I'm in the UK.  I've had great results using Sierra product code 1380, MatchKing .224 69gr '7"-10" bbls. only' but am having a lot of trouble finding more of this particular product.  When I contact UK suppliers they tell me they have these in stock when in fact they have S1380 in stock and others labelled '1"-10 twist' and 'Over 10" twist bbls'.  I really want what I've already got (there are enough variables already without switching heads!).  Is 1380 7"-10" still available?  My custom AR-15 by Southern Guns here in the UK says 1 in 9" on the barrel.
What's the significance of loading the "wrong twist" anyway?
Thanks!

John

I had excellent performance (sub MOA out to 500M) from a 24" barrel with 1/9 twist.

The mass of the bullet doesn't matter so much.  As the bullet gets heavier, it gets longer.  A longer bullet needs more spin to stabilize Generally, a 20" barrlel with a 1x9 twist will work great with 69, but a 77 is tool long.  Many bolt 223 guns will have 1x12 twists which will not provide enough spin for a 69.

Heavier bullets (longer) will not stabilize well in slower twist barrels.  Lighter bullets (shorter) are well suited for slower twist rates.

The lighter bullets usually will work fine with the faster twist rates too.

As barrels get shorter, less bullet velocity will lead to slower spin; all other things being equal, a shorter barrel may need a faster twist rate than a longer barrel to stabilize the same bullet.

Some thinly jacketed light bullets may come apart from spinning too fast if pushed hard through a fast twist barrel.

To complicate matters more, a non lead or non lead core bullet will be longer than an all lead bullet of equivalent mass.

The 69 Sierra 1380 will absolutely work well in a 1x7. 1x8 or 1x9 rifle with a 16" to 20".

I do not personally know how it will perform in a 10" barrel.   If there is enough velocity loss in a 1x9 barrel, a hotter load might boost velocity to help stabilize.

When in doubt send them an email.  I would say call but you’re over seas and it might be costly.  They’re very helpful.

I am not sure what’s going on but I think the 1-10” and over is bad for clarity.   I believe they mean faster not a bigger inch number.  So it be the same as before but written differently.

They have the regular one I have used, then they have the 1380m molycoated, and perhaps a polymer tipped version now.  I looked at their website and didn’t get enough info between 1380, S1380 1380c, and 1380m other than M=moly.

I may have figured out
1380 is 100 count
1380c is 500 count.

I am beginning to think the S is added to the stock number by your retailer for their system.  It’s pretty common to use the original code as the root and add a designator tonsescribe the supplier, Sierra in this case.

There are several stock # in USA
1380 which is a 100CT Box
1380C which is a 500CT Box

I agree with the above. Sierra lists 3 different styles of 1380. None start with "S".
Sierra link

Thanks for the responses guys. I've managed to track some down here in the UK.

get some varget and REm 7.5 or Br4 primers in prepped cases and look for Magic to happen at around 25.0gr or so somewhere were between 24.7-25.3

you can substitute a Nosler 69gr bullet and get same results

The Hornady in a 1in 9 get s a little hairy, it's a longer bullet that the sierra.

The 68gr has the same OAL as the 75gr. Fine from a true or fast 1:9.

The Hornady is the same length bullet for both weights, yes? 68 and 75. But both are longer than the 69 serria.
They "hornady" might shoot fine in 1 in 9's but not usually as good as the serria 69 match, which is shorter, and shoots better on paper.
If you are going to shoot groups, you more than likely will shoot tighter groups with the serria, maybe because they are shorter, hey.