.223 Sierra 69gr Tipped-MK Load Data - Viht N140
- Thread starter Euan
- Start date
@Euan are you just starting rolling your own ?
Is the twist rate of your barrel 1:10 or faster ?
Rifle reloading data | Handloading | Rifle calibers | Centerfire Rifle bullets | Reload your own ammo - Vihtavuori
Is the twist rate of your barrel 1:10 or faster ?
Rifle reloading data | Handloading | Rifle calibers | Centerfire Rifle bullets | Reload your own ammo - Vihtavuori
English Rifleman
Well-Known Member
From Sierra
Euan
Well-Known Member
Thanks pal, already loading was just looking for some recipes that already work to get me in the ball park, 1 in 8 twist barrel
Euan
Well-Known Member
Cheers pal
Malxwal
Well-Known Member
AR15 loads are generally different from bolt action loads I think I gleaned from looking for loads for 69gr HPBT Matchking.
English Rifleman
Well-Known Member
If you look at the data is states AR15 at the top
Malxwal
Well-Known Member
Cool, ta. But I wouldn't have thought the OP looking for gas gun loads ?
No, they're not actually - at least not for allowed peak pressure.
What is different is the chamber form in use here, specifically the freebore length. The Sierra data for the 69gn MK and N140 are very unusual in that the 'bolt-gun' maximum is higher than that for the 'AR-15' version - generally, it's the other way round in this pair of tables. Loading manuals normally use SAAMI compliant test barrels and chambers, and one presumes this is the case with Sierra's 'Bolt-Gun' data. The SAAMI 223 Rem chamber has a very short throat, only 25 thou' length, and a sharp-angle leade (the transition section into the lands), which in combination produce high pressures. The 'AR-15' data are for the Colt AR-15A2 HBar competition rifle which comes out of the box with a heavier barrel, faster (one turn in 8-inches) rifling pitch, but also a different, very long-throated and shallow leade angle chamber. Normally, maximum charges end up higher for the AR table loads in Sierra's data, the reverse of that applying in many other cartridges where higher MAPs, and hence powder charges, are allowed for stronger bolt-action type rifles (eg 6mm ARC and 6.5mm Grendel) compared to AR-15 loads.
All of the Sierra data (either table) are based on the SAAMI 55,000 psi maximum pressure, so it is mostly the chamber differences between the two barrels that change loads, (but see below for the case capacity issue). You can if you wish (but few would) have an AR built with a true SAAMI 223 Remington chamber. Most people use at least the Wylde chamber with its near 70 thou' freebore. However, build a true 223 Rem AR or bolt-action rifle and SAAMI compliant loads are the same irrespective of the platform. The AR-15A2 Hbar used for the gas-gun table has at least a 5.56mm NATO spec chamber (much longer freebore than the SAAMI 223 Rem equivalent), but I suspect its freebore is actually longer still to suit the 80gn SMK. Increase freebore and you reduce pressure from any case/primer/bullet/powder combination.
What complicates the issue yet further is COAL which is very restricted by magazine length for this cartridge. The giveaway that the two tables are based on different chambers is Sierra's COALs for those longer bullets that are single-loaded and not magazine fed. The 80gn SMK has a COAL of 2.430" in the Bolt-Gun tables; 2.550" in the AR-15. (TBH, I doubt if you could chamber this bullet at Sierra's 2.430" COAL in a true SAAMI 223 chamber - I reckon it would still be way over-length - but that's a different matter.) As the 69s (MK or TMK) are intended for rapid-fire from the magazine in gas-gun use, they are shown loaded at the shorter SAAMI 2.26" to fit the magazine, or even a tad less for reliable feed. The issue then for many extruded powders such as N140 is getting enough powder into the case before suffering serious charge compression.
A useful explanation of 223 chamber differences can be found here:
5.56 vs .223 - What You Know May Be Wrong - LuckyGunner.com Labs
which includes a table of reamer dimensions for the different common chamber types for the cartridge. Note that as the author points out, a 223 shooter's chances of actually using a rifle chambered in true SAAMI 223 Rem are miniscule outside of a ballistics lab.
The other factor to be borne in mind with published 223 Rem data is the make / capacity of the case. There are considerable capacity differences between makes, and sometimes over time too in cases from a single maker. In such a small cartridge, this has a significant effect upon the pressures that any given load produces. Just to make life even more complicated, Sierra uses different makes in the two tables - Federal in 'AR-15' and Winchester in 'Bolt-Gun'. Normally, I'd expect Winchester to have significantly greater capacity over Fed allowing higher charges. (For many editions, Speer's manuals used Israeli IMI brass in its 223 data as the company had found it to be the lowest capacity commercial case on the US market and therefore generated the highest pressures. A handloader thoughtlessly changing make of case would therefore always reduce pressures, not risk producing excessive pressures as is possible in the other direction.)
English Rifleman
Well-Known Member
Laurie is spot on as ever. When I started loading for my .223 I used some acquired Lapua brass. What seemed strange was the cols were changing despite using a micrometer match die.
Also some required a bit more umph to seat. Then I realised some were compressed. Carefully looking at the brass head stamp the lettering was of different sizes and clearly I had two different batches confirmed when I weighed them. Also there appears a difference between Lapua .223 brass and .223 match brass. Moral of tale is never mix brass even if it's from the same maker!
D
Also some required a bit more umph to seat. Then I realised some were compressed. Carefully looking at the brass head stamp the lettering was of different sizes and clearly I had two different batches confirmed when I weighed them. Also there appears a difference between Lapua .223 brass and .223 match brass. Moral of tale is never mix brass even if it's from the same maker!
D
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