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Sierra load data for 77 tmk

iukamedic

Silver $$ Contributor
Good morning. Does anyone have the published data for 223 Sierra 77 tmk with tac and varget? Also the over all length. I’m curious about mag length. Thank you ahead of time.
 
Sierra VI Ed gives the following:

AR-15 Data (5.56 long freebore chamber, Federal brass, Rem 71/2 primer, 20-inch AR15A2 HBAR)

VarGet ............. start 22.6 / max 23.9gn for 2,550 fps
TAC ................... start 21.8 / max 24.0gn for 2,750 fps


Bolt Gun Data (standard SAAMI short freebore chamber 24-inch test barrel; Winchester brass, Win WSR primer)

VarGet ............. start 19.6 / max 22.1gn for 1,650 fps
TAC ................... start 19.7 / max 22.6gn for 2,650 fps

These data cover all three Sierra 77s (MK, TMK, MK cannelured), and for the Bolt Gun only, also include the 80gn MK.

All 77s are loaded to 2.260" COAL
 
Laurie said:
Sierra VI Ed gives the following:

AR-15 Data (5.56 long freebore chamber, Federal brass, Rem 71/2 primer, 20-inch AR15A2 HBAR)

VarGet ............. start 22.6 / max 23.9gn for 2,550 fps
TAC ................... start 21.8 / max 24.0gn for 2,750 fps


Bolt Gun Data (standard SAAMI short freebore chamber 24-inch test barrel; Winchester brass, Win WSR primer)

VarGet ............. start 19.6 / max 22.1gn for 1,650 fps
TAC ................... start 19.7 / max 22.6gn for 2,650 fps

These data cover all three Sierra 77s (MK, TMK, MK cannelured), and for the Bolt Gun only, also include the 80gn MK.

All 77s are loaded to 2.260" COAL
Click to expand...
Thank you. Thats weird that the bolt gun was less than ar. I’m trying to work up a load for a couple different different platforms. Sure appreciate you info. Ive seen a standard of 24.5 tac at mag length. That’s more than I load for 77 smk. I’ll do a ladder and see what happens. Thanks again.
 
iukamedic said:
Thank you. Thats weird that the bolt gun was less than ar. I’m trying to work up a load for a couple different different platforms. Sure appreciate you info. Ive seen a standard of 24.5 tac at mag length. That’s more than I load for 77 smk. I’ll do a ladder and see what happens. Thanks again.
Click to expand...

It's because of different chambers between the pair. The presumption with any loading manual data is that the tester has used a SAAMI or CIP compliant test-barrel and chamber. This is hugely restrictive in 223 Rem even for standard 12-twist factory rifles where the manufacturer often provides more freebore than standard spec to reduce pressures and limit liabilities in the event of over-loaded / 5.56 military ammunition producing an accident. Sierra's Bolt-Gun data tables almost certainly conform to this (SAAMI-spec) model.

The Sierra AR data however use a Colt AR15-A2 HBAR for testing which has the 5.56 NATO chamber with a freebore over double the length of SAAMI 223 and a shallower angle leade (the bevelled start to the lands) of 1.2 or 1.5-deg vs 3-deg which allow long bullets to be seated much further out for a longer COAL and reduce pressures irrespective of the load combination. The AR loads are therefore higher within the same Pmax ceiling. In fact, I wonder if the HBAR chamber has more freebore than the standard NATO as Sierra quotes the 80gn SMK COAL (for single-loaded use) at 2.550-inch and I know from having had a rifle chambered in the similar freebore but tighter-clearance Wylde chamber that 2.440 or thereabouts was max COAL before jamming this bullets into the lands.

As well as being an interesting read in itself, Luckygunner's take on this (223 vs 5.56 specs and pressures) aspect of the 223 is useful, especially the table of different chamber reamer dimensions showing the differences.

https://www.luckygunner.com/labs/5-56-vs-223/

When you get into 223 Rem in mid and long-range precision shooting with very fast twists, specialised chambers and 85-95gn bullets, the 0.169" freebore PT&G '223 ISSF' match chamber is the mere starting point. L-R FTR 223 Rem specialists such as @Ned Ludd who has many posts on this forum on 223 FTR rifle specs, bullets, and loads are running chambers with freebores well over 200 thou' these days as opposed to the SAAMI chamber with all of 25 thou' and its steeper leade angle resulting in 90 and 95gn bulleted cartridges with COALs of around 2.7/2.8" same as standard 308 Win.

With the huge variety of chambered barrels in use, the 223 is in effect no longer a single cartridge design (if it ever was) and many people are loading for wildcat versions these days, or at any rate alternative standard versions (such as the excellent and very effective Wylde chambered barrels used in many custom AR15s).
 
Laurie said:
It's because of different chambers between the pair. The presumption with any loading manual data is that the tester has used a SAAMI or CIP compliant test-barrel and chamber. This is hugely restrictive in 223 Rem even for standard 12-twist factory rifles where the manufacturer often provides more freebore than standard spec to reduce pressures and limit liabilities in the event of over-loaded / 5.56 military ammunition producing an accident. Sierra's Bolt-Gun data tables almost certainly conform to this (SAAMI-spec) model.

The Sierra AR data however use a Colt AR15-A2 HBAR for testing which has the 5.56 NATO chamber with a freebore over double the length of SAAMI 223 and a shallower angle leade (the bevelled start to the lands) of 1.2 or 1.5-deg vs 3-deg which allow long bullets to be seated much further out for a longer COAL and reduce pressures irrespective of the load combination. The AR loads are therefore higher within the same Pmax ceiling. In fact, I wonder if the HBAR chamber has more freebore than the standard NATO as Sierra quotes the 80gn SMK COAL (for single-loaded use) at 2.550-inch and I know from having had a rifle chambered in the similar freebore but tighter-clearance Wylde chamber that 2.440 or thereabouts was max COAL before jamming this bullets into the lands.

As well as being an interesting read in itself, Luckygunner's take on this (223 vs 5.56 specs and pressures) aspect of the 223 is useful, especially the table of different chamber reamer dimensions showing the differences.

https://www.luckygunner.com/labs/5-56-vs-223/

When you get into 223 Rem in mid and long-range precision shooting with very fast twists, specialised chambers and 85-95gn bullets, the 0.169" freebore PT&G '223 ISSF' match chamber is the mere starting point. L-R FTR 223 Rem specialists such as @Ned Ludd who has many posts on this forum on 223 FTR rifle specs, bullets, and loads are running chambers with freebores well over 200 thou' these days as opposed to the SAAMI chamber with all of 25 thou' and its steeper leade angle resulting in 90 and 95gn bulleted cartridges with COALs of around 2.7/2.8" same as standard 308 Win.

With the huge variety of chambered barrels in use, the 223 is in effect no longer a single cartridge design (if it ever was) and many people are loading for wildcat versions these days, or at any rate alternative standard versions (such as the excellent and very effective Wylde chambered barrels used in many custom AR15s).
Click to expand...
Man thanks. I appreciate the info. I shoot a Shilen SR from white oak, Odin works 16” and a tikka bolt. It’s neat to me that some rounds and loads I can get to shoot across all 3 and some won’t shoot in any thing. Anyway. Thank you for such an informative comment.
 
SKWERLZ said:
Interesting as it’s still working on my iPhone but not in store?????
Click to expand...
Not in the store that I could find and many reports on the web indicating the same. If you search and click on a link to take you to the iOS App in the store you get the following:
IMG_1458.png
 
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