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FL Resizing vs Neck Sizing

22 Apr 2012
@ 01:27 pm (GMT)


I'm still waiting on my 7mm Remington Magnum and look forward to reloading for it. Currently I reload for a 22-250 and a 270-308. In both cases I get higher velocity for the same pressure signs from brand new and FL resized brass.

I don't get too intense about accuracy from the 270-308 as I treat it as a 200m deer rifle, but I get intense about the 22-250. My last outing with the 12BVSS Savage 26" delivered groups touching and a remarkable 3820 FPS. That performance was supported by my general varmint rifle (Tikka T3 Lite SS in 22-250). From a 22" barrell it gave 3650fps (36.8grn RL-15, 55grn SP Hornady, CCI BR2, fresh Lapua brass).

When I use the same load in fireformed brass it has sticky extraction, sharp edged primers, less FPS, but about the same to a tad less accuracy. I find this in teh 270-308 also.

My thoery (and that's all it is) is two fold. 1. The expanding brass case acts to buffer the peak pressure curve and a give a more consistant pressure graph line. 2. The FL brass is resized using teh case head as its datum point. This provides consistant concentricity.

In line with these thoughts I have ordered a Forster micrometer seating die and a FL resizing die. The neck die doesn't come in a kit with these.

All that said, I note you have commented that neck sizing can produce a more accurate round. I'd like to hear your thoughts on this as I am about to embark on a reloading odessy with my 7mm RM.

Thanks in advance


24 Apr 2012
@ 02:06 pm (GMT)

Nathan Foster

Re: FL Resizing vs Neck Sizing
Hi, it makes sense that the expanding brass acts as a buffer against the pressure curve. Its a good observation. But if we take this to its conclusion, it tells us that the loads are a touch too hot. When you don't FL size, extraction is difficult and the primers are squared off at the outer edges, typical high pressure signs.

Sometimes upon discovering such things, it can pose quite a dilemna if the rifle is not accurate with more mild loads. It can mean having to start all over again and during this process, the discovery of many less than optimal variables that were initially overlooked.

Concentricity cannot be obtained at the case head (just ahead of the rim). The whole case body must be used otherwise the case head becomes an axis point.

Rifle chamber dimensions determine whether neck sizing of FL sizing is optimal. A tight chamber will often require FL sizing simply to allow smooth feeding, a loose dimension chamber definitely requires neck sizing. Each rifle must be considered on an individual basis.

In tight chambered rifles, sometimes, even with mild loads, the case will sometimes not spring back after obturation. This is what can cause sticky extraction. The same goes for hot loads, the case is held at high pressure for a long period of time and does not 'bounce' off the chamber walls.

With neck sized brass in a suitable chamber, a small degree of spring back will occur. The cases, although having good contact with the chamber, are never immensely tight fitting. In some rifles, FL sizing may be required after several reloads or, in the case of my .308, 60 cases may last 1200 rounds without ever having being FL sized.

Often, a tight fit neck sized case is a sign of the shoulder being accidentally bumped back during sizing which swells the body dimensions, making chambering very difficult. It is very important to set up a neck die properly in this regard.
24 Apr 2012
@ 10:40 pm (GMT)


Re: FL Resizing vs Neck Sizing
Thanks for a great answer. I have had this thought about fresh brass absorbing peak pressure for a while and did pass it by some experienced guys. They did agree about the new brass absorbing the peak of the pressure curve, but they didn't then extend that process as you have. You make two very valuable points.

Firstly, I might be squeezing just s few too many FPS out of the two current loads for my 22-250 and the 270-308. I must have a good think about what I want to do there (FPS vs common sense).

Secondly, that neck sizing is good for standard / loose chambers. FL resizing is best for tight chambers. I am still waiting on the final approval to be provided for my Permit to Acquire. As such, I can't get my hands on the rifle to assess chamber size. Its a Remington SPS so I don't think it will be tight.

Again, a great answer. Must have you over for a beer some time.
25 Apr 2012
@ 07:59 am (GMT)

Nathan Foster

Re: FL Resizing vs Neck Sizing
No worries, you are most welcome. Yes, the SPS rifles are generally loose dimensioned but you can't go wrong with an FL die, even if just to begin with.

You may have your work cut out for you getting the SPS 7mm RM into order. Just work through it step by step. I have posted recently about the SPS 7mm RM. Have a read through the post carefully, hope for the best but plan for the worst.

When breaking in the SPS barrel, it is not antique china to be tip toed around. Work it, beat it, break it, force it to conform, force the required finish into the bore. This is the correct attitude to take with the SPS bore. Hand lapping will break the SPS bore in, shooting and cleaning won't.

Refer to the barrel break in article as often as required, refer to the hold that forend article as often as required.

The rifle needs to be bedded and stabilized before you begin, it will then need the trigger tuned.

With a 162 grain A-Max or SST, start test loads at 71 grains 2217 and work up to 73.5 grains initially.

25 Apr 2012
@ 09:01 pm (GMT)


Re: FL Resizing vs Neck Sizing
When breaking in the SPS barrel, it is not antique china to be tip toed around. Work it, beat it, break it, force it

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