Sierra 88 TMK Load Data

Do we have a consensus G1 BC for the 88tmk? I was seeing some chatter that the published number is off?
I can’t speak for anyone else. But on my rig, the 0.263 g7 bc has held up out to 1120yds.
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I’ve also figured out a solution for 5 round 223 aics mags that I’m happy with. But that’s for another post lol.

18” 223
23.0gr 8208xbr
2690fps
Swfa 3-9
Rokstok
 
22 Creed
@hereinaz ls wild 18” PBB .120 fb
88 tmk
43.7 h1000
Alpha brass
Cci 450
2.745 coal
2985 fps

Still in the first 50 rounds, no signs of pressure & hoping it still speeds up a bit. These are just 5 shot groups but so far each one of them looks about the same as these.
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~68% more powder just to get 200 more FPS?

.22 ARC is looking better and better here...

Am liking the ARC, too. My new take with the 88 is 22 ARC wins if a barrel is 16 to 20 inches, 22 CM if 20" or over.

With my criteria being limited to the combination of chambering/bullet seating, case volume limits, performance, and production magazine lengths, the 88 TMK appears to match up best with the 22 ARC.

Just seems the 22 ARC offers the best combination of performance and loading flexibility (lack of limitations).

Pic shows 223 Rem w/88 seating @ 2.53" OAL. That's about max length I can go with a 2.55" magazine and .090" freebore/throat. Even when maxing mag length, note 25% of the bullet length beneath the top of the shoulder.
Screen Shot 2026-04-10 at 8.28.52 PM.png

See crude pic of the same 223 Rem round next to ARC brass. With production magazines at 2.48 inches, appears the 88 can seat with bottom of bullet shank at middle of neck and still have a little mag clearance, allowing case volume to be maxed out.
Screen Shot 2026-05-25 at 3.09.52 PM.png

ARC (vs 223 Rem) advantages are 1) can seat 88 wherever you want to max case volume and not exceed production mag length, 2) ARC has greater fps w/35 grains of capacity vs 223 Rem @ 30 (comparing fired case volume). Keep in mind the 223 Rem case area used up by bullet base, compressing powder, etc.

Looking forward to seeing 88 results for longer-throated 22 ARC bolt guns.
 
22 ARC
16.25"
1/7.5"

Starline virgin brass
Federal 205
28gr of Varget
2.300" COAL

2711fps average
20fps es
6.2fps std

I had one round that had a little heavy bolt lift and an ejector mark, but the other 9 were fine.

Including the heavy bolt lift flyer the group was 1.91".
Screenshot_20260526_194656.jpg

Without the flyer the group was 1.12".
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I had to back my 22 ARC load down a grain after shooting in some higher temps.

Originally, 29.0 gr of Lever gave me 2830 fps (factory 22" howa) with 2 light ejector marks out of 10. Groups were good.

I tried that load again on a day temps were in the mid 80s. Ammo and rifle were in the truck in the sun, so it was pretty warm. Serious ejector marks on all fired.

I backed down to 28.0 grains and no more pressure signs. Accuracy was about the same and speed dropped to 2730 fps.


For reference, my 20" 22 creedmoor is moving them at just under 3100 fps with 12 more grains of powder.
 
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