77 Sierra MK HPBT how fast

Reloading equipment, methods, load data, powder and projectile information.

77 Sierra MK HPBT how fast

Post by andym79 » 25 Jan 2019, 9:02 pm

Hi guys just wondered if anyone has had experience shooting 77 SMKs?

I have a 1:7.7 twist barrel and am wondering how hard you can push them before the RPMs get too high a damage accuracy?

I read 240,000 RPM is the fastest you want to push a bullet, but in a 224 1:7.7 that's only 2500fps!

Does a 77 SMK loose accuracy over 2500fps?

Thanks

In advance
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Re: 77 Sierra MK HPBT how fast

Post by deye243 » 25 Jan 2019, 10:38 pm

Where did you hear that rubish and yes they will be accurate at around 2850 plus .
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Re: 77 Sierra MK HPBT how fast

Post by Ziad » 25 Jan 2019, 11:11 pm

Darn you learn stuff everyday.... most of it wrong. Lol

The rpr should handle 77gr no issues... you likely run into over pressure than rpm issues. Adi manual says 22.7gr 2206h gives 2700fps as the max powder charge, if so I would not think about 2500fps as being too high.

Edit. The is a bullet stability calculator on berger bullets website. It tells you what weight will stabilize in what twist rate.
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Re: 77 Sierra MK HPBT how fast

Post by bladeracer » 26 Jan 2019, 3:53 am

andym79 wrote:Hi guys just wondered if anyone has had experience shooting 77 SMKs?

I have a 1:7.7 twist barrel and am wondering how hard you can push them before the RPMs get too high a damage accuracy?

I read 240,000 RPM is the fastest you want to push a bullet, but in a 224 1:7.7 that's only 2500fps!

Does a 77 SMK loose accuracy over 2500fps?

Thanks

In advance


Where did you get that figure from?
My 8"-twist .223 was spinning 52gn bullets at 308,000rpm and they were disintegrating. Keeping them under about 275,000rpm they're fine.
Punching the 35gn at 3900fps spins it at 350,000rpm with no problems and excellent accuracy.
Practice Strict Gun Control - Precision Counts!
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Re: 77 Sierra MK HPBT how fast

Post by SCJ429 » 26 Jan 2019, 8:35 am

The SMK appears to have a very tough jacket with very little runout. They tolerate high rpm very well, much better than a hunting bullet. A friend shoots 80s out of a 22 Dasher with no stability issues. What case are you using?
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Re: 77 Sierra MK HPBT how fast

Post by straightshooter » 27 Jan 2019, 6:17 am

andym79
Sierra generally give recommendations for maximum muzzle velocity for each of their bullets. At least they used to in their loading manuals.
Do some research and work it out for yourself.
BTW I am currently loading my 223 1in8 twist 28" barrel with 25gn 2208 with excellent results.
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Re: 77 Sierra MK HPBT how fast

Post by andym79 » 28 Jan 2019, 5:33 pm

Hi Straight shooter, thats nice to know, I figured 24 gns would be good!

Do they group well as close as 100 yards, as I wondered if with a 1:8 twist, if the bullet would go to sleep quickly enough to do well at 100 yards?

I know the 77smks are meant to be excellent and longer distances, I ask because I know the benchrest shooters do best with slow twist barrels and small bullets for tight groups at 100 and 200 yards!
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Re: 77 Sierra MK HPBT how fast

Post by SCJ429 » 28 Jan 2019, 6:44 pm

How small a group are you chasing? My factory stock Tikka can shot 80 grain VLDs well at 100, best group of .220 and tons of groups under 1/4 inch. Best group at 500 with the same pill was under three inch. What type of barrel is your 1:7.7 twist? What action are you fitting it to?
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Re: 77 Sierra MK HPBT how fast

Post by andym79 » 28 Jan 2019, 6:50 pm

.220 well thats sweet 1/2" would be okay.

Barrel is Krieger 1 7:7 I got it for 77smks its still a Blank as I haven't decided what to fit it to yet. I got a choice of 5.6x50r in a cadet, 219 zipper improved in a marlin 336, 22-250 in a savage 99, 22-303 in a lee Enfield or a 220 swift on a ruger 3, but which would be best.

To most people this stuff might seem obvious but I have spent all my time shooting bullets 25 cal and up in cast bullets, needle guns are new to me.
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Re: 77 Sierra MK HPBT how fast

Post by marksman » 28 Jan 2019, 7:33 pm

you have some good choices there andym79
mine would be the 22-250 :thumbsup: but that's my opinion only it's up to you mate :drinks:
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Re: 77 Sierra MK HPBT how fast

Post by SCJ429 » 28 Jan 2019, 7:36 pm

I saw a Defience action for sale on Abused Guns that would be a perfect match for you Krieger. I have a Ruger #1 with a Pac Nor barrel which shoots in the .4s, so my vote is for the Ruger #3. A 22BR is my vote for chambering however, it can do what the 220 Swift can do.
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Re: 77 Sierra MK HPBT how fast

Post by andym79 » 28 Jan 2019, 7:53 pm

SCJ429 wrote:I saw a Defience action for sale on Abused Guns that would be a perfect match for you Krieger. I have a Ruger #1 with a Pac Nor barrel which shoots in the .4s, so my vote is for the Ruger #3. A 22BR is my vote for chambering however, it can do what the 220 Swift can do.


Is that with 77smks?
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Re: 77 Sierra MK HPBT how fast

Post by SCJ429 » 28 Jan 2019, 8:45 pm

No it is a 6mmBR.which I use to hunt foxes.
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Re: 77 Sierra MK HPBT how fast

Post by Ziad » 28 Jan 2019, 9:06 pm

6br....I am in love with it. Lol
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Re: 77 Sierra MK HPBT how fast

Post by straightshooter » 29 Jan 2019, 6:51 am

andym79 wrote:Hi Straight shooter, thats nice to know, I figured 24 gns would be good!

Do they group well as close as 100 yards, as I wondered if with a 1:8 twist, if the bullet would go to sleep quickly enough to do well at 100 yards?

I know the 77smks are meant to be excellent and longer distances, I ask because I know the benchrest shooters do best with slow twist barrels and small bullets for tight groups at 100 and 200 yards!


The 77 grainers were designed for use in ar15 rifles for US high power style shooting which is shot up to a maximum range of 600 yards. The jacket profile allows for an overall length compatible with ar15 magazine feed without the excessive deep seating as is required with 80 grainers but still permit close engagement with the throat in a ar15.
Sierra match king bullets are lot tested and must hold 0.5" groups in the Sierra test barrel. If they don't then that lot is downgraded and sold as 'seconds'.
The only reason I have used 77 grainers is that I got a quantity at a good price. Normally 80 grain and 77 grain are about the same price so I would buy 80 grainers every time.
Don't go thinking that superficially imitating what benchresters do will necessarily deliver massive benefits or any benefit for that matter.
It's something along the lines of a car enthusiast thinking that since formula 1 cars put nitrogen in their tyres then if the enthusiast puts nitrogen in the tyres of his 85 Corolla it will handle like an F1 car. It ain't necessarily so.
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