Accuracy problems - mag vs single feed

[Vilk]

Dear Friends,

Need your learned advice.

Both me and my wife are f-class and service rifle competitive shooters in Poland/Europe for many years.
We reload all ammo,and regardless if we shoot 123 grainers or 130 AR Berger Hybrid we cannot get these rifles to shoot. We load low at two muzzle speeds 706 m/s or 730 m/s . Gas system set to just above min.

We have 2 JP custom rifles in 6.5G built for us,and we are devastated by the accuracy results.
We DO NOT do ladder tests at 100y, we do them only at 300m, and we shoot 300/600/800 competitions with the aa rifles.

The competition CTR we shoot will shoot <1MOA ONLY WHEN SINGLE FED.

Groups open imm to >2 MOA when mag feeding (a must for competition).
The funny thing is that POI will change depending on if we use a E-Lander or C-Mags - rifle will shoot with same loads at different POI when using alternate producers mags!

What we found out is that cartridges get demolished when gas reloaded from mag - cartridges with zero concentricity get very crooked and heavily bruised by hitting the star chamber when mag reloaded.

Is there a way to address this problem in 6.5G builds?
My friends shooting same rifles in 308 and 6.5Creed do not have this problem.

Will be very grateful for any kind of advice that can help us!

Rgds to all 6.5 G shooters,
Piotr

[Sticks]

I spoke with a gunsmith at my last rifle match. He has built many a Grendel AR. He opens up the feed ramps in the barrel extension as he had the same problem with the concentrically going sideways when chambering from a mag. I don't have his contact info (I know he lives in New Mexico), but he has done a lot of work with the guys at Proof Research. Contact them to see what the recommended fix is.

I would also recommend contacting JP to get their input.

[VASCAR2]

Sounds like your using reloaded ammunition so I’m curious what reloading dies your using. You need to full length size your 6.5 Grendel brass. Sounds like you might have an issue with case neck tension. Many competitors in the US use bushing dies. Lee 6.5 Grendel dies reportedly over work the case necks which could lead to inconsistent neck tension. I’ve used hornady and RCBS dies and never experienced accuracy issues. Make sure your not using excessive shoulder set back on the brass cases during sizing. You can measure shoulder set back with a Hornady Lock & Load tool with the correct bushing.

Are you using a pinned gas block on your JP barrel? Wierd accuracy issues are encountered when gas blocks touch hand guards during recoil or are not held securely. I use thread locker on my gas block screws and coat the barrel with blue thread locker whether Loctite/Permatex. Are you using an adjustable gas block or fixed and are using a suppressor?

Lapua brass is the most consistent 6.5 Grendel brass and is readily available in Europe so I assume your using Lapua brass.

[37L1]

Measure/inspect your rounds after putting into battery and then ejecting without firing?

Notice any change in OAL, marks on the projectile? Photos of the damaged rounds could help diagnosis.

Maybe just cleaning and polishing your feed ramps?

[LRRPF52]

I blend and polish my feed ramps as a normal procedure before the barrel even gets mounted.

I've seen this happen in LR-308s before, magazine-dependent. They would shoot 2 groups left and right for some reason.

[Vilk]

Dear Guys,

Thanks so much for your feedback and advice.

Will post photos and measurements of unloaded cartridges next week,going to the range for some tests.
Will try to post photo of 300m tests showing the phenomenon.

Using two types of dies:
Custom Forster FL no bushing neck .268" with min shoulder setback.
Full Redding Competition Bushing dies ,using bushings 267 or 268.

Bad Results on paper when mag reloaded are identical irrespective of dies used.
Basically zero problem when single fed.

The JP custom CTR is a " full" version with LMOS stainless bolt,Silent Capture,adjustable gas block,heaviest ss 22" (Krieger?) bbl with a JP radiator "heat dissipator" and barrel/bolt were matched.

No reply yet from JP on the issue.

Also asked AA same question,their response is wrong angle of mag feed lips and that the remedy would be to change buffer springs to 5.5 oz on rifle length or 4,6 oz on standard length.

Thanks for your support!

[Vilk]

Photos of target

Pls disregard the top right hand target sticker - was fireforming 6 Dasher loads with 6 BR

[A5BLASTER]

Ok I'm a bit lost, could be I haven't had my coffee yet but.

Do you have a JP barrel or a Krieger barrel you installed in it yourself?

[bj139]

Vilk,
The bushings you have listed would be for a 6mm not 6.5mm which should be about .285.

Gas operated guns batter the cartridges quite a bit. I don't know what to suggest.

[Bearcatrp]

What type of buffer do you use, carbine? I went through similar issues. Your bolt may be catching just enough to cause issues. I put a H2 and changed to E Lander mags. Runs sweet with no issues now. 23 bucks. If that wouldn't have helped, my next step would have been upgrading the spring, then a adjustable gas block.

[Vilk]

I have a JP original heaviest installed barrel,which I assume they order from Krieger.
With adjustable JP gas block. And original JP Silent Capture Spring (no odea what is original spring weight of this JP buffer!).

I think the type of barrel is irrelevant to the problem of accuracy issues when magazine fed.
There are no issues accuracy wise when single fed.

Clarifying re neck sizing : I use Forster FL with .286" neck, or 285/286 bushings with Redding Comp B/NK die.

Regards!

[Klem]

Sounds like you already know the answer. You have all the best gear and realise the difference is related to the auto loading function. Those bushings will definitely give you enough grip (.004") on the bullet to resist semi-auto inertia. So it has to be how they are being damaged from the mag to the chamber. The answer is in the advice already given. Mimic the action of the semi-auto and inspect the ejected rounds carefully to confirm what changes occur compared to hand-loading. Polish the mag lips and feed ramps.

I can only add that you might also try factory ammo. Hand-feed a few of those and the rest semi-auto. If there's no difference then it's your hand-loads.

[ported45]

Having similar issues again with bullets being inertia pulled when being fed by mechanism; they are NOT being set back. I would have to crimp the crap out of them with the Lee Factory Crimp to keep the bullets from moving.

Using original carbine spring and buffer. This is my first rifle-length gas system. What spring/buffer combo should I be running? Seems like the spring is just too forceful in chambering up the rounds.

[Sticks]

A member on aonther forum is having the same problem if one could call it that.

Odds are good that they are being "pulled" the same amount within .002 every time. If it's more, you would need more neck tension. You just seat the a touch deeper to account for the anticipated "pull".

An option is go go with a JP - SCS and spring kit, adjustable gas block and tune it for the light spring, coupled with a semi auto carrier or low mass.

The same member is super anal and goes through extreme levels of testing and measuring. Factory ammo was being "pulled" farther than his reloads, but was still getting better groups and SDs

[ported45]

Reloads and factory Black COAL is increasing 0.004-0.005" every time.

What I really can't fathom is that 5.56 and .300 Blackout ran with the same spring and buffer, the bullets do not move at all. But those uppers are set up with carbine and pistol length gas tubes.