In a Semi-Auto Rifle, 6mm or 6.5mm Creedmoor?

[Spin Drift]

Guys, I don't know, that's why I'm asking. Yes, the 6mm is a little faster, the 6.5mm uses heavier bullets, what I'm asking is there a practical difference in a semi-auto platform?

Not a 6mm v. 6.5mm pizzin match, not a bolt rifle, I got room for 1 semi-auto, is there any real difference?


I just want something with a little more legs than a .308.

Or, do I get a .260?

Thanks, up front.

[wilson1911]

barrel life..... the 6 sucks @ 1700 or so. The 6.5 will be around 3200. Just do a 6.5 and pick a flavor.

[Kansaswoodguy]

I have a 6.5 Creedmoor and couldn't be happier. I shoot it out to 1000 yards no problem.

[Peshawar]

Another vote for 6.5 Creedmoor here. Got barrels for my AIAT and LMT mws in that caliber and have since replaced anything .308 with 6.5. Really like the change. Ammo is the same price, so why not? It's flatter shooting, a little less recoil, and the moderate barrel life reduction is not a deal breaker for me.

[Spin Drift]

Thanks for the info, 6.5mm CM it will be.

Some very good points, thanks for the help.

I've watched 2 guys shoot them (both bolt guns) at the local 600 yard range, yeah, boringly accurate.

I do like the idea of the heavier slug, 140 grain would kill any deer/hog we have around here.

Thanks guys.

[rjacobs]

I havent seen many semi-auto 6mm barrels either. 6.5cm there are quite a few.

Also be aware with 6.5cm and the heavies(139+) you MAY run into pressure issues at loads below what you would in a bolt gun. JP recommends the 123g AMAX and I have had superb results in my 6.5c gas gun.

[Peshawar]

I havent seen many semi-auto 6mm barrels either. 6.5cm there are quite a few.

Also be aware with 6.5cm and the heavies(139+) you MAY run into pressure issues at loads below what you would in a bolt gun. JP recommends the 123g AMAX and I have had superb results in my 6.5c gas gun.

Yes, good point there. Also, the LMT bolt already has a reduced sized firing pin hole which reduces issues with higher pressure cartridges like the 6.5 CM. JP makes a .308 "High Pressure" bolt which would be a good idea to look into for a semi in this caliber. My AIAT also has the small firing pin for the same reason.

[rjacobs]

Yes, good point there. Also, the LMT bolt already has a reduced sized firing pin hole which reduces issues with higher pressure cartridges like the 6.5 CM. JP makes a .308 "High Pressure" bolt which would be a good idea to look into for a semi in this caliber. My AIAT also has the small firing pin for the same reason.

yes that stuff is important, but not really what I am talking about. That mostly has to do with pierced primers, not any of the other high pressure signs. The ONLY change to the HP bolts that I am aware of is the small firing pin and firing pin hole to give more support to the primer. Wont stop the primer from flowing though.

Say a bolt can shoot 40g of powder behind a 140g bullet safely. A semi might have massive ejector swipe, flat primer, etc... shooting that same load. The semi might only be able to shoot 38g of powder. So obviously your velocity is lower comparing same barrel lengths. Now, thats NOT an absolute obviously because things change. BUT everybody that I talked to when looking at what to spend time developing for my 6.5c gas gun, most people said in the gas guns stick with the lighter weight stuff. Im shooting a 123g AMAX at 2900fps out of my JP barreled/JP high pressure bolt, gas gun. I havent played with the heavies at all because, for me, the 123g does it all out to the 1200 yards I have available to shoot on.

[Peshawar]

Say a bolt can shoot 40g of powder behind a 140g bullet safely. A semi might have massive ejector swipe, flat primer, etc... shooting that same load. The semi might only be able to shoot 38g of powder. So obviously your velocity is lower comparing same barrel lengths. Now, thats NOT an absolute obviously because things change. BUT everybody that I talked to when looking at what to spend time developing for my 6.5c gas gun, most people said in the gas guns stick with the lighter weight stuff. Im shooting a 123g AMAX at 2900fps out of my JP barreled/JP high pressure bolt, gas gun. I havent played with the heavies at all because, for me, the 123g does it all out to the 1200 yards I have available to shoot on.

Gotcha. It's funny, a good friend warned me off of shooting the 140's in my LMT as well. Perhaps I didn't listen carefully enough as to why, but your explanation would spell out the reason. I have only put the 120 AMAX through the LMT so far. But my thinking was mostly that since I can't shoot the big AR as well at my AI that I should save the most expensive ammo for the platform I shoot better. I'm hoping to get better at shooting the LMT and I'm improving, but I definitely shoot the bolt gun more accurately. I know there's a number of reasons for this as well, but I'm glad to learn from what you posted. Thanks for that.

[bigjohn1940]

FYI,

Same boat that I was in, looking for a 6 or 6.5 upper using a 223 case. Found a Sharps 25-45 complete upper. Shoots .257 bullets (6.35mm). High quality stuff from SRC, Sharps Rifle Company. Factory ammo up to 100grs (Hogsmasher). I prefer the 87gr for my use.
JM