6.8 SPC accuracy question

[Lyons7STW]

I have a stag arms 6.8 SPC II 16" upper. Free floated barrel. DPMS lower with Timmney trigger.
I have been shooting SSA 85 grain frangible and a 90 grain Speer TNT hand load. Both these shoot fairly well.

The kicker is my cold bore shot is exceptionally good. But subsequent shots seem to move an 1.5"-2". And start a whole new group.

I can only assume there is some variable in the bolt lockup between when I drop it manually and when it runs it's own cycle.

Anyone have experience in this area?

 

[Lyons7STW]

It if I could could fix this little issue without a new barrel/ matched bolt combo that would be great. It serves its purpose as you can see but more accurate is the goal

 

[J E Custom]

I have a stag arms 6.8 SPC II 16" upper. Free floated barrel. DPMS lower with Timmney trigger.
I have been shooting SSA 85 grain frangible and a 90 grain Speer TNT hand load. Both these shoot fairly well.

The kicker is my cold bore shot is exceptionally good. But subsequent shots seem to move an 1.5"-2". And start a whole new group.

I can only assume there is some variable in the bolt lockup between when I drop it manually and when it runs it's own cycle.

Anyone have experience in this area?

I have several rifles that don,t like the first clean barrel shot so I shoot a fowler, dry patch and they
group well.(Some loads are sensitive to a clean oiled barrel) Also some bullets react differently to
bore conditions. Try setting your zero after shooting one round and if that doesent work try a 110
or 115 grain bullet with more body to engage the rifling.

J E CUSTOM

 

[Lyons7STW]

I probably did no phrase that correctly. I have tried the heavier bullets and was disappointed. The two listed are the best so far.

I shoot a fouler first even in my bolt guns. It can make a big difference. The issue appears to be between first shot from a dropped bolt and cycled rounds. I am not cleaning in between.

Thank you for the response

 

[J E Custom]

I shoot a fouler first even in my bolt guns. It can make a big difference. The issue appears to be between first shot from a dropped bolt and cycled rounds. I am not cleaning in between.

Thank you for the response

Stranger things have happened in the AR platform.

If this appears to be the problem, It sounds like you need to size the brass smaller. (Factory ammo for
autos is small base sized.) with more head space and a smaller body for ease of chambering in a tight
chamber. If your dies are adjuster all the way down you can grind .002 to .003 thousandths off the bottom of the sizing die or buy a small base sizing die. Hornadys New dimension dies will also do this.

At one time all AR15/M16s had a forward assist button to help seat the bolt in battery, if yours doesn't
you will have to size the brass a little more.

Hope this helps.

J E CUSTOM

 

[Lyons7STW]

My dies are small base and I had considered this so I checked and factory ammo produced the same result. I think I will take it to a good smith and see what steps can be taken to true up the receiver face, barrel, and locking lugs. Then insure barrel nut is properly torqued.

I am not as well versed on autos so I had to research and it appears there are some some steps to take and improve this.


Does this sound reasonable?

 

[ICANHITHIMMAN]

This conversation is a bit silly, how much deviation are we talking about at 100m, how fast are you shooting and what is your barrel profile? Also consider the magazine your using it may be a factor, I don't believe bolt lock up it the issue.

 

[Lyons7STW]

Muzzle vel. On factory loads is 2828 fps. Hand loads book indicates 2900 Barrel is older model 16" stag 1 in 10 twist standard Contour.
We are talking 1.5" deviation at 100 yds.

 

[Lyons7STW]

I am using C products mags. I would like to acquire some PRI mags but at the moment it appears I would have more luck finding a unicorn or jackelope. Why would the mag be a factor other than seating depth and that would not play into factory ammo.

I talked to a local AR builder and he suggested a heavier buffer to smooth out the cycle.

 

[J E Custom]

Why would the mag be a factor other than seating depth and that would not play into factory ammo.

I know it sounds strange, but Magazines do effect the accuracy of simi-auto pistols and rifles.

On all of my pistols and rifles I number each magazine and test it in the weapon for accuracy and
consistency. (Some mags scatter brass everywhere, and some will place the brass in a small circle.
This tells me that I have a good load and the mag is adjusted properly).

During mag testing, I will make note of the best performer and It will become the mag I use for
accuracy. Sometimes you can Adjust/Tune some of the other mags to do better but not always.

The fit of the mag, spring tension,the opening in the mag lips, freedom of the follower in the mag,
all make slight differences in the way the mag functions.

Try testing your mags with 5 shot groups each and see if there is a difference between them, you
may be surprised.

Problems finding accuracy issues are part of the game. sometimes it can be a simple fix and other
times you may never figure it out.

Leave no stone unturned and "Press On"

J E CUSTOM

 

[IDbound]

Thanks JE for your insights. While I am fortunate not to have the same issues as the OP with the same setup, I did learn some interesting points to look for if things to go awry.

 

[Firearrow]

I am using C products mags. I would like to acquire some PRI mags but at the moment it appears I would have more luck finding a unicorn or jackelope. Why would the mag be a factor other than seating depth and that would not play into factory ammo.

I talked to a local AR builder and he suggested a heavier buffer to smooth out the cycle.

I have first and third gen PRI mags. Love the first gen as they have a smaller feed lip, but the third gens are good too. If you can find the first gen and just pay the price for them. I have only had 2 or 3 FTF on the third gen's in my ARP.

Try Chris. Last I herd he has some coming.
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