I'm trying to put together a superlight mule deer rig and I find myself vacillating between the 6mm Creed and 6.5 Creedmore. Anyone faced a similar dilemna and if so how did you resolve it.

What’s the argument that favors the 6?

The 6mm will shoot a little faster and flatter, I have killed a bunch of deer and bigger critters a fast twist 6 and 105 gr and 108 gr bullets,

There's no fly's on the 6.5, what ever you think you need, pick a rifle you like that fits you and go kill stuff. Rio7

I keep trying to type a suitable answer, but the splitting of all these hairs is making my eyes hurt, and my Loonyism alarm keeps going off.

I faced a suitable dilemma earlier this year when picking out a rifle for my youngest daughter. I went 6.5. I have my reasons, including the possibility that the rifle will be used for elk, and 6.5 bullets get a lot heavier than 6mm do.

Yeah. I'm probably overthinking it.

I would choose based on the slickest bullets. 6.5CM with 147s is worthy of building a rifle around.

That is coming from a 1-8” twist 243 guy who shot out his barrel shooting mostly 105s. It’s off to become a 6.5CM throated specifically for 147s.

Won't argue with you on the 147 ELD-M, but the 6.5 Creed's i have shot seem to like lighter bullets. YMMV. Rio7

The 105's do good things, particularly on deer and such. They are perhaps marginal for bigger animals in typical hunting conditions. I think that with the fast-twist factory 6 Creedmoor now being a thing, there will eventually be more long and heavy bullets to shoot in it. But the 8-twist is maxed out already. The next 6 I put together will likely be built on a 1:7.

There are so many more long, slick bullet options in 6.5 right now, with higher sectional densities to boot. Just better for hunting in my opinion.

Using the same contour for each, the 6.5 will be a tad lighter....
Then there is the heavier bullet of the 6.5.....

Flip a coin.....grin

Tomato, tomatoe....

If it's a dedicated deer rig can't go wrong with either. Components are equal. Bullets and ballistics are equalish. 6.5 has more ass and will be a skootch lighter due to bore size all equal.

First world problems. grin ..

I have a 6, but if I were where bigger deer were commonly found, along with maybe elk, I'd go 6.5, or 7-08. Barrel life is probably considerably longer too.

Actually, one of my recent hankerings has been for an 8" 7-08, which I guess means an unobtainable Fieldcraft. Unobtainable is good for an old man who already has too many rifles.

Totally agree. 1-7” twist for sure.

Recoil - advantage 6. Most else - advantage 6.5. I would probably go 6.5.
If you want ease and economics, look for a used fieldcraft in either. Both are stellar. Or go balls to the wall for three times the price, maybe 8 oz less, and probably near equal performance
Edit - nm on the Barrett; I forgot you already had the parts coming.

Good post pappy.

What will you be shooting with it other than deer? If predaters & varmints the 6, if elk or larger the 6.5. Their are more VLD type hunting bullets in the 6.5 caliber but not many over 103-5 grains except the Berger 115 in 6mm. But I would lean towards the 6 shorter barrel life and all, and knowing the 6.5 is the practical choice. If we were practical we would all hunt with a 223, a 30-06 and a 12gauge and not be asking these questions.

Being Impractical Matters

Either work, but if a bad shot angle presents, I'd choose any standard 6.5 hunting bullet, over a high BC match 6mm. JS. The 95 BT does great things near and far......but a 6.5 might be a better mousetrap, without making one pause on shot angle or distance. Soft bullets on closer shots may limit reaching vitals from all angles, in the 6.

Either will work well and have a handful of both. I’m a fan of 6 creed with 105/108s and deer sized animals.

If speed is your thing then go with the 6.

Same bullet weight, same case, the bigger bore will shoot faster. I think your logic is backward there.

Same weight bullet in a 6 vs 6.5 ?

I'm not sure I understand your question.

Same weight bullet in both. As in a 95 grain bullet loaded in both a 6 CM and in a 6.5 CM. The 6.5 has a larger bore, so it more efficiently pushes the bullet down the bore. It won't matter much, but various data points to about a 50 fps velocity difference with 95 grain bullets, and the difference is more like 100 fps when you get to the 107. I'm sure if there were 120-123gr bullets in the 6, the difference would be larger still.

Since the OP alluded to deer hunting with a lightweight rifle, I'm guessing that lighter varmint bullets in the 6 are likely off the table.

HnS,
I got it now. My mind was thinking average to heavier weight in the 6.5 not going smaller to match the 6.
Thanks for explaining it .
Carry on....