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Old November 26, 2012, 03:06 PM   #1
hodaka
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6.8 SPC Help

I bought a 16 inch 6.8 upper from JT Distributing about 10 years ago. It had the original Spec I chamber and 10 twist rifling. I worked up a load using 110 Sierra Prohunters and 28 gr of 322 which was very satisfactory, around 1 MOA, with a velocity of 2400 fps.

Thinking that a longer barrel, new Spec II chamber, and 1:11 rifling would be a lot better, I recently bought a Stag upper of 18 inches with no flash suppressor.
Here is my problem; my old, tried and true load throws slugs all over the place out of the new barrel. It is lucky to put them on a paper plate. So much for one load for 2 rifles.

I have since worked up a 115 Sierra load that is around an inch at 100 and another with 110 Hornady’s which is also around an inch. The Hornady’s are clocking 2700 fps with the Sierras around 2630 with H-322. Still, these two loads print about a foot apart from each other on a diagonal.

I have never experienced anything like this before and wanted to know if any of you have experience anything like this or have any suggestions or comments. This works for me, but is not what I was trying to achieve.

Thanks.
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Old November 26, 2012, 04:34 PM   #2
TMD
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I have a Stag model 5h upper and wasnt really all that impressed with the overall accuracy with it until I did a little research and experimenting. What I found out that with the spcII chambers a c.o.l. of 2.290-2.295 makes a world of difference. I load a Hornady 110gr BTHP with 29.0gr's of H322 and am getting about 1" groups @ 100yrds. When I set the c.o.l to 2.260 my groups open up to about 2.5". Hope this helps and check out 68forums.com for some great info.
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Old November 26, 2012, 04:53 PM   #3
hodaka
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A 2.90 OAL sort of defeats the purpose of an AR, right? I've always used 2.255 as something of a constant for all of my AR loads.
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Old November 26, 2012, 05:26 PM   #4
TMD
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Not sure what you mean by defeats the puropse. Some guys are loading as long as 2.305" depending on what magazines you have. If it fits in the mag and you have a SPC II chamber with the longer throat which the Stags do have you will be ok.
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Old November 26, 2012, 05:39 PM   #5
hodaka
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My bad. I meant to say 2.290. What kind of magazines allow this length. None of the ones I have will allow them.
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Old November 26, 2012, 05:51 PM   #6
TMD
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My Stag mags will let me load to 2.290". I think its CPD mags that will allow 2.305" and then some.
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Old November 26, 2012, 08:37 PM   #7
bedlamite
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Newer C Products mags, along with PRI will allow 2.3". Most older mags limit the length to 2.27".

OAL will have a definite effect on both accuracy and POI.

You might also want to try AA2200 powder.
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Old November 27, 2012, 05:16 PM   #8
hodaka
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Great advice. Thanks. I had always used 2.26 as an OAL limit. One of my C Products mags will indeed handle 2.293 and the PRI mag that I have seems to be able to handle 2.3. I also have a pound or two of 2200 that I have been hoarding from the first time it was available 10 years ago. Looks like a project for the next few weekends.
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