Neck Tension Lapua 300prc

[Huntnful]

So follow up.

Do you yourself do neck bushing before or do you only run a mandrel?

You HAVE to bushing the neck down first no matter how you decide to size. It is larger than the bullet diameter after it's fired.

A brand new piece of brass is normally already neck sized small, and you can just run the mandrel into it.

 

[Huntnful]

Is your FL die using a neck bushing or no neck bushing?

I guess does a standard FL die already bring in the neck with out bushing?

Standard FL die sized the neck down also. But may squeeze it down much more than necessary.

 

[243winxb]

Necks need to be SIZED smaller then the mandrel/expander diameter. As said above.

Standard fl dies can size necks .010" smaller then needed.
A bushing die or custom honed die keeps from over working the brass, on sizing.

A Redding type S fl bushing die, with bushing installed gives full control of neck sizing. The correct bushing will allow bullet seating with no expander used. The bullet becomes the expander. (If lazy like me)

The S die can be used as a Body Die & necks can be sized with the Lee Collet Neck size die. If wanting to try different methods.

 

[LocalJW]

You HAVE to bushing the neck down first no matter how you decide to size. It is larger than the bullet diameter after it's fired.

A brand new piece of brass is normally already neck sized small, and you can just run the mandrel into it.

So I need to buy…

-FL die with bushing .003 under diameter
-then mandrel .002

FL die with bring neck smaller then needed,
Then mandrel open back up.

Do this will allow less movement then a standard due would do which should save brass life

 

[243winxb]

Bushing .003 under diameter

Under a loaded rounds neck outside diameter.

 

[243winxb]

My goal is to stop using decap and expander ball with FL die.

The Redding Type S fl Bushing die allows you to choose.

 

[Huntnful]

So I need to buy…

-FL die with bushing .003 under diameter
-then mandrel .002

FL die with bring neck smaller then needed,
Then mandrel open back up.

Do this will allow less movement then a standard due would do which should save brass life

Correct. Type S die. I would go .004 under loaded neck diameter. I have a few .003 under that didn't size down enough

 

[haisardao]

Is your FL die using a neck bushing or no neck bushing?

I guess does a standard FL die already bring in the neck with out bushing?

I have done both, when using a Mandrel I use a non bushing FL sizing die, without the expander ball, and then run the brass through a mandrel, I usually use a .306 Mandrel aiming for .002 of neck tension. That has works for me, many ways of doing it, probably need to try and see what works better with your loads.

 

[mrdinapoli]

I may have missed it but sometimes I and others have found the best results by using a FL die with neck honed to desired final size , no mandrel no bushings. Some die makers will hone for you for $10-$20 or you can do yourself with expandable hone and cordless.

Willys, I have never used a FL die with the neck honed to final size. However, I have used FL bushing dies with neck bushings selected to give me my proper final neck tension. The FL bushing dies will give similar results to using custom honed FL dies. (Although, I too have heard that honed dies might have a slight advantage over bushing dies).

All that said, I have found that I have noticeably improved my accuracy and ES/SD when using a mandrel to set my final neck ID size (6mm CM and 300 Win; SD < 10 fps and groups 0.25-0.5"). My and current thoughts are that setting the final neck tension with a mandrel (from the inside of the neck) instead of with a die or bushing (from the outside of the neck) is that I provides these advantages: 1) more consistent neck tension and neck ID between cases; and 2) it pushes any neck wall thickness inconsistencies to the outside of the neck leaving the inside of the neck more smooth and uniform for its entire length.

As noted in my posts above, after speaking to staff at K&M shooting, they suggest using a fixed die or bushing die to reduce the neck diameter to 0.002-0.003" below final desired neck tension / ID size, and then using a mandrel to re-exapand to final neck tension/ID. This allows the mandrel to be able to fully and consistently expand the neck. If you do not reduce the OD of the neck enough with the die, the mandrel will only partially bring the neck ID to desired size, leading to inconsistencies.

Example from K&M (https://kmshooting.com/product/expand-mandrel-prebuilt-kits/): "When using an expand mandrel to achieve final neck sizing bullet tension we find it best to size your neck 0.002" to 0.003" below your desired final bullet tension size. For example, say you are working with a 7mm caliber (0.284") and you would like 0.004" of bullet tension. Subtract the 0.004" from the standard bullet diameter, 0.284"-0.004"=0.280", this will be the final size after expanding. However, the neck inside diameter needs to be slightly smaller so the expand mandrel can properly size the brass. Now subtract the 0.002" or 0.003" from the final size, 0.280"-0.003"=0.277". Now based on your neck wall thickness select the appropriate bushing that will achieve the 0.277" inside neck diameter. Once this sizing is complete perform the final sizing of the neck with the expand mandrel. Be sure to at least use a light lubricant. Alternatively, you can use a traditional full-length die (expander ball removed) and use the expand mandrel for final sizing."

 

[mrdinapoli]

Local JW. You can use either a FL die without a bushing or a FL die with a bushing small enough to reduce the necks a sufficient amount. A FL die without a bushing tends to reduce necks more than necessary at around 0.005-0.010" -- you can measure this for your dies and cases by measuring the neck OD and ID of your fired cases after you size a case in the die without the expander. In a FL die with a bushing, you need to just select the correct sized bushing to give adequate neck size reduction. I agree with "Huntnful," typically about 0.004" under loaded neck diameter. By using a FL bushing die and selecting a bushing size to not size the case as much as a non-bushing die, you will work the cases less and provide less work-hardening of the brass.

It may sound complicated, but it is much easier than it sounds once you have the parts and just experiment and take your measurements along the way. I was overwhelmed with all the info available about 18 months ago too. I didn't know what to buy and didn't want to make a mistake. However, I spoke to the staff at K&M, took their advice, and just dove in. (See my post immediately above for an example from K&M that may help clarify the sizes and relationships between bushings and mandrels and neck tension calculations.)

