6mm Creed AR10 Feeding

[BigGameJames87]

I recently bought a Seekins SP10 in 6mm Creedmoor that I plan to use in PRS gas gun and other competitions. Naturally I'd like to use as aerodynamic of bullet as possible and I have an assortment to try and see what the gun likes. The good news is that so far it shoots everything pretty well. The bad is that it won't feed Berger 109s. The ogive is long enough that the meplat hits below the bottom of the chamber before the feed ramps kick the bullet up enough for it to run into the chamber like it normally would. The gun feeds 108 ELDMs with no issue but the ogive profile on those is quite different from the 109s. I presume I will have the same feeding issue with 110 SMKs and most of the 115 class bullets as well.

I have been using PMAGs. Would a different mag make a difference or is this a case of AR10s aren't designed to shoot super sleek 6mm bullets? Is there anything else that I can try within reason? The gun shoots the 108s just fine and they will work for what I need so I'm not up a creek but I would like to at least have the option to use some of these other bullets.

 

[Hecouldgoalltheway]

Tune those feed lips. That's where I would start.

 

[LRRPF52]

The AR-10 was never designed around the 6mm with OTM meplats. What happens with the narrower neck is exactly what you’re experiencing.

The neck and projectile are able to present lower than the feed cone cut into the breech.

A very talented machinist, gunsmith, and engineer I know tackled this problem by cutting an extra set of extended feed ramps from the feed cone, without cutting into the feed cone depth (because this will jeopardize case web support under pressure during firing).

It’s very hard to get in there though without damaging the barrel extension or screwing up your breech.
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What I would try before doing any mods is get some Lancer 7.62x51 mags and seeing how they feed the 109s.

That will probably solve your problem since they are thinner lips, allowing higher cartridge presentation.

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You can also reach out to Seekins and ask if they have any recommendations.

Another thing to try would be to make a tool with a .308 case wrapped in 400 grit sandpaper. Install the tool in a hand drill.

Take your PMAG and spin the tool inside the feed lips to change the inside lip angle a bit higher, so the cartridge biases more upwards upon stripping from the magazine.

You can also add material to the back of your PMAG spines right as low as possible in the mag well location where there is contact, so it biases your magazine angle nose-up.

This is what Geissele did with their 6mm ARC, with the trigger guard nose. It protrudes into the mag well to bias the magazine so they don’t experience the same thing you are, as it is a problem with 6mm and certain projectiles, especially secant ogives with OTM meplats.

Let us know and we’ll help you along the way to get it sorted.

 

[BigGameJames87]

@LRRPF52 Thanks for the help. I ordered a Lancer mag and I might fiddle with a Pmag while I wait for it to show up.

 

[Earnhardt]

The AR-10 was never designed around the 6mm with OTM meplats. What happens with the narrower neck is exactly what you’re experiencing.

The neck and projectile are able to present lower than the feed cone cut into the breech.

A very talented machinist, gunsmith, and engineer I know tackled this problem by cutting an extra set of extended feed ramps from the feed cone, without cutting into the feed cone depth (because this will jeopardize case web support under pressure during firing).

It’s very hard to get in there though without damaging the barrel extension or screwing up your breech.
______________________________________________________________________________________________
What I would try before doing any mods is get some Lancer 7.62x51 mags and seeing how they feed the 109s.

That will probably solve your problem since they are thinner lips, allowing higher cartridge presentation.

________________________________________________________________________________________________
You can also reach out to Seekins and ask if they have any recommendations.

Another thing to try would be to make a tool with a .308 case wrapped in 400 grit sandpaper. Install the tool in a hand drill.

Take your PMAG and spin the tool inside the feed lips to change the inside lip angle a bit higher, so the cartridge biases more upwards upon stripping from the magazine.

You can also add material to the back of your PMAG spines right as low as possible in the mag well location where there is contact, so it biases your magazine angle nose-up.

This is what Geissele did with their 6mm ARC, with the trigger guard nose. It protrudes into the mag well to bias the magazine so they don’t experience the same thing you are, as it is a problem with 6mm and certain projectiles, especially secant ogives with OTM meplats.

Let us know and we’ll help you along the way to get it sorted.

Hey, LRRPF52… that’s some next level shit right there man!!
Thanks!

 

[M4guru]

Gas gun feedways hate that bullet, that isn't unique to Seekins. It isn't just AR-10(ish) guns either...try to feed a Berger VLD 6.5 from any mag in my Q Fix and see how that goes...it won't feed shit that isn't a Hornady ELD-X/ELD-M. I would start by calling Seekins, their rifle should work with their provided mag with a SAAMI-spec cartridge it's chambered in. Plus they're awesome to deal with, and they have the most info on their own gun.

Think of cartridge handoff like passing the baton in an Olympic relay, you don't ever want the baton (cartridge) to have "free will", nor do you want two components playing tug-of-war. There is a moment in time where the feed lips reliquish control to the feed ramps and cartridge pickup lug, and that's a delicate transition that is almost certainly optimized for .308 in the mags and likely the feedway/barrel extension as well. In a like-size diameter case with a smaller neck, correspondingly different shoulder and projo length/profile that feed dynamic changes considerably and the systems isn't optimized for it. Depending on cartridge, the feed lips can be too long/short front-to-rear and change that handoff dynamic also, it isn't just a function of presentation heigh/angle.

Obviously it can be made to work, but it can require some tweaking. Try a KAC or LaRue mag if you have access to one. I've found both of them to be much better magazine for reliability and service life that the others with smaller-diameter OTM projos.