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Sierra 6.5mm 123 gr MK, why are we not using it???

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Unread 08-06-2009, 11:33 PM
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Sierra 6.5mm 123 gr MK, why are we not using it???

To be honest, I was really not familiar with this bullet but noticed it the other day and did some looking into it. I understand why we are going with the 140-142 gr class bullets for the larger 6.5mm but I am actually suprised I have not heard more about this bullet.

Sierra is advertising a BC of 0.510 compared to 0.595 for their 142 gr MK. In chamberings like the 6.5mm BR adn up to the 6.5-06 AI, from all the data I can dig up which is not all that much, the lighter 123 gr SMK can be driven from 250 to 300 fps faster then the 142 gr.

Now, in my opinion, a round such as the 6.5x47 Lapua or the 260 Rem is a sub 800 yard chambering. Now, I know it will reach out alot farther then that but at 800 yards, retained energy and velocity is getting pretty low to do anything but punch paper so I personally feel for hunting this is the max limit to this type of chambering.

Just for comparision however, lets look at the 260 Rem loaded with the 123 gr SMK at 3100 fps and the 142 gr loaded to 2850 fps. These are pretty hot numbers and would need long barrels to get it but this is pretty standard for the velocity spread of these bullet weights in this class of chambering from what I can find.

Lets look at drop numbers, not really important but just a way to compare the two, all with 100 yard zero.

123 gr SMK
500 yards...............-39.7"
750 yards...............-114.6"
1000 yards.............-245.7"

142 gr SMK
500 yard.................-46.8"
750 yards...............-132.4"
1000 yards.............-279.4"

Pretty impressive for the little bullet. I know I just said the 260 is not a +800 yard rifle but these numbers are just for comparision or for paper punching.

Now lets look at wind drift with a 10 mph full value wind. The big 142 gr bullet should really stop the lighter bullet. not really.

123 gr SMK

142 gr SMK

Within 1.5" drift out to a full 1000 yards.

Now I know that I have always been a proponant of heavy for caliber bullets for long range shooting and that has not changed. Espeically for large capacity chamberings that have the horsepower to drive the heavy bullets to high velocity but for those smaller chamberings, I see no real disadvantage to using the lighter bullets in place of the 142 gr SMK and actually have some advantages.

Namely, less recoil and less rifle torquing.

Now I am not saying the heavier 140 to 142 gr bullets are not completely at home in these smaller cartridges, my only question is why do we not see more use of this 123 gr SMK in the smaller calibers where it seems more at home with much better velocity potential.

It is my opinion that its best to get 3000 fps for a long range chambering if at all possible, this bullet would allow the likes of the 260 Rem, 6.5x 47 Lapua and the like to accomplish this and do so with a bullet with a pretty impressive BC.

Just wondering your thoughts. By the way, I have 1000 of these headed my way to test out. I think it may also be a real screamer in my 6.5mm WSM. We will see.
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

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Unread 08-07-2009, 10:20 AM
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Join Date: Jan 2007
Location: MS
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Re: Sierra 6.5mm 123 gr MK, why are we not using it???

Kirby I have been shooting the heck out of these in my 6.5x47, great little bullet for this IMO underpowered little round. I ran numbers similar to the numbers you posted before choosing the bullets and they work great for f-class. A buddy of mine who is a member here just started using the 130 JLKs and seems to be having decent luck with them.

My 6.5WSM reamer should be in Monday and I am planning on giving them a try there also.

My only concern has been terminal performance. I posted here about them at least a year ago and was told that performance was not spectacular on game so I have not tried them out and just have not had a chance to test them on anything other than targets.

If you do any terminal testing please share your results.
I admit that I know just enough to be dangerous.....but dangerous at ever extending distances.
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Unread 08-08-2009, 11:13 AM
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Join Date: Mar 2006
Posts: 899
Re: Sierra 6.5mm 123 gr MK, why are we not using it???

You are right on. I've been using them to fireform in my 260ai and they shoot awesome! I can't stop them from going in the same hole. I can use them and the fireform load and get meaningful work done instead of wasting powder and bullets.

I was going to use them on deer but decided on the 140amax which also shoots very well at 2850fps.
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Unread 08-08-2009, 11:31 AM
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Join Date: Jan 2005
Location: OK
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Re: Sierra 6.5mm 123 gr MK, why are we not using it???

I had great luck with the 123 scenars in my straight 260, and have about 950 of the 123 smk that I have started to use in that gun. Mostly target and rock bustin.
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Unread 08-08-2009, 11:54 AM
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Join Date: Apr 2009
Location: western Oregon
Posts: 120
Re: Sierra 6.5mm 123 gr MK, why are we not using it???

They're on my list for trial in my 6.5X.257RAI. I'll post some results when I get them.
I'm still working with the 120 and 140 A-Max's at the moment.
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Unread 08-08-2009, 12:30 PM
alf alf is offline
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Join Date: Nov 2007
Location: S. W. Wisconsin
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Re: Sierra 6.5mm 123 gr MK, why are we not using it???


As what sometimes gets lost, numbers are valid only if the accuracy is at those velocities, but at least it still gives direct comparisons. I think your perfect on the possible velocities.

I've played quite a bit with a 700 VLS for the 1000yd stock class, and I could get those numbers. Trouble was, the 123 Lapua's shot best at 2960. Still beat the 142's in drop but lost to the wind specs. The 142's accuracy was at 2840.
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Unread 08-08-2009, 10:04 PM
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Join Date: Jan 2006
Posts: 374
Re: Sierra 6.5mm 123 gr MK, why are we not using it???

Can the 123's run with an 1/8 twist?
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