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F TR Questions


furrybean

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My variation is now in for another .308 but a couple of musings I cant find the answer to.

 

Will SR Magnum primers be any good with palma brass?

Will a 1:10 twist be okay using the 155.5 Bergers

 

Thanks all

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According to Litz, the 155.5 Berger "Full bore" bullets have a nominal stability factor of 2.14 in a 1:10 twist barrel.

Below 1.4 indicates marginal stability, above 1.4 is good, so it looks like you're good to go........

 

H/man

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The answers are: ...... yes and yes. Most people use Fed205M, CCI-450, or CCI-BR4s with Palma brass. Some of the standard models have thin, 'soft' cups and will blank at Palma brass pressures. The SR primer is at its limits with 308 as to the weight of powder it'll reliably ignite too especially if it's cold outside. (Don't use some ball powders either. The new Hodgdon CFE223 is a no-no in this application even with BR4s.)

 

10-inch twist works very well with the 155.5 even if in theory it's 'over-stabilising'. Many GB league shooters have chamber freebores that accept both the 155.5 and 210gn Berger BT, 200 Hybbrid and suchlike and use whatever suits the weather conditions better on the day, so use 10. They shoot fantastic scores with the lighter bullets on the quieter days with horizontal line shape 'elevations'.

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  • 1 month later...

Next question on the journey to f class. I'm sorting my bullets to .05gr increments but is it necessary to further sort to base ogive or bearing surface or is that just pedantry?

 

One thing I've noticed is most of the 185's are slightly heavy 185-185.20

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It's been said that you can only guarantee consistent neck tension if you anneal after every firing and use a button type necksizer, (or turn the necks if you use a bushing type sizer).

 

Pete

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Ok - thanks

 

I get the point on neck tension and annealing (the softened brass being better able to provide uniform neck tension)

 

But I am struggling with the concept of not having to worry about overly long brass unless you are annealing. Does annealing mitigate the impact of lengthening brass (which I, possibly incorrectly, inferred from the post) or does it stop the growth itself?

 

I had assumed that, annealed or not, having overly long (out of spec) brass would make chambering difficult - Or by too long do we mean at the top end of spec but inside chamber tolerances?

 

Pete, I was about to start asking questions about your button type neck sizer but I am starting to sound like my youngest (why is the sky blue, who makes the clouds* .... ;-)

 

Cheers

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Hobbit - 'don't run your brass too long' was meant to imply 'don't try to get more than five or six firings'. (See university treatise published on here about a year ago on brass hardness).

 

Having said that - we could also look at it the way. Factory chambers are always long in the neck and no matter how long your brass grows, you are unlikely to end up 'crimping' it due to it touching the end of the neck.

 

However, this is not always the case with a custom chamber. My own 308 reamer requires brass to be trimmed after a couple of firings and I actually trim all my new Lapua brass back to 2.00 inches before I even fire it. Then, it would go for four or five firings before hitting the scrap bin.

 

I didn't have an AMP annealer then!

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Right another few questions

 

My rifle is taking about 12 shots to settle down after a clean but in the comps Id normally clean at the end of each day with the number of rounds being fired. Is 12 a lot as it's more than I've known any of my other rifles to need to come back on.

 

Second question. I know the blow offs can be a good indicator before the sighters but Ive got some old Amax I could use up to save all my preciously prepared match bullets. Is there any negative to using this as foulers?

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A few years ago, I did do a test with an RPA 308 Target Rifle (rested with scope). Accuracy noticeably deteriorated after around 45 rounds.

 

My 6PPC benchgun will go 25 rounds without any fall-off in accuracy but I've never tried to find its limit.

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To give a contrary view, the guy who was 4th in last season's FTR league championship only cleans when he notices performance begin to drop off - usually after around 300 rounds. He says he then wants around 30 back through it from a completely clean barrel before he's happy again with its on-range performance.

 

(Personally, I'm a clean it after shooting practitioner.)

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  • 3 weeks later...

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