This thread is a wealth of good and reliable information by a bunch of shooters that know what they are talking about. If you select the suggested bushings and mandrels, you will be in a good safe zone. From there, you can experiment.

I personally use both FL non-bushing dies and FL bushing dies -- good quality, but whichever I have on hand.

Real examples that I hope will make it clearer:

1. .270 Weather Mag: (STARTING WITH FIRED CASES WITH NON-BUSHING DIE)
- Weatherby .270 Wby FL non-bushing die
- Weatherby cases with neck wall thickness approximately 0.014" per side
- Expander ball from die: 0.27495" (measured)
- Expander mandrel chosen to be similar to expander ball diameter, and to provide approximately 0.003" NT:
- 0.275" mandrel selected
(Mandrel at 0.002" under bullet diameter with 0.001" brass spring back should provide 0.003" NT)
- 0.275" mandrel measured: 0.27515"
- Fired unsized cases: neck OD: 0.3075, ID: 0.2775
- Fired cases sized in Wby FL die WITHOUT expander: neck OD: 0.2975, ID: 0.2695
- These necks were reduced 0.008" by the non-bushing FL die (0.2775 - 0.2695)
- Fired and sized cases with necks expanded with 0.27515" expander: neck OD: 0.2995, ID: 0.2735
- These necks were expanded by 0.004" with the mandrel (0.2735 - 0.2695)
- Final Neck Tension = (bullet diameter) - (final neck ID) = (0.277) - (0.2735) = 0.0035"
- Case Neck total indicator runout after case prep and before bullet seating: 0.0005 - 0.0009"
- Accuracy: ⅝" for 3 shots at 100 yds (Weatherby Mark V)

2. 6 mm Creedmoor (STARTING WITH NEW CASES WITH BUSHING DIE)
- Whidden Competition FL bushing die
- Expander ball measured at: 0.24100"
- Lapua 6mm CM cases with neck wall thickness approximately 0.0145"
- Cases necks turned to 0.0140" to clean up high spots only
- Calculated loaded neck OD = (0.014)2 + 0.243 = 0.2710"
- Measured neck OD with 0.243 bullet in neck: 0.2710" (same as calculated)
- Select bushing 0.005" below loaded OD, therefore Bushing size: 0.2710 - 0.005 = 0.266"
- FL sized cases with 0.266" bushing (without expander ball): neck OD: .2675, ID: 0.2372
- Necks reduced by 0.0035" less than loaded round (0.2710 - 0.2675)
- Select mandrel similar to expander ball (0.24100) to give approximately 0.002 - 0.003" NT
(Expander mandrel 0.002"under bullet diameter + 0.001" spring back should give approximate desired NT)
- Expander mandrel measured at: 0.2410
- Expand with 0.2410 mandrel: neck OD: 0.2694, ID: 0.2392
- Necks were expanded by 0.0020" (0.2392 - 0.2372)
- Final Neck Tension = (bullet diameter) - (final neck ID) = (0.243) - (0.2392) = 0.0038"
- AVERAGE Case Neck Total Indicator Run-Out for 5 cases after case prep and before bullet seating:
- New Cases: 0.0007"
- New cases after sizing with bushing die: 0.0005"
- New cases after sizing and then expanding with mandrel: 0.00046
- Accuracy: ⅜" for 5 shots @ 100 yds (Ruger RPR)

From my personal experience, after working with several rifles and cartridges, and both and fired cases, I have found the following general guidelines helpful in selecting bushings and mandrels sizes when using a bushing to reduce the neck sufficiently to allow an expander to set your final neck tension reliably:

1. When you size necks down in a die or with a bushing, the neck diameter will spring back up approximately 0.001" larger than the bushing ( ie. using a 0.266 bushing to reduce the neck, then neck will often spring back to 0.267").

2. When you expand case necks with a mandrel, the neck will often spring back down approximately 0.001" (ie. using a 0.241 mandrel to expand the neck, the ID will often spring back to 0.240").

3. The amount of spring back in both directions is only an estimate, and is effected by brass quality, neck size, number of case firings, annealing, work hardening, and other factors.

4. Bushing Sizes:
- Minimum: 0.004" under loaded neck OD if case necks are turned or < 0.014" thick
- Typical: 0.005" under loaded neck OD if case necks are not turned or > 0.014" thick

5. Mandrel Sizes:
- Minimum: 0.001" under bullet diameter (should produce approximately 0.002" neck tension with spring back)
- Typical: 0.002" under bullet diameter (should produce approximately 0.003" neck tension with spring back)

Good luck.

 

[parshal]

However you choose to set neck tension whether that be with a mandrel or bushing only make sure you test on target. I have a buddy that discovered one of his rifles shot worse when using a mandrel. All his others shoot just fine when using a mandrel.

I use an expander mandrel after a standard FL sizing die (no bushing) for all my calibers which gives me about .0015" neck tension. I do anneal after every firing.

 

[Old Rooster]

I really like the new mandrel body die with windows.It allows you to see how far your pushing your mandrel into your case.
The one I have I bought several years ago and it's blind but you can feel the mandrel going into the brass well enough so as not to damage the brass.I may order one.All at 21st Century

 

[243winxb]

FL bushing dies VS custom honed FL dies.

My Redding fl S bushing dies do NOT size all the way to the shoulder. Sizing 1/2 of the neck improves accuracy. Can not use a bushing die before neck turning brass.

The honed die needs brass to ALWAYS be the same neck wall thickness. Less runout then a bushing, at times. Bushings not great when sizing down more then .008" in 1 step.

I neck turn 223 brass to fit my standard fl die. I control neck wall thickness.