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Magnum primers and MV


Hobbit

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I have a load worked up for my AI AXMC with a 300 win mag, long throated 30” barrel using n165, 225gr elf-m’s and Peterson brass (stays above transonic to 1200 yards without burning the barrel too badly)

i have been using federal standard LRPs but now have some federal magnum printers to try - I will, of coarse, work up the load again but wanted to get an idea what to expect. Higher or lower mv’s, better/worse precision or ES/SD, better pressure tolerance?

what is the usual experience of moving to magnum primers?

thank you

 

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Magnum primers don’t necessarily mean greater velocity, they just have a slightly thicker cup to deal with the typically higher magnum pressures.

I think Laurie did a whole series of articles in Targetshooter magazine, where he looked at different primers from various manufacturers (incl standard vs magnum in both SP and LP).

Edit: http://www.targetshooter.co.uk/?p=2662

Whilst ive also a .300wm (in an AI AWM) Ive yet to shoot it, I have however read that many shooters prefer the performance of standard LP primers over magnums in the .300wm. Seemingly some people feel the standard primers provide lower ES/SD, but I’m not convinced that’s a universal truth. It’ll be interesting to see what your testing shows. Good luck!

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1 hour ago, Catch-22 said:

Magnum primers don’t necessarily mean greater velocity, they just have a slightly thicker cup to deal with the typically higher magnum pressures.

Thicker cups for sure but so are BR primers.  CCI claim 20% hotter flame for magnum primers in their catalogue.  Hotter affects ignition and flame generation from the powder charge in complex ways as was found by Laurie.

Good article here too :https://www.shootingtimes.com/editorial/ammunition_st_mamotaip_200909/100079

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Mr Baggins,

Feel it will be a 'suck it and see' (usual caveats: dropping loads to start with). When I had a 300WM AWM I used Fed LR Mag match and it worked very well. Anecdotal info has the Feb LR Mag primers being developed for the Weatherby cartridges so 'hot' (or it it brisance? ) but have to admit they were the primer on hand as the flavour of the day for BPCR prior to all the under / over primer wads.

If you have a dig round you should be able to find detailed published info from the US Army's load development for the 300WM when they were using it for extended distance sniper duties - about 20 years old now though?

Nice cartridge, forget about the belt bit and get hold of an Innovative Technologies base sizer die.

Cheers Terry

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2 hours ago, Catch-22 said:

Magnum primers don’t necessarily mean greater velocity, they just have a slightly thicker cup to deal with the typically higher magnum pressures.

I think Laurie did a whole series of articles in Targetshooter magazine, where he looked at different primers from various manufacturers (incl standard vs magnum in both SP and LP).

Edit: http://www.targetshooter.co.uk/?p=2662

Whilst ive also a .300wm (in an AI AWM) Ive yet to shoot it, I have however read that many shooters prefer the performance of standard LP primers over magnums in the .300wm. Seemingly some people feel the standard primers provide lower ES/SD, but I’m not convinced that’s a universal truth. It’ll be interesting to see what your testing shows. Good luck!

Thank you for that - a very interesting read!

For the benefit of others the link above is to Laurier piece on SRP's 

The earlier LRP article is here http://www.targetshooter.co.uk/?p=1471

I will let you know how I get on!

 

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1 hour ago, Popsbengo said:

Thicker cups for sure but so are BR primers.  CCI claim 20% hotter flame for magnum primers in their catalogue.  Hotter affects ignition and flame generation from the powder charge in complex ways as was found by Laurie.

Good article here too :https://www.shootingtimes.com/editorial/ammunition_st_mamotaip_200909/100079

Thank you for this

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1 hour ago, terryh said:

 

Nice cartridge, forget about the belt bit and get hold of an Innovative Technologies base sizer die.

Cheers Terry

 

Terry 

Got one! 👍 - have been practising with it and find it very usable - my plan is to use a Lee collet neck die with a redding body die to bump the shoulder 2 thou / headspace of shoulder and resize above the belt with the below when required

I've got a redding competition bushing neck sizing die but have not got the low run out as with the Lee collet die in 308 of 6.5CM - to be honest I can't see how you could without uniformly (turned) case necks - any thoughts here?

 

 

 image.thumb.png.750b7de6bd14f131d5561a780ae65b05.png

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4 minutes ago, Popsbengo said:

Isn't a belted case head-spaced off the belt not the shoulder?

Yes - you are right but if you measure the case stretch (in my case up to 15 thou in both AI and Blaser) and then set the body die to bump it 2 though back you can avoid over working the brass. This is what I meant.

Cheers

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4 hours ago, Popsbengo said:

Isn't a belted case head-spaced off the belt not the shoulder?

PbG in the traditional approach 'yes' due to the original concept of safety over accuracy - something with teeth coming at you and you want the case held against the face of the bolt so the firing pin / primer works.

When reloading for paper targets you can forget the belt and reload as per normal for your rifle i.e. FL size to push the should back 'a bit' and go from there. the only issue can be a bulge near the belt (as the belt creates a stress point) which the IT base sizer die takes care of.

T

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1 hour ago, terryh said:

PbG in the traditional approach 'yes' due to the original concept of safety over accuracy - something with teeth coming at you and you want the case held against the face of the bolt so the firing pin / primer works.

When reloading for paper targets you can forget the belt and reload as per normal for your rifle i.e. FL size to push the should back 'a bit' and go from there. the only issue can be a bulge near the belt (as the belt creates a stress point) which the IT base sizer die takes care of.

T

Interesting, 

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Depends on the case, my 458 Win Mag definitely headspaces on the belt as there is no shoulder! 
With the 7 REM Mag I headspace on the shoulder after cases are fireformed to my chamber

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2 hours ago, terryh said:

PbG in the traditional approach 'yes' due to the original concept of safety over accuracy - something with teeth coming at you and you want the case held against the face of the bolt so the firing pin / primer works.

When reloading for paper targets you can forget the belt and reload as per normal for your rifle i.e. FL size to push the should back 'a bit' and go from there. the only issue can be a bulge near the belt (as the belt creates a stress point) which the IT base sizer die takes care of.

T

Yup, which is why I consider the commonly spoused negative comments about the belt a somewhat moot point.

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