220 grain Sierra HPBTMK's in .308 Win?

NavyShooter

NavyShooter

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Goodday gents,

Looking to try something "completely different" and wondering if anyone has any load data, experience or guidance for me going down the road of looking at heavy bullets at low speeds.

I've visited some websites out there, and will proceed with the necessary caution, but to start with, I'm thinking that I"d like to see what 220 grain Sierra's will do in a .308.

Anyone have comments?

Thanks,

NS
 
I would bet you'd have to have a barrel with a 1 in 9 twist to stabilize those long bullets, my .308 with 1 in 12 won't shoot anything above 168 HPBT in length worth a damn!
 
I have thought of either the 190 or 220 SMK's in my 1-10, but am still scared and sticking to my 175 SMK until I have the money to burn to try it out. I would be willing to bet you couldn't get the 220 going any faster than 2650 without losing a primer pocket. Let me know how it works for you and maybe I will try too.
 
2650? more like 2250, in a 24-26" tube. I dont see the point of going over 175 grain for match shooting in a 308, but hell I like to experiment so let us know how it works or doesnt work :wave:
 
I have heard they are experimenting with this down in the southern states.
1:8 twist barrels and lower velocity. The 220 gr HPBT has a BC of .629. The 175's have a BC around .496. From the reports I hear the 220's will give any 6.5-.284 a run for it's money at long range. Another benifit is less barrel wear then the higher velocity 6.5's.
Run the ballistics at www.eskimo.com/~jbm/ballistics/traj/traj.html
 
I like heavy bullets, and my .308 has a 1:8 barrel for those occasions. A 1:10 twist should stabalize the 220 MK's. You should be able to get 2200 fps from a 220 and a load of 40 grs of H-4350 or H-380 would be close to maximum. I would start with 37 grs, and work up in half grain increments, and if possible use a chronograph.

For the naysayers, this load will stay supersonic beyond 1000 yards, and these long bullets often do not become unstable when they pass through the trans sonic to sub sonic velocities. I personally think it is because the velocity drop is at a slower rate than with shorter bullets.

For any one interested in the long range use of the 220 gr MK's in the .308, check out Precision Shooting at 1000 yards. Seems a fellow in Colorado hit a 16" gong at 3120 yards shooting a 220 gr MK in a custom .308 with an AI chambering. Anyone who can throw rocks that far has quite an arm.

Edited to add - my rifle has a long throat so I can have a heavy bullet contacting the lands while only the boattail extends into the body of the case. With a normal throat, the bullet might extend well into the body of the case, reducing powder capacity, which might result in higher pressures being experienced. Proceed carefully if this is the case. Perhaps a starting load of 35 grs would be more prudent.
 
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A few F(TR) shooters in the US are trying this out to get less wind drift out at 900/1000yds.

The 220gr MK will stabilize just fine in a 10 twist. Of course, there will be experimenting with faster twists just because.

All of these rifles have the chamber throated very long with the bullet just into the case enough to hold tightly. I would think H4350/4831SC as good powders.

Yes, they are pushing 2500 to 2600fps with this heavy a bullet out of 30/32" pipes. Just think really short magnum!!!

Personally, the recoil is way more then I want to deal with and the 223 should be able to be in the ballpark with 1/4 the recoil. There are so many new bullets coming out in the 80-90g range that ballistics have improved tremendously. And you can hot rod this case with far fewer issues then the larger 308.

I think the new 208gr Amax will help the 308 reach the performance goals of launching super heavies (apparently the 210MK isn't doing so hot). Recoil will still be very stout so you have to balance what works on paper vs what you can drive accurately.

Jerry
 
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