7-270 wsm dimensions

[Fast14riot]

Going to make the switch to magnum for F/Open. Decided to go 7-270wsm using ADG brass. Anyone have a loaded neck diameter or wall thickness for 270wsm necked up? Working on reamer specs.

 

[muleystalker]

What's the case capacity of the 270 WSM compared to the 300 WSM or the 7 SAUM?

 

[Fast14riot]

I believe 270 and 300wsm are the same case and 7wsm was longer datum so it could not be chambered in a 270wsm rifle. I was looking at the 7max version but the 7-270wsm makes more sense to me instead of necking down 300wsm or using SAUM brass.

 

[L.Sherm]

The 270 and 300 are the same case other than the neck dia. ive used both on my 6.5x300wsm.
If it helps necked down to 6.5 from 300wsmADG is about .165 unturned

 

[ShaunBrady]

Peterson has neck thickness data on their website under "Ballistician Testing Workbook". ADG lists it in "Additional Information" with the individual cartridges.

I've been using 7/270wsm as an ELR practice round for 10 years. Necking up from 0.277" to 0.284" isn't much of a wildcat and won't change the wall thickness noticeably so the 270 numbers will work. Peterson gave 0.0165", ADG 0.0162".

 

[ShaunBrady]

What's the case capacity of the 270 WSM compared to the 300 WSM or the 7 SAUM?

Those WSMs are ~84 grains of H20, SAUM is ~73 with ADG. 7/6.5PRC is ~68.5.

 

[Springer2]

I happened into a 40X at a gun show in 7mm WSM. It is really a shooter but it seems to be the least popular of the WSM rounds.

 

[L.Sherm]

Fast14, Shaun is correct on the 16.2 I just went back and did the math necked down from 300 wsm to 6.5 its 016.5 ish
sorry about that I corrected my earlier post.

 

[Fast14riot]

Peterson has neck thickness data on their website under "Ballistician Testing Workbook". ADG lists it in "Additional Information" with the individual cartridges.

I've been using 7/270wsm as an ELR practice round for 10 years. Necking up from 0.277" to 0.284" isn't much of a wildcat and won't change the wall thickness noticeably so the 270 numbers will work. Peterson gave 0.0165", ADG 0.0162".

Whats your load with the 7-270wsm?

 

[Fast14riot]

So rough math, about 0.317 loaded neck diameter, and a 0.321ish chamber should be about right. Probably a 0.200" freebore. Will decide body dims once I have brass and dies.

 

[JFrank]

Just as a rough reference , our 270 short mags were running 58.6 gr of H4831sc under a 140 gr AB

Whats your load with the 7-270wsm?

 

[ShaunBrady]

Whats your load with the 7-270wsm?

It won't do you much good. It was mag fed, the brass has a few grains less capacity than ADG and it wasn't optimized for accuracy. It's likely the ADG brass will take noticeably more pressure than the Norma.

Norma Brass, 210M, 62.5 grains H4831sc, 180 ELDm blems @ 2.980". Velocity was 3040 fps from a 32" barrel. Brass would last 8-10 firings before the primer pockets loosened up. I think the blems were a preproduction batch. They had a longer bearing surface and shorter nose. The BC was maybe 6-7% lower than the production bullets. After I ran out of those, I switched to the production 180 ELDm and 0.020" jump which was just out of the magazine. 10 shot velocity ES was usually in the mid 20s. It shot a lot of 1/2" 5 shot groups, a few 3/8". After maybe 1200 rounds, it'd be consistently over 3/4" and I'd replace the barrel.

The gun was initially used as a second gun for ELR practice to 2200 yards. After some experience accumulated, it was used to compare scores with dedicated ELR wildcats. After it became the baseline, I did not try to improve the performance.

 

[L.Sherm]

ADG or Lapua hands down.
I switched over to ADG 300wsm for my 6.5x300wsm and couldn't be happier

 

[ShaunBrady]

So rough math, about 0.317 loaded neck diameter, and a 0.321ish chamber should be about right. Probably a 0.200" freebore. Will decide body dims once I have brass and dies.

I turn necks, so I'm the wrong guy to design a neck turn reamer. I also completely stop working on accuracy at 1/2".

It sounds like your process is similar though.

I think my highest priority with a no turn neck would be landing the rear of the bullet bearing surface 1/4 to 1/3 caliber ahead of the neck shoulder junction. It's a radius so the bullet bearing surface needs to be well clear of the intersection indicated on the drawing. It's the most dimensionally chaotic spot on the case, especially as the brass is repeatedly sized. With a no turn neck, I'd double down on that placement. Same basic dimensions, I'd just make double sure it happened. These days, I set up the freebore for 0.025" jump when the chamber is new and use that OAL for the life of the barrel. Don't get cute with the freebore clearance, just use 0.001".

With turned necks and the bullet bearing surface into the case past the neck/shoulder junction, "donut" formation would start degrading accuracy and velocity spreads by the third firing with 0.003" neck clearance. 0.006" would go at least 8. Keeping the bearing surface out of that joint helps that but even great brass has up to 0.001"variation in neck thickness around the diameter and maybe that again on the average from piece to piece. Interference will happen earlier with no turn brass if the bullet isn't forward enough.

On the other end, sizing fired brass, the minimum neck thickness was set by the die neck diameter. I wanted sized minus 0.004-0.006". Four under, brought to 2 under with a mandrel was the target. With a bushing die, this is easy to control but I needed a one piece die to size the whole neck for turning.

So now we have 0.010" of brass movement on the neck diameter every firing cycle. Annealing is a good idea and saves fiddling with the sizing die bump for the first few loadings. Same with the neck bushing diameter.

My process is optimized more for not getting bit as the brass is reloaded over several cycles or being overly dependent on being able to source exactly the same components next time. If I shot FClass, I'd probably focus more on precision with the components on hand. I'm not sure exactly what that would entail.