5 PRC. No I will not be shooting at game that far out, but it is nice to know what limits you can personally attain.
Click to expand...

I like your common sense ethics.
 
bearhunter said:
I like your common sense ethics.
Click to expand...

Yea I figured someone would jump on that if I was hunting at that distance. Its amazing the accuracy one needs to attain and keep for that distance to make solid, "constant" hits.

Was practicing out to 550 yards off a tripod. That in itself is a challenge. I was not ready to go beyond that yet.

Might source an actual target bullet, and see if I can increase that impacts out at distance. There are a lot of variables that one has to align to shoot out that far. Accurate loads is only one part, but it is nice knowing the loading has the potential. Makes you all confident to 600-700 hunting distances if things are all right.
 
What Cortina does not talk about is the relationship between his reamer and the sizing die.... One or both will be custom at that level of competition. In his interviews, you'll see guys hesitate as they withhold elaborating on what FL means to them.

The key takeaway is that you want to resize just a hair and no more. More is not better.

Any energy that is lost to blowing the case out to fit the side wall of your chamber with translate to a velocity loss and a velocity spread.

If you don't resize, you can get rounds that act like over pressure rounds. You can get stiff bolt lift. If you watch the video between Erik and Speedy, you will see Speedy tied group dispersion to angular tilt of the rifle that was caused by stiff bolt lift.

So your goal is to just resize the length without meaningfully resizing the side wall. Saying that is easy. Doing it well, not so easy, but without getting all technical, most will be pleased by using bolt feel. Remove the firing pin assembly and test how it feels to chamber a sized round. If its tight, then it needs more sizing. If it feels loose, you probably went too far.

The best way is to use some sort of headspace gage.

BTW, it was stated above to use a fired case as the starting point... That is subjective. You may want to use a twice fired case or even a 3x fired case as your starting point. A once fired case is more than likely exactly where you want a 3 x fired case to finish at.
 
wallz said:
Yea I figured someone would jump on that if I was hunting at that distance. Its amazing the accuracy one needs to attain and keep for that distance to make solid, "constant" hits.

Was practicing out to 550 yards off a tripod. That in itself is a challenge. I was not ready to go beyond that yet.

Might source an actual target bullet, and see if I can increase that impacts out at distance. There are a lot of variables that one has to align to shoot out that far. Accurate loads is only one part, but it is nice knowing the loading has the potential. Makes you all confident to 600-700 hunting distances if things are all right.
Click to expand...

Most hunters I've seen, aren't capable of shots over 100yards, simply because they do all of their practice off a bench.

Maybe one in a hundred is capable of an offhand shot at 100yards and keep their shots within 4moa of Point Of Aim.

The ratio gets lower after that.

Even professional long range shooters insist on a stable shooting position for most shots.

Then, there are other factors, such as wind/rain/mirage etc.
 
bearhunter said:
Most hunters I've seen, aren't capable of shots over 100yards, simply because they do all of their practice off a bench.

Maybe one in a hundred is capable of an offhand shot at 100yards and keep their shots within 4moa of Point Of Aim.

The ratio gets lower after that.

Even professional long range shooters insist on a stable shooting position for most shots.

Then, there are other factors, such as wind/rain/mirage etc.
Click to expand...

I agree I have never taken a shot at an animal with out a rest, and I never will....
 
I'm thinking the OP got confused between the base to datum length needing to be bumped back .002 from fired, and the base to ogive being set at .020 off jam in the barrel. Possibly a case of his not understanding terminology in the video.
 
209jones said:
I'm thinking the OP got confused between the base to datum length needing to be bumped back .002 from fired, and the base to ogive being set at .020 off jam in the barrel. Possibly a case of his not understanding terminology in the video.
Click to expand...

I’m guessing he doesn’t know how to write 2 thousandths.
 
You must log in or register to reply here.
Back
Top Bottom