• This Forum is for adults 18 years of age or over. By continuing to use this Forum you are confirming that you are 18 or older. No content shall be viewed by any person under 18 in California.

Bushing and mandrel size questions....

fatelvis

Silver $$ Contributor
My once fired 6BR necks (necks not turned) measures .271" outside. I anneal after every firing, and before sizing of any kind. A loaded round measures .268" outside.
What neck size bushing, and what size mandrel would you use, and what would your target neck tension be using this combination? Thanks Guys!
 
I have rifles running from .001" to .005" neck tension. The big problem with mandrels is the lack of different sizes. I dont want to lube the necks (unless I do) so I also only like carbide for mandrels. A set of carbide mandrels from .001-.005 under bullet diameter would be ideal. But since that doesn't exist I stick to bushings alone. You will want to test from .001-.005 on target to know what is the correct neck tension for your rifle. Measure the sized vs bullet seated neck diameter to get actual neck tension/interference fit. Dont trust the number on the bushing. This is as critical to the load as seating depth or powder charge, it should be tested. Picking a certain neck tension for everything would be like picking one seating depth for everything.
 
I belive the more you jam the less neck tension needed to get same pressure.
The less jam the more NT to keep pressure. I dont conagraph. I go by grouping.

I found my groups spreading out at my depth with tight necks.
I start at touch with 266 bushing.
I dont use a mandrel. I shoot a no turn 272.

Im no expert by any means this is what i have experienced.
 
If my fired brass's necks measure .271", can I assume I have a .272" neck chamber? It is a Shilen barrel made for my RPR, and the neck size was never specified when I ordered it. I told them I wasn't going to turn the necks.
 
Last edited:
If my fired brass's necks measure .271", can I assume I have a .272" neck chamber? It is a Lilja barrel made for my RPR, and the neck size was never specified when I ordered it. I told them I wasn't going to turn the necks.
Probably a pretty safe assumption, but why assume? Get a .272- pin and verify.
 
@fatelvis
Here is how I determine my neck tension and what bushing and mandrel to get:

Neck Tension
0.0141​
0.01475​
0.01505​
0.01435​
Total
0.05825​
Average
0.0145625​
Thickness
0.029125​
OD
0.337​
0.0145​
0.0147​
0.01435​
0.0147​
Total
0.05825​
Average
0.0145625​
Thickness
0.029125​
OD
0.337​
0.01455​
0.01445​
0.01485​
0.0146​
Total
0.05845​
Average
0.0146125​
Thickness
0.029225​
OD
0.337​
0.0148​
0.01475​
0.0145​
0.0147​
Total
0.05875​
Average
0.0146875​
Thickness
0.029375​
OD
0.337​
0.0146​
0.0148​
0.0147​
0.0143​
Total
0.0584​
Average
0.0146​
Thickness
0.0292​
OD
0.337​
Overall
Average
0.014605​
Thickness
0.02921​
OD
0.33721​
Bushing
0.335​

This is for 0.308. I use either a 0.306 or 0.3065 mandrel. I want 2 thousands tension so the average neck size is .337 and I run a .335 bushing. To determine this I measure the neck wall thickness at four points then average it and divide by 2 then add the diameter of my bullet, IE .308. So 0.02921 + 0.308 = -.33721. After all is said and done I get .3345 -.335 Neck OD and .3045-.305 Neck ID
 
If my fired brass's necks measure .271", can I assume I have a .272" neck chamber? It is a Lilja barrel made for my RPR, and the neck size was never specified when I ordered it. I told them I wasn't going to turn the necks.
Yeah, i was told by gun Smith that all measurements are ''close". Humans and measuring devices ya know.
IMO
Not really important enough to buy pins for unless you just want to play with your toys.
 
I have rifles running from .001" to .005" neck tension. The big problem with mandrels is the lack of different sizes. I dont want to lube the necks (unless I do) so I also only like carbide for mandrels. A set of carbide mandrels from .001-.005 under bullet diameter would be ideal. But since that doesn't exist I stick to bushings alone. You will want to test from .001-.005 on target to know what is the correct neck tension for your rifle. Measure the sized vs bullet seated neck diameter to get actual neck tension/interference fit. Dont trust the number on the bushing. This is as critical to the load as seating depth or powder charge, it should be tested. Picking a certain neck tension for everything would be like picking one seating depth for everything.
Where in the process of load development do you suggest a neck tension experiment? After finding a good seating depth and powder charge?

Thanks,

David
 
Where in the process of load development do you suggest a neck tension experiment? After finding a good seating depth and powder charge?

Thanks,

David
This is a good question and I'm also interested in hearing Alex's response. I have done some [limited] testing of the effects of varying neck tension (interference fit), which were carried out using already well-developed/proven loads. If one were to start load development from scratch, it's less clear to me where the optimal position of neck tension testing in the load development process would be, although it would seem as though you'd want/need a load that is shooting reasonably well to test anything that might have a relatively subtle effect.
 
Where in the process of load development do you suggest a neck tension experiment? After finding a good seating depth and powder charge?

Thanks,

David
If you can get a good load then yes. Sometimes if your on the wrong bushing you cant even get a good load. In that case I shoot little ladders at each bushing and try to pick one that looks promising.
 

Upgrades & Donations

This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.


Click Upgrade Membership Button ABOVE to get Gold or Silver Status.

You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.


To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.

Forum statistics

Threads
166,257
Messages
2,214,836
Members
79,496
Latest member
Bie
Back
Top