How tight do you size the neck of a SAMMI chamber

[Vomact]

I recently purchaed a Saavage 12 lpv, DBM in .22-250.

I am in the process of buying dies and I want to have a decent 'spread' of neck bushings to control neck tighness.

The SAMMI spec on a .22-250 is .254". I have\will be turning necks. I will be shooting

Bergers almost exclusively from the 52 Match FB to the 73 grn BT target.

Varmit bulletts will include the 55 Match grade to the 64 Matche grad

Questions for the forum:

1) How thing would you go on the necks? I have turned some to 'just' clean up ant high spots.....which leads to the next question

2) What is the max. size bushing you would use? I have bushings up to. .252 however I ws conidering a .253.


Thanks,

Vomact

 

[AZShooter]

Ignore the SAMMI specs of chamber. Measure the neck OD of a loaded round and subtract .001", .002" and .003 for the sizes of the bushings you should use. To be honest I don't use a .003" difference unless there is evidence that the bullet moves while sitting in the magazine for three for four rounds of firing. Usually .002" difference is enough to hold the bullet in place. Now if you are single shot loading you can get away with even less neck tension.

If this is a factory chambering don't go past the skim turning the necks. The more you take off the greater the difference there is between the neck dimension in the chamber and the one you will use for proper neck tension. Typical SAMMI specs are generous so there will be some working of the brass which leads to it getting harder and eventually it will split unless you anneal.

You are helping to extend the useful life of the brass some by not using a FL sizing die with a sizer ball. That setup reduces the neck diameter even smaller so the sizer ball can bring it back to a dimension that will yield some neck tension.

 

[dkhunt14]

I agree with Arizona. You need to measure a loaded round and use .002 to .003 under that. It all depends on what the thickness of the necks are. I have seen guns that like a lot of tension on loaded rounds. Some don't like quite as much. I usually run pretty good tension and most of my guns shoot best that way. Matt

 

[Vomact]

Thanks guys!

I had already measured some loaded factory ammo (at .251) so I have .258,259, 250 and .251 bushings. I used a K&M neck turner and just took off the high spots.

I use RCBS Gold Medal dies (without the expander ball) when first prepping new cases. From then on I use Wilson dies.

I am using two different types of brass. I went for my brains and bought 100 Lapua (that stuff is HARD). I did a weight analysis and the case weights were very uniform. The weight variation on the box was practically a straight line. I purchased 50 rounds of Norma in a 'what the heck' mood an these are TOTALLY different. The weight distribution is a straight sloped line, not a flat line or a normal distribution that I would have expected. At first I though the scale was drifting so I weighed them again. Sme results. Same results with the balance beam.

Any Ideas why this happens.

Thanks,

Vomact

 

[AZShooter]

looks like the only bushing you could use is the .250 bushing. You will need to get a .249 and maybe a .248

I would think if you are sizing the necks down in FL sizer without the sizer ball the inside diameter of the necks would be very small and seating a bullet would be difficult. I think it would be better to use the expanding mandrel you used for neck turning then use a bushing to reduce the neck diameter.

Lapua obviously made more consistent brass than Norma. It has to do with how good they draw the brass for consistent wall thicknesses which in turn makes the cases weigh the same.

IMO You probably would have had excellent results with the Lapua brass if you didn't bother to skim neck turn, but it is a bit late for that.

 

[Varmint Hunter]

I wasn't too sure exactly what you were asking in your original post. However, if you are neck turning, it would be a good idea to know what the specific neck diameter of your chamber is. Too much clearance between the loaded round neck diameter and the chamber neck isn't normally conducive to the best accuracy and thinning necks more than necessary will likely shorten brass life.
IMO, when using high quality brass in a factory SAMMI chamber, neck turning is completely unnecessary and may even be counterproductive.
However, if you are intent on neck turning, then a minimum amount of turning that removes no more than 25% (highest spots) of the circumference would probably be best.
As indicated above, a bushing that is .002-.003 smaller than your loaded round neck diameter is good. That would mean that you need to turn necks first, keeping in mind that different lots or manufacturers often have different neck thicknesses to begin with. More than one bushing may be necessary.