6 Creedmoor help

[Twistedtrucker1]

Question: Should I send a dummy round or stick with SAAMI for McGowen 6mm Creedmoor pre-fit?

I have a Ruger American Predator short action, and I’m planning to order a pre-fit 6mm Creedmoor barrel from McGowen. I’ll be shooting the 108gr ELD-M and using the Magpul AICS-pattern short action mags (internal COAL is 2.860”).

Would it be better to send them a dummy round seated to around 2.850” and ask them to throat it so I’m ~0.010” off the lands? Or should I just stick with SAAMI spec?


My main goal is good accuracy and consistent mag-fed performance for long-range steel shooting. Any advice or experience would be appreciated!

 

[khuber84]

Saami spec 6cm has plenty of freebore for the 108eldm, and pretty much every other heavy for cal 6mm bullet. I've shot 108 factory ammo through several Sammi spec chambers and it's performed very well in 18-22in barrels.

I'd definitely give the mcgowan prefit a heavy qc once in hand. Many reports of subpar machining of chamber and threads. Have a box of factory ammo on hand. The rounds should freely drop into the bottom of the chamber, and freely fall out, barring excessive runout of the factory ammo. If you have to push the round to bottom and use your finger or a screwdrive to unseat the round to get it to fall free, the chamber is undersized.

I have a ls wild(preferred barrels) Tikka 6cm prefit and the machining was quite good, chamber looked concentric in the freebore, it shoots well. Ammo dropped in and fell out with no resistance. I'd look into them as well, compare pricing and lead times, this may be a better option as their track record of deliver a quality product is high.

 

[Go West Old Man]

Not an apples to apples comparison, but for sharing 6CM notes & experiences, I had a 6CM built in 2023 on a Bartlein #13 ss barrel. Defiance Rukus , McMillan stock, Hawkins bm, etc. Kept it SAAMI simply for one less decision probably & was confident in the builders advice to do just that. Started break-in & initial scope zero with factory box ammo 108 ELD-M’s and immediately results & groups were darn impressive!

I’d already decided to work up a Lapua & 105 VLD hunting load, and I did. JAM on that load was COAL 2.869 I believe. Backed off that slightly, started workup, & got very lucky on first few rounds of hand loads that produced a repeatable < 0.5 MOA. Less than a month later it proved itself with that same flawless accuracy on a WY antelope. That 105 VLD is a bad little dude! OK, I’ll land the plan here on this story & just say 6CM SAAMI did fine for me.

 

[Titanmoose]

Saami spec 6cm has plenty of freebore for the 108eldm, and pretty much every other heavy for cal 6mm bullet. I've shot 108 factory ammo through several Sammi spec chambers and it's performed very well in 18-22in barrels.

I'd definitely give the mcgowan prefit a heavy qc once in hand. Many reports of subpar machining of chamber and threads. Have a box of factory ammo on hand. The rounds should freely drop into the bottom of the chamber, and freely fall out, barring excessive runout of the factory ammo. If you have to push the round to bottom and use your finger or a screwdrive to unseat the round to get it to fall free, the chamber is undersized.

I have a ls wild(preferred barrels) Tikka 6cm prefit and the machining was quite good, chamber looked concentric in the freebore, it shoots well. Ammo dropped in and fell out with no resistance. I'd look into them as well, compare pricing and lead times, this may be a better option as their track record of deliver a quality product is high.

I had the opposite experience with PBB recently and head to sent it to a smith to inspect and add FB along with another guy who ordered a barrel the same time I did both lacked proper FB and had light rifling marks all the way to the edge of the throat. (6 PRC) not CM but I think anyone pumping out a lot pre-fits/barrel stand to have a couple bad ones once in awhile wither its human or tool error.

 

[bojangles808]

Saami spec 6cm has plenty of freebore for the 108eldm, and pretty much every other heavy for cal 6mm bullet. I've shot 108 factory ammo through several Sammi spec chambers and it's performed very well in 18-22in barrels.

I'd definitely give the mcgowan prefit a heavy qc once in hand. Many reports of subpar machining of chamber and threads. Have a box of factory ammo on hand. The rounds should freely drop into the bottom of the chamber, and freely fall out, barring excessive runout of the factory ammo. If you have to push the round to bottom and use your finger or a screwdrive to unseat the round to get it to fall free, the chamber is undersized.

Thanks for posting this. I tried the drop the bullet in and let it fall out trick and I think my McGowan chamber is undersized. Dropped the bullet in and it wouldnt fall out freely it needed to be pulled out. Then I spin the on, headspaces fine and fit and finish are fine but factory Hornady black 105 bthp chambers rounds pretty poorly and there's marks from the rifling on the bullet when ejected. Didn't get to the range yet, but wanted to see if it would cycle rounds. I try factory 108 eldm and it's a little sticky but not as bad. Theres marring on the 108 bullets too but not at bad as the 105s. My 6cm PVA that I sent back for undersized free bore that got fixed drops bullets in and out fine and cycles flawlessly with same rounds. Before I sent it in it had similar marring on the 108s and then wouldn't cycle at all around round 80 I'm assuming from carbon buildup tightened up the chamber. I suppose I could go shoot it but I think what happened with the PVA is likely what's going to happen here right? It's only going to get worse with more and more carbon buildup? I was hoping to shoot105s in this one but now I'm 2 for 2 on prefit issues not very stoked. Feel like I should just send it back now to get it sorted so I don't have a surprise down the road where all of a sudden it won't chamber a round at all on a hunt or something. esp when this builds for my kid

 

[pods8 (Rugged Stitching)]

I had the opposite experience with PBB recently and head to sent it to a smith to inspect and add FB along with another guy who ordered a barrel the same time I did both lacked proper FB and had light rifling marks all the way to the edge of the throat. (6 PRC) not CM but I think anyone pumping out a lot pre-fits/barrel stand to have a couple bad ones once in awhile wither its human or tool error.

Did you discuss it with PBB before sending it to a different smith?

 

[Libtard McSocalist]

I would run it Sammi if you’re set on the 108s. You should have plenty of room with that bullet. If you want to shoot something longer might want to look into sending a dummy and mdt mags without binder plates they go to about 2.960.

 

[Willie IV]

I had very similar issues. There's some consistency/tolerance issues with the 108 ELD-M's. In fact I have one round that absolutely will not chamber - the other 19 in the box chambered fine.

My 6CM is gonna be a carbon problem child. I bought a cheap Teslong borescope off Amazon for like $60. Sure helps seeing the carbon ring and how your cleaning procedure is working.

 

[wind gypsy]

Just get SAAMI. Hornady designed it around the heavies. Unlike custom chambers based off of traditional cartridges, the "Custom" creedmoor reamers are frequently shorter than SAAMI freebore for bullets with short bearing surface like the 105 hybrids. Problem with them is you risk ending up factory ammo that jams into the lands.